Re: [CAD_CAM_EDM_DRO] Re: Gecko and Anaheim

Mariss
Thank you for you response. I am familiar with constant current
devices.
I just was concerned about the motors getting too hot, very good
explanation
as usual. I will be trying some of your drives before too long,
waiting for a project
to mature into a product.
Jim

----- Original Message -----
From: Mariss Freimanis <geckohall@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: Thursday, August 10, 2000 11:03 PM
Subject: [CAD_CAM_EDM_DRO] Re: Gecko and Anaheim


> Hi, The question is what is too hot regarding a step motor. Usually
> the maximum rated case temperature will be 85C or 185F. At this
> temperature skin blistering (2nd degree burn)will occur if contact
is
> maintained for more than 5 sec. To my mind this is too hot.
>
> This heating is caused by eddy current and hysterisis losses in the
> motor. For those who are interested try this:
>
> Chuck up a step motor in a drill press. Adjust the belts for highest
> RPM. Leave the motor leads unconnected. Clamp the motor in a vise
and
> turn on the drill press. Come back in 5 minutes and see if you can
> touch the motor. My prediction is it will be too hot to touch.
>
> The heat is caused by the iron magnetic domains flipping back and
> forth under the influence of the rotor magnet. This motion causes
> friction and results in heat. This is a gross oversimplification but
> it helps visualize what happens.
>
> A 4 volt motor operated at 80VDC will be below this level. The
> overdrive ratio is 20:1 (80VDC/4VDC). Above that ratio the temp will
> reach or exceed 85C. The ultimate result will be molten nylon
winding
> bobbins, degradation and embrittlement of winding insulation
> resulting in inter-winding shorting. I.E. a destroyed motor.
>
> Don't confuse what happens when a 4VDC motor is being run from an
> 80VDC supply. The drive is a current source. It will only deliver
> what voltage is necessary to maintain the motor's rated current. At
> low speeds it will be 4VDC, at higher speeds the voltage will be
much
> higher. The rated current however will never be exceeded.
>
> Mariss
>
>
> --- In CAD_CAM_EDM_DRO@egroups.com, john@m... wrote:
> > Sorry to butt in on this thread but Mariss's original reply is
> copied
> > below.
> > Mariss states
> > >" To get the maximum power from a 7A, 80V drive, pick a 7 Amp, 4
> > >volt motor. "
> >
> > Surely a 4V motor running on 80v supply will burn out.
> > Am I missing something here ?
> >
> > > ----- Original Message -----
> > > From: Mariss Freimanis <geckohall@h...>
> > > To: <CAD_CAM_EDM_DRO@egroups.com>
> > > Sent: Monday, June 12, 2000 6:14 PM
> > > Subject: [CAD_CAM_EDM_DRO] Re: Gecko and Anaheim
> > > > Now to bring this all together. Size 42 motors I'm sure you
have
> > > > noticed have much higher detent torque than size 34 or 23
> motors.
> > > > This is the reason why size 42 motors run out of steam before
> the
> > > > smaller motors do. Second, for the same amperage, a size 42
> motor
> > > has
> > > > much higher inductance and rated voltage than a 34 motor. That
> > means
> > > > they come into their own at much higher supply voltages; 160
to
> > 200
> > > > VDC. To get the maximum power from a 7A, 80V drive, pick a 7
> Amp,
> > 4
> > > > volt motor. This will be either a 4 stack 34 or a single stack
> 42.
> > > > For peak power, gear the motor to run just past the speed
where
> > the
> > > > drive ceases chopping (i.e. current limiting).
> > > >
>
>
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