Another melted blower brushes story (and how to fix)

[billjam]

Because my fresh air blower didn’t run but had power at the connector, I figured that I was another victim of the dreaded melted blower brushes.
Sure enough, one brush holder was completely melted and the brush was at a crazy angle to the commutator.



It isn’t obvious how to remove the red plastic clip which holds the brushes from the motor frame it without breaking it, but it can be levered off with a small screwdriver.





After removing the brush and all the melted crud from the brush holder, there was one small flat unmelted area still intact so I super-glued the brush to it. This gave me some hope of getting its alignment reasonably close.



Next step was to add some epoxy glue to hold the parts together more firmly.
At about this stage, I realised that I had to glue the wire against the brush but there was no easy way to do this and be sure of good electrical contact, so I drilled a 1mm hole in the end of the brush and reshaped the wire.





With the wire pushed firmly into the brush, I gooped it all up with more epoxy.



Once it had set, I held the brush in place to check how well it fitted against the commutator. Spinning the motor while holding the brush in place puts some marks on the brush so that you can see where it touches the commutator.



The brush is very soft and is easily filed or sanded, so just keep test fitting and removing the shiny area until you have at least half the brush in contact.



I have been running the blower on and off during the past week and it runs just fine.
Cost =$0 plus an hour of my time.

During this exercise, I started wondering why one brush was toast, but the other one still looked fine. Considering that both brushes always pass the same current, the only reason I can see for one of them melting is poor electrical contact between the brush and the wire within the brush holder. If this contact degrades and its resistance increases, the heat generated due to the resistance melts the plastic holder.
Well, that’s my theory anyway.

[tito911s]

What kind of glue/adhesive would you use for this?

[billjam]

Any two part epoxy will work. Some are runnier than others so may take a few applications to build up the thickness.

[tito911s]

Just want to thank you for the tutorial. Hopefully I will be save the $80 it would cost for the new motor.

[DanielDudley]

How do those brushes advance ? I see the spring, but I can't figure out the articulation.

[86911cab]

Wrap the commentator bars with Emory cloth then set the brushes and spin the armature until the brush surfaces have been sanded. Take the cloth and tear it to the width of the bars. Take a small piece of tape and tape the cloth to the bars so that it will wrap all the way around. This will lap the brushes for a good contact

[tito911s]

86911cab's description sounds very well informed, but my technical knowledge falls short to fully grasp it.

From what I can tell, based on taking it all apart, there is a spring that "pulls" the bar.


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