Re: [CAD_CAM_EDM_DRO] Re: query - 2HP PM DC motor controller - pointers please

If it is a dc servo type motor then it may not have a fan and be sealed
(don't rely on the sealing as it may not be fully sealed.)

You should be able to run it stalled at rated current for ever as long as it
does not have a shaft mounted fan nor is it supposed to be fan cooled by a
separate fan.

Regards Peter

----- Original Message -----
From: "Jan Kok" <kok@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Saturday, October 26, 2002 9:50 AM
Subject: [CAD_CAM_EDM_DRO] Re: query - 2HP PM DC motor controller - pointers
please


> > From: "tedinoue" <etinoue@...>
> > Subject: query - 2HP PM DC motor controller - pointers please
> >
> > I recently purchased a 2HP PM DC motor, hoping to build/buy a
> > controller so that I could use this on a small lathe. For those
> > interested, it's a Leeson motor, designated 120v 14A, 4800 RPM.
> > Model C42D340T7A. I plan to reduce the maximum speed then feed it
> > into my existing lathe drive system.
> ...
> > 1) I've seen a lot of postings discussing 90v DC from 110v AC and
> > 180v DC from 220v AC, but little to nothing on driving a motor rated
> > for 120v. I'd get plenty of power out if I ran it at 90v, so I'm ok
> > with a controller that does the basic 110AC -> 90DC conversion. Any
> > reason why this wouldn't be suggested?
>
> How does one get 90VDC from 110VAC? By using a switching power supply, or
> PWM? (In which case there is nothing magic about 90V, you could get any
> amount of DC up to sqrt(2) * 110V minus a few volts for various losses.)
>
> > 2) If I do run it at 90VDC, that's 3/4 of 120VDC, so would I simply
> > then treat the controller needs as 1.5HP / 90 VDC and 10.5Amps?
>
> The current drawn by a DC motor is proportional to the torque that is
> generated. The speed of a DC motor is proportional to the voltage across
> the motor terminals minus the voltage drop through the resistance of the
> motor windings and brushes. You can use the full torque (full current) at
> any speed (voltage). One thing to watch out for is that the motor has
> adequate cooling if running at low speed and high torque, because the heat
> generated is proportional to the current, but the built-in fan won't
provide
> much cooling at low speeds.
>
> I haven't seen mention of this elsewhere, so maybe it isn't a concern, but
> if you operate a DC motor at full torque and stalled or nearly stalled (<
1
> rev/sec), the current will go through a single winding for a long time,
thus
> all the heat is concentrated in that one winding, possibly leading to
> overheating of that winding. If the motor is intended for servo
> applications, this should be accounted for in the ratings, but otherwise,
> you may want to limit the current to less than the rated current if the
> motor will be operated in high torque and stalled or near-stalled
> conditions.
>
> Cheers,
> - Jan
>
>
>
>
>
>
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