Need Help!- Custom toroidal tansformer

[Johan Cnczone]

I want to make power supply for 80V servo / 20 A peak
A friend of mine can make me custom toridal transformer but he ask about :
1) input voltage ( no problem )
2) frequency ( no problem )
3) output voltage load/ no load ( this is my problem )
4) output amperage ( this is also my problem )

I read on some websites that I should use following spec:
48 v load / 56v noload / 36 A (RMS ) output

Is this correct ?

[Al_The_Man]

Is the servo rated for 80v and driven from a PWM drive?
If so you want some reserve, A-M-C recommend the power supply voltage can be 110% -150% higher than servo voltage.
I would consider 100DC. (70vac).
Also is this peak servo current or stall torque current?
Peak current is usually the maximum before demagnetization or destruction.
If you design for peak, you will most likely design for overkill on the Toroid KVA.
Al.

[acondit]

I would say that the choice of appropriate voltage is really dependent on the specifications/limits of the drive that you choose to use. I would not recommend using 100v no load input if the drive specs an 80v no load input. In short I would choose the drive that you intend to use and then design your power supply to match it.

Alan

[Al_The_Man]

A servo motor is rarely fed direct from power supply to motor, there is a drive in between, PWM etc.
IMO the drive should be rated last, the motor and supply should be decided on and then a drive selected to suit.
Higher voltage per se does not harm a motor, unless excessive of course, as long as excess current is not allowed to flow due to this higher voltage then there is no cause for alarm, and also max rpm is never exceeded.
In a PWM drive, there is generally means of controlling current limit.
Designing the power supply and drive to exact motor specs means you probabally are going to limit flexibility in the control.
http://electronicdesign.com/Articles...leID=7635&pg=1
Al.

[acondit]

Al,

I agree with you in an ideal situation, however, many of us in the DIY-CNC world don't have unlimited budgets. Therefore, what is available as a drive at an affordable price may have to drive (no pun intended) our power supply decisions.

So I guess the question is really, what does the budget allow?

Alan

[Al_The_Man]

OK I will concede that, but the poster only mentioned he has the servo, and depending if there is a drive involved, it should not cost any more to size the Toroid correctly.
But anyway, there is a lot of useful information in the link, especially the last couple of pages on Fusing, Wiring and Grounding which may prove a useful reference.
Al.

[Johan Cnczone]

Thank you for your replies.
Yes , I am planning to use the transformer ( + rectifier) to feed granite servo drives ( VSDE ). VSDE need 80VDC input, it has max 20 A output
As for the servo motors , they are 80VDC brushless / 7A continues, 20 A peak

[Al_The_Man]

You should use the 7 amps number rather than the 20, which you should never want to reach.
This would unnecessarily give you a much larger VA rating for the Toroid.
If you need any auxiliary winding(s), get him to wind them on at the same time.
Al.

[acondit]

OK, Al, what about the voltage recommendation? I know nothing about the Granite drives, so just on the numbers provided I would think that one would want a secondary AC voltage of 51 to 57 volts. Using a full wave bridge rectifier, that would provide a DC voltage of 72 to approximately 80 volts. Does that sound right?

Alan

[Al_The_Man]

Yes, but as the article points out, you would want a drive that would be rated higher than the supplied voltage.
57v would take you right up to the drive rating.
in this case a max of 50v may be more prudent.
Al.

[Johan Cnczone]

Ok, I will go with 50volt
Thanks for the informations