Siemens XL1200 motor running hot after new brushes fitted.

[JohnyV]

Hi all.

My Siemens Extraklasse 1200 was running a treat 'till the brushes wore out. I fitted a new set and it has been fine for a week or two of pretty heavy use but now the motor has started smelling hot, though it runs and sounds ok. The motor case is up around 60 deg c towards the end of a cycle. Is it just bad luck and new motor time or have I missed a trick?

Cheers.

 

[jj4091]

Did you smell it or check the temp. before you fitted the brushes? Not 100% sure but I do not think that sounds like a problem. Personally I would just keep an eye on it for a while.

 

[JohnyV]

No, the first sign of the brushes going south was when it packed up. No smells or clues before.

 

[jj4091]

No, the first sign of the brushes going south was when it packed up. No smells or clues before.

Think you are just sensitive to the symptoms because you've worked on it, as I said, see how it goes.

 

[zipper]

Did you use pattern brushes or genuine Bosch parts? Was the commutator badly marked/scorched by brush arcing?

 

[JohnyV]

Did you use pattern brushes or genuine Bosch parts? Was the commutator badly marked/scorched by brush arcing?

No, they where pattern brushes, can they be problematical? I didn't check the com but looking at the dead brushes on my desk they look to be fairly even/smooth.

 

[zipper]

Genuine Bosch brushes prolong motor life. They are made from high quality laminated carbon & the spring pressure is correct for the motor design. Pattern brushes shorten motor life. They cost a around third of the price of genuine brushes (depending where you buy them) but they are made from cheap non-laminated carbon & the spring pressure is often far too high. Laminated brushes have a higher current density, the correct spring tension & they help reduce sparking under heavy/varying load. Hope that answers your question

 

[JohnyV]

I will try some genuine brushes and report back! Thanks for your help.

 

[zipper]

Check the commutator surface & make sure the brushes are not sticking in their holders. The comm may have stall marks, a badly pitted surface, high/low segments etc. I always redress the commutator if there is evidence of previous arcing. Use some very fine scotchbrite if it looks bad & give it a good blow out with compressed air afterwards.

 

[JohnyV]

Amazing. Our local repair bod had some mid price but not oe brushes in stock which he said he fits and has no problems with. Did as you suggested, cleaned the com and blew everything out, fitted the new set and BINGO, it's right as ninepence. Cheers for your help Zipper.

 

[zipper]

Good for you
In general...Fitting new brushes to a commutator that is pitted & scarred by previous arcing is akin to them running on sandpaper. Friction & poor electrical contact cause more sparking, which in turn results in heavier brush wear, more carbon dust, & poor motor function. It is a downward spiral that can lead to wiping out the motor altogether or even damaging the pcb. The commutator should always be cleaned & the new brushes preferably re-seated to the existing commutator profile by using a commutator grinding/brush seating stone while the motor is running. These stones are hard to get hold of & expensive for the average "one-off" DIY job. But as a bare minimum if the comm is badly marked it should be cleaned with either very fine scotch-brite pad or a fine type sandpaper (but nothing containing aluminum oxide). Preferably the gaps between segments should also be scraped out to remove embedded carbon etc. Once the commutator is clean & prepared the new brushes will run smoother, sparking is reduced, & wear comes down to a minimum. After a while the commutator will eventually take on a medium brown patina, this is the optimal condition for correct brush commutation.