What size resistor ( reducing 12v wiper speed)

[russelltatedotcom]

This question has probably been answered many times before, I just can’t find it?

What size resistor should I use if I have a 6v wiper motor ( with a 12v armature) to reduce the wiper speed to a 2nd slower speed. I have one at the moment which has no markings but the speed does not seem significantly slower?
I did a test: Over 30 seconds
Normal speed was 23 revolutions
With resistor was 17 revolutions
Not significantly slower?

Any advice appreciated!
Cheers
Russell

[runamoc]

The voltage of the armature IS the voltage of the motor. The fields are magnets. The way VW did it was place the brushes at less than 180° apart for a slower speed. At 180° the motor is turning as fast as it can. Here is an adjustable DC voltage reducer.

https://www.amazon.com/RED-WOLF-Regulator-Accessor...2&th=1

The way VW did the slower speed by moving the brush

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[russelltatedotcom]

Thanks runamoc, I was actually after info on the resistor that could drop the motor speed, what size folks are using. The 12v supply and 12v armature are working great for full speed it's just trying to reduce the speed for the slow wiper setting i'm having problems working out

[runamoc]

[russelltatedotcom]

Thanks for that Runamoc , very helpful

[Eric&Barb]

Problem with dropping voltage below the armature standard voltage, is that you too easily can burn out the motor by doing so especially when the motor is under stress like snow and ice.

Better to get a PWM module that does not affect voltage, instead it turns off and on the grounding of it multiple times a second to give the slower speeds. Plus it gives one just about infinite adjustment of the wipers, so better than just two speeds.

Can not find the exact module we have on Ebay anymore, but anyone can do a search there for "DC PWM module 0-60 volt".

This one is as close what we have:

https://www.ebay.com/itm/162836712937?hash=item25e...BMsq_Nhalj

One needs to run a ground wire from the inside of the wiper motor to the PWM module for it to work, and disable the stock grounding of the motor. Good idea to add in a manual switch to ground the motor just in case the PWM ever failed out on the road.
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