Re: Power supply surge above the Va rating?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "cnc_4_me" <cnc4me@g...>
wrote:

>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers <rogersmach@y...>
> wrote:
> > Yes, it happened one afternoon and not since as far as I know. I
> put the 100volt 1000uF caps at each drive to protect them, machine
> runs much better. I'm trying to size a transformer for a new

control

> and curious about surge. Will demand from the motors cause the
> transformer to surge above the Va rating? With a proportional DC
> voltage drop of course.
> > Ron
>
>
> Current draw for the motors will not cause the power supply voltage
> to rise. But rapidly slowing motors down can cause a rise. As Jon
> Elson reported you can expect a typical value of 2 volts.
>
>
> Wally

The voltage rise depends on MANY things. not the least of which is
the load. Many people use motors attached to screw with a
reduction. the whole flywheel effect is rather minimal.

Others might be driving a 200 pound gantry on a rack and pinion where
the gantry movement would act like a weight, and the spur gear would
need to stop it.

Mariss did a test on a NEMA23 motor running at 48 volts.

In the first test, the motor was spun to 6,000 RPM, then stopped. in
the second, a cap was added to see how much energy was returned.

In the first test, the 48 volt line rose to 116VDC for 100 milisecond.

Note a diode was on the power supply to prevent it from absorbing any
returned energy.


About 2/3 of the returned energy was injected back into the power
line, the other 1/3 was dissapated mechanically.

All those numbers don't mean a whole lot on your machine. First, you
(hopefully) would never put a diode between your drive and the
capacitor.

Second, the test was to be as abrupt as possible to generate the
spike.

But, also, there was no mention of a large flywheel. An L pulley of
40 teeth is about 4.7" diameter and would have much higher stored
energy than the motor rotor.

I remember a post (vaguely) on here from Mariss about such a test and
seem to recall ( I have sometimers so don't know how accurate this
is) something like a 10-20 volt rise on a more typical, albeit
pushing the envelope, motor.

The main filter cap should handle the returned energy in most cases.
there is a small on-board cap on the Geckos to handle some small
amount, and if the PS is more than a foot or so of wire from the
driver, a third cap, 470uF, on the driver terminals, is recomended.

And like Chicken soup for a cold, koud ent hoyt !

Dave