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Tool Talk Discussion Forum

Motor Brushes

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PaulW_NJ

12-23-2006 20:13:28




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I"ve experienced something twice in the past few weeks that I don"t understand. I wouldn"t think it"s normal.

What would cause one carbon brush on a 110v motor to be totally consumed (down to the holder), while the other brush looks like new and is it"s full original length? I discovered this last week on my B&D 4 1/2" angle grinder, and then tonight on my girlfriend"s vacuum cleaner motor. Both motors had quit. I can replace the brushes, but wonder if there is some underlying problem that would cause such unequal wear, and would just do the same to the replacements.

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Ken in Mich

12-25-2006 13:39:10




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 Re: Motor Brushes in reply to PaulW_NJ, 12-23-2006 20:13:28  
There was quite a news story here this fall when the USCG Mackinaw was replaced with a new ice breaker by the same. The old one had six disel electrics, I dont know if it was repowered or not, but it was in use for 62 years. Here is a link of some cool pics.



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PaulW_NJ

12-25-2006 10:29:57




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 Re: Motor Brushes in reply to PaulW_NJ, 12-23-2006 20:13:28  
I"m always fascinated to listen to posts on this forum, and learn what an amazing diversity of folks are also connecting and participating. This one is particularly interesting. DC Fan, just where are you and what do you do? Any photos of those machines you could share? What is the tractor connection? Would be interested in hearing more.

Oh by the way, Merry Christmas, and thanks.



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dc fan

12-24-2006 05:30:56




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 Re: Motor Brushes in reply to PaulW_NJ, 12-23-2006 20:13:28  
Good Day, without getting into deep as to how and why a dc motor runs on ac etc etc. Really your small motors like that are dc series motors, but due to magic of how they are built they work.
Anyway: if one brush is burnt off check the spring tension on it[ too much] and the tension on the "good" brush[ too little] higher pressure can cause excessive friction wear/heat/sparking resulting brush desruction, low pressure results in sparking/arcing/bruning of brush material.
Brush pressure on large machine is in range of 3lb per square inch of brush surface contact, a bit of math to do, lets say that you can feel about the same spring resistance when using your finger nail to lift the spring?? on your sixe motor.
Check comm condition clean? scored? burn/dark spots? loose solder on comm bars? if you polish it use very fine "sand" paper lightly and squarely applied. do not use "emery "paper as it has metal wove into it.
Final clean blow out dust and polish with a piece of canvas rubbed around it[ hand pressure]
once your done try hard not to touch the surface as finger oils can cause a non=communating area when the new brushes are installed.
of course the new ones have to be seated to the shape of the comm with same fine sandpaper, between the brush and the comm surface.
This is normal on the 10,000 hp units i run sounds like overkill for your, but hope it helps.
regards

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Jon Hagen

12-24-2006 07:59:40




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 Re: Motor Brushes in reply to dc fan, 12-24-2006 05:30:56  
Hey DC fan,that 10,000 hp number got my attention. If that was not a typo,what uses a 10,000 hp dc motor ? Submarine is the only thing that comes to mind,or huge water pump,but I don't have a clue why that would be dc. How many amps at what voltage would it take to make that kind of power ? Also how many and how large would the brushes be to transfer that kind of power ? Thanks for an interesting post :)

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dcfan

12-24-2006 12:45:41




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 Re: Motor Brushes in reply to Jon Hagen, 12-24-2006 07:59:40  
No not a typo, i run 3 of them all together or seperatly either direction, and your close with the sub,its asurface vessel although i don't enjoy having the bow put under,been there didn't like it:( Those motors are in a ice breaker, triple screw, one per shaftline, generation is 6600vac transformed and rectified to 900 dc. generation capacity is 35,000hp with losses we end up with the 10,000 shaft hp, times 3. [30,000]
These were built in 1966[ yes 66] and are still great units, picture 1 person 6ft, by high 200's in weigh. he can enter the casing on one side. slide down and under the comm/brush rigging turn around and exit on the opposite side. if that gives you an idea to size, casing/housing is a box 10wide x 12long x 12high in feets:)
and final tibit of trivial: factory specs state full ahead to full astern directional change rating is 4 seconds at maximum torque/shaft speed of 118RPM, and again that is 4 seconds, impressive and scary electric stress noises/diesel strain when it happens. hope it was what you wanted to know

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buickanddeere

12-27-2006 18:28:08




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 Re: Motor Brushes in reply to dcfan, 12-24-2006 12:45:41  
There are some MG sets in steel rolling mills in that HP range. 25 hz AC to DC. D*mmed operators, they always think something is wrong and want "something done/fixed". Well duh, it's normal for a small amount of arc to be seen along the edge of the brush(s) and commutator or slip rings. Pull the unit down again to install more new brushes and bed them in. It's ruining the machines with so many new brushes and polishing the commuator and slip rings. That's usually on the 250KW mg sets. At least the excitation for the rotor on a 650MW alternator scares the operators away. 250VDC and 2600amps. I've seen condensation form on the air cooling coils in the summer time humidity and drip into the assmbly and actually see watermist spraying around the slip rings and water 2-3 inches deep in the bottom of the case. The water is clean enough it only brings in a ground fault alarm. We vacuum the condensation out while the machine is running and dial the coolant flow down a little to the HX coils.

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Jon Hagen

12-24-2006 14:33:25




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 Re: Motor Brushes in reply to dcfan, 12-24-2006 12:45:41  
Thank you,thats interesting. The History or Discovery channel ? Did a story about ice breakers and mentioned that they are Diesel/electric,but gave no details of the driveline. I was amazed how strong those ships are built to break through or ride up on and crush feet thick ice.



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dc fan

12-24-2006 17:27:33




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 Re: Motor Brushes in reply to Jon Hagen, 12-24-2006 14:33:25  
i believe both channels have had various items on a times, trivial again: orginally the vessel was a steam turbine electric, following a mid-life refit to diesel electric[ 5 V16 Krupp MAK engines[ now owned by Caterpillar] we went from burning 200+ tons of bunker C fuel down to 40/45 tons of arctic diesel, thats in a 24 hours period of escorting/ice operations.
Gave us enough fuel saving/capacity to make the North Pole in 94 along with the USCG Polar Sea
Of course the Russian breaker "YAMAL" being a steam powered nuc was interesting to meet and visit. They served a Mighty "smooth" liquid to warm the insides, frost bite prevention they called it:)
have a good season.

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PaulW_NJ

12-24-2006 06:02:06




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 Re: Motor Brushes in reply to dc fan, 12-24-2006 05:30:56  
DC

Thanks for your reply! I will follow your directions.

Merry Christmas!



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dc fan

12-26-2006 13:20:24




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 Re: Motor Brushes in reply to PaulW_NJ, 12-24-2006 06:02:06  
Good Day: guess i sort of overtook your posting with trivial, sorry about that boss. Hope the info was good to get your gear going, surprised there wasen't more offered, nothing said that i right:)
tractor connection: Like machinery, wish to save all the old stuff but time and funding limit such actions[ massey/case/russian/ford].
If you web search for the "woods Hole Insitute"
known as WHOI in the trade they have a link to WHOI at SEA, from there scroll down to IN Thick Ice, they have yearly links to daily operations. I would pick 2005 about Augest 19th onward to get an idea of where and what we do.
Of course 04 and 06 are there also, also trips they have planned or done elsewhere.
i know of the old Mack, i would be guessing as to propulsion method.
There is most likely a link to the USCG Healy, but not sure if it has been updated after a diving accident and fire this summer.
Anyway this is long and taking up space, good luck with the motors.

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