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  #11  
Old 05-08-2012, 07:37 AM
Salty9 Salty9 is offline
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Default Re: AMD FB1-4001 motor failure

Does one of the com bars have a "loose tooth wiggle"?
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  #12  
Old 05-08-2012, 08:01 AM
dladd dladd is offline
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Default Re: AMD FB1-4001 motor failure

i could see this mode of failure. Something caused that mica stuff to rise up from between the comm bars. Overspeed? perhaps it was like that from the manufacturer?

Once that piece is sticking up, it kicked the front 4 brushes up. The others are now doing twice the work, and eventually overheat.

Your setup doesn't sound unique, a 9" motor in an S-10 with transmission and Curtis 1231 is probably about the most common conversion out there, right? Certainly not a case of poor component choice.

Is there any chance you ever overspeeded the motor? Ever try pulling out of the garage thinking you were in reverse, but were really in neutral? (I've done that a few times...). An unloaded motor spins up REAL quickly.

Isn't it at least 'possible' that whatever is sticking up between the comm bars was there from the beginning, and it's been running on 4 brushes till now?
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  #13  
Old 05-08-2012, 08:57 AM
sbjohnston sbjohnston is offline
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Default Re: AMD FB1-4001 motor failure

Here's a photo illustrating the positions I found the brushes in after the motor failure.

http://www.flickr.com/photos/3202513...57627254806189


Steve

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  #14  
Old 05-08-2012, 09:08 AM
GerhardRP GerhardRP is offline
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Default Re: AMD FB1-4001 motor failure

Quote:
Originally Posted by sbjohnston View Post
Here's a photo illustrating the positions I found the brushes in after the motor failure.

http://www.flickr.com/photos/3202513...57627254806189


Steve

Do you have pictures of the working surfaces of the brushes and the comm surfaces?
Gerhard
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  #15  
Old 05-08-2012, 05:45 PM
sbjohnston sbjohnston is offline
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Default Re: AMD FB1-4001 motor failure

I have never subjected the motor to an overspeed condition, nor have I applied power with the shaft held fixed. My safety interlocks help prevent the latter situation. Details of my calculation of the RPM of the motor at the time of the failure is in my original post - it was 3320 rpm as I recall.

The edges of the front brushes are not knocked off entirely - they are carved out in rough correspondence to the shape of the mica protruding from the commutator.

I detect very little variation in height from one commutator bar to another. I don't have a precision measuring device but the bars feel the same height each to its neighbors.

This motor comes set up with the brushes mounted offset from the line of the pole piece bolts in the anti-rotational direction. Thus I did not need to advance the timing - the motor was meant for electric vehicle use at this voltage and was supposed to be ready to go for this application.

I'm going to clean up the commutator and install a new brush-holder, springs, and brushes, and then first see how it turns by hand, watching the brushes ride and listening.

Steve


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  #16  
Old 05-08-2012, 10:57 PM
electro wrks electro wrks is offline
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Default Re: AMD FB1-4001 motor failure

I wonder if the brush holder came apart in your bottom brush position, causing part of its metal frame to contact the connection between the com bars and the arm winding(s). Was it touching when you first looked at it? If this was the case, it would cause all kinds of hell to break loose, arcing and overheating-wise.
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  #17  
Old 05-09-2012, 07:06 AM
sbjohnston sbjohnston is offline
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Default Re: AMD FB1-4001 motor failure

Interesting thought, "electro-wrks" - I can't say it had touched but it was somewhat deformed.

gottdi wrote:

>With that mica bit protruding you should not just run the motor.
Huh? Who would do that? I trimmed it away with a razor.

>When pushing the brush from beneath, you can't push it out like
>you can pull it out. The spring pressure and position won't allow that.

Thanks for the video demo. The dimensions of the holder, brushes, and springs are different in my motor.
You mentioned the small bit of insulation being too small to kick the brushes up. The insulation is only
protruding a small bit after the failure. I feel confident that it was a big "flap" when it started, and
after the passes of the brushes it was be worn down to the nub we see now.

The worn out areas on the front brushes are larger, but the same shape as the protruding insulation,
further supporting the idea that the protrusion was larger at first.

Steve


Steve
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  #18  
Old 05-09-2012, 03:20 PM
sbjohnston sbjohnston is offline
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Default Re: AMD FB1-4001 motor failure

I really appreciate everyone's thoughts on this problem. I am not comfortable saying there is "no chance" of one theory or another - in my years I've learned to never say never! Surprise lurks around every corner. But I do play the odds and appreciate your appraisals of the situation.

I cleaned up the commutator and installed the new brush holder, brushes, and springs and rotated the shaft by hand while watching the motion of the brushes. There is a very tiny "wave" to their motion in and out as the shaft goes around, so I think the overall shape of the commutator is not a perfect circle. I hear no clicking as the commutator runs under the brushes, so they seem to be riding smoothly over the bars.

There has been some talk of the need to "seat" the brushes before using them - is there anything special to be done when new brushes are installed?

Thanks...

Steve
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  #19  
Old 05-09-2012, 05:30 PM
sbjohnston sbjohnston is offline
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Default Re: AMD FB1-4001 motor failure

I've added a photo of the front brushes to my collection.

http://www.flickr.com/photos/3202513...7627254806189/

Steve
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  #20  
Old 05-11-2012, 12:14 AM
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PStechPaul PStechPaul is offline
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Default Re: AMD FB1-4001 motor failure

Very interesting thread. Sort of like "Forensic Files"! I've had to do some similar sleuthing when some of the test sets I've designed or modified have had problems in the field. There are usually several plausible solutions. And sometimes (as Sherlock Ohms has said), if you can eliminate all the usual causes, that which remains, however unlikely, is the culprit.

The only way I can see the brush being pushed out into that position would be if the mica piece had been longer, and flexible enough to initially bend and then extend far enough to push the brush out, and perhaps the leads of the brush could have pressed against the screen to keep the brush from popping out all the way. But then there probably would have been arc marks on the screen, since I assume the brushes have a high potential with respect to the frame.

ISTM, as gottdi asserts, that the motor must have failed previous to purchase because of the mica insulation hitting the brushes, and someone was in the process of servicing it. But then the cover was replaced and maybe the motor was put back in stock. Even if it was basically inspected and bench tested it probably would have seemed OK, and only after an extended period of normal use the remaining brushes were overloaded and eventually failed by overheating. The customer should not be expected to inspect a new motor except to check for obvious shipping damage and such.

I do recommend that the armature should be removed and the commutator with the loose mica insulation should be carefully inspected, perhaps with a new piece of mica forced in place and glued. It may be worthwhile to take it to a motor repair shop to have it done properly. If the commutator segments get loose and short out it could cause a catrastrophic failure.
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