dryer motor

[Jerry Trumball]

I have a GE DDE7208 dryer with a 5KH26JJ motor. When the motor is stationary, the centrifugal switch energizes the start winding along with the run winding. When I depress the starter, the motor hums but does not turn even with the belt off. That points to a bad motor, but I want to be sure.

Winding resistances are 3 and 4 ohms. That doesn't prove the insulation is holding up at 120 VAC, but if there were a leak so bad that the motor wouldn't turn even unloaded, wouldn't the overload protector break the circuit?

At 2 amps DC, there are only 6 mv across the centrifugal switch, so the contacts appear to be fine.

Bearings have no slop or noise but more friction than some motors I've seen. It takes 0.7 inch-pounds to get the shaft moving.

What could be wrong?

[Jerry Trumball]

I was sort of hoping for that, but this motor doesn't use one.

[Boden]

My experience with motors is that under normal operation windings don't fail. Usually the problem is with the "stuff" surrounding the magnetics. Switches, capacitors, bearings, clutches, etc. Make sure everything is clean and lubricated. The motor may not have much starting torque so compromised bearings mare be a problem. Can you safely give the motor a bit of help when starting to verify or rule this out?

Boden

[gfretwell]

Capacitor?

[Jerry Trumball]

Thanks. The switch I push to start gave a consistent hum, but I could check it with a couple of amps to be sure the voltage drop is tiny and consistent.

That leaves friction. The 0.7 inch-pounds I measured would be equivalent to 1 pound of pull on the belt. That doesn't sound like much, but maybe it was higher before I removed the motor to measure. One website said removing the motor and vacuuming the dust can sometimes reduce friction enough to get it working again.

I started the motor several times a few days ago because I was removing items a few at a time. There was no starting trouble. I wonder if whatever lubricates the plain bearings got a little gummier since then. Should I try to lubricate the bearings? I have WD-40, sewing-machine oil, and motor oil.

[Boden]

WD-40 should not be used as a lubricant. It is not a good long term lubricant. The other two, motor oil or sewing machine oil are fine.

[Jerry Trumball]

That looks like the solution. I measured the friction again, wrapping the string around the shaft at the blower end, and got 0.5 inch-pounds. Last night I wrapped the string around the pulley, which is probably less accurate.

All that friction made me think they were plain bearings. That seems to be wrong. It's an open-frame motor, so I think I can apply a tiny bit of "small motor" oil without making a mess.

... Well, I applied a little oil, spun it, and found that the friction had risen to 5.5 inch-pounds. Now it's back down to 5. It looks as if something is funny in the bearings, and the oil may do the trick.

[Mark]

put the belt back on, open the door, hold the door button in, press the start button and spin the dryer by hand to see if that will start it.

Mark

[Jerry Trumball]

Good idea. I wish I'd thought of it before I removed the motor. If the motor doesn't work when I put it back in, I'll try turning the drum. Somehow I'll need to press the door interlock and the start switch as I turn the drum.

Above, I meant .55 and .5 inch pounds. It's going much lower if I pull the cord two or three times in a row, but higher if I let the shaft sit a couple of minutes. Maybe the oil needs time to work.

[Jerry Trumball]

On the red side of the power plug, the side that supplies the motor, I have about 0.8 ohm, and it varies when I move the cord. I guess a tug years ago, and countless cycles of heating current, and perhaps oxidation, have damaged it. Maybe when I hit the start button, the cord resistance was high enough to severely limit starting torque, and the cord was big enough not to get hot instantly.

Much of the motor friction was coming from the plastic ring that throws the motor switches when it stops. Without springs pushing that ring, the motor feels like roller bearings when it turns.

[Jeff Wisnia]

Some portions of the motor housing or end caps may have "warped" enough so the outer surface of the rotor will get pulled into mechanical contact with the inside of the stator when magnetic fields are present and then "stick there".

Can you try powering the motor and rotating the pully carefully by hand and see if it seems "stuck" when power is applied?

Can you disassemble the motor and see if there are any "rub marks" on the outer surface of the rotor?

I've encountered this phenomena a couple of times over the years.

Let us know what you find,

Jeff

[Jerry Trumball]

The frame is riveted. Before reassembly I tried looking between rotor and stator to see if there was dust. The spaces looked even.

After reading your post, I plugged it in and pressed Start. It started every time. I think maybe oxidation in the damaged stranded wire at the plug kept the motor from starting, and wiggling the cord has reduced resistance for now. I'd better get a cord before I try drying laundry.

I have a rattle now. Investigating, I found about 5mm endplay for the drum. Maybe that's normal. The rattle seems to be coming from the sheet metal behind the drum, where the heating elements are mounted. Opening the unit will be much easier this time!

[Stormin Mormon]

Clean the berrings with a shot of brake cleaner, Gumout spray, or other areosol solvent. Let it dry throroughly, specially if the spray is flammable. The proper lube is something like ND 30 (non detergent). Failing that, 10w30 should give you years of service.

WD and sewing machine oil are totally not suited. They dry and get gummy.

[Stormin Mormon]

I've found 3 in 1 to dry out. I'm not totally sure about sewing machine oil.

Still, I'd choose 10w30 of those choices.

[Stormin Mormon]

You are an engineer?

[Jerry Trumball]

No. The bearings had a little more friction than I've felt on some 1/4 hp electric motors. Not knowing why the motor didn't turn when I pressed the button and whether this much friction was normal, all I could think to do was get a number by pulling a cord.

Isn't 3-in-1 like 5W motor oil without additives?

I want to cut open the old power cord. I'll bet there a lot of broken copper strands. I wonder how many dryer cords get like that. I wonder if they are a fire hazard.

[Jeff Wisnia]

It's likely time to replace the whole cord set, they don't cost all that much.

Jeff

[Stormin Mormon]

For whatever reason, the three in one oil I've had dries out after a while. I think it's different.

Broken strands. That's why they have so many strands. So one or two can break, but the rest keep carrying electric. They break in different places along the cord.

[Stormin Mormon]

Please let us know if that fixes.

[Jerry Trumball]

I replaced the cord and cut the old one apart. The wire was fine. Apparently the trouble was where the the wire was soldered (?) to the brass (?) spade in the plug. Cutting up that thick rubber plug was tough enough that I didn't finish the autopsy.

The noise came from the blower's plastic impeller. It turned silently with the power off sounded as if it were out of balance when the motor came on. Clamping it a mm closer to the end of the shaft made it smoother. I don't understand why.