Re: [CAD_CAM_EDM_DRO] electrical advice needed

----- Original Message -----
From: <JanRwl@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Saturday, January 05, 2002 12:04 AM
Subject: Re: [CAD_CAM_EDM_DRO] electrical advice needed


> In a message dated 04-Jan-02 14:20:14 Central Standard Time,
> apollo@... writes:
>
>
> > My question is, will that be 67VDC @ 4A? Or would that turn into 67VDC @
> > 2.8A, so as to conserve the 192 Watt rating?
> > Secondly, I'm trying to determine what the actual current draw will
be
> > from the 110VAC side... if the transformer can supply 192 Watts, then
how
> > much current would it be safe to assume it will draw from the AC? I'm
> > planning on using four of these (one for each axis), so I'm concerned
about
> > having a cord & switch rated high enough. I'm assuming the transformers
> > aren't 100% efficient, so how much higher than the rated power should I
go
> > to be safe?
>
>
> Rick: GOOD questions! Lemme see if I can coax my feeble tiny mind
into a
> comprehensible answer: First question: The filter-capacitor (if of
proper
> adequate size) will "lift" the RMS rectified voltage to near "peak", which
is
> that 67 volts. At "NO load". If you load that DC to 4 amps, the DC (with
> ripple) will drop to about 48 volts. (s'posed to, anyway!). So, "sorta",
> yes, the 67 VDC would be at the lower amperage. HOWEVER, note: These
Gecko
> drives were something totally NEW to me, when I purchased my first two,
which
> I am just-beginning to try out, with some small Size 23 steppers.
> INTERESTING: The higher DC, being "chopped" at a high-audio-freq.,
combined
> with the motors self-inductance and the filter-capacitors (also in the
Gecko
> drive) can provide full-torque, while drawing MUCH less current from the
DC
> supply! For example, if you have a stepper with coils rated at one-amp
> (there are two of those), you might think you'd need 48 or 67 VDC at 2
amps
> for that motor. NOT! Would you believe maybe 0.4 amp! The VOLTAGE is
much
> higher than the coil-rating, and this is "chopped" to give an average
"max.
> rated" V-A, so the supply is called upon to supply considerably LESS
current
> than the motors would draw, were their "rated coil voltage" applied as
steady
> DC, directly to the windings. (Don't forget! You can't GET this magic
with
> old-fashioned "L-R stepper-drives" using those 50 or 100 watt 6 ohm
"ballast
> resistors" in series with the +common center-taps of the motor-windings
(on
> "six-wire stepper motors").
>
> Cord rating? Even if you loaded this transformer to its full 192 watts,
at
> 110 volts (might be as high as 125 VAC, if the utility-supply to your lab
is
> near-perfect) you'd be drawing only 192/110 = 1.75 amps. A lamp's
"zip-cord"
> is #18, and that can comfortably handle 3 amps! So, no need for #12
"motor
> cable" for the power supply! (If it don't smoke, nor burn your hand when
you
> touch the cord, it is heavy enough!)
>
> OK? Hope this helps! Jan Rowland, old troll
>
>
> [Non-text portions of this message have been removed]
>
>
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