Motor Repair BMC or MAC in fact Any type ** FIXED **

Hi

My main BMC geared motor that I have been using for 7 years now (daily driver) started to play up a while back and as it was too cold outside to fix it I used one of my other bikes in the meantime. I got the bike back out and had a look, the symptoms sounded so much like the gears grinding (it had had a new set the first set since new! So I doubted this but anyway) I wiggled the lead as it entered the motor and the motor ran so I figured that it was the wire broken inside, I resoldered some of the joints in the hall plug on both sides and it continued to work, problem solved or so I thought.

Anyway come out of work on Friday and it’s a no go, the fault was odd through, it would run fine lifting the wheel off the ground but soon as I got on it it wouldn’t go, growled and refused leaving me to think it was the gear slipping as I had seen this before.

So yesterday armed with some new cable I snipped off the connectors and pulled the motor apart, I cut all of the wires at the base of the motor leaving just the coloured stubs from each set of windings so I could easily identify them and re connect the new wires, I snipped open the sleeving on all three of the phase wires to get to the joints it was then that I found my problem and I should have known because it has done this before.

DOH! The yellow phase wire has come unsoldered and was only just making the driest of contacts! Grrrrrr should have checked this before I cut all the wires off! Ha ha oh well and I know how this happened as it happened before, previous to the bike going bad I had fitted a little booster pack to the bike taking it up from 50 to 60V in other words out of my usual sweet spot for reliability at the expense of lots of fun of course! This puts a lot more power down through the windings and of course the solder joints to each phase, the heat dries out and unsolders the joint!

Posting this to try and help others not just with a BMC this can happen with any motor and even someone with lots of experience with bike motors like me can sometimes forget the obvious, Intermittent faults like this one are always hard to find though because my DVM tested fine across phases the joint just didn’t like any serious current flowing through it.

So nice hot soldering iron and some decent heat sleeving got the motor repaired in a little under an hour (which must be a record repair for me) new phase and hall wires in and it has never run as well, there is so much more power there it must have been so down on that one phase for a long time, so before you snip! check check and check again, oh and the gears were perfect not a mark on them, we are happy again.

Knoxie

do you think it would have shown up on a test of resistance of the phase wires before you opened the motor or did it still have enuff contact to appear continuous to the voltmeter?

Yes all phases were OK on the digital volt meter, intermittent faults like this are a pain but its great when you get them fixed, most of the hub motor manufacturers use sleeving to cover the phase wire to coil joints, well worth cutting them apart and resoldering them if you are experiencing similar problems like loss of power and or intermittent operation like me.

Ha ha well I thought that I had fixed it.

OK so the bike ran fine for a couple of days then it stopped again, so I checked the halls again with the bike upside down and sure enough one of the halls wasnt firing, so i took the wheel off and had another look, I then connected another controller and checked again, still no joy OK so I think I will just swap all the hall sensors for new ones, I dig around in my box of spares but can only find 2 sensors, 2 is better than none so I change the one that I think is faulty and the one next to it, when I say change I snip out the body of the sensor from the epoxy and fit new ones over the old legs, I then check continuity between the newly soldered pins and the pins where the wires connect back out to the hub.

This is where the problem was, the original return or ground leg from the centre hall sensor had a high resistance of about 1.5 meg ohms, bah! the pad on the board was covered in that epoxy resin they insist on covering the solder with (i Guess to help prevent corrosion) anyways I made a solder bridge from some old wire and we were back in business, I checked with my meter and all halls were firing, the halls that I replaced them with were genuine honeywell sensors, I am pretty sure that the last one in there isnt however I dont think that the halls failed this time.



The above image explains it a little better, it has taken 7 years for this joint to go dry on me so no complaints, the above picture is not the motor in question (its the BMX) but its near as makes no difference the same, my board had loads of that epoxy on, using the chisel end on the soldering Iron I managed to scrape it off and clean the board before re-soldering, I sleeved the legs of the hall sensors as the legs from the old sensors were still embedded in the epoxy.

So she is alive again and I am 100% this is fixed now, so In short I need not have replaced the halls although if you are going to the trouble of checking the solder joints and remaking them you may as well replace them for brand name ones, I used SS413A halls, they are nice and small and can operate from 4 to 30V DC, the controller I have switched out at 13V DC, they can sink 20ma and have a rise time of just .05 micro seconds, more than good enough for my little old hub motor.

You can get them in the UK from RS part number 181 1479 http://tinyurl.com/cq27apt I must get some spares now pleased to get the bike back on the road, I also gave it a good clean too as my hands were getting so dirty each time I have been trying to fix this damn thing! thanks Muc-off.

If you have ebike problems dont give up! keep trying you will fix it in the end