This is a 12 volt brushed motor from one of the furnaces in my bus.
It and one other started running quite slowly so I presumed either the brushes were worn or there was a bearing issue. I removed it and disassembled it and the brushes are an excellent condition and the bearings are also fine. It spins easily and quietly by hand. But now it will no longer even spin slowly. All of the connections and soldering seem fine and it was at least turning albeit slowly until I removed it. But now I got nothing and it's obsolete so difficult to find a replacement. Seems like I'm missing something very simple and hoping one of you all can help me out. Thank you.
Since two motors were slow I start thinking about bad grounds or power. How does it run if you put the leads directly on a known good battery?
Sounds like you have toasted windings.
Occasionally you can run into a situation where corrosion or buildup on the windings or commutator bars will create resistance and inhibit the motor from spinning; you can remedy this with a little bit of Scotch-brite and solvent, but it will be pretty obvious if this is the issue.
What about that motor is special? Can you not just find a generic replacement and reuse or replace the shaft? That shaft looks easy enough to turn on a lathe. Given that you mention that this is from a furnace I doubt you're in the Phoenix area, but if you are I'd knock one out for you right quick.
Dirty commutation.
Clean it with some green scotch Brite and then run a ball point pen down each "segment" of the comutator (where the brushes touch). I'm betting it's brownish black.
If it is coppery colored, it's supply voltage or ground.
Excellent thank you. I will try the cleaning suggestions.
There's no problem with 12 volt power and of the three furnaces only two are running slow. I expect I could find another one but apparently RPMs are critical for suburban furnaces and since it doesn't seem to be anything significantly wrong with this one I would prefer just to make it spin again and put it back to work.
Make sure the brushes are not stuck in their guides, or the springs that push them against the commutator aren't weak or broken. If the brushes don't have good, firm physical contact with the commutator, there won't be much current flow. A lot of times on old motors, the springs get weak and/or the brushes get worn down so much that they don't touch the commutator. A common symptom is that the motor won't start, but give it a good whack to unstick the brushes, and it'll take off and run - sometimes slowly and/or unevenly, but it'll run.
I started fixing dc motors when I was a kid, slot cars, trains, and R/C cars are a great way to learn basic electrics - if you want them to work, you gotta learn how to fix them. I used erasers, my sisters' emery boards, and mom's sewing machine oil to fix 'em and improve performance.
I'm going with stuck brushes. Probably due to buildup on the brush hoods.
It could also be a dirty commutator but not running at all suggests a stuck brush.
I got busy so its still sitting on my bench. Not a priority because its not camping season. But whwen i get around to it I will report back.
