Wednesday morning I had a disaster on the way to work. I had been having some trouble driving and the motor controller kept cutting out with direction contactor open circuit fault. I managed to get some way to work and I pulled up to some traffic lights on a slight hill and it decided to stop completely. I had loads of cars honking horns as I was stuck. I rolled back a bit then got drive again and moved off the traffic lights, round a side turning, up a hill and into a lay-by. By this time the motor was making a loud whining noise and started smoking heavily. I opened the hood and smoke billowed out of the motor brushes. My travel partner got a taxi the rest of the way and I got a rescue truck. When I got home I went through the motor controller book and read about the fault code and it suggested a problem with the motor brushes not making contact. I stripped back some units under the hood to get access to the motor brushes and it was obvious when I looked into the motor that the problem was a little worse than just worn brushes. It took me another hour or so to get the motor out as I only had a trolley jack, some wooden blocks and some old wire. By tying the wire and dropping it down a bit at a time I eventually got it free. I took the motor apart and marked the pieces at the joins so it goes back together with everything the same. The photo below shows the commutator end of the motor armature.
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This photo shows a closer view of the motor commutator and you can see heavy scoring, grooves, heavy pitting as the brushes must have been glowing to cause this level of pitting. I have found a local company that can undercut the comm for a reasonable price. Most of the brushes were completely worn down to the spring limits and the pigtails were making contact with the commutator.
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The photo below shows what is left of the some of the brushes. There is another 2 on my garage floor somewhere, but I can't be asked to find them at the moment. They will get swept up some time soon no doubt. I have found that it may be cheaper to get my brushes from USA as they are expensive here, even from a firm that only does brushes and knew my size exactly just by me telling them a little about them was very expensive. I would save half the price by getting them from USA.
As usual everything in the UK is twice the price than in USA. This is really biting me as I know people who have conversion businesses in USA that are making good money, but when the parts are generally half price and readily available this is all possible. Over here it would be very difficult to make a profit even with a full order book. I believe the cause of this rapid wear of the brushes is due to the DC regen braking causing bad arcing at heavy loads. This is equivalent to going flat out in reverse on a motor that has the brushes advanced to the field windings. I have turned off all the regen controls now and won't be recommending them anymore, except on brushless and AC motors. The motor is only 3 years old.
