Re: sizing transformer for servo system ?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Anders Wallin
<anders.wallin@...> wrote:

>
> Hi All,
>
> I am setting up a servo control system for a 3-axis mill using 90VDC
> servos which are specified as 7.8A maximum continuous current and 38A
> peak current.
>
> On the transformers I am looking at, 2x38VAC seems to be a common
> secondary configuration. Wired in series this is 76VAC and rectified
> about 107 VDC minus two diode drops.

This would be too high of a voltage if you are using Gecko drives.
Figure about 80v max. Your servos are rated for 90v so you may
not want to go higher with the voltage. I bought these transformers
for my machine with servos that are similar in specs to your:

http://cgi.ebay.com/50-50V-800VA-Toroid-Servo-Motor-Power-Amp-Transformer_W0QQitemZ7540254271QQihZ017QQcategoryZ4660QQcmdZViewItem

I am using 1 transformer but I bought 2 just incase I need to
parallel them up. I use the same transformers that are 55v
secondary and it yield me about 78v DC. Perfect for the Gecko
drives. One transformer runs my servos fine. I would suspect,
based on my experience, that paralleling 2 of these 800VA transformers
would be plenty. If you are using different drives and need a
higher voltage, anything in the 800VA to 1000VA range should
be OK.

Scott