output from transformer is coming not as expected

[VickySalunkhe]

I have made 2 psu 48v 5a each using 2, 12-0-12v 5A transformer
I have connected those psu in parallel so that i can get double current, i.e, 10amp

My load is brushless dc motor which can draw current upto 13amps
But the problem here is

When i am connecting the psu with controller and motor
Current draw goes to max 1.5 amp starting from 0.5 amp

I have connected the terminals of multimeter in series to the +ve wire of psu(incase if someone finds me wrong here for checking the current)

And because of less current the voltage comes down drastically as soon as i use throttle to run the motor faster

Plz help,
Why the output current so low,
How can i draw 10amps as i am using 2 5amp transformer in parallel

Thanks the

[schmitt trigger]

the motor current with a motion-less rotor, is several times higher than the full load current.

So it could be loading down your supplies.

 This plus the fact that two supplies in parallel, even if they are identical (which you have NOT shown), will never share the load current equally. Unless ballasting or an active load controller is employed.

[wraper]

PSU schematic please. If they are regulated PSUs, connecting in parallel likely will cause issues like oscillation unless PSUs are made to cope with that. You write about current without measuring actual voltage.

[rstofer]

What is the open circuit voltage of each power supply individually?  What is the voltage when they are in parallel.
I'm missing something because a 12-0-12 transformer isn't going to deliver 48 volts.  No doubt I am just not comprehending what is going on.
Figure the motor draws 6x full load current at startup.  If you want the right answer, measure the winding resistance and use that in Ohm's Law.  It's often hard to get the resistance of motor winding because it is so small.  Some DMMs can do it...

[BenKenobi]

I find this description confusing how - and where - are you trying to measure this, how exactly are you connecting the motor ?

what are you using as an 'inverter' - i.e. an ESC you can't power a brushless motor directly with DC and I wouldn't recommend putting AC across it.

In any event to measure current on a brushless motor you measure the input to the motor controller not the motor feeds since these get switched to simulate 'brushes'.

Are you running the motor with a load would be the next question - load the spindle down with friction and see what the current does.

[schmitt trigger]

I'm missing something because a 12-0-12 transformer isn't going to deliver 48 volts.  No doubt I am just not comprehending what is going on.

I had read the OP quickly and did not pay much attention to the actual values,
But.......after re-reading the original post, count me in as another person that doesn't understand what is going on.

[BenKenobi]

I kind of did the same, I'm thinking now that the motor is running without a load so it's bound to draw below rated current - which is a maximum rating not a target.

I'm guessing also that there are two 12 0 12 in series so that does provide 48V, I don't know many ESC's that can handle this - 44V DC is about the biggest I know of that is off the shelf (at reasonable cost).

Transformers in series - question to OP - are you sure these are 'phased' correctly and both identical. In any event two transformers in series doubles the voltage NOT the current though - the most you can draw is 5A.

[VickySalunkhe]

I have attached circuit diagram of one psu
I have made two psu like this then connected it in parallel

I am using controller to run the brushless dc motor

[BenKenobi]

The output is in series not parallel. The most current you can pull is the lowest TX amps rating.

http://engineering.electrical-equipment.org/forum/general-discussion/difference-between-series-parallel-transformer

You should be linking before the rectifiers and use a single rectifier too.

[tooki]

The output is in series not parallel. The most current you can pull is the lowest TX amps rating.

http://engineering.electrical-equipment.org/forum/general-discussion/difference-between-series-parallel-transformer

You should be linking before the rectifiers and use a single rectifier too.

The schematic is of one PSU. He said he put two of these PSUs in parallel.

[BenKenobi]

My bad -

but still don't understand why he's rectifying both TX's - I'm thinking there is a phasing issue here - in any event just because a motor is rated at 13 amps doesn't mean it will pull 13 amps - it needs a load, the measurement has to be before the motor controller.

[VickySalunkhe]

So do you suggest me to use one rectifier for two transformers?

And i have a motor controller with a throttle to control the motor
As per my testing
I get 50V at the starting
But as soon as i use throttle to speed up the motor(which will conclude controller will try to fetch more current)
The voltage rating goes down till 37v and stops as controller doesn't supply power to motor below that voltage rating
I have checked current and i have got max 1.5 amps
Thats the main issure despite of using 10amp psu
Plz suggest me and do tell me where am i going wrong
Thanks 

[BenKenobi]

How did you confirm the phasing on the transformers ? i.e. are the sides of highest potential 'aligned'

https://www.linkedin.com/pulse/transformer-polarity-mike-hennesey/

I think that by putting the TX's in series and using a single rectifier will reduce complexity for sure, you only need to do what you show if you want to tap 24VDC for some reason, the voltage shouldn't decay that much if at all - what are you using as a controller - I'm guessing some kind of ESC - many of these need to be programmed they generally aren't plug and play.

[VickySalunkhe]

Well i have purchased a kit
I have got motor , controller and throttle with it

What do you mean by phasing sry but i didn't get it
What do you suggest what should be the noble approach to meet my final requirements
As i want to give output of 48v 10am which is said to be possible with the transformer i have
Thanks

[BenKenobi]

Been looking for something to explain. Take a look at the vid in the link, notice what happens when one transformer isn't doing what you think, also notice what happens if you get the wires crossed on the TX outputs. I'm not sure whether the rectifiers are there to try and overcome some of this but it's a messy way of doing things, you'd have been better off with a single 50V transformer and a single rectifier, but you could still go single rectifier by moving your series link to the transformer side of the rectifier then you only need one - depending what your diodes are rated for (I assume you have diodes and not a package).



Beyond that need to know much more about this motor and its associated controller - brushless motor controllers are quite complex



or (this is basic but explains brushless control very well)

[Damianos]

I have attached circuit diagram of one psu
I have made two psu like this then connected it in parallel

I am using controller to run the brushless dc motor

So you there is a series and parallel combination of four power supplies.
To take the maximum of the above, ALL the secondary coils of the transformers have to be connected IN-PHASE, except if there is really huge capacitance on each one.
By the way, how much capacitance is on the filters? I see something like 2.2M?, that does not make sense.

Hope that you know and understand about the hazards in what you are doing! An exploding capacitor is not an enjoyable experience!

[VickySalunkhe]

So do you suggest me to increase the capacitor
And if yes how much ?
As you can see i have four transformer

At the very first of building this psu
I was using 13.2 mF cap (6 ,  2.2mF cap in parallel)
But due to less current output i thought to remove some of the cap
As i got to know cap stops the current flow once they are charged
But that doesn't seem to make a lot of changes.

I have some doubts
What do you mean by in phase connection?
Can i connect the transformer in series and parallel and then give that supply to bridge rectifier
Will it be safe?
Thanks

[tooki]

If you are confusing what capacitors (measured in Farads) and resistors (measured in ohms) are, you are NOT yet ready to be building this thing!! You should be nowhere near mains wiring yet!!!!!

[BenKenobi]

What do you mean by in phase connection?

I sense that you really need to study the basics of electricity / electronics - understand how AC works and how transformers 'transform' it.

Some basic ohms Ohm’s law and Joule’s law isn't going to hurt alongside equivalent resistance and capacitance, Kirchhoff’s current and voltage Laws - sorry but electronics is something of a mathematical sport.

For example your 'capacitor' is nothing to do with current - that's a hint - go find out why it is there and how to calculate what size it needs to be - go and study full wave rectification to find this out.

Whilst power supplies are amongst the first things that many build they require you to understand a lot of basic theory to build a good one. Dave did a really good series on power supply building

[Damianos]

So do you suggest me to increase the capacitor...

No, not exactly!
The only advisement, that I can give to you, is to stop this project until you acquire some knowledge and understanding, at least on the basics, as already mentioned by others.
It seems that you cannot see the dangers that exist in what you are doing!

As you can see i have four transformer

I see, but...

I was using 11m ohm cap

I don't know if a thing like this exists!

But due to less current output i thought some of it
As i got to know cap stops the current flow once they are charged
But that doesn't seem to make a lot of changes.

? ? ?

What do you mean by in phase connection?

This is important, at least, when combining coils...
It's one more indication of missing knowledge and understanding.

Can i connect the transformer in series and parallel and then give that supply to bridge rectifier

Of course yes! But, the way of doing that, will give as result:
- what you want to have
- absolutely nothing
- damages to surroundings from transients
- more or less serious injuries up to death
- put in fire your house

Will it be safe?

As it seems, no!

Thanks

You are welcome!

Start studying the basics, there are people here that will help you by answering specific questions. It's a little difficult to design and implement a Formula-1 vehicle, if you don't know the properties of the wheel!

[IanB]

How did you confirm the phasing on the transformers ? i.e. are the sides of highest potential 'aligned'

To take the maximum of the above, ALL the secondary coils of the transformers have to be connected IN-PHASE, except if there is really huge capacitance on each one.

Phasing of transformer windings doesn't matter if the outputs are rectified before they connected in series/parallel.

Why are people giving the OP confusing information?

Phasing only matters if you are connecting the windings together in AC mode before rectification.

[Audioguru]

The transformers are 24V each. The peak voltage is 24 x 1.414= 33.9V and the bridge rectifier reduces it to 31.9V that is filtered by the capacitor. Two in series provide 63.8VDC, not 50V.

Each transformer is rated for 24V at 5A which is 120VA. But when rectified the voltage is 33.9V so the maximum allowed output current is 120VA/33.9V= 3.54A DC.

What is 2.2M? If it is 2200uF then it will produce a lot of ripple voltage when the high current is drawn which will reduce the average output voltage. Use capacitors with much more capacitance. 

[Brumby]

Phasing of transformer windings doesn't matter if the outputs are rectified before they connected in series/parallel.

Why are people giving the OP confusing information?

Phasing only matters if you are connecting the windings together in AC mode before rectification.

I was thinking this as well.

With the original layout from the OP, there was no problem with phasing - None, Zero, Zilch!!!  Yet we have had someone throw this into the conversation and then others jump on the bandwagon.  There is only ONE benefit from paralleling the transformers - and that is to save a voltage drop across a couple of diodes.  For the voltages under discussion, that is not a big deal.

SO ... rather than confuse this person with details that are essentially irrelevant, how about we forget all about stuffing around with transformers, revert back to their original design and discuss the real problems - starting with their basic lack of knowledge.  (Please - let's not do transformer phasing just yet.)

As far as the OP's ability to work with mains is concerned - I share the concern ... to a point.  There is not a lot to go wrong if they understand which side of a transformer is the primary and connect it to the mains appropriately.



Why do people continue to want to display their "knowledge" and confusing an already challenged person instead of paying attention to the real issues and looking at actually helping them?

[Damianos]

Let's for a moment we remove the capacitors from the circuit. What will be the maximum (peak) voltage at the output?
Now let's connect them again and find the maximum output voltage. What about the maximum (peak) voltage of the ripple? In this case it is needed to do it twice, without a load and with a "heavy enough load", that represents the motor.

If we do the above for both connections (in-phase and anti-phase), in paper, using a simulator or doing it in the lab and take the results, we can start thinking about the behavior of the motor in each case.
Similarly we can do it for the availability of current, that we can draw, without "zeroing" the output voltage...

As the voltage is peaking in higher value the motor has the chance to start rotating, producing back-EMF, reducing the loading ... ... Here, of course, the behavior of the controller has a role...

To take the maximum of the above, ALL the secondary coils of the transformers have to be connected IN-PHASE, except if there is really huge capacitance on each one.

Before you comment, try to read the entire sentence!
If there is not enough capacitance, to "support" the loading, then the voltage maybe drop up to half of what is expected!
I don't thing that a capacitor of 2.2 milli- or mega- Ohm can do that!

That comment is really vague! I did not tried to "improve" it, because, in the continuance of the discussion, appeared things that, in my opinion, show that the experimenter is missing basic knowledge and he is not in a position to understand what is doing.
EDIT: The mentioned comment, by me, is not only vague but it is ... <put here what you wish!>!

[IanB]

If we do the above for both connections (in-phase and anti-phase)

In phase or anti-phase is irrelevant, because in the circuit diagram the transformer outputs are DC rectified.

To take the maximum of the above, ALL the secondary coils of the transformers have to be connected IN-PHASE, except if there is really huge capacitance on each one.

Before you comment, try to read the entire sentence!
If there is not enough capacitance, to "support" the loading, then the voltage maybe drop up to half of what is expected!

Once more, the capacitors have nothing to do with it. The transformer outputs have been full wave rectified before being connected, therefore phasing is irrelevant. Phasing is irrelevant if there are smoothing capacitors and phasing is irrelevant if there are no smoothing capacitors. We are talking about DC.

So can we please stop confusing the OP with comments about phase?

[Damianos]

...
As far as the OP's ability to work with mains is concerned - I share the concern ... to a point.  There is not a lot to go wrong if they understand which side of a transformer is the primary and connect it to the mains appropriately.



Why do people continue to want to display their "knowledge" and confusing an already challenged person instead of paying attention to the real issues and looking at actually helping them?

If your knowledge and experience says that overheating a capacitor, by ripple current, is safe...
And that "the low load-current is the reason of the voltage drop", is an indication of understanding things.
I have to disagree!

For the rest I tried to explain...

[Damianos]

If we do the above for both connections (in-phase and anti-phase)

In phase or anti-phase is irrelevant, because in the circuit diagram the transformer outputs are DC rectified.

To take the maximum of the above, ALL the secondary coils of the transformers have to be connected IN-PHASE, except if there is really huge capacitance on each one.

Before you comment, try to read the entire sentence!
If there is not enough capacitance, to "support" the loading, then the voltage maybe drop up to half of what is expected!

Once more, the capacitors have nothing to do with it. The transformer outputs have been full wave rectified before being connected, therefore phasing is irrelevant. Phasing is irrelevant if there are smoothing capacitors and phasing is irrelevant if there are no smoothing capacitors. We are talking about DC.

So can we please stop confusing the OP with comments about phase?

Suddenly, by reading this, I had a flash and my mind detached! I don't know how and what happened! Maybe I need some relax. My mind was sticked with other things and I confused myself...
The one that for sure I have to do is to go back and "repair" my comments...

If anyone have spotted any other stupid thinking by me, let me know to try to correct that.
Thanks for your patience and tolerance!

[BenKenobi]

Sometimes the novice or trainee is not best served by providing the answer - but being led too the answer, to understand how and why things should work is the only way to know why they don't. I've trained many engineers and sometimes they just need to be made to think, they learn nothing from being given the answer on a silver platter constantly, it's a process whereby they read, they clarify, they gain understanding.

The use of full wave rectification in this manner is not efficient, to understand rectifiers and the implications of their use you must first understand AC, to understand the output from rectifiers and the purpose of the 11 ohm 'capacitor' and DC side requires you to know what the limits and capabilities of the load are.

Either way I stand by my remarks there is no way even two of these PSU's are going to provide 13 amps DC @ 48V - the builder needs to understand why.

[Brumby]

If your knowledge and experience says that overheating a capacitor, by ripple current, is safe...
And that "the low load-current is the reason of the voltage drop", is an indication of understanding things.
I have to disagree!

What on Earth are you talking about?

[Brumby]

Sometimes the novice or trainee is not best served by providing the answer - but being led too the answer, to understand how and why things should work is the only way to know why they don't. I've trained many engineers and sometimes they just need to be made to think, they learn nothing from being given the answer on a silver platter constantly, it's a process whereby they read, they clarify, they gain understanding.

Did you ever "train" someone thousands of miles away via teletype?  Because that's what is what you are trying to do here.

The OP has presented a schematic for a very basic power supply, which should work. (Before you jump in here ... read on)

The use of full wave rectification in this manner is not efficient

Maybe ... but efficiency isn't the key issue here.

to understand rectifiers and the implications of their use you must first understand AC,

For this exercise?  Please, NO.  The diodes are there, connected properly.  That's all that is needed for this exercise.

to understand the output from rectifiers and the purpose of the 11 ohm 'capacitor' and DC side requires you to know what the limits and capabilities of the load are.

That is just a confusing group of words.

The only thing that concerns me is that 11 ohm capacitor thing.  There is a big knowledge gap there.

Either way I stand by my remarks there is no way even two of these PSU's are going to provide 13 amps DC @ 48V - the builder needs to understand why.

You need to pay more attention to the information that has been supplied....

My load is brushless dc motor which can draw current upto 13amps

Up to .... keep reading.

How can i draw 10amps as i am using 2 5amp transformer in parallel

10 Amps ..... the OP only wants 10 Amps - which is not beyond the realms of possibility with the supplies built in the configuration presented.

So - if you want to challenge something, get the facts right first - please - otherwise you are just speculating.  If you keep guessing without checking the basis of your comments are accurate, you aren't going to do anything but confuse the heck out of the OP ... who is already struggling with what has been posted here.

...and as far as the 13 amps is concerned - it IS possible for the OP's original system to supply 13 amps ... for a very short time.


There is clearly something going on here - but nobody has obtained any information that can actually make definitive statements about what that is.

[VickySalunkhe]

By connecting the 2 transformer in series i am getting 52v after the bridge rectifier

In india its rare to find 15MF cap so i am using 6 , 2.2MF cap in parallel is that okay
But the problem is still unknown current drawn is max 1.5amp by using 4 transformer connected in series and parallel to achieve 52v 10A
But getting 52v 1.5A only

[BenKenobi]

So Brumby how about you step in - instead of just posting to berate those that do try to support.

I'm done here

[IanB]

By connecting the 2 transformer in series i am getting 52v after the bridge rectifier

In india its rare to find 15MF cap so i am using 6 , 2.2MF cap in parallel is that okay
But the problem is still unknown current drawn is max 1.5amp by using 4 transformer connected in series and parallel to achieve 52v 10A
But getting 52v 1.5A only

You've got to break the problem down, simplify things and test step by step.

First of all, take away the capacitors and test your system with a simple resistive load. See what current, voltage and power you can get just with that setup.

You have a nominal 48 V supply. You need a load that can draw up to 10 amps from it. That requires a low value, high power resistor. Let's see if we can improvise. Do you have an electric kettle, 3000 W preferably? That will have a resistance of 3000^2/240 = 19 ohms. If you put that across a 48 V supply you should draw a current of about 48/19 = 2.5 A. Can you try that and see if you do in fact get a current of about 2.5 A? And does the voltage stay up around 48 V when you do so? (And of course, make sure there is water in the kettle when you make the test, so it doesn't overheat and trip the thermal fuse.)

Make a test like that and get back to us.

[VickySalunkhe]

First of all Thanks everyone

I think too much confusion has been created in this post since it started
So I'll clear out what i have tried and what is the requirement.

I have made 2 psu 52v 5amp each
Using 4 transformer of 12-0-12 v 5amp transformer
CIRCUIT DIAGRAM IS ATTACHED

i have connected those 2 psu in parallel hoping that I'll get 10amp output
But not succeed in it (GOT 1.5 A MAX) by connecting the load

I have got brushless dc motor which is connected to controller and a throttle to speed up the motor
Controller can draw upto 13Amps

I have connected the single psu with Multimeter with no load to check current
DIAGRAM ATTACHED
i have a strong feeling what i have done to check current is inappropriate and dangerous
But just telling you what i have tried
I got 8.6amp from single psu

I have got readings while connecting the psu with motor
At no throttle i was getting 52V but as soon as i started using throttle the voltage started dropping and went down to 37V and tested current
At no throttle current was 0.5 amp and at full throttle current was 1.5amp
This time i have tested current by connecting the multimeter is series with +ve wire(correct way)

Now the real problem
I am expecting 10amp current draw from the psu but not able to get it and voltage is dropping drastically as i increase throttle
I would like to know should i connect fuse in the circuit to prevent and dangerous situation
I have got 10amp fuse and 500ma fuse
 
And as i am using basic multimeter which has no fuse would it be beneficial if i connect a fuse with the red lead
To prevent the multimeter from problem?

I don't have the kettle so I'll not be able to test it like you suggested.
Any other way you suggest to check current with no actual load?
Or
Shall i test it using resistor lower than 15ohm so that i can get current more than 3.3amp

Thanks

[IanB]

I have connected the single psu with Multimeter with no load to check current
DIAGRAM ATTACHED
i have a strong feeling what i have done to check current is inappropriate and dangerous
But just telling you what i have tried
I got 8.6amp from single psu

It seems like you connected the multimeter in the current range directly across the output of the power supply?

Yes, this is the wrong way to do it. It is very inappropriate.

But here's the thing. If you had a properly working power supply, the multimeter should have gone way off scale and blown the fuse. If there is no fuse, the multimeter should have started smoking and might have caught fire. You are lucky that didn't happen.

However, the fact that you didn't smoke your meter tells us your power supply is not working properly.

I think you should first test the transformers to see if they can really provide 5 A at 24 V, without any rectifiers or capacitors. You need to get a load from somewhere to test them with. How about car headlight bulbs? They will be typically 12 V and 50-60 W. Put two of them in series on a transformer and measure the current and voltage. Is it what it should be?

Next, put the rectifier after the transformer and try again. Do you still get the expected voltage and current?

[VickySalunkhe]

Could you plz suggest me any other way of testing it

As availability of load which runs on 12 or 24v with 100w power rating doesn't seem to be available with me.

[IanB]

If you wish to test a power supply, there is no other way than to use a testing load.

You have presumably purchased expensive transformers and rectifiers and capacitors. I am not sure why you cannot purchase some automotive bulbs to test with?

Another way it to get a very long length of thin steel wire with a resistance of about 5 ohms and use that. Since it will get hot you may wish to submerge it in a bucket of water.

[Damianos]

The 52V does not match with the voltages of the transformers. Without load it has to be at least ten volts higher.
What are the real characteristics of the transformers?
How are connected the primaries of the transformers?
What types of rectifiers are used?
...
Is possible to present any photos of the construction?

[Brumby]

So Brumby how about you step in

I have in the past - and will continue to do so .... so long as I am not adding to the confusion.

- instead of just posting to berate those that do try to support.

I don't mean to berate - I only want to point out when certain actions are less than helpful.  It is easy for people with specific knowledge to want to "share" it - even when doing so is just adding to the whirlpool which many beginners are already struggling with.

Any such comments of mine were aimed at helping the OP - not pandering to someone's ego.

[Brumby]

The 52V does not match with the voltages of the transformers. Without load it has to be at least ten volts higher.
What are the real characteristics of the transformers?
How are connected the primaries of the transformers?
What types of rectifiers are used?
...
Is possible to present any photos of the construction?

This is better.  Asking questions - and more importantly - relevant questions.

[Brumby]

An exercise for VickySalunkhe...

 * You say the output of your power supplies is 52V without any load connected.
 * You say you have a 15 ohm resistor.  What power rating is this resistor?  Can you provide a photo of it?  If it is at least several watts, then try the test below.

If it is not, then try to find a load resistor that has high power capacity - so it won't burn up during this test.  I have a 27 ohm resistor rated to 1800W.  It's an element from an old electric jug - and 27 ohms is a value that would still be useful for this test...

The Test:
1. Measure the resistance of the load resistor and make a note.
2. Power up one half of your supply that will give you the 52V output (disconnect the output from the other half)
3. Connect your meter to this output and confirm this voltage.  Make a note of the exact reading.
4. With the supply still on and the meter still connected, briefly connect the load resistor across the output of the supply.  DO NOT keep it connected for more than a second or two as it will heat up very quickly.  While it is connected, make a note of the voltage on the meter.

Tell us what the two voltage readings are and the value of the resistance.  We can work out a couple of things from that.

If you like, you can perform the exact same test on the other half of the supply and give us those numbers as well.  In fact, it is a good idea if you do.


Now I can hear murmurings about the fact that the resistance is going to be affected by the heating - but for this exercise, I am looking at getting some "ball park" calculations that might help guide further investigations.

[VickySalunkhe]

Sir first of all let me clear some stuff.
I get 52v output without load and with load also(when throttle is at ideal position)

I don't have the resistor i was thinking to buy one
It's hard to find resistor of that much wattage rating around here.

Can i try the method IanB suggested?
I.e, connect a steel wire whose resistance should be near to 5ohm
Then connect it to the psu and leave that steel wire in water (as wire will get hot)
If i can try this, Can i try with a long copper wire as it will have resistance too, i have got 70m of wire with me.

And i will try to bring you the readings asap

Thanks 

[Audioguru]

The DC voltage is too low and is full of ripple because the capacitors are probably 2.2uF instead of 2200uF. He wrote 2.2mF that does not say how many microfarads.
but with no load the voltage should be about 66VDC.

[VickySalunkhe]

It's 2.2mF
i.e, 2200uf
I have given all the values by checking it thrice

I have used 6 such cap in parallel i.e, 2200 * 6 = 13200uf  or 13.2mF
And i have also tried by connecting only 1 cap i.e, 2200uf or 2.2mF
But this both combination doesn't seem to make a diff more than a volt and current

[Ian.M]

Take a look at the Hammond Transformers Design Guide for Rectifier Use

The circuit configuration you are using is shown there as 'FULLWAVE BRIDGE Capacitor Input Load', and the maximum DC current you can draw is 62% of the RMS AC current, so your 12-0-12 5A transformer secondaries are only good for 3.1A DC (continuous rating) after the bridge rectifier and reservoir capacitor.  I'm assuming your transformer ratings are correct but that's yet to be confirmed by a load test as suggested by Brumby.

Calculating the required value of the reservoir capacitor for a particular application gets quite complex - it directly affects the amplitude of the ripple on the DC output, from Q=CV.  As a rough approximation, since you are in a country with a 50Hz mains supply, the capacitor has to hold the output voltage up for 10ms between peaks of the rectified waveform so the peak to trough ripple will be about (Iload*10ms)/C volts.  A rough rule of thumb, suitable for many applications is to use 2000uF per amp of load current, which gives about 5V ripple (actually a little less due to the conduction angle of the diodes in the bridge reducing the time the capacitor has to hold the voltage up for).  The capacitors used need to be able to handle the ripple current. This is a PITA to calculate without using a simulator as it involves determining the RMS of a non-sinusoidal waveform, but if you take it as 4/3 the DC load current its near enough.   Using too much reservoir capacitance is problematic - you risk exceeding the surge rating of your bridge rectifier diodes and may blow fuses on the secondary side of the transformer or trip over-current protection on the primary side.  Worst case, you may need a sequenced soft start circuit that limits the inrush current into the primary, and keeps the load disconnected until the reservoir capacitor is fully charged.

Transformers can handle large current overloads for a short time, a factor of two for under a second isn't usually a problem if you have sized your bridge rectifier and reservoir caps to cope with the surge, so done right, your transformers in series-parallel, if each is actually rated for 5A RMS (120VA), should be good for 6A running and a 12A startup surge.

[Brumby]

Sir first of all let me clear some stuff.
I get 52v output without load

This is clear

and with load also(when throttle is at ideal position)

This seems strange.  When there is a load placed on an unregulated supply, we would expect a voltage drop - but that does depend on what the load is and how much current it will draw.  When you say "when throttle is at ideal position" - it does not tell us a lot, since we do not know exactly what the load is.  Using a fixed resistor value and the voltage that is across it allows us to make accurate current measurements and perform some meaningful calculations in determining the capabilities of the power supply.

I don't have the resistor i was thinking to buy one
It's hard to find resistor of that much wattage rating around here.

The "resistor" I was talking about is an old-fashioned electric jug element.  Do you have them in your area?  They are mains rated with high power capability and if fitted to a jug, can be water cooled - this is perfect for this type of testing.  (Edit: While I don't believe it would be a problem, the actual resistance of such a jug element is important in choosing an appropriate configuration of your individual supplies.  See comment below. **)

But, there are other alternatives.....

Can i try the method IanB suggested?
I.e, connect a steel wire whose resistance should be near to 5ohm
Then connect it to the psu and leave that steel wire in water (as wire will get hot)
If i can try this, Can i try with a long copper wire as it will have resistance too, i have got 70m of wire with me.

You can certainly do this - but if you do, please make note of the following.....
** If your 'long wire' resistance is less than 10 ohms, you must do the test I suggested with either:
A. Both halves of the supply (all 4 sections) connected as you have shown in your complete supply
-or-
B. Separate all four sections and do an individual test on each one

If your 'long wire' resistance is less than 5 ohms, then it is too low to test anything.

These values are for testing the supplies at the maximum load condition you have specified - but a resistance a bit higher can still give us very useful information.  If your "long wire" resistor is 7, 12 or 19 ohms (under the rules above), then the results are still quite useful - we just need to know its resistance as accurately as you can provide.

[Damianos]

The 52V does not match with the voltages of the transformers. Without load it has to be at least ten volts higher.
What are the real characteristics of the transformers?
How are connected the primaries of the transformers?
What types of rectifiers are used?
...
Is possible to present any photos of the construction?

Some additional points:
What is the secondary voltage of each transformer (measured)?
What is the output voltage of each one of the four supplies? Independently, without connections between them and without any load.
Do the capacitors keep the voltage, when the mains is disconnected?
What is the voltage of each one when they are connected together? Again, without load.
...
Leave it running for a while without load. Is there any acoustic noise from the transformers or any other component?
After few minutes, disconnect the mains and check if anything has warmed up. Normally, all the parts must be at environment temperature. Use a thermometer, if available, otherwise be careful of what you are touching.
...
What are the specifications of the motor's controller?
Is the measured current stable or is it pulsing?

[Brumby]

The 52V does not match with the voltages of the transformers. Without load it has to be at least ten volts higher.
What are the real characteristics of the transformers?
How are connected the primaries of the transformers?
What types of rectifiers are used?
...
Is possible to present any photos of the construction?

Some additional points:
What is the secondary voltage of each transformer (measured)?
What is the output voltage of each one of the four supplies? Independently, without connections between them and without any load.
Do the capacitors keep the voltage, when the mains is disconnected?
What is the voltage of each one when they are connected together? Again, without load.
...
Leave it running for a while without load. Is there any acoustic noise from the transformers or any other component?
After few minutes, disconnect the mains and check if anything has warmed up. Normally, all the parts must be at environment temperature. Use a thermometer, if available, otherwise be careful of what you are touching.
...
What are the specifications of the motor's controller?
Is the measured current stable or is it pulsing?

Those are all reasonable questions - but there are a lot of them.

I would suggest the OP does the load test with the wire resistor and supply that information first.  That way, we should get a better idea of which particular questions should be asked next.

[VickySalunkhe]

Sry but due to some confusion i told you the wrong reading of voltage without load
Actual voltage lies between 58 v to 61v (no load voltage) depending on the place as i have tested it at some location I get voltage between 230v ac and 250v ac
And the load voltage is 52v

IMAGE OF PSU IS ATTACHED AND VOLTAGE IS CHECKED WITH NO LOAD

What is the secondary voltage of each transformer (measured)?

52V with no load (all four transformer connected with each other)

What is the output voltage of each one of the four supplies? Independently, without connections between them and without any load.

No load output of every transformer
Transformer 1 (12-0-12V 5amp)  :
  ac voltage  28.4V 
  dc voltage 25.7V

Transformer 2 (12-0-12V 5amp)  :
  ac voltage  28.4V 
  dc voltage 25.7V

Transformer 3 (12-0-12V 5amp)  :
  ac voltage  28V 
  dc voltage 25.2V

Transformer 4 (0-12V 5amp)  :
  ac voltage  13.5V 
  dc voltage 12.2V

(1)Transformer 1 & 2 is connected in series gaining 55.8V AC   and  51.1V DC
(2)Transformer 3 & 4 is connected in series gaining 41V AC   and  36V DC
(1) & (2) is connected in parallel

 

Do the capacitors keep the voltage, when the mains is disconnected?
What is the voltage of each one when they are connected together? Again, without load

Yes they keep the voltage
Voltage lies between 58v to 61v

 

Leave it running for a while without load. Is there any acoustic noise from the transformers or any other component?
After few minutes, disconnect the mains and check if anything has warmed up. Normally, all the parts must be at environment temperature. Use a thermometer, if available, otherwise be careful of what you are touching

Yes from one transformer , transformer no. 4
Not so much change in temperature
But once i have felt heating in transformer but after that never had noticed that

 

What are the specifications of the motor's controller?

IMAGE OF CONTROLLER
IMAGE OF THROTTLE
IMAGE OF BOTH CONNECTION IS ATTACHED

500w motor controller
Max current it can handle is 13A

I'll update more values by testing the psu as asked

Thanks guys

[Brumby]

Transformer 4 (0-12V) is not the same as the other 3 (12-0-12V)?  From your description and voltages, this would seem to be the case....

(1)Transformer 1 & 2 is connected in series gaining 55.8V AC   and  51.1V DC
(2)Transformer 3 & 4 is connected in series gaining 41V AC   and  36V DC
(1) & (2) is connected in parallel

This is not what we were expecting.  We were expecting the output of (1)Transformer 1 & 2 and (2)Transformer 3 & 4 to be the same - or very close to each other.  With the figures you have given, they should NOT be connected in parallel.

Aside from any other issues, this supply is not going to provide you with the output you want.  Section (1) is going to provide all the power until the supply is pulled below 36V.  Only then will section (2) start contributing.  If you want to draw 10A at 50V or so, you will be overloading section (1) since it can only deliver 5A.

Transformer 4 needs to be the same - and wired the same - as the other 3.


There is no need to do the "long wire resistor" test until this has been corrected.

[Brumby]

Had a closer look at your photo - and, yes, transformer 4 only has two wires on the secondary.

Just to be clear ... the description 12-0-12 can be written as 0-12-24 or 24-12-0.  They all are just as correct.  Transformers 1, 2 and 3 can be described as having 0-12-24V secondaries, with only the 0V and 24V connections used.

This is not compatible with the 0-12V secondary of transformer 4, for the symmetrical design you created.

[VickySalunkhe]

So sir do you mean
Because of transformer 4 or the connection (2)
The full supply is not given to the load .and it will power the supply only after the voltage readings goes down to 36V?

[Brumby]

(1) can only ever provide a maximum of 36V DC.

That means that (1) cannot contribute any power until the voltage of (2) has dropped to below this value.


For your circuit to work as expected, transformer 4 must have the same 24V output as the other three.

[Raj]

Add 2 separate current limiter and diodes to the mix assuming you want dc volts

it'll also make it start softly

[adras]

Let's try the diagnostic somewhere else, BenKenobi already mentioned it but it seems like everyone missed it.

Is your motor running at full speed when it draws just 1.5Amps? If this is the case the motor doesn't need more current. Try to slow it down while it is running, give it something to work, put a load on it, try to slow it own with your fingers, then the current will increase. And everything is working as it should.

[Brumby]

Before we try and get the OP to do anything else - how about we focus on getting them to sort out transformer 4?

[VickySalunkhe]

The motor is running on the full speed

I have tried stopping it but the voltage levels go down to 37v and push occurs from the motor and thr voltagr level starts again from  52v snd speed starts from 0 again

[adras]

That sounds good, how about the current draw? Does it still use only 1.5Amps when you try to stop it or does the current increase?

[VickySalunkhe]

Sir i have done the testing of my transformer individually
With a load of graphite present in a pencil it did get burst out in few seconds but i got the readings
Resistance on which i tested the transformer was around 7ohm

Readings for transformer 1,2,3 is almost same
Transformer 1,2,3 (12-0-12v 5A)
254V AC IN
29.8V AC OUT
26.3V DC OUT (AFTER RECTIFIER)
39.9V DC OUT (AFTER 6.6mF capacitor)
MAX CURRENT USING LOAD   5.9A

Transformer 4 (0-12v 5A)
254V AC IN
14.3V AC OUT
12.9V DC OUT (AFTER RECTIFIER)
19.14V DC OUT (AFTER 6.6mF capacitor)
MAX CURRENT USING LOAD   5.2A

Through all this reading i think the transformer is working fine
But I don't understand why the controller/motor is not able to fetch the current more than 1.5amp
Do tell me which other test reading should i provide
So you all can help me resolve my issue properly

Thanks

[Brumby]

Thank you for those readings.  They indicate the four sections of the power supply are basically functioning properly.

While there is still an issue with transformer 4 not being the same as the other 3, if the maximum current draw is less than 5A, it doesn't really matter.

The next question is: How thick and how long are the wires which carry the heavy current?  All wires have some resistance.  The thinner they are and the longer they are means higher resistance - and that will limit the current that can pass for any given voltage.

Some measurements can be helpful here.

The simplest is to select a reference point and connect one lead from your multimeter and leave it there for the rest of these measurements.  Connect the controller and motor so they are drawing the 1.5A current. Then measure the voltage at each end of each current carrying wire.  It would be good to draw a schematic and write those values at the appropriate places.



When you do want to draw more than 5A though, you must either replace transformer 4 with one the same as the other 3 or get another one the same as transformer 4 and connect it in series to give the necessary 24V AC (nominal).  (If you do the latter, this is where phasing is important: connecting the two secondaries in series will provide an AC voltage of either 0V or 24V, depending on whether you connect them in phase or out of phase.  You only need to get 24V output to know you've got it right - and this is fed into the diode bridge.)

[Brumby]

I understand we have a language barrier - and I have been trying to understand, but I am a bit lost here.  Can anyone else shed some light?

[adras]

Readings for transformer 1,2,3 is almost same
Transformer 1,2,3 (12-0-12v 5A)
254V AC IN
29.8V AC OUT
26.3V DC OUT (AFTER RECTIFIER)
39.9V DC OUT (AFTER 6.6mF capacitor)
MAX CURRENT USING LOAD   5.9A

Transformer 4 (0-12v 5A)
254V AC IN
14.3V AC OUT
12.9V DC OUT (AFTER RECTIFIER)
19.14V DC OUT (AFTER 6.6mF capacitor)
MAX CURRENT USING LOAD   5.2A

Those two values should be the same I guess. So transformer 4 seems to "broken". So let's get rid of that transformer. Only use transformer 1 and 2 which are identical. Both together provide at least 5Amp. Use only these two transformers, and check if the motor is using more current, something like 5Amp. If that works, it shows that transformer 4 is the problem. If it still not works, the motor is running idle and doesn't need more current and you need to give it some load like a propeller.

[VickySalunkhe]

The next question is: How thick and how long are the wires which carry the heavy current?  All wires have some resistance.  The thinner they are and the longer they are means higher resistance - and that will limit the current that can pass for any given voltage.

I will try to change something in new response
I too felt the old response a little confusing

Sir i have tried two combinations of connection  (main supply, psu, motor and controller)
as far as the length of wire is concerned
I have not measured the thickness but i have measured the resistance of wire
The wire is about 70meter long having a resistance of 3ohm which is used

1st connection
The long wire is connected before the psu (between main supply and psu) and then after the psu controller and motor is connected with a wire in between having a length of less than a 30cm
   
2nd connection
This is just opposite of above
Long wire is connected after the psu (between psu and controller).
  In this type i felt less torque compared to (1st connection)

Is this the answer you asked for ?
If not plz do tell me what readings you wanted to give you.

Thanks

[jm_araujo]

This topic is very confusing, and it seem it's approached the problem in the wrong angle.

I couldn't find any reference from the OP that the motor is loaded. The current on the motor will only increase if it has a load. If if running without a load it's expected that the current is low.

Also it's not very good idea to parallel 2 different power supplies, but in your case as they're not regulated the diode bridges will avoid any current flowing between them. The lower voltage one will only contribute when the parallel output voltage is lower than the voltage without load.

[VickySalunkhe]

Sir i have connected the controller and then the controller with motor only

Do you mean i need to connect any other load to the psu with the controller+motor to draw more current?

[jm_araujo]

A load to the motor is something mechanical connected to it. A propeller, a water pump, a bicycle wheel. It depends on the application.

A motor converts electrical power to mechanical. If it has no mechanical load, all the electricity that's consumed is for the inefficiencies (drag, winding resistance, etc).

[IanB]

as far as the length of wire is concerned
I have not measured the thickness but i have measured the resistance of wire
The wire is about 70meter long having a resistance of 3ohm which is used

This is very wrong. Why is the wire so long? A wire conducting power should be as short as possible and should have a resistance of a fraction of an ohm.

[VickySalunkhe]

Sir my ultimate aim was to build a psu to run the motor
JUST FOR TESTING PURPOSE


in later stage I'll be purchasing li-ion cell pack of 13s4p
But that is costing me too much at the stage i am present so I thought to think for that in a later stage

So i thought to build a psu to give the power to motor for testing purposes
I am building an E-Bike as a college project

So the motor here is (Hub motor with wheel)

Thats why i have used 70Meter of wire to test the body of bike and other stuffs

[VickySalunkhe]

Motor used here is a hub motor
Used in a vehicle so ultimately i am giving a mechanical load on it...

[adras]

Can you run a test with a wire length of 30cm? I mean the wires between motor and transformer

[Ian.M]

Due to the voltage drop from a long cable  or a poorly smoothed or regulated supply the operating conditions wont be at all similar to operating your motor controller from batteries, as intended in the final application.

You'd probably do better to source four used 12V Lead Acid car batteries of similar capacity, which could be in relatively poor condition as long as they can still hold a charge and don't have any dead cells so hopefully would be fairly cheap.   Batteries with removable caps so you can check the acid level and top up with distilled water are preferable but they are fairly rare nowadays.


Connect them in series to get a ripple free nominal 48V, that closely resembles the output of your proposed LiPO pack.  The load circuit should either be fused or have an appropriately DC rated circuit breaker, with the fuse or breaker rated to interrupt a minimum of 60V DC, as such a set of batteries even in poor condition could put a very large current through a short, and there is a risk of explosion if you short a recently charged Lead Acid battery and there is a cracked internal connection that cant carry the full short circuit current, or if the electrolyte boils due to Joule heating. 

Then you need to charge them - you could do so one at a time from a CC/CV bench supply with a series Schottky diode to prevent reverse current if input power is lost, or you could build a charger for them - probably the easiest would be 48V RMS from your transformers, a bridge rectifier and a series ballast resistor to limit the maximum charging current + a relay to disconnect its input power when fully charged.   Due to the unknown history of the batteries they are likely to have dissimilar actual capacities so will require balancing - for that you can simply add a shunt regulator across each one set to about 14V, that can pass the full charger output current.  Detect when all four shunt regulators are passing significant current, and start a timer to terminate the charge using the relay and disconnect the shunt regulators.  Charging should ONLY be performed with adequate ventilation.  Alternatively if you can obtain four small smart float chargers for Lead Acid batteries, with two wire mains leads (no ground), simply connect one across each 12V battery. 

[VickySalunkhe]

Sorry but the readings which i posted last time out of that
One of the transformer reading was wrong

New and correct readings are as such

259V AC IN

Transformer 1 (12-0-12v 5A)
29.8V AC OUT
26.3V DC OUT (AFTER RECTIFIER)
39.9V DC OUT (AFTER 6.6mF capacitor)
MAX CURRENT USING LOAD   5.2A

Transformer 2 (12-0-12v 5A)
14.8V AC OUT
13.01V DC OUT (AFTER RECTIFIER)
20V DC OUT (AFTER 6.6mF capacitor)
MAX CURRENT USING LOAD   4.3A

Transformer 3 (12-0-12v 5A)
29.9V AC OUT
26.6V DC OUT (AFTER RECTIFIER)
40.8V DC OUT (AFTER 6.6mF capacitor)
MAX CURRENT USING LOAD   5.2A

Transformer 4 (0-12v 5A)
14.3V AC OUT
12.7V DC OUT (AFTER RECTIFIER)
19.8V DC OUT (AFTER 6.6mF capacitor)
MAX CURRENT USING LOAD   4.3A

For a complete psu giving out 59V DC (without load)
(1)Transformer 1&2 are in series
(2)Transformer 3&4 are in series
(1) & (2) are in parallel

[adras]

Ok, to simplify things, please run the following test.

Use Transformer 1 and 3 only to power the motor. Use 30cm/11" cables between transformer and motor.

@All, if the wires have a too small diameter they should get hot/burn through, right? I doubt that too slim wires would just reduce the current flow in this "high" current scenario. 

[Brumby]

@All, if the wires have a too small diameter they should get hot/burn through, right? I doubt that too slim wires would just reduce the current flow in this "high" current scenario.

It depends ... but significant voltage drop over short lengths would be expected to heat things up noticeably.

Sorry but the readings which i posted last time out of that
One of the transformer reading was wrong

Transformer 2 (12-0-12v 5A)
14.8V AC OUT
13.01V DC OUT (AFTER RECTIFIER)
20V DC OUT (AFTER 6.6mF capacitor)
MAX CURRENT USING LOAD   4.3A

From this it seems you have only wired half of the secondary (the photo seems to support that).  In this case, the total voltage of (1) and (2) are close, so all 4 transformers of the supply can be used as you originally intended. 

From the current tests, you say "MAX CURRENT USING LOAD".  But what is the load?  This is very important for the readings to be meaningful.

Aside from the precise current capability, I am feeling less concerned about the supply at this point - but, as has been mentioned earlier, there are some questions surrounding the operation of the controller and the specific loading of the motor...

[VickySalunkhe]

A load of graphite present in a pencil is used as a load, it did get burst out in few seconds but i got the readings
Resistance on which i tested the transformer was around 7ohm
 

[Brumby]

So - just to confirm - your meter was in series with the 7 ohm graphite pencil - and this combination was then connected across the power supply being tested?  Thus the total load will be 7 ohms plus the resistance of the internal 10A shunt.

This cannot be right.  The maths simply does not work for transformer 2 and transformer 4 - even just using the 7 ohms as the total load.

Using Ohm's Law:  V=IR  rewritten as I=V/R

Thus: 20V DC / 7 ohms = 2.86A
and... 19.8V DC / 7 ohms = 2.8A

as such, these are maximum possible values and neither of these agree with the current readings given.

Something is wrong.


Can you please show us exactly how everything is connected when doing these current measurements.

[VickySalunkhe]

As soon as i turn on the psu the graphite used heat up and smoke used to come and the current rating increases drastically
I have given you the highest rating of current before the graphite has torn out leaving the circuit open.(ALL THIS HAPPEN WITHIN COUPLE OF SECOND)
So I don't know what is the actual resistance as the graphite heats up i think resistance will come down thus giving out more current

But the main task which was to test whether transformer can give out 5A or not was completed so i gave out the readings which i have got

[VickySalunkhe]

Final readings of motor connected to vehicle body and tested it by using a load of 70kg on the vehicle

70 meter long wire between main supply and psu
15 cm long wire between psu and controller
Width of wire  1mm

Transformer 1 (12-0-12v 5A)                                    Transformer 2 (12-0-12v 5A)
RATINGS WITHOUT LOAD
30V AC OUT                                                                      14.8V AC OUT
26.7V DC OUT (AFTER RECTIFIER)                                 13.01V DC OUT (AFTER RECTIFIER)
40.7V DC OUT (AFTER 6.6mF capacitor)                        20V DC OUT (AFTER 6.6mF capacitor)
RATINGS WITH CONTROLLER,MOTOR, THROTTLE (NO MECHANICAL INPUT ISGIVEN TO THROTTLE)
36V DV    0.06A                                                                 17V DC 0.11A

Transformer 1&2 in series
Without load      58.6V
With some input to throttle and controller, motor is connected
52.5V      0.05A
44.1V      0.55A
38V         1.11A
35V         1.45A
After 35V controller stops to give any power to motor and starts from 52V again


Transformer 3 (12-0-12v 5A)                                    Transformer 4 (0-12v 5A)
RATINGS WITHOUT LOAD
29.9V AC OUT                                                                  14.5V AC OUT
26.6V DC OUT (AFTER RECTIFIER)                                12.7V DC OUT (AFTER RECTIFIER)
40.8V DC OUT (AFTER 6.6mF capacitor)                       19.8V DC OUT (AFTER 6.6mF capacitor)
RATINGS WITH CONTROLLER,MOTOR, THROTTLE (NO MECHANICAL INPUT IS GIVEN TO THROTTLE)
36.1V DV    0.06A                                                                 16.8V DC 0.11A

Transformer 3&4 in series
Without load      58.5V
With some input to throttle and controller, motor is connected
52.5V      0.05A
44.4V      0.55A
38.4V         1.15A
34V         1.5A
After 34V-37V controller stops to give any power to motor and starts from 52V again

1+2   connected parallel with 3+4
53V         0.05A
47.9V      0.57A
43.9V      1.2A
37.1V      2.62A
42.2V      1.75A
49.6V      0.55A
36V          2.85A


As soon as the voltage drops down between 34V - 37V motor starts from starting i.e, 52V
Current reached to 2.6A max with a load of 70Kg on vehicle
With all 4 transformer connection


With 2 transformer connected serially
Max 1.36A current is attained


But theoretically i can get 7A of current
But practically current i am gettung is 2.6A
That's the problem
Plz help me to resolve the issue if any


Thanks

[StillTrying]

"After 35V controller stops to give any power to motor and starts from 52V again"

As the motor controller is expecting to be powered by lipo batteries it's probably switching off to protect the lipo batteries from over discharging.
I don't think you'll be able to get the current much higher than you already have from a transformer and bridge rectifier.

[VickySalunkhe]

I don't think you'll be able to get the current much higher than you already have from a transformer and bridge rectifier.

But why?
The configuration of transformer i purchased should deliver (5A) for what they are made for right?

Or is it like
In a center tap transformer
If 1,3 wire is joined with a bridge rectifier we get half the current for what the transformer was made for.

[Ian.M]

No.  If from an honest manufacturer, a transformer fed from a supply of its nominal primary voltage can supply its full rated RMS secondary current into a resistive load, without overheating if cooled as specified, and without the secondary voltage dropping below its rated value, *HOWEVER* a bridge rectifier followed by a capacitor is *NOT* a resistive load, even if there is a resistive DC load after the bridge rectifier.   You have to apply the derating factor of 0.62 for this configuration, as shown in  the PDF I linked back in reply#44:

Take a look at the Hammond Transformers Design Guide for Rectifier Use
...

That derating factor can be confirmed by circuit analysis, either manually or by SPICE simulation.

Therefore your 5A RMS transformer secondaries are only good for fractionally over 3A DC, when used with a bridge rectifier and reservoir capacitor.

[IanB]

I disagree. There is no derating factor for this application. The derating factor protects against overheating, it does not limit the maximum current the transformer can produce. For short periods of maximum load all that will happen is that the transformer might get a bit warm.

I think instead we have to look to the 70 m long wire. This was said to have a resistance of 3 ohms in a previous post. Is this resistance for just one leg, or for out and back combined?

5 A through 3 ohms will drop 15 V, and 5 A through 6 ohms will drop 30 V. This will drastically limit the voltage the motor sees when you open the the throttle and put a load on it.

[VickySalunkhe]

Therefore your 5A RMS transformer secondaries are only good for fractionally over 3A DC, when used with a bridge rectifier and reservoir capacitor.

Thats what i am worried about sir
As per your saying
I should get 3A from one transformer
But i am getting 1.3A from it
Which is the problem

[IanB]

Get your 70 m wire, join the two conductors together at one end, then measure the resistance between the two conductors at the other end. What is the total round trip resistance of the wire, out and back?

[VickySalunkhe]

Sir today i have tried to replace the 70meter wire with 30cm wire
But there was not any major difference between the readings which i have posted today only...

[Ian.M]

The derating factor is applicable if you dont want to burn up your transformer in continuous operation.  Transformers are not fussy pieces of silicon, they are Iron, Copper and usually plastic insulation, and they tolerate brief overloads well as long as the deep winding temperature stays under the maximum temperature rating of the wire insulation.   Better manufacturers will even specify permissible overload factors and duty cycles.

Therefore your 5A RMS transformer secondaries are only good for fractionally over 3A DC, when used with a bridge rectifier and reservoir capacitor.

Thats what i am worried about sir
As per your saying
I should get 3A from one transformer
But i am getting 1.3A from it
Which is the problem

You can get UP TO 3A continuously without burning out your transformer, and probably 6A for a few seconds, but that doesn't mean your motor controller *will* draw 3A (or 6A).

I think instead we have to look to the 70 m long wire. This was said to have a resistance of 3 ohms in a previous post. Is this resistance for just one leg, or for out and back combined?

5 A through 3 ohms will drop 15 V, and 5 A through 6 ohms will drop 30 V. This will drastically limit the voltage the motor sees when you open the the throttle and put a load on it.

I agree that much of the problem is the wire resistance.  1mm dia wire is near enough 18AWG, which if made from good quality electrical grade copper should be about 21 milliohms per meter.  For 140 meters (70 m there and back), that comes to almost exactly 3 ohms.

[VickySalunkhe]

Get your 70 m wire, join the two conductors together at one end, then measure the resistance between the two conductors at the other end. What is the total round trip resistance of the wire, out and back?

5 Ohm

[Ian.M]

Can you confirm the 1mm wire diameter?  Also, what's its strand count and individual strand diameter?   Stranded wire can have up to 1/3 more resistance than solid wire of the same diameter, due to its packing fraction (i.e. the voids between close packed circular strands), but that would only account for 4 Ohms of resistance.  If you are measuring 5 Ohms and its not a measurement error, and the diameter is actually 1mm, it implies the copper is crappy, with a bulk resistivity 25% higher than pure electrical grade copper.

[WaveyDipole]

I had a look at the photo and am concerned as to how TX2 is wired. It is difficult to tell on the photo but I fear that there may perhaps be some confusion because instead of red-blk-red as per TX1 and TX3, TX2 has the opposite, i.e. blk-red-blk. It is difficult to tell which wire goes to the right side of the terminal block, but the direction of loops in the black wires seem to suggest that one of the black wires is wired into the left side of the connector block but has had a length of insulation stripped back at its mid point (just left of exit point of the red wire) and then the end of the topmost black wire loops back and its end is wrapped around this same point. The red wire then seems to go to the right terminal of the connector block. I hope that is NOT what is going on here and perhaps this is the bare end of one black dangling loose above the other and obscuring the insulation otherwise that TX would be getting really hot! The red wire should be the center tap and ought to be left disconnected. The two black wires should be connected to the connector block, but apologies if I have mis-interpreted the picture.

[VickySalunkhe]

Can you confirm the 1mm wire diameter?  Also, what's its strand count and individual strand diameter?   

Wire diameter 0.83mm
Strand count   10
Strand diameter   0.3mm

[Ian.M]

There's something wrong there as the sum of the strand cross section areas (CSA) comes to more than the overall CSA calculated from the overall diameter.

70m of a solid pure copper wire of 0.83mm diameter would be 2.174 ohms, so with the loss due to the voids between strands 5 ohms is in the right ballpark for 70m x 2 wires.

That wire is ludicrously thin for the purpose - 2.5 mm² mains flex would be a far better choice, and I would strongly advise at least 2000uF per Amp bulk decouping at the motor controller as I bet it draws high current pulses.

[VickySalunkhe]

Sir can you plz
Tell me how you calculated all this calculation
And what do they mean?

And what minimum diameter wire shall i use for this purpose
Thanks

[Ian.M]

resistance = resistivity × length / area
area=Pi*(d/2)²

Wikipedia says: Pure Copper electrical resistivity = 16.78 nanoohm·m (at 20 °C)

The rest is just simple maths.

In practice it will be worse than the calculation gives because the copper wont be 100% pure and the overall diameter makes no allowance for the voids between strands.

The minimum wire diameter is determined by how much voltage drop your application can tolerate.   Calculate the maximum wire resistance you can tolerate then look through a cable manufacturer's catalog for a cable with a low enough resistance per meter to be under that after multiplying by the total wire length there and back.

[VickySalunkhe]

The minimum wire diameter is determined by how much voltage drop your application can tolerate.   Calculate the maximum wire resistance you can tolerate then look through a cable manufacturer's catalog for a cable with a low enough resistance per meter to be under that after multiplying by the total wire length there and back.

Sry
But I didn't get any of this sir.

How would i know how much minimum voltage drop my application can tolerate or what does it mean actually?

How would i know what is the max wire resistance i can tolerate?

How would i know what diameter wire can support 5A current and have minimum resistance.....

[Damianos]

Most of the presented measurements seem a little or a lot strange!
For example, the voltage with a 50mA load is six volts lower than what measured without load!
It is not clear where the measurements are done. Are these on the controller or at the output of the circuit?

You forgot to say what are the types of the rectifiers. Have you found a datasheet of them?
Are the transformers of any "special" type? What is showed on their labels?
Are all the capacitors of the same type/model? What is their working voltage rating?

How is the circuit constructed, under the cartons? Is possible to show a photo?
Are connected the components with very thin wires? There are mentioned measurements with and without the capacitors, how are they connected and it is so easy to disconnect and reconnect them?
... ...

One more test that you can do, is to try to measure the ripple voltage of the power supply. Set your meter to AC voltage, measure at the output without and with a little load, on each of the four and the entire combination of them. [with capacitors connected]
If an instrument with peak detect is available, the above will be more informative.

[Brumby]

The minimum wire diameter is determined by how much voltage drop your application can tolerate.   Calculate the maximum wire resistance you can tolerate then look through a cable manufacturer's catalog for a cable with a low enough resistance per meter to be under that after multiplying by the total wire length there and back.

While straightforward to many of us, I was concerned that this was too much of an ask from our OP.  So, rather than set them on a difficult task, I had a look at the cable they have at hand.

From the photo, it would seem the OP is using a mains rated cable - thick white sheath with red and black insulated wires within - but that it would be at the lower end of current carrying capacity.  My guess is it would be for lighting circuits.  Also, at 5 ohm for 140m it works out as 0.036 ohms per metre.  With 10A current that is about 0.7V drop per metre of twin cable.  So long as the cabling throughout the supply is of at least this gauge and the total length from the transformers to the load is less than, say, 2m I can't see a 1.5V drop being a problem.  Going heavier gauge is never a bad idea - but this should work for testing.

Questions to OP:
 1. Is all the wiring connecting all your components of this gauge or thicker?
 2. What is the total length of wiring from the transformer to the load?  (Just answer for a single wire - and we will double it for any maths.)

How is the circuit constructed, under the cartons? Is possible to show a photo?

This is something I have wondered as well.  In the photo, I don't see any soldered joints, just the terminal blocks used to connect the transformers.  How are the connections we can't see being made?  If you are simply twisting wires together, then there is going to be a lot of potentially poor connections, especially for pulling currents of 5A and more.  Heavy current connections need to have very good contact or you will lose a lot of power.  The terminal blocks are a good move, but what else are we not seeing...?

Request to OP:
 3. Can you please show us a photograph of the hidden wiring?

It is not clear where the measurements are done. Are these on the controller or at the output of the circuit?

This has been a problem from the very outset.  Where you measure a voltage is important and for higher current situations can be absolutely critical for understanding what is actually going on.  There is also the issue that we are not seeing the complete setup, so there may be some hints or obvious errors that are invisible to us.

Request to OP:
 4. Can you please provide a schematic of the entire circuit - from the supply, through the controller to the load?  (Do not try to look inside the controller - just show the connections to it.)

One more test that you can do, is to try to measure the ripple voltage of the power supply. Set your meter to AC voltage, measure at the output without and with a little load, on each of the four and the entire combination of them. [with capacitors connected]

This would be an interesting - and useful - test.

With no load, we would expect this AC voltage to be pretty small and, essentially, insignificant.  When this DOES become interesting is when you put a load on it.  I would be interested to see what it was like at around 1A load current.  The actual current isn't hugely important - but if you can measure it accurately, that will help in doing some math.  Oh, and don't forget to do the DC voltage measurement as well.

Request to OP:
 5. Can you test the supply as suggested showing:
    a) DC volts, AC volts - with no load  and..
    b) DC volts, AC volts, DC amps - for a load current between 0.5a and, say, 3A

[Connoiseur]

Suggestion to OP:

You can make your own crude resistive load from nichrome wire wound on a suitable former like ceramic tile or a mud brick, although personally, I prefer brick as it does not crack on heating. Nichrome wire is easily available in most of the electrical shops as heater wire rated 1500W at 230V. Alternatively you can buy a rheostat of suitable rating.

In practice it will be worse than the calculation gives because the copper wont be 100% pure and the overall diameter makes no allowance for the voids between strands.
 

I beg to differ. Commercial copper wires available today have more than 100% of IACS conductivity. Also, the area mentioned on the wire (at least the ones IS 694:2010 certified) is the actual area of all the strands combined, so the "packing void factor" is ruled out. But yeah, the temperature may not be 25 deg. C at OP's location, so the resistance will be a bit higher.

[Ian.M]

In practice it will be worse than the calculation gives because the copper wont be 100% pure and the overall diameter makes no allowance for the voids between strands.
 

I beg to differ. Commercial copper wires available today have more than 100% of IACS conductivity. Also, the area mentioned on the wire (at least the ones IS 694:2010 certified) is the actual area of all the strands combined, so the "packing void factor" is ruled out. But yeah, the temperature may not be 25 deg. C at OP's location, so the resistance will be a bit higher.

IACS commercial grade annealed copper: 17.241 nanoohm·m, 
Wikipedia's figure for Pure Copper: 16.78 nanoohm·m, both at  20 °C.
Modern commercial grade copper is between the two, due to process improvements since the IACS standard was set in 1913.

I would no longer bet on cheap wire being made with pure commercial copper - if its made of low purity recycled copper, contaminated with brass, solder and other metals, its resistivity can be significantly higher, before the impurity level rises to the point where the decreased ductility adversely affects the wire drawing process.

Also the O.P. quoted the wire diameter as 0.83mm (presumably measured), which I then calculated the area from, as the strand diameter and count was inconsistent and did not give the CSA.  Therefore I stand by what I said.

[VickySalunkhe]

First i have done some changes in the circuit with wires
which resulted in increase of output current by 1 amp i.e, max i can get is 3.5A from my psu. But still its half way down considering the fact my output current will be 62% of rated current value.

and an update in readings of previous wire  used  length of wire was 35 meter sorry, but because of some confusion i told you 70 meter earlier

Wire used between psu and controller
and between capacitor, rectifier.....
TOTAL length of wire used back and forth 1.9 meter
Diameter of wire     2.5 mm
No. of strands         36
Strand diameter     0.33 mm

same wire was used between main supply and psu for carrying 252 V AC
Length of that wire 37 Meter [of one wire   double it for two wires]
resistance of above wire (two wires connected) 1.3 ohm

1. Is all the wiring connecting all your components of this gauge or thicker?

Previously wire was thin of 0.83mm  but now as i have said earlier because of changes done
Thicker wire .

2. What is the total length of wiring from the transformer to the load?  (Just answer for a single wire - and we will double it for any maths.)

TOTAL LENGTH  both side  1.9 Meter ( don't  double this value)

How is the circuit constructed, under the cartons? Is possible to show a photo?

 3. Can you please show us a photograph of the hidden wiring?

IMAGES ATTACHED OF CONNECTION AND HOW MULTIMETER IS USED AND WHERE.

4. Can you please provide a schematic of the entire circuit - from the supply, through the controller to the load?  (Do not try to look inside the controller - just show the connections to it.)

IMAGE OF SCHEMATIC ATTACHED

One more test that you can do, is to try to measure the ripple voltage of the power supply. Set your meter to AC voltage, measure at the output without and with a little load, on each of the four and the entire combination of them. [with capacitors connected]

5. Can you test the supply as suggested showing:
    a) DC volts, AC volts - with no load  and..

Transformer / Circuit                DC VOLTAGE                  AC VOLTAGE                  Full Circuit 58.6V 128.6V 1 & 2 (IN SERIES) 58.2V 127.6V 3 & 4 (IN SERIES) 58V 127.6V transformer 1 39.2V 85.7V transformer 2 19.2V 41.8V transformer 3 39.4V 86V transformer 4 18.93V 40.8V     b) DC volts, AC volts, DC amps - for a load current between 0.5a and, say, 3A Full Circuit 1 & 2 (IN SERIES) 3 & 4 (IN SERIES) 56.8VDC      125VAC     0.05 A                56.1VDC      123.2VAC     0.05 A                55.8VDC      122.9VAC     0.05 A 46.5VDC      99VAC     1.5 A 49.1VDC      108.2VAC     0.5 A 49.8VDC      109.3VAC     0.5 A 43.5VDC      95VAC     2 A 43.5VDC      96.2VAC     1 A 44.6VDC      98.1VAC     1 A 37VDC      81VAC     3.4 A(MAX) 42VDC      92VAC     1.16 A(MAX) 43VDC      94.3VAC     1.17 A(MAX) Readings for full circuit are not accurate as i was not able to take readings on specific current value as i have taken for half circuit I have some doubts now despite of changing the wire which can handle 10amps psu is not able to supply even 7A I have strong doubt about the center tap transformer i think i have read somewhere by connecting wire 1 and 3 we get half the rated current is that true ? All the connections are rigid now so there will be no leakage current think so... TWO MORE REPLIES ARE ADDED BECAUSE I WAS NOT ABLE TO UPLOAD ALL THE IMAGES BECAUSE OF POST RESTRICTIONS

[VickySalunkhe]

Two more images

need to upload two more
was not able to do so because of post restriction
sorry for inconvenience 

[VickySalunkhe]

Last two images

Query still remains the same
Despite of bulding psu for giving output of 10A or 7A( because of losses)
I am still getting 3.5A max which is still half than what i am expecting.

[Zero999]

My bet is poor wiring. The solder joints are not wetted properly and twisting wires together like that doesn't ensure a good electrical connection!

[Damianos]

Bad wiring, that's for sure.
As mentioned all the solder joints need "repair", also the twisted wires need soldering, especially the connections of the rectifiers.
By the way, are the mains' connections well made and safe? It looks like there are bare feet there!

Some more notes:
- if the rectifiers are all the same, they are 35A/1000V, that is good enough. But this seems that is the only one good thing here!
- if the capacitors are all the same, some of them are abused! On one of them it is written 50V![Edit: it seems that I have confused the numbers! These capacitors have enough voltage margin.]
- the transformers have all the same dimensions, but two of them are 60VA and the others are 120VA, this is not possible!

The refereed AC values are not related with something else, at least they don't seem as ripple voltages. Where are they measured? Maybe the instrument has a strange behavior when it has AC over DC at its input(?).

[VickySalunkhe]

- if the capacitors are all the same, some of them are abused! On one of them it is written 50V!
- the transformers have all the same dimensions, but two of them are 60VA and the others are 120VA, this is not possible!

I have made the connections to the transformer as such to get
Around 38V from two transformers
Around 14V from remaining two transformers
I have total 4 transformer
3 of them are center tapped transformer 12-0-12V 5amp
4th transformer is 0-12V 5amp
Out of 3 center tapped transformer one transformer wiring had been done (wire 1,2 connected) so as to get 14V to match up with 4th transformer



And I tried to solder the wire with the rectifier but the solder wire is not getting stuck woth rectifier metal points.

[Ian.M]

What soldering iron are you using?

If the iron isn't up to the job, you'd be better off connecting the rectifiers with female spade crimp terminals, and joining the wires with screw terminals - either with ring crimp terminals secured by the terminal screw, no more that three ring terminals per screw, or by screw 'choc' block terminals with no more than two wires per side per hole.

[VickySalunkhe]

Will replacing the copper wire used for connections
With metal wire solve the issue of bad wiring?
Single Metal wire of thick width of about 2mm?
Will that work?

[Brumby]

Will replacing the copper wire used for connections
With metal wire solve the issue of bad wiring?
Single Metal wire of thick width of about 2mm?
Will that work?

Don't bother with that.  The copper wire used here should be more than good enough to solve your major problems.  Whether you need to go any thicker is a question for later.

When the phrase "bad wiring" is used here, we are talking about how well the terminations have been done.  In short - your connections are poor.

If we were to criticise the actual wire you have used, we would have said things like "poor quality wire", "inadequate" or things like that.

[Brumby]

I have strong doubt about the center tap transformer
i think i have read somewhere
by connecting wire 1 and 3 we get half the rated current is that true ?

No.

Only the voltage of a centre-tapped secondary is different, depending on which connections you use.  The current rating will be the same for any combination.

[Brumby]

5. Can you test the supply as suggested showing:
    a) DC volts, AC volts - with no load  and..

Transformer / Circuit	DC VOLTAGE	AC VOLTAGE
Full Circuit	58.6V	128.6V
1 & 2 (IN SERIES)	58.2V	127.6V
3 & 4 (IN SERIES)	58V	127.6V
transformer 1	39.2V	85.7V
transformer 2	19.2V	41.8V
transformer 3	39.4V	86V
transformer 4	18.93V	40.8V

    b) DC volts, AC volts, DC amps - for a load current between 0.5a and, say, 3A

Full Circuit	1 & 2 (IN SERIES)	3 & 4 (IN SERIES)
56.8VDC      125VAC     0.05 A	56.1VDC      123.2VAC     0.05 A	55.8VDC      122.9VAC     0.05 A
46.5VDC      99VAC     1.5 A	49.1VDC      108.2VAC     0.5 A	49.8VDC      109.3VAC     0.5 A
43.5VDC      95VAC     2 A	43.5VDC      96.2VAC     1 A	44.6VDC      98.1VAC     1 A
37VDC      81VAC     3.4 A(MAX)	42VDC      92VAC     1.16 A(MAX)	43VDC      94.3VAC     1.17 A(MAX)

Readings for full circuit are not accurate as i was not able to take readings on specific current value as i have taken for half circuit

Those AC volts readings are bizarre.

[Damianos]

- if the capacitors are all the same, some of them are abused! On one of them it is written 50V!
- the transformers have all the same dimensions, but two of them are 60VA and the others are 120VA, this is not possible!

I have made the connections to the transformer as such to get
Around 38V from two transformers
Around 14V from remaining two transformers
I have total 4 transformer
3 of them are center tapped transformer 12-0-12V 5amp
4th transformer is 0-12V 5amp
Out of 3 center tapped transformer one transformer wiring had been done (wire 1,2 connected) so as to get 14V to match up with 4th transformer



And I tried to solder the wire with the rectifier but the solder wire is not getting stuck woth rectifier metal points.

I was wrong! The voltage rating of the capacitors looks good enough.

The power of the transformers that you have are 12V*5A=60VA and 24V*5A=120VA, but they have the same dimensions.

[Brumby]

The power of the transformers that you have are 12V*5A=60VA and 24V*5A=120VA, but they have the same dimensions.

My guess is that the manufacturer got a great deal on E-I cores and made up a couple of variants with different secondaries.  (There's less copper in the 60VA versions.)

[Brumby]

5. Can you test the supply as suggested showing:
    a) DC volts, AC volts - with no load  and..

Transformer / Circuit	DC VOLTAGE	AC VOLTAGE
Full Circuit	58.6V	128.6V
1 & 2 (IN SERIES)	58.2V	127.6V
3 & 4 (IN SERIES)	58V	127.6V
transformer 1	39.2V	85.7V
transformer 2	19.2V	41.8V
transformer 3	39.4V	86V
transformer 4	18.93V	40.8V

    b) DC volts, AC volts, DC amps - for a load current between 0.5a and, say, 3A

Full Circuit	1 & 2 (IN SERIES)	3 & 4 (IN SERIES)
56.8VDC      125VAC     0.05 A	56.1VDC      123.2VAC     0.05 A	55.8VDC      122.9VAC     0.05 A
46.5VDC      99VAC     1.5 A	49.1VDC      108.2VAC     0.5 A	49.8VDC      109.3VAC     0.5 A
43.5VDC      95VAC     2 A	43.5VDC      96.2VAC     1 A	44.6VDC      98.1VAC     1 A
37VDC      81VAC     3.4 A(MAX)	42VDC      92VAC     1.16 A(MAX)	43VDC      94.3VAC     1.17 A(MAX)

Readings for full circuit are not accurate as i was not able to take readings on specific current value as i have taken for half circuit

Those AC volts readings are bizarre.

Not only are those AC voltage readings way too high, but they should be increasing with greater load, not decreasing.

These AC voltage readings should have been made across the capacitors - exactly the same points as the DC voltages.  Is that where they were made?

[VickySalunkhe]

These AC voltage readings should have been made across the capacitors - exactly the same points as the DC voltages.  Is that where they were made?

YES

[Brumby]

This may sound like a strange request - but repeat just one of those AC voltage measurements and then swap the meter leads and measure it again...

Does the meter give you the same reading?

[VickySalunkhe]

This may sound like a strange request - but repeat just one of those AC voltage measurements and then swap the meter leads and measure it again...

Does the meter give you the same reading?

NO

While testing the AC voltages swapping the meter leads gave output of 0V for all combinations

[Brumby]

Now I am officially confused.

How come we have gone from AC measurements ranging from 40V to 126V - to 0V?

[Damianos]

The power of the transformers that you have are 12V*5A=60VA and 24V*5A=120VA, but they have the same dimensions.

My guess is that the manufacturer got a great deal on E-I cores and made up a couple of variants with different secondaries.  (There's less copper in the 60VA versions.)

Maybe it is more cost effective for them to use the same cores and bobbins (?).

[VickySalunkhe]

Sir
I am testing a dc voltage by setting the dial on ac
So it must give high voltage on one side and 0 voltage on other side right

Am i right?
Or
You are asking something different which i have not got yet

[Damianos]

Obviously the instrument has not an AC coupling, so it shows strange results. It is seemed that it uses half wave rectification...
If there is a capacitor available, of more than 1 micro Farad, putting it in series with the instrument will give an indication of the ripple. This has to be zero without load and increasing with the output current.

[Brumby]

Obviously the instrument has not an AC coupling, so it shows strange results. It is seemed that it uses half wave rectification...

That is not obvious - but it is a possibility.

What is obvious is that we have some measurement issues.

If there is a capacitor available, of more than 1 micro Farad, putting it in series with the instrument will give an indication of the ripple. This has to be zero without load and increasing with the output current.

This is an idea - but the capacitor must be allowed to charge up to match the DC offset.

[Damianos]

Obviously the instrument has not an AC coupling, so it shows strange results. It is seemed that it uses half wave rectification...

That is not obvious - but it is a possibility.

What is obvious is that we have some measurement issues.

How do you explain this:

This may sound like a strange request - but repeat just one of those AC voltage measurements and then swap the meter leads and measure it again...

Does the meter give you the same reading?

NO

While testing the AC voltages swapping the meter leads gave output of 0V for all combinations

... if it is AC coupled?

If there is a capacitor available, of more than 1 micro Farad, putting it in series with the instrument will give an indication of the ripple. This has to be zero without load and increasing with the output current.

This is an idea - but the capacitor must be allowed to charge up to match the DC offset.

What prohibits the capacitor to charge up?

[VickySalunkhe]

How do you explain this:

This may sound like a strange request - but repeat just one of those AC voltage measurements and then swap the meter leads and measure it again...

Does the meter give you the same reading?

NO

While testing the AC voltages swapping the meter leads gave output of 0V for all combinations

... if it is AC coupled?

Sir as i am using full wave rectifier to convert ac to dc
One side will be double of the orginal amplitude
So acc. To that other side will have 0 V

So that's what i am getting
While i am getting some reading when i swap the meter leads of multimeter to the connection
It shows 0V and it should right?

[Damianos]

I can not understand the meaning of your description. Where do you mean there is a double voltage?
What are you measuring? Can you show this on a diagram?

[Brumby]

Obviously the instrument has not an AC coupling, so it shows strange results. It is seemed that it uses half wave rectification...

That is not obvious - but it is a possibility.

What is obvious is that we have some measurement issues.

How do you explain this:

This may sound like a strange request - but repeat just one of those AC voltage measurements and then swap the meter leads and measure it again...

Does the meter give you the same reading?

NO

While testing the AC voltages swapping the meter leads gave output of 0V for all combinations

... if it is AC coupled?

The OP isn't measuring what you think they are measuring.  This is borne out by this post of yours...

I can not understand the meaning of your description. Where do you mean there is a double voltage?
What are you measuring? Can you show this on a diagram?

... and this is something that I have been wanting to see for some time.  I have an answer in the pipeline...

If there is a capacitor available, of more than 1 micro Farad, putting it in series with the instrument will give an indication of the ripple. This has to be zero without load and increasing with the output current.

This is an idea - but the capacitor must be allowed to charge up to match the DC offset.

What prohibits the capacitor to charge up?

The impedance of the multimeter and time.  With a fully discharged 1uF cap and a 10M DMM input impedance, it will take around a minute for it to charge within 10% of the supply voltage and close to 2 minutes to get within 1%.  If there are any DC offset issues with the meter, then the DC component of the measurement setup needs to be zero.  There is a way to speed this up, though.  Simply charge the capacitor directly off the supply first.  One more consideration - that the capacitor have low leakage, otherwise the DC current flow could cause problems.

[Gregg]

Sometimes it is better to just start over.  By that I mean take it all apart and put it back together one part at a time making sure all connections are really good.  Test each part before connecting it to another and then test in circuit at each logical step of the assembly process.  Labeling the wires may help to test further as you assemble each power supply. 
1.   Take one transformer and test the input AC voltage and output voltage no load.  Make sure the output is what you expect and for the dual winding ones this will ensure they two aren’t cancelling each other.
2.   If possible put a load on the transformer output and measure the voltage again both in and out.  Write down the results
3.   Next add a bridge rectifier and test again both open circuit and with a load for AC volts on the input of the rectifier and DC volts on the output terminals
4.   I would leave the capacitors out until near the final testing
5.   After you have assembled the two higher voltage systems, try paralleling them and take some more readings.  If they are what you expect try them on the motor control and see what happens.
6.   Continue piece by piece in an orderly fashion until it either works or you see something that isn’t right.
7.   Post the results.

This is how you learn, by making mistakes and figuring them out; lessons you won’t forget.

( It is quite rare to officially confuse Brumby )

[VickySalunkhe]

Sir
Readings on
Post no. 98 was taken by rebuilding the circuit part by part as you suggested
By which i got an increase of output current by 1amp
But still it wasn't upto expectation

I have provided you all the true readings
I don't know
Whether i have been wrong with the readings you all asked for or not.

I think brumby got confused as soon as i posted readings of ac voltage to find out the ripple

Can any one plz tell me little bit clearly what was he actually asking for
And from where should i measure it and with which parts connected to thr transformer


I have taken all those reading while all parts (cap, rectifier,motor) were connected

And took the readings from the points where i have taken the readings of dc voltage
For ac i just switched the dial of multimeter to ac voltage

Is that wrong  or something is?

[Brumby]

I am drawing up something that will make the measurement process clear....  I have some pressing priorities, so please be patient.

[Gregg]

I guess I thought I could slip in a lesson in basic physics for you to see hands on what happens when trying to parallel rudimentary DC power supplies.  Also I was curious as to how much the mains voltage dropped when this system was attempting to power your full load and to see if there was significant voltage drop across any of the twisted wire connections or bridge rectifiers with a bad diode.

Basically the power supply with the greatest potential (voltage) will try to power the entire load.  Other power supplies at lower potential won’t contribute anything unless the highest potential one sags to the next supply’s potential and even then the load won’t be shared equally.

This is very similar to charging lithium batteries and need for balancing every cell (only in reverse). 

You could make actively controlled rectifiers using things like SCRs and balancing control circuitry to effectively force each power supply to the same potential with current control for dissimilar transformer output capacities but that is way beyond the scope of this thread and hardly worth the time and effort considering a single transformer of suitable capacity would be much cheaper in your case.

The telco industry uses nominal 48 volts DC supplied by huge batteries and multiple chargers (called rectifiers in telco language) that all parallel and share the load.  If the share wiring between the chargers gets compromised then they fail to share but they have the safety of current limiting where some rectifiers go to full load and others go to zero load.  They also have at least one more rectifier on line at any given time than absolutely necessary (N+1 redundancy) 

In your system the transformer with the highest potential provides current until magnetic saturation and there is no current limiting or voltage regulation to save it.

[Brumby]

OK...  Reference schematic....



How I envisage measurement requests...
V_AB = Voltage between points A and B
V_JK = Voltage between points J and K
I_L = Current flowing past point L
I_J1 = Current from Section 1 flowing past point J
I_J2 = Current from Section 2 flowing past point J
I_J = I_J1 + I_J2  (Kirchhoff's current law)

V_KQ = Voltage drop from point K (supply) to point Q (controller)

.. and how they would be reported.


I hope I have it right.  All equipotential points within the supply have been considered to be exactly that.  Only for the longer wires has there been an allowance to measure voltage drops.

Hopefully this will allow for unambiguous measurement reference points - which I hope will be a start in clearing some confusion.  We still need to be conscious of clear communication with regards to specifying AC and DC ... and anything else we need to be aware of - such as the specific conditions (eg load) under which these measurements are made.


Apologies if I don't participate as significantly over the next several days... some other priorities I cannot ignore.

[VickySalunkhe]

Hello sir
First of all thankyou very much for helping me out

Just wanted to tell you that i have told you all the readings from the points you have mentioned above
Expect for the current from point L

I don't understand there one thing
I'm connecting a +ve and -ve wire for a series connection
How can i measure current from there ,   can i ?

And how can i measure this
VKQ = Voltage drop from point K (supply) to point Q (controller)

I am sorry but it got me little confusing.

Thanks

[Brumby]

Just wanted to tell you that i have told you all the readings from the points you have mentioned above
Expect for the current from point L

I expect you have ... but there is the question: Which ones are they exactly?  This may sound strange, but what you think is clear and what others think is clear - may not be the same thing.  Most of the time, it would be straightforward - but as we get deeper into this, being exact is important.

I don't understand there one thing
I'm connecting a +ve and -ve wire for a series connection
How can i measure current from there ,   can i ?

Unless you have a clamp meter that can do DC current (which most beginners won't have) you measure current the old fashioned way - break the circuit at that point an insert an ammeter.

And how can i measure this
VKQ = Voltage drop from point K (supply) to point Q (controller)

Just use the reference as a definition - such as this:
V_KQ
 - Meter on Volts (probably DC)
 - Red lead of meter on point K
 - Black lead of meter on point Q
That is how.

It may seem strange to measure the voltage from one end of a piece of wire to the other - but it is not.  It is important to make sure that when you put your meter lead on point K, that it is as close to the power supply negative rail as possible.  Likewise, point Q should be as close to the controller as possible.

The measurement, however, will be dependent on the current flowing.  If there is no current flowing, the answer will be zero, but if there is a heavy current flowing - there will be a measurable voltage drop.  In this example, expect the answer to be negative, since point K is on the negative supply rail and will be below the potential of every other point of the DC circuit.

If your connections are good and the wire gauge is heavy enough - then these "end-to-end" measurements on the wires should be very low under load.  You are getting large voltage drops which shouldn't be happening according to what we are understanding - so there must be some part of the circuit that is NOT behaving as expected.

[VickySalunkhe]

How I envisage measurement requests...
V_AB = Voltage between points A and B
V_JK = Voltage between points J and K
I_L = Current flowing past point L
I_J1 = Current from Section 1 flowing past point J
I_J2 = Current from Section 2 flowing past point J
I_J = I_J1 + I_J2  (Kirchhoff's current law)

V_KQ = Voltage drop from point K (supply) to point Q (controller)

V_AB = 30V AC
V_JK = 54V DC
All current values are max value i got by motor running at full speed
I_L = 1.42A
I_J1 = 1.42A
I_J2 = 1.42A
I_J = I_J1 + I_J2  (Kirchhoff's current law)
I_J = 2.84A

V_KQ = 0V
No change of voltage occurred when motor was at 0 speed and full speed

And sir i have replaced the LONG WIRE
so don't consider the voltage drop for that
The total wire distance back and forth between transformers and controller is 1.9meter

[Brumby]

V_AB = 30V AC
V_JK = 54V DC
All current values are max value i got by motor running at full speed
I_L = 1.42A
I_J1 = 1.42A
I_J2 = 1.42A
I_J = I_J1 + I_J2  (Kirchhoff's current law)
I_J = 2.84A

V_KQ = 0V
No change of voltage occurred when motor was at 0 speed and full speed

And sir i have replaced the LONG WIRE
so don't consider the voltage drop for that
The total wire distance back and forth between transformers and controller is 1.9meter

OK ... Now we have some clear measurement points.  If we all use this nomenclature, then there will be much less confusion as to what is being measured.

However, from the above figures, someone could ask ... So what is the problem?  V_JK looks good and the current measurements seem reasonable.

From these figures, V_JK is always 54V ... which, from previous discussion, does not seem to be the case.  This means you need to specify the conditions under which any given measurement is taken.

For example:
V_JK = 54V DC  @  I_J = 2.84A
 -or-
V_JK = 54V DC  @  I_J = 0A
 -or-
V_JK = 54V DC  @  some other condition

Knowing what the circumstances are for any given measurement are just as important as the measurement itself.  Power supply and high current circuitry are classic examples - so are electric motors.

Without even thinking, I can name 4 states for an electric motor that will completely change the load characteristics...
 - disconnected
 - unloaded  (free spinning - just the motor shaft with nothing connected to it)
 - typical load  (doing the work it would need to do to move a scooter with someone on it)
 - stalled  (shaft prevented from rotating)

These are arranged in ascending order of the electric load on the power supply - and they will drastically affect the current demands from the power supply.  The mechanical load condition of the motor is, therefore, critical in understanding the electrical load put on the power supply.  This information MUST be provided if we are to be able to help.

[VickySalunkhe]

Voltage readings taken
In 4 different stages as you suggested

INPUT AC 234 V

DISCONNECTED
V_JK = 55.2V @ 0A

UNLOADED  (free spinning - just the motor shaft with nothing connected to it)
V_JK = 53.6V @ 0.05A
V_JK = 46V @ 1A
V_JK = 45V @ 1.19A MAX
Max speed of motor was achieved at 1.19A i think thats why motor didn't ask for more current

According to that i think motor will draw more current to displace the load present on the vehicle


TYPICAL LOAD  (doing the work it would need to do to move a scooter with someone on it)
V_JK = 53.6V @ 0.05A
V_JK = 39V @ 2A
V_JK = 37V @ 2.6A MAX

STALLED (shaft prevented from rotating)
V_JK = 53.6V @ 0.05A
V_JK = 37.1V @ 2.7A MAX

As soon as the voltage reaches to 37V the motor stars all over again from 0  and gives a sudden jerk

[IanB]

If I understood correctly you have a 24 V transformer in series with a 12 V transformer which would give a 36 V supply. And you have a voltage that drops to about 37 V when the motor is loaded. So your measurements seem entirely reasonable. I think you can ignore the measured 55 V when the motor is not drawing a load--this is a "fake" voltage produced by the capacitors.

It might be interesting in fact to remove the capacitors from the circuit completely and repeat the measurements. Does the motor controller still work with no capacitors in the supply? I would guess the motor itself might work if connected directly to the supply without the controller.

If you want to supply enough voltage to the motor and controller you will need a 48 V supply instead of a 36 V supply, which means you will need to put two 24 V transformer secondaries in series rather than 24 V and 12 V. But if you do this with the capacitors you will get nearly 70 V unloaded. You have to be careful about not exceeding the maximum voltage on the controller.

[VickySalunkhe]

Sir you have understood it correctly

I cannot connect the psu to the motor directly as it is an brushless dc motor

I have tried two 24V transformers in series in earlier stages of testing the psu
And you guessed it right it gave 74V as ouput
And as soon as i connected that psu with controller

No power was given to the motor
that's why i have used 24V and 12V in series

May be some security is present in the controller

[IanB]

Have you tried the existing arrangement of 24 V and 12 V with no capacitors to find out if it works or not?

[VickySalunkhe]

Not yet
Will do it asap
But wouldn't it create a problem as too much ripple will be present in power supply

[IanB]

But wouldn't it create a problem as too much ripple will be present in power supply

Maybe, maybe not. There is no way to know without trying it.

[Brumby]

With clear measurements, the issues are also much clearer.

For the conditions specified, the power supply is performing pretty much as you might expect.  The problem is that this power supply is not appropriate for the need.

When you look at the transformers, the voltages are given as 12V and 24V - which are AC voltages.  AC voltages like this are typically given as RMS.  If I skip quickly through the math, this means that you should only expect DC voltages of 12V and 24V when your power supply is operating at its rated load.  Considering diode voltage drops and other circuit parameters, this supply is actually operating within reasonable expectations.

The first point of understanding is that the "no load" voltage of V_JK = 55.2V @ 0A relates to the peak voltage.  The capacitors will charge up to this and keep the voltage high - but it is meaningless.  It's like a weightlifter lifting only the bar - with no weights on it.

The under load measurement of V_JK = 37V @ 2.6A is a more realistic reflection on the demands of the load and the capabilities of the supply.  However, as you have observed, at this voltage, the controller has a problem.

This is the obvious solution -

If you want to supply enough voltage to the motor and controller you will need a 48 V supply instead of a 36 V supply, which means you will need to put two 24 V transformer secondaries in series rather than 24 V and 12 V.

but with one significant caveat...

But if you do this with the capacitors you will get nearly 70 V unloaded. You have to be careful about not exceeding the maximum voltage on the controller.

The answer is that your power supply needs to be voltage regulated.  The regulator must keep the voltage to a respectable level across a range of current - and allow the required current to pass.

You might be asking yourself ... So why is this so hard? - and the answer lies in the normal mode of operation for which the scooter equipment was designed to operate - batteries.  Four 12V, high capacity batteries will produce a reasonably stable 48V (nominal) over the range of current drawn by the motor.  A simple unregulated supply will not do this (unless it was massively overrated).


To continue your project, you will need to regulate your supply - or run off batteries.

[VickySalunkhe]

Sir
At the very start only
I thought to make a regulated power supply
For which i have created a post for it also
Here is the link
https://www.eevblog.com/forum/beginners/design-of-circuit-for-0-24v-5amp-regulated-power-supply/

This is for half part of my psu
In this i have tried the regulated psu
It was running perfectly with loads other than motor like led, fan etc...

But as soon as i have connected this psu with motor by switching the voltage level to 53V
as max voltage levels were 73V
No power was given to the motor
Because of which i thought to go for a simple way i.e, without regulated psu
But now which comes to a conclusion i have to move back to regulated psu

SCHEMATIC IS ATTACHED FOR HALF PORTION
lm338 voltage regulator is used

[Brumby]

That circuit is very basic.  Since you want to parallel two of these, there are more things to consider.

Personally, I would take a different approach - but rather than muddy the waters with my thoughts, I will defer to those who have had more experience in building custom power supplies.

[VickySalunkhe]

Sir
I would really like to know your approach

As i have searched a lot for regulated power supply for 48V 10amp
But i found no results for it
And certainly results which were showing up were 24V 1amp
That's where this circuit belongs to just some changes with cap and voltage regulator were done.

[IanB]

As i have searched a lot for regulated power supply for 48V 10amp
But i found no results for it

That's because it is not reasonable or practical to build such a supply from commonly available inexpensive parts or from simple instructions. In simple terms, it is not possible to make one.

You can buy a switched-mode supply with those specifications that has been designed and engineered by a manufacturer with the necessary expertise, but you cannot make one yourself as a hobby project. I can't do it and you can't do it.

So, to get what you require you need to obtain four 12 V lead-acid batteries and wire them in series to make 48 V. That will work, you can do it yourself with readily available parts, and it will perform exactly as required.

[VickySalunkhe]

Sir
But wouldn't it be a problem to lead acid battery to provide current of 13amps
As I have read the configuration of lead acid battery which are available there output is about 1amp

Can i draw more current from them without harming them?

[IanB]

It depends on the size of the battery. A car battery or a motorcycle battery can provide very high currents, up to hundreds of amps for short periods. Any moderately sized battery can provide 10 amps.