### Author Topic: wiper motor current draw  (Read 21652 times)

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#### Robotics12

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##### wiper motor current draw
« on: April 18, 2012, 02:18:32 AM »
I have a wiper motor that will be steering the wheels on a full size go-cart.
http://monsterguts.com/index.php?act=viewProd&productId=4

I see it says at full load 12V/2A. I tested the wiper motor and it has 9-10A continuous output with a load(person) on it sitting stationary. A 13A stall current. Well, I have a 18V 15A motor controller for the wiper motor with a 15A fuse in between. The wiper motor is on the front of the go cart to turn the wheels. When a person is on the cart, and the person tries to operate the steering, the 15A fuse blows. I have measured the stall current on the low speed and it pulls approx 13A. But when we try to drive it and steer with it moving it blows the fuse. Would there be a reason it pulls more than 15A when the stall current I re-measured earlier is 13A?

We actually had it stationary and had someone sit on the cart, and measured the current output for 10-15 seconds and it was pulling 8-10A continuously. But then when we connect it to our 12V power supply and roll the cart and try to steer it blows the fuse.

#### Soeren

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##### Re: wiper motor current draw
« Reply #1 on: April 19, 2012, 05:09:10 PM »
Hi,

I have a wiper motor that will be steering the wheels on a full size go-cart.
http://monsterguts.com/index.php?act=viewProd&productId=4
Is it the very same motor or just something that "looks close"?

I see it says at full load 12V/2A. I tested the wiper motor and it has 9-10A continuous output with a load(person) on it sitting stationary. A 13A stall current.
Doesn't sound like that motor.
How dd you measure the continous current?
At what supply voltage?
And how did you measure the stall current?

If the stall current is indeed 13A, then it is overloaded under normal use - check your drive link for friction.

Well, I have a 18V 15A motor controller for the wiper motor with a 15A fuse in between. The wiper motor is on the front of the go cart to turn the wheels. When a person is on the cart, and the person tries to operate the steering, the 15A fuse blows. I have measured the stall current on the low speed and it pulls approx 13A. But when we try to drive it and steer with it moving it blows the fuse. Would there be a reason it pulls more than 15A when the stall current I re-measured earlier is 13A?
Not if it's made properly, but if the motor turns the same axle that you turn by the steering wheel and you try to steer opposite of what the motor tries to, you'll get a higher current than stall.

We actually had it stationary and had someone sit on the cart, and measured the current output for 10-15 seconds and it was pulling 8-10A continuously. But then when we connect it to our 12V power supply and roll the cart and try to steer it blows the fuse.
Stationary, is the hardest to turn. Even a slow movement will greatly reduce the friction wheel-pavement and hence the force needed to turn the wheels.
Did you use another power supply when testing?

You need to be more clear on how you did the tests - too many uncommented variables - like how much force is needed to turn the wheel, did you check for friction in the steering linkage, what was your power supply under each condition, how did you measure (I don't see how you can test for continous current in 10..15s, as you'd reach the end stops in less than a tenth of that?).

Keeping a small notebook handy and using it vigorously when testing, can shorten most trouble shooting quite a lot
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

#### jkerns

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##### Re: wiper motor current draw
« Reply #2 on: April 19, 2012, 08:02:54 PM »
Dunno if this is the problem, but...

When you measured the current, did you try with it connected in both directions (+- and =-+) and with the motor mounted in the device? Automotive parts are often made with the assumption of a + supply and a ground. When you hook up the positive power to the side that is negitive in a car, you may be shorting it to ground through the housing.
I get paid to play with robots - can't beat that with a stick.

http://www.ltu.edu/engineering/mechanical/bachelor-science-robotics-engineering.asp

#### Soeren

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##### Re: wiper motor current draw
« Reply #3 on: April 19, 2012, 10:40:56 PM »
Hi,

When you hook up the positive power to the side that is negitive in a car, you may be shorting it to ground through the housing.
I doubt that to be the case, as that would manifest itself in a much more "violent" way (like de-smoking the switch element completely and/or boiling the insulation off the power wires).
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

#### jkerns

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##### Re: wiper motor current draw
« Reply #4 on: April 20, 2012, 10:28:27 AM »
Hi,

When you hook up the positive power to the side that is negitive in a car, you may be shorting it to ground through the housing.
I doubt that to be the case, as that would manifest itself in a much more "violent" way (like de-smoking the switch element completely and/or boiling the insulation off the power wires).

Probably. But, we don't know where the fuse is that keeps blowing, or how it was tested. It could go either way. And it Could explain why it works differently on the vehicle than it does on the bench.

Dunno.
I get paid to play with robots - can't beat that with a stick.

http://www.ltu.edu/engineering/mechanical/bachelor-science-robotics-engineering.asp

#### Daanii

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##### Re: wiper motor current draw
« Reply #5 on: April 20, 2012, 11:58:15 AM »
I have that same windshield wiper motor, and use a Pololu jrk motor controller that allows me to set a current limit. If I set the current limit at 15 Amps, the current limit will get triggered fairly soon. If I set it at 20 Amps, it rarely gets triggered. My guess is that the stall current is over 20 Amps, not 13.

Perhaps if you used a 20 Amp fuse, you would get better results. Pololu only gives the continuous rating of 15 Amps for the motor controller you are using (in another thread you said it is a Pololu high-power 28v15 motor controller), not the maximum. But typically the Pololu motor controllers will take more than twice the power as peak without burning out.

That said, the downside of using a bigger fuse may be a burned-out motor controller. I burned out one of Pololu's Simple Motor Controllers using that kind of motor, which is why I went with the jrk. (Pololu gave me a credit of half the price of the burned-out controller towards the price of the new one, even though it was my fault.)

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