Re: DC Motor Control - Heat Issue

From: Rich Grise (richgrise_at_example.net)
Date: 01/18/05 

Date: Tue, 18 Jan 2005 21:04:31 GMT

On Tue, 18 Jan 2005 18:12:39 +0000, John Woodgate wrote:

> I read in sci.electronics.design that Mark Jones <abuse@127.0.0.1> wrote
> (in <Go2dnQM1GP9u1HDcRVn-2g@buckeye-express.com>) about 'DC Motor
> Control - Heat Issue', on Tue, 18 Jan 2005:
>
>> For the hardcore experimenter, maybe the primary coil of a microwave
>>oven transformer (MOT) could be used as an inductor, or rewinding such a
>>core. But as far as I understand it, the laminated silicon-steel is not
>>going to work well at high frequencies,
>
> Billions of audio transformers use laminated silicon iron cores. But the
> stuff used for microwave transformers isn't likely to be very good at 8
> kHz; it may, however, be good enough. Generally, one would choose grain-
> oriented silicon-iron 0.3 mm thick maximum for 8 kHz, but this inductor
> carries 15 A DC and therefore needs a large air-gap. This means that the
> iron quality need not be so critical.

What's he trying to do? Make a big tuned circuit, or make a shaft go
'round and 'round?

Why is he trying to drive a 10 amp motor with the equivalent of RF? 7800
times a second, he's getting inductive kick.

At _LEAST_ put a catch diode, preferably fast recovery, or drive it with a
lower frequency such that the motor winding current has a chance to
actually increase to its spec before being switched into a flyback.

Good Luck!
Rich

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