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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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12V , 200W , DC motor
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. |
#2
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12V , 200W , DC motor
Meat Plow wrote in message
... On Sun, 4 Oct 2009 14:44:20 +0100, "N_Cook" wrote: 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. Clean the com with extra fine emery and stone with rotor in a lathe or other apparatus. This is a scooter motor correct? 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. ? |
#3
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12V , 200W , DC motor
golf trolley, not cart |
#4
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12V , 200W , DC motor
"N_Cook" wrote in
: Meat Plow wrote in message ... On Sun, 4 Oct 2009 14:44:20 +0100, "N_Cook" wrote: 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. Clean the com with extra fine emery and stone with rotor in a lathe or other apparatus. This is a scooter motor correct? Actualy on a golf cart. seems like a rather weak motor for a golf cart. 12v,200 Watt? -- Jim Yanik jyanik at localnet dot com |
#5
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12V , 200W , DC motor
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). -- Cheers, WB .............. "N_Cook" wrote in message ... 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. |
#6
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12V , 200W , DC motor
Wild_Bill wrote in message
... 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). -- Cheers, WB ............. "N_Cook" wrote in message ... 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. 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. |
#7
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12V , 200W , DC motor
Did you perhaps mean 200A rather than watts? Anyway, just a nit, I've
heard it's not a good i idea to use emery cloth on the commutator, as the abrasive is metallic. N_Cook wrote: Wild_Bill wrote in message ... 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). -- Cheers, WB ............. "N_Cook" wrote in message ... 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. 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. |
#8
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12V , 200W , DC motor
N_Cook wrote: 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. 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. -- You can't have a sense of humor, if you have no sense! |
#9
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12V , 200W , DC motor
Michael A. Terrell wrote in message
m... N_Cook wrote: 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. 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. -- 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 http://home.graffiti.net/diverse:graffiti.net/ |
#10
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12V , 200W , DC motor
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 http://home.graffiti.net/diverse:graffiti.net/ |
#11
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12V , 200W , DC motor
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 http://home.graffiti.net/diverse:graffiti.net/ |
#12
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12V , 200W , DC motor
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. -- Cheers, WB .............. "N_Cook" wrote in message ... 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. |
#13
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12V , 200W , DC motor
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 ? |
#14
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12V , 200W , DC motor
50 amp not 500
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#15
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12V , 200W , DC motor
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. -- Cheers, WB .............. "N_Cook" wrote in message ... 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 ? |
#16
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12V , 200W , DC motor
Wild_Bill wrote in message
... 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. -- Cheers, WB ............. "N_Cook" wrote in message ... 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 ? 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 |
#17
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12V , 200W , DC motor
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 |
#18
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12V , 200W , DC motor
"N_Cook" wrote in
: Wild_Bill wrote in message ... 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. -- Cheers, WB ............. "N_Cook" wrote in message ... 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 ? 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 maybe it's a current probe test point? a loop you can hook a current probe over,without breaking the circuit. -- Jim Yanik jyanik at localnet dot com |
#19
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12V , 200W , DC motor
Jim Yanik wrote in message
4... "N_Cook" wrote in : Wild_Bill wrote in message ... maybe it's a current probe test point? a loop you can hook a current probe over,without breaking the circuit. -- Jim Yanik jyanik at localnet dot com I'd not thought of that possibility The thick wires to the battery are widely separated as it is a cuboid SLA, so plenty of run to put a current probe around at that point. At the moment I'm struggling to get the tubular framework back together. I assume when they assemble it, it is done under force so each corner joint keeps everything else in place, the screws must be for show or they do not hold it all together as far as i can see. It is made to be foldable like a folding bike and triangular sections and one triangle locked and braced against another |
#20
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12V , 200W , DC motor
If there is a next time I'd reverse the jaws of a sash cramp to force the
tubes apart, the 2 inches or so to release the cross tie tube. I wonder if the chassis of those disability/mobility scooters are built the same way. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#21
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12V , 200W , DC motor
Now road tested I see how the traction works. Gearbox will spin backwards
because of course pitch and angle of the worm / spur gears, I hope there is protection against the reverse emf generated as off on the control is not fully off, 5volt measured just by leasurely hand spinning.. Then presumably "spring" clutches in the wheels one L and opposite sense in the R one to again allow for total freewheeling in one sense and somewhat braked in the other direction. |
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