# Bad motor - pauses every 1/4 rev



## MalcolmB (Jun 10, 2008)

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


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## jaspersk (Jun 26, 2008)

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.


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## major (Apr 4, 2008)

jaspersk said:


> 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.


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## jaspersk (Jun 26, 2008)

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.


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## jaspersk (Jun 26, 2008)

Here is a picture of the spot that failed.


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## kennybobby (Aug 10, 2012)

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?


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## major (Apr 4, 2008)

kennybobby said:


> 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.


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## kennybobby (Aug 10, 2012)

*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.


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## Qer (May 7, 2008)

jaspersk said:


> 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.


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## jaspersk (Jun 26, 2008)

major said:


> 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.


Thanks Major. I forgot to take a picture but there was some melted copper thrown up on the case up against the field windings. The tech at Warfield said that was from the armature winding. They said they could clean it up and it would not hurt anything. When it failed, I lost 90% of power but was able to limp into a parking lot. However, once the car had come to a stop, there was no getting it to move again. In neutral, the whole transmission/motor shook pretty violently. I incorrectly thought it was the transmission until I took it apart and saw the same behavior with the motor on a 12V by itself. I think this failure was in the making for several weeks. Occasionally, I would hear a noise from the engine compartment but I was not sure what it was. Looking back, I think there might have been some small arcing before it finally had a significant failure.

The real question is how to prevent this from happening again. I am planning to install a forced air blower as a precaution although I am not looking forward to the noise that will add. I think I have my Zilla set to 800 motor amps. My battery amps rarely exceed 300 but my motor is probably seeing a lot more than that at lower speeds. I typically start off in 3rd gear. I think I will change that habit as well since that was putting more amps on the motor than was necessary. I'll start using 2cd as my accelerating gear. I rarely exceed 3500 rpm. I don't think it was a high speed problem but I suppose I may have forgotten to shift and not noticed although the Zilla does have a speed sensor that would cut out at 5000 RPM.

Steve


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## major (Apr 4, 2008)

jaspersk said:


> The real question is how to prevent this from happening again.


Keeping the motor cooler helps. Selecting gears to keep RPM up and motor amps lower helps. But I suspect this particular type of failure is caused by a defect at the time of manufacture. I've seen several other similar armature shorts on motors with low miles and no signs of abuse. I'm not sure how long in service or miles were on your motor, but I didn't get the impression of or see evidence of overheating or overspeed or foreign object intrusion or other cause for the short, so I presume there was some insulation damage and/or lack of impregnation at the failure site when the motor was made. And after so many thermal cycles and vibrations, it finally gave way.


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## kennybobby (Aug 10, 2012)

jaspersk said:


> ...The real question is how to prevent this from happening again.


i would want to ask them how are they going to fix the last six loose laminations that slipped on the rotor, and get a picture of the repair before reassembly, etc. That sharp corner as the coils exit the stack is a critical area obviously...


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## jaspersk (Jun 26, 2008)

major said:


> Keeping the motor cooler helps. Selecting gears to keep RPM up and motor amps lower helps. But I suspect this particular type of failure is caused by a defect at the time of manufacture. I've seen several other similar armature shorts on motors with low miles and no signs of abuse. I'm not sure how long in service or miles were on your motor, but I didn't get the impression of or see evidence of overheating or overspeed or foreign object intrusion or other cause for the short, so I presume there was some insulation damage and/or lack of impregnation at the failure site when the motor was made. And after so many thermal cycles and vibrations, it finally gave way.


You know your stuff! This is pretty much what Warfield said as well. Initially, the assumption was it was probably overheating due to high amps but after opening it up and not seeing signs of thermal damage, they said it was likely just some type of manufacturing defect. I am still planning a blower though to minimize the foreign objects. I also get stuck in stop and go traffic. Netgain provided a link to their shop manual:
go-ev.com/Shop_Manual2.pdf
This is a good read. It also talks about the advantages of filtered cooling air.


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## jaspersk (Jun 26, 2008)

kennybobby said:


> i would want to ask them how are they going to fix the last six loose laminations that slipped on the rotor, and get a picture of the repair before reassembly, etc. That sharp corner as the coils exit the stack is a critical area obviously...


They basically rewound the whole armature. Netgain considered it a new armature. Netgain was really helpful and actually handled all of the billing through Warfield since they have a "volume discount" with Warfield. They also met me out there to see if their forced air band would work on the ADC since the diameter is slightly different and we wanted to double check the termination locations. They found it would work fine with a gasket. There are really good people there and I would work with them again. Fortunately, I was able to save a lot of money in shipping as I was driving through the area on vacation and I dropped the motor off on my way up and returned it on the way home.


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## ElectriCar (Jun 15, 2008)

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.


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