Re: It's more VOLTAGE needed to overcome back emf in the coil

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Mark <mfraser@h...> wrote:

> Voltage is the force (water pressure), current is the amount of
> volume (water - think water current) resulting from the voltage
> overcoming resistance or back-flow. Regardless of the current
> available from the power supply, only the amount that the voltage
> can stuff thru the circuit (motors) will be drawn. / mark

Correct, but this is one of those mysteries to those of us who do not
have the education in the electronics field and who don't have a nice
array of scopes and things to test with.

I built a machine with a nice 30 amp power supply, re-wired and
swapped out the supply for a much smaller one. the unit runs fine,
but it is a non-contact on X and Y, just positioning and Z is a drill.
So, even though X and Y can run at the same time, they don't have
much need for power. So, in my experiance...... I was able to get by
with a much smaller power supply.

My next machine was smaller and I used the motor watts for the power
supply and that worked also.

Seems I have not been needed high power.

So, anyway, it seems that power supply DC voltage times motor amps is
the starting point.

Steve mentioned 1.8 times voltage to allow for the transformer
inefficiencies, and I keep seeing Mariss's 0.6 multiplier.

So, the last piece of the puzzle is about transfromer efficiencies and
filtering of power.

With the formula of (80,000 times current) / voltage we get the
capacitor sizing needed for the power supply. So, that brings up the
question of how closly couplied the transfromer is to the load when
the capacitor is used.

If the pulse to the motor is in the 5uS range, wouldn't the cap filter
that to the point the transformer never sees that ?

Dave

>
>
> > Date: Mon, 12 Sep 2005 01:51:04 -0000
> > From: "turbulatordude" <dave_mucha@y...>
> > Subject: Re: Power Supply for 4-axis CNC stepper driver
>
> >
> > Hi Guys,
>
> > Noboby argued with what Steve had said that more current is needed to
> > overcome the back EMF in the coil, so I'll work with that.
> >