Re: [CAD_CAM_EDM_DRO] RE: Power supply transformer setup questions...

If you are using a chopper drive (which the G101 is), then the current
through the windings of the motor is limited by the chopper drive to the
current rating of the motor, regardless of the supply voltage that you are
using. The effect is that the power consumption of the motor is equal to
the square of the rated current times the coil resistance for each coil
(rather than the supply voltage times the rated current). So, to a first
approximation, the average current drawn from the power supply can be
calculated by summing the wattages of the motors & then dividing that by
the supply voltage. So in your example, your 3 motors, with both coils
energized, will consume a total of 76.8 Watts. With a 50 volt supply, that
is only a little over 1.5 Amps. Even adding 30% to allow for power
dissipation in the drive itself (which is probably excessive), the supply
still only needs to deliver around 2 amps - maybe 3 if you were being
really conservative.

(Actually, the above calculation can be an over-estimate with microstepping
drives, because they often limit the current in each winding to approx 0.7
times the rated current at the "full step" position, in order to allow even
spacing of the microsteps.)

So, the important thing for sizing the PSU isn't the current rating of the
motor per se, but the power it will consume. (If you don't believe me, find
a bench power supply with a current meter on it, hook up a drive and a
motor to it, check out the current reading and the PSU voltage, and compare
with the value you might expect from the above calculations. I did just
that with a Xylotex 3-axis drive, and the results were very close to the
calculated value.)

Regards,
Tony


At 17:08 10/09/2003 -0400, you wrote:

>Not that I doubt you, but can you explain why then it is suggested that I
>use 2/3rd of the sum of the motor amperages then?
>
>The setup will be using 3 G201 drives, connected to three motors.
>One 3A/3V motor, and two 3.5A/4.2V motors.
>
>I would have thought that a 6.7Amp rated transformer is required.
>
>
>
>
>-----Original Message-----
>From: JanRwl@... [mailto:JanRwl@...]
>Sent: September 10, 2003 3:47 PM
>To: CAD_CAM_EDM_DRO@yahoogroups.com
>Subject: Re: Power supply transformer setup questions...
>
>In a message dated 9/10/2003 6:29:48 AM Central Standard Time,
>lloyd@... writes:
>
> > 167L50 (50VAC/2AMP)
> >
>
>If you are using bipolar CHOPPER drives, such as the Gecko G201 or G 210,
>this transformer, alone, should do! So long as you have the correct
>filter-caps,
>and use full-wave bridge rectification.
>
>
>
>
>
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Regards,
Tony