P80 wiper motor protection - How?

[scot850]

Having re-hab'd the headlight wiper motors, I need help from those of an electrical persuasion. Realising that to get the motors to work I had to remove the thermal protection overload resistors, I would like to put an in-line fuse on each wiper motor wire to prevent them blowing the main fuse should they freeze in the winter. The main fuse is a 25A, how do I put a in-line fuse in that will blow taking a motor off-line and not blowing the main fuse. Is it as simple as fitting an in-line fuse holder with some type of slow burn fuse, and if so, what value of fuse?

Thanks,

Neil.

[abscate]

I doubt they draw more tha 5 amps or so, you canmeasurecit on the bench.

Ypu could overrate the fuse by 25% or so but don't use a Slow blow, you want it to pop right away.

I'll confess my engineering solution would be to free the headlight blades like your windshield blades as a startup procedure like we do in winter.

[Teddy1975]

Neil,

You can put an inline fuse on the black (ground/negative) wire of the three going to the wiper motor.

That way you will protect both the intermittent and constant power to the motor. Purple arrow is where to cut and solder in a waterproof fuse holder. You can strip away some of the outer insulation to make more room of course.

/Teddy

[abscate]

Oh yeah, you don't have to measure the current, you can measure the resistance of the motor on the bench, and then use some yoga to calculate the current


Oooooooohhhhhhmmmmmmmmm

I ( Amps) = V (volts)/ R( ohms)

Use 12 volts for V, I'll guess you will measure 3.14159 Ohms for resistance

[abscate]

Uh oh, hold the phone on this mod, folks. Look at this wiring diagram...this is a bit more complicated than measuring resistance

[Teddy1975]

If we forget the wiring diagram for a second, measuring resistance on an electric motor won't give you the max power consumption as it depends on torque and a lot of other things. You'd need to measure the amps in situ, with the wiper motor installed on the car and the motor operating the wiper arm with installed wiper blade.

It's easiest to measure on the black wire, the ground, as one of the two positive/live wires will be switched on/off according to wiper arm position.

[scot850]

Thanks for the help guys. I will measure this as Teddy suggests and see what it gives. Will have to wait for a helper to be available!

Neil.

[scot850]

Come to think of it, I tested the motor with a 2A, 12V line on a battery charger. Now I did not have the arm and blade on (and when tested on the car the same is true as no headlights currently in place). So I am thinking I could try a 5A fuse in line (main fuse is 25A) and see what happens, and up it 10A if there are issues.

Teddy, your point on making sure the arms are not frozen is a good one, but I am not the only one that drives the car and the other family members are not so careful when clearing stuff of the front of the car. We also get Chinook winds that melt the snow quickly and the car design allows melted water to pool under the arms and then if we get a quick freeze you get a thick chunk of ice across the full headlight too. So having circuit protection is preferable for that 'one time' event.

Thanks guys.

Neil.

[Teddy1975]

5A should be enough, the wiring inside the motor would probably burn out before a 10A fuse.

I tested my seized up wiper motor with a 3A power supply and while I did get it to "sort of" work on the bench, it would only move about half an inch back on the car. Unfortunately it is the passenger side, but with a lot of fiddling I got it out and back on without dismantling half the car. I'll go back in when I get the replacement. At least I learnt how it is un/installed and how it is built

Btw, it was abscate who suggested lifting the wiper blades before driving.

[BEJinFbk]

This may also be a viable alternative:
http://www.wiringproducts.com/bussmann- ... t-breakers