Arcing Brushes

bilyo

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I just purchased a used MM1800 Type 1 corded mower for my daughter to use on her small patch. While cleaning it up and checking it out I noticed that when the power lever is released there is a bright arc from each brush. The arcs are bright enough to be seen through the orange plastic cover. Otherwise the mower runs fine. The brushes look OK with about 1/2" of each brush remaining in the holder. The commutator also looks OK. I've never seen this from and electric motor before and I'm skeptical that it is normal. Having said that, I took the cover off of the MM875 that I use to see what it does and it does the same thing, but the arcing is not quite as bright. I've never noticed it before because the cover is black. I'm thinking of contacting the local service center about it next week, but thought I would check with you folks first.
Thanks
 

reynoldston

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Its normal to have some arcing on DC motors. The only thing that may cause this is weak brush springs. Another thing you can do is clean the commutator in which they make a tool to do this. It looks like a large pencil eraser on a wooden stick in which you clean the commutator when the motor is running.
 

bilyo

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Mark, Thanks for the link. While I don't see anything in the manual covering this issue, I always like to have the manual.

Reynoldston, This is a DC motor? The MM1800 is corded. Where do I buy the commutator cleaner? Or, is it something that I can make?
 

reynoldston

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Mark, Thanks for the link. While I don't see anything in the manual covering this issue, I always like to have the manual.

Reynoldston, This is a DC motor? The MM1800 is corded. Where do I buy the commutator cleaner? Or, is it something that I can make?
I bought mine from a electric fork truck dealer years ago. You might check the net or E-Bay. I did look on E-Bay and they look like a different style then I have. I don't know how to make one seeing they look like they have a abrasive in the rubber part? Maybe a large eraser on a stick might work??? never tried it.
 

bilyo

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Thanks for the info. To the motor question. Is it really a DC motor working of AC current? How does that work? BTW, searching around for some more information, I ran across a FAQ regarding the arcing. It agreed with you that it is normal. All B&D mowers do it. Some are not so noticeable because of the black cover.
 

tgriscom

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I just purchased a used MM1800 Type 1 corded mower for my daughter to use on her small patch. While cleaning it up and checking it out I noticed that when the power lever is released there is a bright arc from each brush. The arcs are bright enough to be seen through the orange plastic cover. Otherwise the mower runs fine. The brushes look OK with about 1/2" of each brush remaining in the holder. The commutator also looks OK. I've never seen this from and electric motor before and I'm skeptical that it is normal. Having said that, I took the cover off of the MM875 that I use to see what it does and it does the same thing, but the arcing is not quite as bright. I've never noticed it before because the cover is black. I'm thinking of contacting the local service center about it next week, but thought I would check with you folks first. Thanks
The "arcing" that you see is the blade brake.
 

tgriscom

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I just purchased a used MM1800 Type 1 corded mower for my daughter to use on her small patch. While cleaning it up and checking it out I noticed that when the power lever is released there is a bright arc from each brush. The arcs are bright enough to be seen through the orange plastic cover. Otherwise the mower runs fine. The brushes look OK with about 1/2" of each brush remaining in the holder. The commutator also looks OK. I've never seen this from and electric motor before and I'm skeptical that it is normal. Having said that, I took the cover off of the MM875 that I use to see what it does and it does the same thing, but the arcing is not quite as bright. I've never noticed it before because the cover is black. I'm thinking of contacting the local service center about it next week, but thought I would check with you folks first. Thanks
The"arcing" that you see is the blade brake.
 

tgriscom

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The"arcing" that you see is the blade brake.
That is, when you release the safety switch, power is cut and the motor is shorted, causing it to stop quickly. The spinning motor is generating electricity. The short puts maximum load on the generating motor, causing it to stop quickly.

Try this: cut the power while still holding the safety switch. The motor spins down slowly with no arcing.

The arcing on stop is normal.
 
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