Wiper Motor Speed Control

**thisain'tmayberry** · 08-24-2010,02:05 PM

Here is an image of a document I made awhile back on how to control the speed of a wiper motor used in prop building. I've been answering a lot of posts in the prop forum regarding motor speed control so I thought I would post this here. I also have it in PDF for email if you find the image hard to read.

I hope this helps anyone contemplating a wiper motor driven prop. More than happy to answer any questions on the topic. Good luck!

**phil121** · 08-24-2010,04:05 PM

Thanks for creating this thread, its very useful. Do you think this speed regulator unit would work just as well http://www.maplin.co.uk/Module.aspx?ModuleNo=9312

thanks

phil

**thisain'tmayberry** · 08-24-2010,04:14 PM

If I'm reading the specs on that unit, it looks like it would work, however the performance envelope is much narrower vs. the Qkits model; Maplin unit 6-15v input, 3amp output vs. Qkits unit 12-24v input, 15amp output. A wiper motor under heavy load could draw more than 3 amps but (hopefully) not more than 15 or you would probably be poppin' circuit breakers!

**phil121** · 08-24-2010,04:32 PM

Oh i think it should be ok, its just for a tomstone peeper using a foam head.

Thanks thisain'tmayberry your great

phil

**phil121** · 08-24-2010,04:37 PM

You seem to know your stuff , could you possibly answer this question for me. If i have a 12vdc power supply rated at 0.5 Amps lets say, and i hook it up to a speed regulator such as the one you suggested
would the wiper motor still work even though the amps from the 12v power supply were alot lower than the 15 amps coming from the speed regulator ?

thanks

phil

**thisain'tmayberry** · 08-25-2010,06:36 AM

Amps are like gas in your car. You can't run down the highway at 55 (haha) with only enough gas to keep the engine at idle. The engine needs more gas to make the car go faster. A V-8 engine uses more gas than a 4 cylinder engine. If you try to run a V-8 on the same amount of gas as a 4 cyl. you won't be able to tow a heavy load, take advantage of any of the power of the engine and might damage it. Why would you spend the money to buy a V8 if you intend only to use it like an econobox?

A wiper motor is kinda like a V-8. If you "step on the gas" in the form of driving/moving/lifting a heavy prop, the motor will require more "gas" which are amps. Starving the wiper motor with too little amps is equivalent to the example above. If you're "coasting down a hill" you only sip gas, with a light prop, no load, etc. you will "sip" amps. If you're "powering up a hill", you gulp gas; likewise with the wiper motor. It could draw a significant number of amps. Scary Terry (http://www.scary-terry.com/wipmtr/wipmtr.htm) once measured a wiper motor pulling 14 amps!

In my opinion, a .5 amp (or 500 milliamp, same thing) power supply is inadequate for a wiper motor, if you're using a wiper motor to drive a prop in the first place.

**phil121** · 08-25-2010,08:14 AM

Although im not old enough to drive yet and know nothing about engines :L
i still get your point

thanks

phil

**dsw** · 09-11-2011,08:31 AM

Trying to get a unit like Qkits unit 12-24v input, 15amp output this but from the UK, anyone know where in the UK i could get one, i don't have paypal or ebay account so i cant use the option, i have looked cant seem to find any...

Cheers
DSW