Power supply design for my JGRO.

[Snipes44]

Trying to figure out if this is going to work for my JGRO. Here is what I have

Hobby pro 3-axis board
3 - 23lm-c057-02 nema 23 steppers
2.6V 2.5A 1.8Deg 1.04 ohms

I have an old GE transformer that I pulled from some old control equipment. Here are the specs on that transformer.

part # 9T55Y47G2 Type 1P
Primary 460V/230V (There is a tab that you connect up depending on what input voltage is needed)
Secondary 115V
KVA .250

If I connect 120V to the 460V windings I get 32v on the secondary. which I think is about right for my HobbyCNC board.

First questions is trying to figure out the amp rating on this transformer.

This is how I calculated it from info that I found on the net.

KVA=(A * E)/1000
so that is
.250=(A * 32V)/1000

which gets you A=8.04A

I was not sure if that is correct since the transformer was design for 230/460 primary voltage with a 115 secondary.

Second question, is 8A going to be enough to run the 3 steppers with the hobbycnc board.

Hopefully will have this thing running sometime tomorrow.

[Al_The_Man]

At 250VA that means that the normal rating for the secondary is 2amps, The wire gauge may or may not be rated for 8amps.
The same applies to the higher current through the primary.
Al.

[Snipes44]

Well glade I asked. Could you explain how you got 2A from 250KVA? Not really understanding the KVA rating.

[irving2008]

Originally Posted by Snipes44 Well glade I asked. Could you explain how you got 2A from 250KVA? Not really understanding the KVA rating.

KVA = kiloVoltAmp i.e. VoltAmp x 1000, so 0.25KVA = 250VA, which at 115V secondary volts = 250/115 = 2.18A. The secondary wiring is probably good for 4A max if the usual derating was applied. Short answer, not really good enough for your needs.

Is it a toroidal (donut) or stack (square) transformer? If the former you may well be able to rewind it relatively easily. I personally wouldn't bother if it was a stack type.

[Al_The_Man]

But even if you beef up the present secondary, you unfortunately will still have a primary that will also have 4x its rated current reflected back from the secondary, when used on 120v.
Al.

[Snipes44]

Thanks for the replies guys. I see now how you get 2A on the secondary. I had misunderstood the KVA formal when it said the E was the Secondary voltage. Had not realized that it was suppose to me the rate secondary voltage and not the voltage that I was trying to get. And ya its a square transformer.

Guess I will be trying the 2 atx power supply trick then. Only other thing I think that i might be able to try is a I have a couple 24V 4.8A PSU that came from some equipment. Is there a way that I could parallel these to get 9.6 amps?

I'm sure that 4.8 is not enough for my motors.

Thanks again for the help guys.

[Al_The_Man]

Originally Posted by Snipes44 I have a couple 24V 4.8A PSU that came from some equipment. Is there a way that I could parallel these to get 9.6 amps? I'm sure that 4.8 is not enough for my motors. Thanks again for the help guys.

You can parallel up two transformers, but they have to be very closely matched, or ideally, identical.
If you parallel up the AC you will have to ensure they are phased correctly, there are quite a few previous links on how to do this.
If you parallel the DC you do not need to phase them.
Al.