Re: [CAD_CAM_EDM_DRO] Power Supplies for Stepper Motors

int3man wrote:

>Hi all, I'm working on my converting my Manual Taig to CNC and
>acquiring parts. I purchased a 28 volt Switching Power Supply from
>MPJA. It's made by Lambda. The fellow that made the Driver cards is
>now telling me that the switching power supplies have a problem with
>instantly responding to demands. The switcher needs a load to be
>outputting voltage. I suggested that I install a couple of filter
>Caps to assist in providing the instant current demands. But in
>retrospect a 100 meg. resistor would probably do a better job of
>getting it up on it's toes and ready to supply. So did I just waste
>$150 purchasing the wrong supply? Or are there others out there
>using Switching Power supplies? Or should I drop it and get
>something more along the lines of a transformer for a power supply?
>
>

First, try it. I suspect you will find it works quite well. I think
some other people
have used these supplies with good results. Yes, some specific supplies
intended
for some specific use may not be able to cope with large current
transients. A good
general-purpose supply designed by competent engineers (and I think
Lambda, as
one of the oldest and best makers of high-end industrial, aerospace and
mil-spec
power supplies has a BUNCH of very competent engineers) should have no
problem
supplying such a load. People use similar supplies for running banks of
relays,
small motors, etc. If you DO have any problems with the supply shutting
down,
then placing a good-sized electrolytic capacitor across the 28 V bus
should fix it.
A few thousand uF would be a good place to start.

A 100 Meg Ohm resistor would not have any effect on a 28 V supply. The
idling
current draw of the drivers would be thousands of times higher.

In the remote possibility that the power supply overshoots the 28 V
setpoint and
triggers the crowbar, you might need to put a resistor of about 28 Ohms
(to get
a nominal 1 A load) across the 28 V bus. Note this resistor would draw
28 W!
One of the aluminum-cased power resistors mounted to the case would be a
good
way to deal with this. The Gecko drives, for instance, don't turn on
the motor
drive for a second after power is applied, and might cause such a condition.

Jon