Voltage regulator for heated grips

[jimboinvt]

I have some heated grips on my motorcycle 13.2vdc. I need to regulate the heat because theyare too hot. The two grips are in series and are supposed to be about 11W each. Of course the temperatue varies a little from idle to 3-4000 rpm due to voltage. Using a 10W 2ohm resistor in series gets them to the perfect low temperature but I would like to control it with a potentiometer. The closest one I could find is a 3W 25 ohm at the Shack. I'm thinking of that with another 5 ohm resistor in parallel. Will this give me the control I need? Ultimately a 5W 5 ohm pot would be ideal, but I cannot find one.

 

[crutschow]

You might consider a simple PWM circuit to control the current. A 555 configured as a PMW driving a MOSFET can be controlled by a small pot and will dissipate very little power. **broken link removed** is an example circuit. Just substitute the grip heater for the motor.

 

[jimboinvt]

Mosfet

Thank you Carl. I have a MOSFET type controller from a set of snow machine grips that never really worked. I was told they were ambient temperature sensitive but did not see how, based on what I saw of the circuit components. It seems that only +-2V makes a huge difference betreen cold and too hot. I have a friend that might help with the link you sent. Worth a try!

 

[stevez]

An alternative that is less efficient but that might be simpler for you to implement is an LM317 regulator with a pass transistor (2N3055). There will be an upper limit to the range as there will be voltage drop that will limit the applied voltage to 80 or 90% of system voltage. Again, not necessarily better than PWM but it's possible that this is easier for you to implement. In either case you might still be able to get the parts from a local Radio Shack.

 

[crutschow]

An alternative that is less efficient but that might be simpler for you to implement is an LM317 regulator with a pass transistor (2N3055). There will be an upper limit to the range as there will be voltage drop that will limit the applied voltage to 80 or 90% of system voltage. Again, not necessarily better than PWM but it's possible that this is easier for you to implement. In either case you might still be able to get the parts from a local Radio Shack.

That should work also but remember that you will need a heat sink for the transistor to dissipate the power.

 

[MikeMl]

Any chance you could just wire the two grips in series on cool days, and in parallel on realy cold days?

 

[Boncuk]

I look at the problem from another point of view.

As already posted here a temperature difference of ±2deg/C might be felt either too hot or too cold.

Manipulating a pot while driving - also under icy conditions - is not desireable for safety reasons.

I have designed a PWM control circuit controlling the temperature of each grip individually. Instead of a digital temperature readout it uses a bargraph display of 2 lines and 32 bars each for a quick check (not to disattract from road traffic while reading).

The display background light is also PWM controlled to dim at night (to avoid blinding of the driver).

Operation is very simple. One UP and one DOWN pushbutton set the the desired temperature which is stored if no button is pushed within a time period of 30 seconds. A third button in the center is a "Manual override" button (with a photo transistor mounted underneath), which causes the heaters to be fed at 100% of power until reaching the preset temperature (useful after refuelling to avoid unnecessary waiting for the temperature to rise and stabilize).

The buttons are located at a position to make thumb operation easy. The power MosFets are located at the far right side to be bolted to a metal enclosure which acts as heatsink. The LC-display works reliably at temperatures of -25deg/C.

Here is the pdf file of the PCB. Dimensions are 5.85X2.24inches

The project was put on ice because the customer imagined an equivalent price of kg potatoes.

Boncuk

 

[jimboinvt]

Mike ML
the grips operate on 6+VDC and are too hot at 100% power. operating parallel circuits would burn them up -and me, Ouch! : )