Needs new brushes as one had cracked along half the length but not broke away, so forming a wedge in the slideway. Along with some conglomeration of carbon etc in that part of the slideway and beyond into the gap and presumably into the crack , until it jammed out of contact. Anything to be aware of for the brush composition ? otherwise looks like a mains voltage carbon/graphite brush. No name motor for spares. How to clean off the build up of carbon on the commutator and is there an equivalent , for low V high A motors, of bedding in with bedding stone ? as no aperature available to poke any stone in there when assembled.
Actualy on a golf cart. A bugger to get at as one retaining bolt was seized, steel bolt into tapped aluminium. Al had corroded rather than the steel on our wet links. Is there a recognised way of chemically dissolving the aluminium oxide for the next time of doing this. Luckily I could hack into reinforced heavy duty structural plastic to release the mount , then undo the bolt with molegrips, Impact driver after penetrating oil would not shift it, only deforming the bolt head. Would grinding/drilling a well under the head of such a bolt and a few drops of battery acid in there do anything. ?
I would cut or snap the head off then drill it out and re-thread the hole or if you are lucky enough to find a drill bit the same size of the bolt you would just need to chase the threads that remain.
Sounds like a good bit of work but I have done it on an engine block on a snapped thermostat housing bolt and it turned out well. And I just used a powered hand drill. Engine coolant baked into bolt threads seize the bolt beyond removal. I don't think your plan will work but you might as well try it first as it will do no harm.
I'd say that's a very unusual brush failure. Some general comments:
Brushes for DC motors typically have a copper and graphite content that makes them feel slippery surface when rubbed between thumb/finger. I've found that AC motor brushes just feel like plain carbon.
One of the guys at my local motor shop pointed out that it's important to use brushes specifically for DC motors, as AC brushes can tear up a DC commutator.
According to a technical course at a Reliance industrial drives training school, the best surface contact that brushes can have, is the completely smooth, slick black surface that brushes make after they're properly seated.
Any surface abnormalities need to be addressed before installing new brushes, or the new brush life will be significantly reduced, while aggravating and continuing the commutator damage. Commutators are often recut to zero runout and a smooth surface by turning them in a lathe, and copper isn't an easy material to get a very nice finish with for a very light cut, for an inexperienced lathe user.
Over the years, I've used numerous easy procedures to "clean up" commutators, and they have generally worked at least, well enough. Different abrasives from ink erasers (with pumice imbedded in them) to various ultra-fine sandpapers can sometimes smooth minor surface irregularities, but don't do a good job of truing and smoothing such as on a lathe. One should be sure that any abrasive they might use doesn't imbed itelf into the soft copper, and that the abrasive isn't electrically conductive.
In high powered, expensive industrial motors, the face of the brushes are recut to match the lightly smaller diameter of the commutator, after servicing.
In industrial motor applications, there are special brushes which are only intalled temporarily at regular service intervals, which are used to refresh and clean the commutator surface, then replaced with regular-duty brushes for production runs.
Many low-priced motors aren't intended to be serviced, and any commutator problems other than very minor scoring, indicate that it would be better to replace the motor for reliable use.
Creating flat or low spots on a commutator needs to be avoided, as these will lead to the brushes hopping and/or losing contact which will promote arcing and damage to the brushes and commutator.
When brushes are removed for inspection, they should only be reinstalled in their original orientation (not rotated 180 degrees).
It looks as though another feature of low V / high A motors is the brushes have copper wire tails melded into the graphite , wheras mains ones can often get away with end of conducting phosphor-bronze spring just resting against end of brush and no copper braid.
I use a variable DC power supply and a gray ink eraser to polish the commutator, then a modified Exacto knife blade to undercut the mica insulation between segments. I run the motor at 100 to 200 RPM, and use a light touch with the eraser so the dust isn't pulled between the brush and commutator. I polished hundreds of commutators that way.
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You can\'t have a sense of humor, if you have no sense!
Unfortunately no access to the commutator when assembled. I'd have to mount a pair of magnets near the rotor and bodge up some brushes. I will adopt the compromise of spinning between centres on a lathe and use non-metallic abbrasion/honing
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Some Bosch 12V,250W automotive fuel pump brushes are about right, needing cutting down half a mm W and H to fit, side entry copper wire tails as in this use.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Well that's 2 impossible jobs done reassembling the motor
1/ Tying back the brushes to get them over the armature and then removing the cord when in place.
2/ How to replace the 5 inch long steel screws , without any built-in guides, passing between 2 powerful magnets. They go where the magnets want them, not some midway path. Obviously made scratch marks before disassempling but required the head of the screw held in molegrips until you can feel it is in the tapped hole, screwdriver placed in head still in the molegrips, pushing down, while you release the molegrips.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
I've worked on a few 220vac Baldor single phase 15 hp repulsion/induction motors. Replaced brushes and stoned the comm. Removed rotors for rewind and comm replacement. Needed a hoist to load and work on these at around 450 lbs. The brushes were embedded with a braided copper lead and were only in use upon startup. After that the comm was shorted and the brushes floated. This was the popular motor used over here for oil well pumping units up to 120,000 LBS rod and downhole pump weight for a five to six thousand foot well.
The copper pigtails on brushes are a very good feature for almost any application. They ensure that the current has a low resistance path, instead of relying on the brush spring and/or the metal guide (usually brass) in the brush holder.
There is a special compound that's used to bond the pigtail to the brush, which has been discussed in rec.crafts.metalworking before, but I don't recall it's name.. but it's not commonly available anyway (and requires a special process, IIRC).
Brushes with pigtails generally have a metal disk or other type of terminal that needs to be securely constrained by the brush cap or connected in a pressure-type terminal. Some of the disk-type terminals have small tabs to engage slots at the sides of the brush guides, which reduce the risk of the pigtail twisting tightly as the brush cap is installed.
I've encountered heat damaged brush springs, most often due to improper brush installation, and have ended up replacing them with other springs for other motors of similar size, with approximately the same sized brushes. This has worked well enough, while realizing that the replacements may not have been optimal as far as extended long term reliability of the motor.
I don't recall ever seeing a method to calculate a proper brush spring, a far as contact pressure. There's likely to be a method of selecting the best spring pressure, maybe based upon the surface area of the brush.
The 2 paralelled output TO220 thyristors had their identities ground off before insertion. 200W, 12V motor so 17 amp so would they be say 30V 8amp,
10amp or 15 amp rating each? No fuse in the control anywhere but there is a main relay and more electronics than just for controlling speed so could there be an overload sensing cct that drops out the relay ? While at it there is an off board loop of copper coloured wire, perhaps microbore copper tube could that be a 20 or 500 amp fuse or just a dropper element for overload sensing ?
I don't know about the semiconductors, but the loop of wire may be a braking "resistor". Battery powered power tools with permanent magnet fields sometimes have a loop of wire to dump the spinning motor current into, when the trigger is released. This causes the cutting blade, in a saw for example, to stop sooner than just letting the armature to coast to a stop.
You may know a procedure for testing the LRA locked rotor amperage of the motor, which may be a useful indicator for selecting the semiconductors.
Metal current feedback circuit "resistors" that I've seen in DC motor drives and treadmill drive circuits sometimes look like strips of bare sheetmetal, or just a half-circle of very heavy gage copper wire. I guess the type of material used will depend upon the circuit designer's background and material/part cost.
Taking a closer look it is probably solid 1.7mm copper wire in a loop above the board of about 1 inch diameter. It is in the supply line to the power devices (maybe powfets rather than thyristors) not the power to the electronics. But operation is via rotary pot with switch so have to go throu gh minimum revs (pulses) before switching off. So still a mystery, no way a fuse , the cross section of the tracks, wide yes, must be less than 1.7mm solid wire. Incidently now all in working order on the bench, not reassembled yet onto the caddy a G Caddy TEDC 12201 that I find no www ref to
Perhaps it is just a wire link, it does cross over some tracks, perhaps someone decided 1mm was too small a section for copper wire to reliably hold up in a vibrational environment. Still I cannot see any obvious track knecking or other possible weak link/fuse possibility
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