Help me fix my electric motor

Long story short... I have to fix a shop vac for work. (Home Depot) Its a Ridgid 12 gallon that a customer returned because it was sparking. We were going to trash it and have Ridgid send us a new one, but I decided to fix it and use it for the shop. Customer had it for one week.

I ran it a while and saw slightly more than normal arcing at the brushes. After about 5 minutes it started sparking a lot and slowing down.

I pulled it apart. Bearings are super smooth. Brushes are massive carbon plugs (about 3" long). Good even carbon transfer on the commutator, brushes are nicely "polished" in the arc of the contact with no pitting. The springs are free and properly holding the brushes against the contacts.

I cleaned the carbon off with a scotch-brite and resurfaced the brushes. I ran it for a while to let the brushes re-wear into an arc and transfer carbon. It looks sexy... but its sparking again. I verified that the endplay isn't excessive which would allow the armature to contact.

I'm kinda lost. Cheap chinese junk? Pitch it?

Bad brush material heats up and sticks?

Brush material OR...

Is there agap between the contacts on the commutator? If so, when I raced R/C in the past, we would take a ball point pen and smooth the edges between the contacts. This would help the brushes from getting chipped on the edges of the contacts.

Check that the power cord isn't internally shorted, just measure the resistence through the each wire while bending it every which way. I could imagine a short in the cord causing issues with the power supply to to brushes. Good luck.

If you had a "growler" you could check the armature for shorts/opens.

I was thinking similar things to wvumtnbkr, but also just wondering whether there's a machining defect and the comm isn't round...

I'm going to guess the armature it mis-timed. As in the commutator isn't properly aligned with the segments of the armature. Too advanced and you get lots of sparks from the bushes and the motor slows down. To retarded and you get few sparks but a lot less RPMs, it also tends to make the armature run hot. The problem will get progressively worse on a new motor as the brushes seat to the commutator. Check to see if you can rotate the commutator on the armature shaft. If so, retard the timing a little. If not, you can time it by cutting the brushes back on one side so they contact the next segment on the commutator a little later in the rotation of the motor. I used to build cheater motors for RC cars doing this many years ago.

Another thing that will make brushes spark a lot is if you get oil on them. Usually the sparks will travel around the commutator. It will look like streaks of fire.

Without looking at it, this is probably worth less than you paid for it.

You can also re-time the can by rotating the end bell. I assume that the can and bell are locked together some how. If you could separate them (I'm thinking pressed in tabs at the end of the can) you can advance/retard the timing.

Wow... I asked the right group.

Rotating the end bell isn't really an option since its a square plastic molding. I'll try rotating the comm on the shaft. I might also try shaving off the leading edge of the brushes.

The bell could be off by 90 degrees since its square and could be assembled clocked in any one of four positions.

I'm sure its a cheap chinese motor that was assembled poorly, so the whole thing isn't worth what I paid (which was free) but its fun to learn and experiment.

How far should I rotate? are we talking like 1 degree or 45 degrees? Would there be a "timing mark" or a tell-tale way of knowing what the "correct" alignment is?

Toyman01 wrote: Usually the sparks will travel around the commutator. It will look like streaks of fire.

Exactly - streaks of white, blue, and yellow fire. Sometimes it stops completely and cycling the switch will make one quick spark. Continuing to cycle the switch will usually get it running again with sparks trailing around the com.

That sounds like it's out of time. I'd try moving the end bell around to the various positions, see what happens. What's the worst that could happen?

We used to advance the commutator timing on R/C car motors by sticking a small screwdriver in the brush holder, then grip the shaft with a pair of Vise Grips and turn it in the desired direction. When R.O.A.R. got wind of this, they specified a 'Mabuchi cross wrap) wind which would break the commutator wires if twisted. You can get the same advance/retard effect by twisting the brush holders. The rule of thumb was a max 44 degree advance, they'd fry themselves pretty quick if it went past that. Most stock sealed motors were (IIRC) 27 degrees advance. It was pretty easy on a DC motor to tell which way to go, you simply swapped the leads. A zero degree motor would run the same speed either direction, an advanced motor would turn faster one way than the other. I don't think that will work on an A/C motor, but then again I have never tried it.

One other thing: to cut down on RFI it was necessary to put a capacitor across the terminals. If this wasn't done, the brushes would spark like hell and drive the radio stuff nuts. This was really bad on carbon fiber and aluminum chassis which could conduct electricity. You might see if there's a capacitor missing or not connected.

So you were the guy that was always "cranking" motors?

Bastard!

Let me guess: there is no logical and effective method for storing the power cord or vacuum hose? We can put a man on the moon, but Rigid can't figure out how to store cords and hoses on a vacuum...

pinchvalve wrote: Let me guess: there is no logical and effective method for storing the power cord or vacuum hose? We can put a man on the moon, but Rigid can't figure out how to store cords and hoses on a vacuum...

Right?!?! They've figured it out for the one in the house but not the one that sits in the garage! WTF!

pinchvalve wrote: Let me guess: there is no logical and effective method for storing the power cord or vacuum hose? We can put a man on the moon, but Rigid can't figure out how to store cords and hoses on a vacuum...

Amen to that. The Ridgid shop vac I have at home came with 6 places for attachments and 7 attachments. Nice.

wvumtnbkr wrote: So you were the guy that was always "cranking" motors? Bastard!

(looks around and whistles)

In reply to curtis73:

6 in the clip and 1 in the hole.

Ok, I tried all of the above. I clocked the bell 90 degrees, no good. I tried twisting the comm, but it won't budge. Its hard to see but it looks like its keyed and epoxied. I tried shaving off about a 1/4 of the one side of the brushes and it ran a little better until it snapped one of the brushes in half.

This electric motor has now gone in the circular file.

Sure, sure, but did you figure out a better way to store the hose??!!