Re: Power needed to drive 3 nema 42 motors?

--- In CAD_CAM_EDM_DRO@y..., "bdrmachine" <bdrmachine@h...> wrote:

> I have a bp clone that I'm retrofitting with 3 nema 42 1070 oz-in
> motors. They draw 6 amps per phase each. I'm driving them with
> Gecko 201 drives. What amperage power supply will I need? Three
> motors times 2 phases times 6 amps equals 36 amps! Do I need to
> shoot for this size supply? Where do you get a transfomer that

size

> ( 70v, 40a )? Can I uses a variable transformer and a full bridge
> recitifier set to approx. 70 volts?
>
> Thanks
> Brian

Don't use a variable transformer. Most of them are Autotransformers
(one winding) and provide no isolation (that's a bad thing). Either
order a transformer of the voltage and current range you want or get
creative and find a surplus unit that has several secondaries you can
use to get the voltage you want. A multi-winding transformer is a
versatile thing. Depending on how you phase the windings you can add
or subtract AC voltages. You can even take a secondary winding and
put it in series with a primary winding and use it to lower the high
current secondary.

There is nothing wrong with using a surplus regulated supply if you
can find one with enough volts and amps. The only thing you need to
do is diode isolate the regulated output so possible negative spikes
don't get back into the unit. If you design to the minimum then
often you will have to deal with greater heat dissipation. Most
components are rated at 70 deg C. That means a 12A bridge running at
12Amps will get real hot. By over designing the system you will have
longer component life and cooler temps (they are pretty much the same)