Re: [CAD_CAM_EDM_DRO] Help with a bipolar driver.

questo999 wrote:

>Hello guys,
>
>I am in need of a little help. I have just finished building the
>PAP8ABL bipolar driver from Laurent Fouga's website. I intend to use
>it with size 34 double stack bipolar motors.Details are 1.8 deg. 4.6
>amp per phase and 0.55 ohms per phase. However for testing purposes I
>decided to use a motor salvaged from an old printer. The details are
>1.5 ohms and 2.1 volts. The driver steps the motor without the
>chopper enabled but maxes out on current, pulling about 6 amps and
>the motor gets very hot very quick. When the chopper is enabled I
>cannot 'tune' the motor to any set current say 2 amps. If I turn the
>pot fully one way the motor will turn freely and when I turn it fully
>the other way , the current maxes out. About halfway the motor makes
>a chopping sound but becomes highly unstable. It tends to spin
>rapidly one way or the other. If it does settle , when I step the
>motor using turbocnc it starts to spin rapidly again. No matter how
>much I adjust the pot it remains unstable.
>
>

It sounds like there is feedback from the chopping circuit to the step
command inputs, or something
similar to that. Anyway, the current limiting circuit is unstable in
some manner. Are you sure
you followed the PCB layout exactly? These circuits switch amps in
microseconds, or even
nanoseconds if it uses FETs. These high di/dt values cause one part of
the circuit to interfere
with other parts unless the layout of each part and wire is very
carefully thought out with respect
to radiation and reception of interfering signals.

Jon