Thread: PWM Question

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I bought a pulse width modulator dimmer switch to regulate the speed for a wiper motor. It's rated at 12V DC @8 amps. I want to run the wiper motor on 5V DC, to achieve a lower speed.

My question is, will this PWM work running only 5 V DC through it, or do I need a different PWM ??

Can you post a pic of the dimmer, or more specifically the data plate on it that shows the input voltage range? It will depend on the range allowable for the input power and you will also have to, more than likely, de-rate the current capabilities of the dimme. As voltage goes down the current draw will go up.

This is the one. The only technical info on it is DC 12V -8A. Four posts on the front are V+ V- in and V+ V- out. The place I got it from sells LED spotlights.

EDIT: I'm using a wiper motor from Monster Guts. The website says they're rated at 2000mA @ 12 VDC and 1080 mA @ 5VDC at full load. The application I'm using it for will be a very light load.

I just checked the data sheet, it says it accepts 12VDC with no range given. About the only thing you could do would be to connect up an LED and see if it works for that at 5 volts. It will depend on whether or not the chip that is performing the PWM will be able to run with the lower voltage. That data sheet left a lot to be desired. Let me know what you find out. The best person to ask would be Otaku. Keith

Thanks so much for the info, soundman. I really appreciate the help.

I'm learning how to do things on this forum that I never dreamed I could do, thanks to all the great folks here.

Have you tried connecting it to 12v and seeing if it will run at the speed you want? Chances are it'll work fine, & give you better results than 5v.

Sticking 5v to a PWM devise that is meant for 12v (both your motor and controller) defeats the purpose of having PWM. Pulse Width Modulation controls the motor speed by cycling that 12v on and off slowly or faster depending on your setting. By doing this you are getting full torque out of your motor while controlling speed but you will quickly see that it will also make your motor “noisy”.

PS, you would be surprised how easy it is to stall a wiper motor @ 5v.

Nosferatu, Good thought, sometimes I get so involved in answering a question, I get tunnel vision. Of course stick with 12V and turn the controller down and that should slow the speed of the motor while maintaining torque. Do you think the 8 amp limit will come into play? Not sure what torque it will be pulling but I would recommend fuse protecting it to keep from burning the PWM box out. What do you think?

I don't think torque will be a factor. Monster Guts says it draws 1020 mA under no load and 2 A under full load. I'm doing a cauldron creep, and the motor will be turning an arm to move the stirring stick. Very low load. The motor turns 38 rpms on the low speed setting; I'd like to get it down to 8-10 rpms, if possible.

By low speed do you mean with the PWM control all the way counter clock wise?