RE: [CAD_CAM_EDM_DRO] Re: sizing transformer for servo system ?

As a guide line

I have a big commercial Avon CNC machine with three axis driven with 160V DC
brushed servos that will run at up to 48 amps continuous, that’s 7.6KW per
motor WOW.

It came with a three phase transformer delivering 1.5KVA at 110V which is
about 155V rectified just less than 10 amps. Being three phase it had a
smaller capacitor than one would use for single phase at 6800uF. The old
servo cards were analogue ones with 250 count encoder and tacho
synchronisers.



It is being coverted to mach3, since the old Anilam controller wasn’t
reliable. We actually managed to repair all of it except a faulty encoder,
while waiting for my Rutex drives ang G100 to arrive. I am presently using a
110V mains isolation transformer of 3.3KVA because it was cheap at £30 and
28800uF caps as six 4800uF ones. But from the original spec it didn’t need
to be this big.



I am running Rutex R2020 drives and finding that only 15 amps will run all
axis at 8.5meters/second with ease which is fast enough for now, flat out it
will do about 15m/second. It is worth noting a 40A rated Rutex drive is
really good for about 15 to 20 amps if you want it to survive occasional
accidents and the like.



Rutex have a file on their site called mystique which offers good advice for
transformer choices.



Regs Mark



_____

From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Polaraligned
Sent: 27 December 2006 14:10
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: sizing transformer for servo system ?



--- In CAD_CAM_EDM_ <mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
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
<http://cgi.ebay.com/50-50V-800VA-Toroid-Servo-Motor-Power-Amp-Transformer_W
0QQitemZ7540254271QQihZ017QQcategoryZ4660QQcmdZViewItem>
com/50-50V-800VA-Toroid-Servo-Motor-Power-Amp-Transformer_W0QQitemZ754025427
1QQihZ017QQcategoryZ4660QQcmdZViewItem

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





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