Thanks to all who responded.

I am doing this to learn more about driving brushless motors. This model is
a 30W unit but I may eventually have to do a design for a ~300W motor
(going in an electric powered model helicopter). I may have given people
the wrong impression with my message: I'm not usually the sort of person
who just "tries all combinations" until something works. The only reason
why I did that was because I had such scant info on how the hall outputs
corresponded to the phases that I thought it couldn't hurt to try every
combination as an easy way to start (as long as I didn't let the current
flow long enough to damage anything).

As it turns out, I was given an older copy of the Maxon catalog today and
it has a diagram in it that isn't included in my motor's datasheet, which
shows how their motors are meant to be driven. I must say, Morgan is right,
they apparently do expect you to tristate each phase for part of its cycle
(actually, this would be roughly the same as setting it to half voltage
since the wye neutral point sits around half voltage anyway, and this
happens when the back emf for that phase is near zero).

As for current vs. voltage drive, I haven't heard that either, Roman,
although I suppose it doesn't matter which way you do it as long as you
achieve the same operating point. The maxon motor has about 1.2 ohm from
phase to phase. Of course, the 300W one that I may have to do later has
only a few tens of milliohms.

Tomorrow night or Wednesday I hope to try running it with the sequence from
the catalog and see what happens. I thought it through and I think I can
see why it would help reduce the current greatly (since the way I was doing
it before causes full voltage to be applied even during the point in the
cycle when the back emf is near zero). I'll let you know how it goes.

Thanks!

Sean

At 09:01 AM 8/6/2002 +1000, you wrote:
>Peter L. Peres wrote:
> >
> > >Second, brushless motors are current operated devices
> > >(obviously) and you should operate them at the correct
> > >spec current. Like steppers they usually have low-turns
> > >(low ohms) coils, and are meant to be driven with some type
> > >of constant current supply, like a chopper etc. In short,
> > >you need some type of pwm etc on the motor coils to establish
> > >correct running current.
> >
> > This is new to me. Could you indicate a reference for brushless motors
> > being made for use with constant current supplies ?
>
>
>Hi Peter, maybe "constant current supply" is a little
>too literal, I meant that the motors are very low turns
>and attention to CORRECT current needs to be a function
>of PWM current limiting etc, ie deliberate, rather than
>just connecting a power supply which will cause the
>symptoms he saw, of 40x the specified current.
>
>Most of the VCR 3-coil flatmotors I have here have
>only a handful of turns on each of the 3 coils, they
>are almost short circuit to measure.
>
>So by "constant current supply" I meant a "current-controlled
>supply that only allows a fraction of the current that
>would flow it it was turned on constantly". ;o)
>-Roman
>
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