Prince of Darkness?

[V_Mad]

I just had some weird faults on my wipers. They started running on their own, and would not switch off! After a bit of messing around I could not get them to work at all. Motor was taking current but no motion.

I took out the motor (DR3 type), and noticed the field winding looked blackened. It turned out that the blackened wire was not the winding but was the resistance wire (about 10 ohms). It had overheated, and part of the circuit seemed to be shorted. Apart from that the brushes look a bit short but the motor is generally in great condition with little wear; not bad for 40 years service. Who said that Lucas was the prince of darkness?

I am going to repair it (replace the resistance wire with a 10 ohms resistor) and see if I can get it working.

 

[V_Mad]

Update: it now seems to work OK, but gets quite hot. I think I will bench test it for about 1 hour. If it survives I guess it should be OK. I wish I had some new longer brushes though.

 

[Ken Ellis]

Chris,
Is the gearbox lubricated well? That grease may be 40 years old, too...
I've not been in one of those motors, but would it be possible to shim the brushes and still maintain continuity? Or are they just down to the quick? A motor specialist may have a generic brush that could be made to fit, and you'd be good for another 40.

Ken
Ken

 

[nickraymond]

Hi Chris
(We're trading threads now!)
Not sure if this is what the previous poster means, but your problem could be at the two little boxes on the drive cable that comes out of the motor.
I had problems with this, if yours jammed and couldn't get to their off position.. they would have stayed on until they could, getting hot and causing damage.

Nick

 

[V_Mad]

Hi Nick. Not sure what little boxes you mean; I think you have a different motor, not the DR3? Plenty of grease in the gearbox, which I have moved around to the parts that need it, and there was no problem with jamming of the drive cable as the motor seems to run freely enough, except for one thing I found: there is an armature end float adjustment which, when I loosened it, the motor speed went up slightly. I have now reset it and the motor still runs fine but does still gets hot. I guess it must be normal as it seems to work OK.

 

[mikephillips]

He means the 2 little drives for the wiper arms on the cable run.

 

[64beam]

Hi Chris,

Is the resistor that you replaced supposed to be 10 ohms or was it what you actually measured? It may have also changed slightly over the last forty or so years. If it seems hotter than normal, it may also have a bad connection elsewhere in the circuit.

Regards, Robin.

 

[V_Mad]

The slow speed works fine now, and the motor gets hot on slow or fast (ie with or without the resistor in circuit), so I am confident that the resistor is now working effectively. The old resistance wire measured about 10 ohms, so thats the basis of selecting the new resistor, which dissipates only 4.4 watts. The field coil measures 8.6 ohms, so I think most of the heat must come from the armature winding.

Now installed back into the car, it runs faster than before, which must be a good sign. I am hoping the heat is normal as there are no signs of trouble now. I would be interested though if anyone else can tell me how hot their motor gets after about 10-15 minutes running.

 

[nickraymond]

Hi Chris yeah, I meant the two little drive boxes, kinda like matchbox sized on the cable (not sure if cables the right word!)
I haven't felt the heat from mine, but I guess it would get warm when running for that length of time, whether it would get hot...
I'm not sure.

Keep an eye on it I suppose.

Nick

 

[nickraymond]

Hi Chris yeah, I meant the two little drive boxes, kinda like matchbox sized on the cable (not sure if cables the right word!)
I haven't felt the heat from mine, but I guess it would get warm when running for that length of time, whether it would get hot...
I'm not sure.

Keep an eye on it I suppose.

Nick