Hi all,

One of the things I'm working on involves controlling brushless DC motors.
As a first step to understanding them better, I built a three half-H bridge
driver and I am trying to just get one of them to run, driven by my driver
circuit. The motor I'm using is a Maxon EC45 with Hall effect sensors. I
was under the impression that each hall effect sensor output simply told
you what polarity to feed to it's particular winding (ideally, you would be
feeding it with a sine wave but I think that a square wave should be close
enough for a rough test if not for most applications). I.e., all I need to
do with my three half H-bridge circuit is to connect each winding to +
voltage when its hall output is high and to gnd when its hall output is
low. When I do this, the motor runs, but at about 1/4 of the correct RPM
and drawing about 40 times the correct no-load current. I have tried
swapping the sensors around in every combination possible (i.e., use sensor
1 to control winding 2, etc.) and even tried inverting all the hall outputs
and then trying all combinations again. The best I can get is to have it
run at about 1.5 times the correct rpm for my input voltage (!) drawing
about 7 times the correct current.

The motor datasheet does not describe how to do the commutation, and the
info I have found on the web so far seems to vindicate my initial simple
guess.

Any ideas?

Thanks!

Sean

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