output from transformer is coming not as expected

[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.