Brushes in an electric motor

[PeterT]

Hello not sure where to post this,

I have a Skill wormdrive circular saw and it seemed to be getting weak on power and so I put new brushes in it. Now it barely comes up to speed and the brushes have a lot and I mean a lot of arcing and it seems to follow around the armature while running. Not sure what causes this or how to fix the saw now. /forums/images/graemlins/frown.gif

Any Ideas welcome.

Thanks PeterT

I thought the new brushes wood fix it but seems to have made it worse

 

[johnday]

PeterT; Sounds like the brushes aren't making good contact. Take the armature out and clean it with some acetone where the brushes make contact. Then rough up the brushes a little where they make contact with the armature. I'll bet the brushes just need to be worn in. Just reassemble and give it a shot. The bearing surface should be the same concave angle as the convex on the armature. New brushes usually wear in pretty fast. /forums/images/graemlins/grin.gif

 

[Jagmandave]

Brushes usually have a curve in them, did you match the curve to the armature when you put them in, or turn them 90*?
also, clean the armature and blow it out good if you have an air compressor, it sounds like it's dirty........

 

[PeterT]

Thanks guys

I just took it back apart and cleaned it good, used a real fine emery paper on the armature and blew it out and put it back together and it did not help, still lots of arcing and not at full speed. I am not sure where to turn now. Yes the brushes are in the right direction they will only go in one way. /forums/images/graemlins/confused.gif

Thanks again
PeterT

 

[nobull1]

If when running the saw the fire seems to make a continuous ring around the commutator it probably has a open circuit armature. You "might" be able to see where the wire is open at the commutator and attempt to solder it in place. Another thing that can cause sparks is a shorted/burned field that will cause high amperage/sparking. If possible try to look at the field and see if you can see any burning/melting. If you find the field is bad there is a real good chance the armature is not long for this tool. The excessive heat from a shorted field usually will take out the armature. A bad armature doesn't usually take out the field. The easiest thing to do is check with a amp meter if you have one. Excessive fluctuating high amperage is a good sign of a bad field. Relatively normal amperage that is fluctuating is usually bad brushes or armature.

 

[PeterT]

Nobull

That sounds exactly like what it is doing, with the fire going all the way around. Can you tell me how to check the field with an amp meter also the armature?

Thanks for the help
PeterT

 

[nobull1]

If the fire is going all the way around it is almost for sure a open circuit armature. You really have to take it apart to know for sure. One thing you can do is remove a brush and look in through the brush holder. While looking at the commutator turn the blade shaft(probably need a wrench) and you will most likely see a wider separation(burnt area) between the commutator bars in at least two spots 180 degrees apart. If this is what you see it is open circuited. Another thing you can do is hook up a test light/meter and slowly turn the blade shaft to see if it opens at a certain spot. The cause of this can be a few things,to name a few 1) poor crimping of wires on the commutator 2) excessive load or undersized extension cord causing low voltage 3) shorted field causing high heat. If you have a induction amp meter just clamp on and see what it says. The amps should be somewhat lower that the rated amps, when tool is unloaded. If the amps are more than the rating you also have a bad field that may have caused the open circuit in the armature. I would pull the tool apart and do a visual inspection of the armature and field. Some times the field might just show the slightest amount of melted insulation on the bindings and that is a tell tale sign of excessive heat. The biggest mistake people make is to replace the armature without knowing the field is bad. It takes but seconds to take out a new armature with a bad field. If you take it apart post a couple of close ups of the arm/field and I will give my opinion. By the way one of the worst things people do to their saws is use a dull blade. I have seen numerous electrical/mechanical failures due exclusively to excessive loading.

 

[Soundguy]

One other thing to look at is to see if there is any proud mica sticking up on the commie. If so.. use a hacksaw blade and trim it just a hair below the copper.. then clean. Also.. as mentioned... try to use a round file and put a bit of a matching curve ont he new brushes. Otherwise.. you are getting good info here.

Soundguy

 

[PeterT]

Thanks for the help guys, I priced a new armature ($65) and new field ($40) plus shipping. I don't think I want to put that much money into a used saw. I may just hang onto it and buy a new one. Then I will have some spare parts just in case the new one dies.

Thanks again
PeterT

 

[Junkman]

If there is an authorized Skill repair center near you, bring it in and see how much they will want to repair it. Sometimes they will just plug it in and say it will be around xxx dollars or they will say that it isn't worth fixing. I have found that the Milwaukee repair station fixes them economically.