Can a 12v motor lose power

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Corky

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Joined
Nov 29, 2011
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Great Black Swamp
I have been working on a reoccurring windshield wiper problem for the past year.
At speeds above 45mph the right side wiper will get stuck beyond the curve of the windshield.
But once below the 45mph threshold the wiper returns and acts in normal fashion.
I have replaced all of the hardware from pivot assemblies, arms and even new pantographs & blades.

So now my focus is on the motor.
I have removed the motor, and pulled the can to inspect the inside for clues.
It looked like new, no wear on the brushes, no carbon dust inside the can.

This motor is rated at 32nm and costs around $135.00 to replace.
I am looking at a 55nm unit at $200.00, but this will need modifications.

At this point I'm stumped, and looking for ideas.


Corky
 
check out this attachment
 

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  • Windshield_Wiper_Over_Travel_Revised.pdf
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I don't see how speed would have anything to do with it??  But I would probably sit idle, turn them on, get out, and see if I could stop them with just a little resistance of holding them back  ::)  I also would check, and double check connections.
 
Wind resistance increases dramatically with speed, so at 45+ mph the wiper simply cannot overcome the wind pressure. That suggests the motor is weak or the arm is  out of position or bent enough that the added pressure overwhelms the normal operation. Over-travel is a distinct possibility too (see the attachment above).
 
I think I have pretty much eliminated the working mechanisms buy replacing with new.
However before I go and modify a new motor I just wanted to explore the possibility of the original motor losing power, and if there is any way determine that is the case.

 
How are the wiring connections?  A bad connection anywhere in the positive lead feeding the motor, or in the ground will reduce the voltage at the motor and thus reduce the power the motor can deliver.

Put a voltmeter directly at the motor and verify it's getting full voltage when you stall it by holding onto the wiper blade arm.
 
All of the connections seem to be good and tight. I've cleaned and reattached the ground.
But I didn't check voltage when the motor is stalled --- good idea, thanks.

Corky
 
The problem: Many RV's are built on a TRUCK design but ther RV windshield is way way bigger than say a F-350 or a Chevy 30...  But they do not put in a bigger windshield wiper motor.. (Some are based on SEMI trucks and they WILL have a bigger motor)

As your speed increases the pressure of the wind on the wiper arm increases and it comes to a point where the motor can no longer overcome. Double that if it is raining cats and canines.
 
Thanks for the suggestions but I'm focused on just the motor.
Nothing has been altered, changed nor been rewired, from the original design and for some reason I have this problem.
I have done my best to eliminate any problems with worn out parts by replacing everthing except the motor, and the problem persists.
Seems to me that would point to the motor being the problem. This is, as far as I know the original motor. At least it carries the correct part number for my coach. So here I am thinking that all of a sudden the motor now is too weak to return the wipers while under pressure. Hmmmm - how does a 12v motor lose power?
Causes me to scratch my head.

Corky
 
Corky said:
Thanks for the suggestions but I'm focused on just the motor.
Nothing has been altered, changed nor been rewired, from the original design and for some reason I have this problem.
I have done my best to eliminate any problems with worn out parts by replacing everthing except the motor, and the problem persists.
Seems to me that would point to the motor being the problem. This is, as far as I know the original motor. At least it carries the correct part number for my coach. So here I am thinking that all of a sudden the motor now is too weak to return the wipers while under pressure. Hmmmm - how does a 12v motor lose power?
Causes me to scratch my head.

Corky
Click to expand...

I bet if you took it apart and cleaned the brushes it would run like new.
 
When did this problem start?  Have the wipers ever worked properly since you owned it?

Presumably you installed the new parts in the same fashion as the old ones, so if something was out of alignment it may still be so.

The power wire suggestion is a good one. Check it out.
 
One possible issue (And yes a motor can loose power as it ages) is the voltage delivered to the motor. Connections tarnish and as a result the voltage loss in the wires and connections between alternator/battery and motor may have gained resistance.

This assumes the motor had the power needed to start with.
 
Not directly on topic, but 1st gen Ford Tauruses had this problem in a big way. Even a mild crosswind was enough to blow the wipers to one side where they would stay until the wind stopped. It wasn't a huge problem on run of the mill cars which were limited to, what, 38mph or something... but the SHO had the same wiper, and at high speed the wipers could get sucked out of the resting position and then blown aside. You had to be ready at around 100mph for it to happen, because it was loud and sudden.

I *absolutely* would expect motorhome wipers to behave similarly. As noted, these component were for the most part undersized to start with. I have never turned mine on. Just a good application of Rain-X ahead of time and I've had little need. There's an aluminum step ladder in the basement right next to the microfiber towels. :D
 
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