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?