Re: [CAD_CAM_EDM_DRO] Re: Servo Motor Current - follow-up

Peter wrote:

> Me again,
>
> I fitted a second cap in parallel so now I have 36,000uF across the
> diode bridge and a 1000uF cap across the power-in terminals of each
> Gecko. What I've observed is that the peak currents are still up in the
> 25amp range and during a big acceleration, the psu output voltage still
> sags by around 5 volts. I would say that the addition of the 1000uF
> caps right at the inputs terminals of the Geckos had more of a
> beneficial effect than adding the 2nd big cap.
>
> I've ordered a bigger transformer so we'll see how that affects
> regulation during peak current draw. In the mean time I'll just run at
> lower accel/decel settings - not as much fun...

A gradual (as in mS) droop of 10 % on a servo system is not likely to
cause much of a problem. it WILL limit your top speed by about 10 %,
though. If you are running your max velocity right up against the headroom
of the servo motor/power supply system, that is not a good idea. it is
much better to have a reserve of at least 10 % to allow for the motor's winding
resistance to drop the apparent voltage at the motor under heavy load.
If you have high-resistance motors, then a greater margin, sometimes up
to 50% is needed. (Personally, I shy away from any servo systems where
large IR drops inside the motor will develop.) I see some people using
surplus Ametek motors with 5+ Ohms resistance and 10 A peak servo
amps, and just shudder! If it doesn't burn up the motor, it is sure going
to play hob with system performance.

Jon