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Splint
04-26-2004, 12:14 PM
Hi,
I intend rewinding an existing transformer to use as a power supply for some 60VDC brush servos and to my understanding its desirable to have more than the motors rated voltage available to the controler board (Rutex R990H in this case). My question is how much higher than the rated 60VDC should I aim to get from the transformer?
My other question is in regard to limiting amps to each individual board since it looks like I will have access to the transformer and other componants from a mig welder to use, which means lots of amps, so I would like to regulate the current to each board, any ideas?
Thanks
Splint

Al_The_Man
04-26-2004, 01:14 PM
Originally posted by Splint
Hi,
understanding its desirable to have more than the motors rated voltage available to the controler board (Rutex R990H in this case). My question is how much higher than the rated 60VDC should I aim to get from the transformer?
Splint
I think you may be confusing DC servo's with stepper motors, If the max rating for the motors is 60vdc that is all you require to supply. Also the current is dependant on the supply voltage and load demanded, If you are using a MIG transformer rated at 100amps, this does not mean 100amps will flow. Only what the load calls for. If you are rewinding the Txfr, make sure you use a gauge of wire suitable to take the maximum load you are likely to draw.
Al
BTW if you want to end up with 60vdc, the ac secondary should be 40~42vac.

Splint
04-26-2004, 11:49 PM
Thanks Al,
I was just little concerned with having excess amperage since the MOFSET bridge in the R990H is rated at 34a/100v continuous and may result in burning out the bridge. If I undersatnd correctly having 50 or 60 amps available to the driver card is not an issue, it only becomes a problem if the software is trying to make more than the upper limit of amps pass through the bridge. I think I'll aim for 60vdc and let the driver card deal with the amps. Thanks for the tip on the ac to dc voltage step up, from what I understand the ratio is 141.4% minus the voltage drop for the diodes which I think is about 0.7volts.
Thanks
Splint

ynneb
04-27-2004, 12:40 AM
Sorry Splint for not sending you the deatils of that transformer guy. I just cant find them.

The Rutex cards also have a current limiting contol on them. So for instance if the servo is asking for 60 amps (unlikely) the current limiting control will only give it 10 amps or whatever setting it is at.


If I undersatnd correctly having 50 or 60 amps available to the driver card is not an issue, it only becomes a problem if the software is trying to make more than the upper limit of amps pass through the bridge. Heres how it works. The software drives the Rutex cards that chops the voltage only.
The current pull is only determined by the windings on the servo.
If a servo has a 10 amp rating then that is only ever what is going to pull ( unless its faulty). Even if your power supply can give 1000 amps the servo will only pull 10 amps.
However, if your servo has a 60 volt rateing and you give it more volts then that is where you have to worry.

When designing your power supply make it as high amped as you can, but stick to the specified voltage of the servo ratings.

Splint
04-27-2004, 04:46 AM
Thanks Ynneb, I'm clear now with what's required. Dont worry about the transformer guys details, I origionaly wanted them because I didn't understand how a power supply worked and the idea of making my own seemed all too hard but after spending some time trawling the net for info I'm feeling confident about building my own. I guess there are two advantages, one being a cost saving and the other being a good educational opportunity.
Thanks
Splint