Dead motor? Think again

While hobby brush motors are pretty cheap now adays, there’s always that feeling of why replace when you can rebuild and reuse. As such [John Carr] presents how to change the brush position in motors to revive a dead motor. So long as the motor dies from natural causes commutator wear, the idea is the brushes can be moved along the axes and fixed to a new portion of commutator that’s not worn at all. [John] also goes through the details of some tricky reassembly, but we think to make this complete a guide on brush replacement and commutator replacement might be in order hint hint.

Comments

  1. Sprite_tm says:

    Lol @ mouseover on the picture :)

  2. Andrew H says:

    That was a pretty interesting read, but It seems like a considerable amount of work. I could only see this being useful for nonstandard motors that can’t just be replaced.

  3. Hahahahahahaha mouseover is nice

  4. sky says:

    This may actually come in handy. I am restoring an old German car and a replacement motor for the heater fan is $300.

  5. jim says:

    Just use non-standard motors, guys.

  6. DMattox says:

    Fix your spellcheck! When Communism gets worn down, a wall gets put up… More Seriously, I run into quite a few non standard motors when fixing older stuff, but I found a common hobby motor in the strangest place the other day; the blend door actuator in my car…

  7. daniel says:

    I used to take these to a local guy who just rebuilt them for me. Back when things were fixed instead of replaced there were a lot of shops that would service them and even special little lathes for turning the bits down.

  8. Anonymous Coward says:

    This trick really saved my ass one time.

    In the middle of an isolated road, my car alternator chewed up the last remnants of its brushes.

    I had an electric Dewalt impact in the trunk that I gutted and sanded the graphite brushes until they fitted the alternator. Soldered the copper ribbon with a lighter and presto.

    It held on for 3 yrs.
    ;p

  9. Jeremy says:

    Like @sky’s comment above, I did this to a german car too. I had a VW Golf decades ago that had the A/C blower fan die. The replacement was hundreds of dollars and I was a poor college student. After disassembly, I noticed it was just the brushes were worn out, so for about $2 I bought some new brushes. It worked beautifully.

  10. jakdedert says:

    I replaced the motor in Oester beard trimmer with the one in a discarded Oral B toothbrush. It was an exact fit…merely needed to swap out the widget on the shaft.

  11. jakdedert says:

    My question is why the commutator would wear like that, leaving the brushes seemingly in pristine condition. Is that a hallmark of bad design, or or bad circuitry, or both. It seems there must be a lot of arcing to cause that much wear….

  12. Andrew H says:

    @jakedert

    The carbon brushes are deceptively complicated bit of chemical engineering. My guess, since I’ve never actually seen this happen to a motor before, is that this particular motor had brushes that were to hard or abrasive.

  13. r_d says:

    @Andrew H
    It’s really not that much work. I used to do this kind of thing when I used to race slot cars. It can save you a decent amount of money, too.
    @jakdedert:
    Motor brushes usually have a whole lot more material than the commutator, but I think usually the brushes still wear out first (they’re usually made from a softer material). He may have replaced them.

  14. BeagleBreath says:

    Posts like this one are the reason I never throw away my old junk.

    I had a customer bring me a variable speed motor from a CNC machine. The commutator was made from thin metal sheets glued to a nonconductive spindle. The sheets had worn through and were ripped and broken from use. I used some PC Board conductive paint/glue to reproduce the metal sheets. The motor has been running fine since then (several years ago).

  15. Tachikoma says:

    @jakdedert: Some forms graphite is quite hard, much harder than the copper it contacts.

  16. jim says:

    Dirt in the motor. He must live in a sandstorm.

  17. Taylor Alexander says:

    And it sounds like we’re all aware, but sometimes all you have to do is swap out the brushes! They often have screws on the outside holding them in, and you can usually find replacements for ~<$5. Its so satisfying too, because its cheap to do and saves you a lot of money versus replacing the whole motor! :)
    -Taylor

  18. mike says:

    if the brushes get too small they wear down to the embedded spring or braided copper wire within the soft carbon. that’s what wears them out so badly.

    when you resurface, some motors have a lot of endplay such that if a groove wears into the brush it will shear off if the motor has a lot of thrust motion and the brushes have a lip hanging off into some groove (or so i imagine) and since they chip away so readily..

  19. blue carbuncle says:

    That is why I keep my wife’s old emery boards in my tool bag lol. Hopefully this will inspire a couple of folks to burnish some “dead” gear out there. Corrosion or oxidation is a common problem on audio gear that has helped me plenty of times securing a piece of nice gear that is listed as “for repair”. Nice article :)

  20. jakdedert says:

    I’ve done a number of brush replacements in starter motors and alternators. Most recently, fixed starter in my van for $20, which would have cost me at least $100 more to replace. The only time I ever saw a commutator (actually ‘slip ring’ in this case) worn like that, the brush had broken off and was wedged sideways….

  21. D_ says:

    That motor has a lot of “miles” on it @jim I believe that dirt is copper and graphite residue.

  22. mightygobot says:

    I onced used the carbons in a D-Cell battery for brushes in a pinch. They worked supprisingly well for a long time.

  23. Hunnter says:

    I have so many old motors sitting around waiting for projects where i can fix them. Fans, hand-held fans, toy motors, water pumps from fountains and the like.

    A new friend to the group was a fan. Poor thing vibrated itself off and broke the blades… twice. First 2, taped back on badly, then the last one.
    I miss my fan.

    Oh well, at least it died before it killed me from fan-death!

  24. gcat122 says:

    Good information. If you do not have fine fishing line you can use thread from sewing or mending.

  25. Jake says:

    This is nothing. I’ve been rebuilding motors (common or not) for at least a decade. All you need is a good supplier that has a decent selection of bushings, brushes, bearings, etc, and a little time.

    @sky
    You can save money doing that, but if it’s for a mercedes, make sure to check a retail aftermarket supplier like Advance Auto/etc. – I recently rebuilt a Mercedes 300E blower motor as it was the weekend and I couldn’t get one from them for 3 days. Pressing the plastic cages off of german blower motors is a PAIN to do without warping them. I was able to get a “permanent” replacement (though the rebuilt one was working fine) for under $100, and though it came in a brown cardboard box, the part inside was an OEM Behr motor like what the car shipped with!!!

  26. signal7 says:

    Please forgive me for saying this (since I’m guilty of butchering english as much as anyone else), but I think the following statement is either incomplete or just incredibly awkward: “but we think to make this complete a guide on brush replacement and commutator replacement might be in order”

    I wouldn’t make a post to point that out, but it does underline the fact that a spell checker is no substitute for proof reading. I can’t even figure out what you were trying to say. There’s enough bad english online, imho.

  27. Jake says:

    @signal7

    That’s par for HAD, but it’s OK since I believe the writers (posters/admins/whatev) are either high school or early college students? Probably should give them a break.

  28. Allan Scott says:

    i used to be a power tool repair tech , Motor commutator bars can be turned in a Lathe than clean in between them with sharp knife to make shure there is no copper dust inbetween them

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