rewinding a burnt out hub motor and speed change

[richard purchon]

I burnt my 500w bpm cst motor out.
this motor has been bad news since it got it from bms battery.
it arrived damaged with a bent spoke flange,only got 35 spokes.
it should be 270rpm but its way faster than another one I have.
10cells 26" wheel 25mph. 15 cells 35 mph great,but the battery doesn't last long and when it comes to a decent hill its melted.
so I decided to have a go at rewiring.
first dismantle the motor and take some pictures of the stator.
where the wires come out cross over etc
remove and save the tabs in the slots.these keep the wires in the slots.
carefully unwind the wire from the stator starting at the wye connection [oppsite side from phase wires]
take note how many turns of wire there are around each slot.
this determines the speed of the motor.
try to get one the of phase wires off complete, so you know how long the new wires needs to be.
my motor had 5 strands of 0.5mm wire wrapped 8 times around each slot. 6 in total
here is a link to motor calculator.how the motor is wound.
the bpm has 18 slots. 16 poles or magnets.double layer and is y connected
http://www.bavaria-direct.co.za/scheme/calculator/

 

[richard purchon]

I ordered some new wire from
https://www.scientificwire.com/
I ordered 500gram roll 200degC 0.5mm D/C POLYESTER GRADE 2 E/Cu WIRE.
and a tin of laquer .
500g will rewind a bpm motor 3 times.
next make something to wrap your wire around to stop it all getting tangled which it will.

 

[richard purchon]

 

[richard purchon]

 

[richard purchon]

winding the coils around make sure you go all the way round.and get a full circle, 3/4 turn will not count.
its hard to keep count.but it does gets easier with practice.
when you have wound your ist phase check with a multi meter to make sure there is no short.[ I did not]
if there is a short don't unwind it first try manipulating the wires away from the stator.
a old rc propeller is good old credit card etc. squeeze the wires with your fingers.
if you can remove the short it will be ok because you will be coating the wires when finished with laquer.
continue wind the next 2 phases.
refit the tabs in the slots.
solder the 3 sets of phase wires at the y conection.look at the photos you took before starting.
and phase wires to controller.im lucky I don't have to bother with hall sensors. I run sensorless controller.
next laquer the wires I used a aerosol and really give it 3 or 4 soakings.
not only to insulate the wires but to stop them moving

motor all finished 500g roll of wire and tin of 180c laquer

 

[Alan B]

Nice job. How does it work now? Kv?

 

[richard purchon]

when I put motor back toghether tested with multimeter and dead short.[doh]
gave it try and it ran ok and I used it for 3 months no problems [strange]
but it was still too fast as before.so I decided to rewire it and slow it down.
sent for some more wire .56mm this time.
originaly it had 5 strands of wire wound 8 times around each coil.
striped wire of motor.
then using 1 strand of wire experimented with different turns.
it was quick and easy to wind with just 1 wire.
with the bare motor stator and magnet/bell held in a vice,and bike computer found the following =for 26" wheel @ 10 cell 42v
8 turns 30mph original winding
12turns 20 mph
16 turns 16mph.
rough calc 5 strands 8 turns 5x8 = 40 or 40 pieces of wire around each coil or in each slot.
in the end I wound it 4 strands 14 turns.
apx 12 mph which is what I want for riding off road in local woods which is v hilly.
hope this is some use to others to have a go ,I am sure there are loads of burnt out motors which can be repaired for apx £20
and a bit of patience.
richard