Lotus Elan

Bench testing wiper motor

PostPost by: Craven » Wed Dec 09, 2015 11:06 am

Hi,
I don?t think it?s been mentioned and it's years since a played around with wiper motors, but a technique used to cause a motor to stop dead and not run on when switched off is to arrange a short circuit across it.
I know this is used on the later round wiper motors, can you find this feature on yours. It may explain some anomaly in your findings.
Ron.
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PostPost by: crypto » Thu Dec 10, 2015 7:19 pm

Dan, I don't know how good your soldering skills are. But if it was my motor, I would take the field winding out and repair/re-solder the resistor wire. Typically, wire resistors break at one point like ordinary bulbs. Unfortunately I can not recognize the resistor filament in your picture. It should be on top of the field winding as in this picture:

https://www.google.ch/imgres?imgurl=htt ... MwhLKCQwJA

An external resistor may need permanent cooling, e.g. attaching it to the motor case. Let me know If you really want to go this way and we will find a suitable part. However, putting ten turns of Nickel-iron wire on top of the field winding seems a lot easier to me.

Peter
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PostPost by: tesprit » Sun Dec 13, 2015 9:28 pm

Peter,
I finally found a 10 Ohm, 10W resistor to test adding it to the red lead to see if it would allow the fast speed to work. Unfortunately the resistor does not allow the motor to run at all, even when the red and yellow wires are connected together for slow speed. Adding the resistor did greatly reduce the sparks when only the resistor/red wire was attached to negative. I also took a good look at the field winding to see if I could find the resistor wire that your photo shows but it is not there. So it appears there is more to this than just adding a resistor in line with the red wire.

Dan
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PostPost by: crypto » Mon Dec 14, 2015 7:28 pm

Hmm,

from what I have read about these motors, it seems that power sequencing/connections may be important. In other words, I doubt you can switch the motor from "off" to "fast" directly.
wiring-wiper-dr3a.jpg
wiring-wiper-dr3a.jpg (18.03 KiB) Viewed 704 times

from the discussion before, it is my understanding that the wiring should look like in the pic as above now ?
the switches sw-1 & 2 are probably wire-leads in your setup and only one may make/break at the time.

1) In the off position, resistor R is shorted by sw-2 and if not parked, the motor should move to park and then stop.
2) turning on sw-1, the motor should be running slow, it was my understanding you have confirmed this
3) turning off sw-2, should speed up the motor as current is now flowing via R (instead thru sw-2)
4) turning off sw-1, should park the motor but to start again, sw-2 needs to be closed first.

I assume you already have measured and checked the resistor has really 10 Ohm ?

Peter
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PostPost by: tesprit » Tue Dec 15, 2015 12:10 am

Peter,
Yes, your diagram looks correct according to what I have read as well as how my motor acts when running on slow speed and when parking. Oddly the original rotary wiper switch in my Elan does not go to slow speed when switched from "off" to position one, rather it connects the red wire to earth which should give the fast speed. Switching to the second position connects red and yellow to earth for slow speed and then the knob can be turned further with a smooth action like a rheostat which may allow fine tuning of the motor speed? I have never had a functioning wiper motor in my Elan having purchased the car with a burnt wiper motor so I cant confirm this is exactly what happens with the different switch positions. I did test the 10 Ohm resistor I purchased using my multi-meter and it does indeed give 10 Ohm resistance.

I think my next test will be to connect the wiper motor to the original switch and wiring in my car, but leave the motor loose and disconnected from the rack which should allow it to start and run without it having to do any work. This will allow me to switch on and off the motor quickly so if there is any trouble with shorting or the motor not running I can shut down the motor before anything burns up. I didn't want to test the motor using the original switch because they are very rare making it nearly impossible to source a new switch if I burn up this one. I will just be extra careful not to leave it in any switched on position for very long until I am sure everything is working correctly.

Dan
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PostPost by: tesprit » Sun Dec 20, 2015 12:39 am

I finally got a chance to try testing the wiper motor today in the car using the original wiring and switch and it ran perfectly fine on both speeds as well as on the adjustable speed rheostat with nothing burning up or acting strange. I next installed it onto the wiper rack and tested it under load after spraying some water on the windshield and the wipers worked perfectly on all speeds and even parked themselves in the correct position each time. :D Of course, the motor wouldn't run at all the first time I tested it this way and that is why I was trying to bench test it in the first place. It is obvious there is something more to the original switch and wiring than what is shown in the wiring and motor diagrams and that is why I was never able to successfully bench test the motor. I wish I knew what the difference was between the first time when it wouldn't run at all in the car and this time when it worked perfectly, but I guess it doesn't matter now and I will just chalk it up to another Lucas anomaly! :?

On another note, I did learn something very important while attempting to test this motor. If the motor is allowed to stop in a gear position other than in park, the motor will continue to pull a significant amount of current as long as the ignition switch is in the "on" position even though the motor isn't running. This is due to the motor always having it's body grounded (earthed) and the power lead to the motor is always "hot" as long as the ignition switch is on. The wiper switch causes the motor to run when it connects to ground bypassing the dead spot caused by the park position switch. The main point here is to make sure the ground strap from the motor is always connected to ground to prevent the motor from stopping off the parking position which leaves the motor stalled and drawing current until the armature winding burns up. Unfortunately with the way the original wiring is set up this current draw is less than than necessary to burn out the fuse for the circuit, but plenty enough to burn up the armature.

Dan
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