windscreen wiper motor rotisserie

[wally7]

Windscreen wiper motor runs at 44rpm on 12v battery. This is too fast and want to reduce it to 1 to 5 RPM without using gears or pulleys?
I tried a cigarette lighter 12v to 1.5/9v reducer thingy but it obviously burnt out in 20 seconds.
Can it be done electronically, cheaply and 'oh so simply' explained?
Would I lose much torque if it could be done?
Cooking small joints of about 10kgs not huge great pigs of 70kgs.

 

[Reloadron]

If the moror will work with it you may be able to control the motor speed using PWM and a circuit similar to this. Part of doing this right is to know how much current the motor draws under normal operation. I don't know if you will get from 44 RPM down to the 1 to 5 range and again don't know if the motor (wiper motor) will react well to PWM speed control.

Ron

 

[blueroomelectronics]

You could try a PWM motor controller, but your torque will suffer at such a low RPM. Why not use a simple gear reducer?

 

[crutschow]

If you reduce the voltage enough to get a speed of 1 to 5 rpm, then the torque may be too low to properly rotate the rotisserie. The best bet may be to generate a short intermittent pulse with a couple of 555 timers driving a transistor motor driver to cause the motor to rotate a few degrees at a time using full voltage. For example if it were on for 1 second every 10 seconds, that would reduce the speed by 1/10 to give about 4.4 RPM.

 

[MikeMl]

... For example if it were on for 1 second every 10 seconds, that would reduce the speed by 1/10 to give about 4.4 RPM.

, or if you pulse the motor on for 1ms every 10ms, that would do the same, but because the motor has inertia, it would just appear to be running slower. btw- that is what we call Pulse Width Modulation (PWM).

 

[bryan1]

Hi Wally,
Welcome to the forum mate , a few years ago I did a YouTube - Wiper motor test
and even on as little as 4 volts the torque was still near 100%. The only wiper motors that would be suitable are the worm drive one's like the one shown.

Regards Bryan

 

[carmusic]

you may try pwm driver made for automobile blowers there is a lot on ebay for cheap

 

[YaranAyr]

If you have any concerns about lugging (and burning up) your motor on low voltage,
Here's alink to an intermiitent windshield wiper design that I made.
It goes one full swipe then "parks" about 1 per second to 1 per 20 seconds.
This went into a pretty simple system on a 1982 Chevy Truck.
YouTube - INTERMITTENT WIPER FLASH OF GENIUS

 

[wally7]

Thanks for all your great replies. I am not very knowledgable about electrickery (as I call it) so bear with me please.
I am still trying to locate a PWM but have an idea of using the inbuilt intermittent switch on wiper motor, and using some gearing down so it doesn't stop at the same place.
Problem I have is =where is it?
I've taken the end cap off the gear box (worm/worm wheel) and there are 5 terminals that connect with a copper plate imbedded in worm wheel. Presumably the power is changed to different brush layouts in the motor but how do I determine which is which?
Can I just apply 12v in a fairly random manner until I get the intermittent switch?
What direction does a wiper motor normally run.
Would the break in power to the motor be on the - wire?
I hope that makes sense and you're not all laughing at me?

 

[carmusic]

i would use that very simple to connect
**broken link removed**

 

[YaranAyr]

Slow Wipe

Here's a simple Wiper Circuit.
Interrupt the Brown wire of the low speed setting, insert a pulsing on/off circuit with a duty cycle like Mike ML suggested. (F.I. Look into some 555 circuits that pulse a big transistor for this.) This is what the factory intermittent circuit does except it turns on the motor just long enough to bump the wiper off the park node on the wiper gear, then the motor runs it back to the park position until the next pulse bumps it off again.

Maybe you could elaborate on your application...
Is this actually going to be on a car?
And you just want some REALLY slow moving wipers?

 

[wally7]

Thanks for that good answer. No it came off a car but the motor is to drive a bush spit rotisserie off a 12V batterie.
And 44rpm is too fast to roast a pig.
I don't have my workshop and welder now or I would have made a reduction sprocket linkage. Reduction gear boxesare too expensive or too small. Hoepfully I can reduce speed enough without losing too much torque. A whole pig would be too heavy but a 10Kg joint should be o/k?

Another crazy idea! Could I (don't laugh) hook up to my low speed terminal and put a common trafficator 3 pin relay in its line so motor goes slower AND incrementally (jerkily) round as the trafficator works.
If this is feasable how (I know little about circuits) would a dummy wire a 3 pin relay up to the motor.
(My basic knowledge is black to black and red to red, but the colours have changed since WW2 I think)

 

[YaranAyr]

Wow. Pigs and trafficators, who'd have thought. I guess that way one could be warned which way that road hog is going to turn. Maybe send a picture of the relay, but otherwise, I'd say try all the combinations of pin pairs, including the case as ground, and listen for the click of the relay. Check the other terminals for continuity. I'd say put that right in series with the PWM interruptor on that "brown" wire. Now you got dancing pigs like HEE HAW. Attach a picture or a video when you're done. I'll give you an address for some of that Windshield Wiper Meat when it's done.

 

[SABorn]

You could just buy a PWM unit off ebay and wire it in rather easy.
Here is a link to a 12 volt 15 amp controller.

**broken link removed**

Pete.

 

[wally7]

Pete thank you. That looks right up my street, easy.
I am not very sure of myself wiring it in. When I get that PWM, how will I know which wires go where on the motor?
thanks again
wally

 

[SABorn]

Simple ... follow the instructions.

Red...to 12 battery (+) positive
Green..... to Battery (-) negative

White..... To motor
Yellow.... To motor

If the motor runs in the wrong direction swap the white and yellow wires around.

The speed control pot should be already wired in on the end of a short set of leads and will need some sort of bracket/box to mount it onto.

Must say the wiring diagram is a little like Chinglish but still clear enough to understand.
You might want to have a look at a new motor to, they have several if you have a look at their store.

15 RPM 12v motor link. (same suppier)

**broken link removed**
Pete.

 

[paulm]

this is probably way old now , but about this time of this forum i made a beast spit with a ford wiper motor geared with bicycle sprockets to turn a full lamb at 2 or 3 RPM at about 8 volts . after all my ohms law calculations i worked out about 15 - 20 amp current draw. i was lucky enough to have found a 240V variac at an estate sale sometime before. i had a rumage through my junk box & made a rectifier with a hefty smoothing cap complete with output voltmeter (made with a discarded hifi VU meter & a custom printed dial) the only component i purchased was a 35 amp rated diode bridge rectifier for $10 (if i had 4 equal heavy duty diodes in the junk box i would have used them )