My 10.*V Bosch Pro d/d emitted sparkles and magic smoke yesterday. I assume that it hash brushes as this was near the rear end and I could see what looked like the commutator in the sparks. It's 5 years old and hasn't had heavy use - the Makita 18V combi has had far more use - and over 8 years, although it now has a Floureon NiMH battery that, so far, seems to be doing well.
Do you think that it's repairable? If not, I'll be tempted to get another
10.8V - the Makita 12V d/d seems big and heavy now.
Not sure about getting another Bosch, although a bare one and no charger would be cheaper so long as the battery fits.
Look at what is available these days - the latest brushless motor models appear to be much smaller than the previous models. Don't judge your purchase based on what was available the technology available 5+ years ago.
You probably know what a brush dispenser looks like. The brush is a squared rod of carbon, that slides in and out of the holder. There is a spring to apply mechanical pressure, so the brush contacts the commutator.
You can have damage to the commutator itself. On larger motors, they use "generous" commutator slabs, and the commutator can be "turned down" to give a fresh surface. On smaller motors, materials can "impact" the gap between contacts. Or, perhaps abrasive material collects in there.
Some brush assemblies go ohmic during failure, the brush holder is cheesy, and there could be thermal damage to that area (brush holder melts). Some brush/commutator setups are bad enough, you know from experience they can't be repaired (old B&D weed cutters). Others aren't like that, and the company making the product sometimes tries to arrange a small number of brush designs, to cover a large number of products. This allows a trip to the parts store to be successful. When every item has custom-one-off parts, you can never get the stuff you need.
For me, the first question would be:
1) Can it be disassembled ?
2) Can it be disassembled and put back together ?
Usually, there's a little bit of fiddling to load a new brush or brushes, depress the spring(s) and fit the brushed where they're supposed to go. But it's easier than reassembling a wind up alarm clock :-) (Ask me how I know that some time. it took *hours*.)
The brush typically has a "copper braid" sticking out the side. Notice how, during disassembly, there is a "crimp" between the brush plus copper braid, and the internal wiring from the handle. When you buy a pair of brushes at the store, ask for a "crimp" for each. If you're a butter fingers, ask for two crimps per brush. But be aware, that fitting the new crimp, means cutting off the old material, and sooner or later, you'll run out of slack wire from the handle. This implies that maybe one or two brush replacements is about as much as you can expect to do to a device. And by then, the commutator is likely to be pretty ratty looking anyway.
The purpose of a crimp, is if it gets hot, it won't melt. Unlike solder. And solder would make the braid stiff, which you don't want. That's why they use a crimp.
The last one I did, one brush had 2x as much wear as the other. There can be differences in spring pressure. But the surface of the commutator, could rough up both brushes and lead to short operating life for the brush. And you don't want to become too enamored with cleaning the commutator, because you could leave a burr on the edge that eats the brush.
It's good if you notice a "reduction in power" from the device. Which means the brush is about to eject from the holder. Then the spring, maybe with a pusher plate on the end, is contacting the commutator. And maybe that's where the sparks came from. I managed to do my last one, before there was a catastrophic failure. Just lucky. I could notice the loss of power, and the device lasted until the job was done. And then it was repair time. There was still a short piece of brush in the holder.
I'm surprised ast such self destruction, Bosch are normally well up on stopping that sort of thing, indeed many of their devices simply stop or slow down if a fault is detected. You got the black pea in the harvest! Brian
Thanks for this, Paul. I'll have a look at dismantling it, see how bad the brushes and comm. are, then work out if it's worth doing. Actually, you've just given me a refresher course - one place I worked, we used to machine the comm. a bit if needed and replace the brushes. Last time I replaced brushes - on a car - was about 50 years ago. My vehicles since then haven't had brushes, or motors or bodywork... I no longer have any way of turning a comm. unless I can rig up something with a drill. Only one end held - what could possibly go wrong?
Yes, brushless became fairly common, albeit expensive, just after I bought this one. However, the Maks have done better - indeed I had more work out of a 14.4V Parkside combi, far heavier use than it should have had.
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