voltage changes when connected to load

[VickySalunkhe]

There is a problem
About Which i am not sure why it is occurring

I have connected my power supply with my motor controller and throttle
When the key is switch off of throttle i am getting 61v as output
((IMAGES ATTACHED))
But as soon as i switch on the throttle voltage drastically drops down to 4.8V ad output

Why such behaviour is happening?
How to resolve this issue?

I have also attached circuit diagram

Plz help sir

Thanks 

[Ian.M]

Your power supply cant supply enough current for the motor. 

[VickySalunkhe]

But i am using 5A transformer

Why isn't it generating the current then
Is there anything wrong with the circuit?

[VickySalunkhe]

Sir i faced a new scenario
I have directly taken supply after the capacitor
Not from the output after voltage regulation

So now the motor runs

So what is the actual problem???

[Ian.M]

What's the DC resistance of the motor?   Divide the rated voltage by the DC resistance to get the stall current.  That's what the PSU has to supply at startup unless you ramp the voltage up gradually.

[Brumby]

Like most voltage regulators, the 338 has overload protection.  If you want to pull excessive current it will limit the output to ensure the regulator can survive.

As Ian.M has said, If the motor is being started from stationary, then the stall current could easily exceed the limits built into the chip.  The chip limits the output and your motor never gets the power it needs to get up enough speed for the current to drop back.

I'd put my 2 cents on that.

[MAD MACRO]

You should power the chip from regulator output to the chip and another connection directly from power source to a transistor or a relay (controlled by a chip) to the motor.

[David Hess]

The surge current is causing one of the 338 to current limit.  When the voltage drop across the 338 rises, it *lowers* its current limit further to prevent secondary breakdown.  Usually this would not be a problem but the second 338 maintains the current through the first one preventing it from recovering.

I am surprised you did not destroy the 338s because operating them in series like that can force a reverse voltage across one if it current limits.  The solution is to add a reverse protection diodes capable of carrying the maximum current across each output.  Dual tracking regulators include these diodes internally as shown below as D10 and D12.  In an extreme case, tracking might be implemented so that the regulators share the output voltage.

Motors are not usually run from regulated outputs.

[2N3055]

Lm317 350 338 have problems starting with inductive load.. Plus motor start current that others already mentioned..

[IanB]

It is still not clear to me why you are including the voltage regulators at all. As you have observed, the motor runs if you take the supply directly from the capacitors. And you don't even need the capacitors. The motor will run if you take the supply directly from the rectifier.

[VickySalunkhe]

But wouldn't it create a problem to motor

As too much ripple will be present if output is taken directly from rectifier

And sir
One thing i noticed
When i started using the throttle the voltage started to decrease why did that happen i have no clue
But that limited my motor to run more as thr motot doesn't run after voltage is lower than 30V
I really want to clear the concepts hope so you'll help me out

Help will be really appreciated
Thanks all of you 

[IanB]

The motor doesn't care about the ripple. It is not important.

The supply voltage will decrease if you try to draw more current from the supply than it is able to provide. Either your motor is too large or your supply is too small.

[VickySalunkhe]

Sir does connecting 1st and 3rd wire as output from  center tap transformer gives half of the current as an output

For ex say
12-0-12v 5A center tap transformer is there
If i use 1,3 wire and connect it with bridge rectifier does the output has 24v 2.5A as an output
I am clear about the voltage part i am not aure about the current

I have heard someone say
connecting 1,3 wire-> half of the total rated current
Connecting 1,2 or 2,3 -> same rated  current

Is that true?

Thanks

[IanB]

If you connect the two outer wires of a 12-0-12 V, 5 A transformer you will have 24 V and 5 A available.

Also, the transformer will not stop at 5 A, that is just the continuous rated current. You can take more current for short periods as long as the transformer doesn't get too hot. With every increase in current there will be a decrease in voltage.

[VickySalunkhe]

Sir i just got an idea.

What if i make same power supply one more time
Then connect that psu with previous one
So I'll have  2 psu with 51v 5A each
And then I'll connect it in parallel so that i can double the output current
I.e I'll get 51V 10A right?

But the only doubt i was having is whether it will create a major problem to the motor or not
If it is going to create a problem how to prevent it ?

Thanks

[David Hess]

What if i make same power supply one more time
Then connect that psu with previous one
So I'll have  2 psu with 51v 5A each
And then I'll connect it in parallel so that i can double the output current
I.e I'll get 51V 10A right?

This will work however the regulators will not share current well when paralleled unless their design is changed.  Diodes placed in series with the output should be sufficient to allow parallel operation.  A single 51 volt and 5 or 10 amp regulator would be better.

[Spaghetti_142]

COMMON

[IanB]

COMMON

Do you mean "Come on" ?

[Brumby]

You tell me and we'll both know.

COMMON

We aren't mind readers - and while sometimes a single word might communicate something immediately useful ... this does not.

We can't see your face or hear the intonation in your voice.  We can't see how your arms are waving around, nor can we see the doodles on the notebook in front of you.

Can you at least try to put together a whole sentence?