Hi Steve,
I had a similar problem when a slight brake fluid leak fouled the commutator. It produced visible glazed spots on the comm. I fixed it by removing the brushes and gently sanding the brush surfaces with a suitably shaped sanding block. I cleaned up the commutator with isopropyl alcohol and removed the glazed areas with fine grit paper, then refitted the brushes and reseated them by running the motor at 12V for a few hours.

I would have replaced the brushes if I had any spares, as I'd guess they're slightly porous and could retain some of the oil, but it seems to have worked so far.

Malcolm

 

Thanks for the advice Malcolm. I cleaned up the commutator but it has had no affect. It is strange the way it stops quickly ever quarter turn.

 

You may have a shorted armature coil. Or some other fault in the motor. Hard to tell from here. Can you post some pics? That motor is fairly typical of a forklift motor, so you could take it to a repair shop which handles forklift motors and have them diagnose the problem and estimate repair.

 

I dropped the motor off at Warfield. They opened it up and found a shorted armature. They are repairing it for me. Hunter from Netgain met me there and gave me a tour of the factory and helped me verify that their forced air band would fit my adc. Great folks there. If/when I have to buy my next motor it will be a Netgain. They said the motor did not look overheated but they say they are seeing more people overamping their motor with more lithium out there. They said they didn't see as many problems when everyone was on lead. My battery amps rarely exceed 300 but I need to start watching my motor amps more closely in the future. I don't want to repair the armature every 15k miles.

 

Here is a picture of the spot that failed.

 

Here is a picture of the spot that failed.

I love it when people actually comes back and explain what was the cause instead of just going silent. It's really annoying when people just ask questions and then there's no follow up or explanation so the only one that (possibly) learned something from it all is the thread starter.

Good pic too. Very informative. And, well, then there's Major too, of course, this constant source of useful motor trivia.

 

Is it a shorted coil to coil in the windings, or a coil to the armature? i wonder how the laminations are held together. Do you suppose that fiberglass tape is strong enough to hold the coils in place when it's spinning up around 5k rpm?

 

The laminations are pressed onto the shaft like all rotors. The glass tape is applied to the green armature and then it is treated with a polyester resin under controlled conditions of temperature and such. The result is a thick layer with deep penetration of a very strong and high temperature encapsulation/insulation. This process has been used since the 1970/80's and eliminated the top slot stick armature assembly method. On an armature this size it would probably hold to 10kRPM but the comm and balance putty would likely hold the recommended speed to 5k.

Each of the copper bars you see in the photo is an armature coil side. I'm thinking this particular armature has 37 of these armature coils, sometimes called hairpins due to their shape before they are inserted into the core. Each of the 37 armature coils has a single turn, or 1 T/c. There are 37 segments (or bars) on the commutator and 37 slots in the lamination core. Each slot has 2 coils sides one on top of the other. Each of these 2 coil sides belongs to an armature coil of opposite polarity, so to speak. So, these 2 coil sides in the common core slot must be insulated from each other. If that insulation fails, there exists a "shorted" armature coil. It may in fact actually be a pair of shorted coils, but the result is the same.

When that short first occurred, it was likely at high speed/high voltage and there was arcing and burning of the surrounding area. It could have resulted in a catastrophic failure or a lesser of an event even allowing the user to get home. But then jas notices this 1/4 turn behavior. And that is indicative of a shorted armature coil attempting to be rotated thru a 4 pole energized field. Shorted coils do not like to move in the presence of magnetic fields.

 

Twisted laminations?

Thanks for the great explanation Major.

When i zoom in on the picture i can see a charred spot on one of the coils as it exits the lamination stack--it appears that the last six core laminations have slipped and rotated on the stack in the vicinity of the charred coil--looks like it cut the paper and probably into the wire insulation causing the short and arcing damage.

i have seen stacks with long rivets or thru-bolts or a bead of welds holding the laminations together, but did not know how it was done for these motors.

 

I have the same motor and recently had the armature replaced with a shorted armature. I did manage 19K miles on it first. Cost of new armature $750 and $400 for having it replaced and new precision bearings installed.

I didn't have a rev limiting feature in place before this and a few times I saw the tach hit 8000 accidentally, usually after putting it in neutral for stopping then hitting the throttle on green light. It only takes a split second to hit that speed with no load! I HIGHLY recommend some means of limiting RPM in these motors. The Soliton controllers have this feature.

I figured the high RPM occurrences may have caused it.

But I did go back and limit the motor amps to 700 or so and also limited the motor voltage as well. My pack is 165V on lithium. Was 144 lead for 1st 10K miles.