Sorry for the long question...
I've been asked to look (and repair) an electric bicycle controller - it
seems to be a reasonable straight forward design; power mosfet output with
PWM drive, 24V supply, etc. etc. and so far I've managed to get it largely
working and the motor control part of it seems OK.

The only issue now is the relay - this connects the motor to the mosfest.
I've bypassed this and the motor runs as it should do (as far as I can
tell), BUT what I can't tell is exactly how or when this relay should be on.
Its driven by a microcontroller (a Elan EM78P156EL if you really want to
know), via a few transistors and various other bits, and I'm at a loss as to
why the particular control pin on the micro isn't being driven.. either
there's some fault detection in place that I've so far missed, or for some
reason that particular output pin on the micro has failed.

...so - I can either:

* somehow figure out a way of switching the relay on ONLY when the motor is
being driven - which is at a guess what is supposed to happen.

* bypass the relay control and make the relay 'on' all the time.

What I'm unsure about is how the circuit would cope with the back emf
generated by the motor on downhill runs..there's a few big diodes near the
mosfets which would probably soak the current, but not having any other
experience with such items I'm unsure as to what the 'normal' way of these
things working is.

Any advice? -- Idealy not 'tell them to sod off' ....which is
tempting....

"Harvey" wrote in message
...
[..]

Actually - describing it as a bicycle is probably a bit misleading, its more
of a scooter, with the motor permanently connected to the rear wheel by a
belt drive. There's no freewheel.