Lotus Elan

S3 variable speed wipers

PostPost by: David1953 » Tue Oct 08, 2019 10:26 pm

I have a single speed wiper motor, and a rheostat speed control switch.
I have found several threads on this site discussing these so I believe this is original, although none of the wiring diagrams I have seen show this.
My understanding is the rheostat adds a few ohms in series with motor to reduce its power and thus speed. Which is not the same as the 2 speed where the field winding are separate.
However this resistance is in the path to ground and as soon as the wiper is away from the park position there is a direct path to ground so the motor will run at full speed.

Am I missing something or did this slow down never work?

David
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PostPost by: ericbushby » Tue Oct 08, 2019 10:38 pm

Mine works but there is not much difference in speed from one end of the resistor to the other.
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PostPost by: billwill » Tue Oct 08, 2019 10:40 pm

I used to have one of those and the slow variable rate did used to work, but I don't know what motor it was used with or what the circuit was.

I was changed out by Vegantune of Spalding during my 1982 re-furb.

I suspect that your idea of the circuit is wrong, my vague recollection is that it was wired so that if you switched it off unparked it would go to the parked position at full speed, but not what you described.
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PostPost by: billwill » Tue Oct 08, 2019 10:44 pm

As you are probably aware the modern slow wipers work by switching on the power briefly at a variable time interval. The electronic on-pulse is long enough for the wipers to leave the parked position, then despite the electronic pulse being off, the wiper completes the wipe both ways and back to the parked position.
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PostPost by: David1953 » Wed Oct 09, 2019 8:10 am

billwill wrote:I suspect that your idea of the circuit is wrong, my vague recollection is that it was wired so that if you switched it off unparked it would go to the parked position at full speed, but not what you described.


This would make more sense than my wiring. So the question is does anyone know how it should be wired?
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PostPost by: David1953 » Wed Oct 09, 2019 8:14 am

billwill wrote:As you are probably aware the modern slow wipers work by switching on the power briefly at a variable time interval. The electronic on-pulse is long enough for the wipers to leave the parked position, then despite the electronic pulse being off, the wiper completes the wipe both ways and back to the parked position.


I can see the next project is to create a circuit that does this using the existing 10ohm rheostat as the speed control. But after the car is back on the road!
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PostPost by: ericbushby » Wed Oct 09, 2019 9:13 am

David,
Unfortunately, the wiring diagram only shows the wiper switch and control as a rectangle with four wires to it.
I can look more closely at the control itself, but not for a couple of days.
I will let you know what I find unless someone else can do it easier before then.
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PostPost by: billwill » Wed Oct 09, 2019 6:19 pm

David1953 wrote:
billwill wrote:As you are probably aware the modern slow wipers work by switching on the power briefly at a variable time interval. The electronic on-pulse is long enough for the wipers to leave the parked position, then despite the electronic pulse being off, the wiper completes the wipe both ways and back to the parked position.


I can see the next project is to create a circuit that does this using the existing 10ohm rheostat as the speed control. But after the car is back on the road!



I had thought of doing something like that but 10 ohms is far too low a figure (i think) for an electronic slow wipe circuit, you need something like 100,000 ohms

I bought a Veleman kit from Maplin some time ago, but it has a multi position switch instead of a variable resistor, so I've not go around to making up a suitable conversion.

My rheostat & associated manual water pump failed on my S3 long ago.
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PostPost by: David1953 » Wed Oct 09, 2019 6:43 pm

billwill wrote:I had thought of doing something like that but 10 ohms is far too low a figure (i think) for an electronic slow wipe circuit, you need something like 100,000 ohms


100 ohms in series on 10v supply should give 0-1v signal, for only 100ma, a pic controller should be happy to use that for control........

Now stop I am trying to get the car going not start new projects.
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PostPost by: ericbushby » Sun Oct 13, 2019 10:22 am

Hi David,
I have taken the wiper control out to have a look at it.
I have not done very well but this is what I have learnt.

The control has three wires to it.
The motor has three wires to it.

Clockwise from the front of the control,
1st terminal, Red with light green tracer (LG) goes to red on the motor.
2nd terminal, Black goes to ground.
3rd terminal, yellow/LG goes to yellow on the motor.
1st is switched to 2nd to start.

On the motor the 3rd wire goes to 12 volt supply ( colour is indefinite )
The rheostat is 10 ohms

Slow speed is approximately 2 seconds for a full return sweep
maximum speed is about 1 second
I hope this is useful.

Hi Bill,
I bought a complete wiper switch and pump on ebay a bit since. It was advertised and labelled for a Ford Corsair. I only wanted the tapered recessed tube and the knob, so I put the rest back on ebay.
I wish I had kept it now. Perhaps this shows there is still hope.
Eric in Burnley
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PostPost by: David1953 » Sun Oct 13, 2019 3:29 pm

Eric
Thank you for looking at this in such detail.
I may leave it alone as I have effectively a working single speed system, and getting to where I can put a windscreen in place may be a better priority.

The 3 connections on my motor are labelled 1 2 and E. E being the screw that holds the motor together. So I am guessing your yellow cable is connected to this E. And this on the 3rd terminal of the switch is connected to ground when the switch is off.

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PostPost by: billwill » Sun Oct 13, 2019 8:26 pm

The normal switched 2-speed wiper circuit looks like this:
Image

I guess that if you used a rheostat and both motor wires (plus the ground) instead of a switch you might get a variable speed effect, but I've never tried it. Unfortunately a dumbo motor electrician when installing a new wiper motor in about 2002, wired it as single speed and clipped off the unused wire so close to the motor body that I can't connect to it.
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