# 12v boot heater design help needed

Thread Starter

#### bmurphy

Joined Sep 11, 2022
1
Hi,
I would like to build a wintertime boot heater using power from a 12v tailight on a snowmobile. I will be using the heater to keep an extra set a boots warm that I will not be wearing while they are being heated. My goal would be to keep the boots warmed to 80-100 degrees F.
I am an electronic newbie and don't really know where to start on this project or what components I will need. I'm hoping someone here could offer me some guidance on how to accomplish this....

A bit more information...
The power to the tailight I would be taking off of is about 2.5A and is only powered when the snowmobile is running. There is no battery on the snowmobile, so possibility of constant power draw. I was thinking of using a heat mat similar to this: Amazon.com: 4PCS Silicone Heater Mat, Icstation Rubber Heating Mat 12V 25W Electric Blanket Flexible Mat Constant Temperature 80X100mm: Home & Kitchen . However, I think I will need a way to regulate the temperature so that it doesn't melt my boot liners. Can I use a thermostat of some sort to keep the temp down?

Any help would be appreciated.

Thanks,
Brian

#### Tonyr1084

Joined Sep 24, 2015
8,006
Welcome to AAC.

Whether you can accomplish this depends on how much power is available at the tail light. You said "12V". How many amps will your boot heater draw?  You DID say 2.5A. When the mobile is idling its voltage "Probably drops" (but I don't know that for a fact). [end edit]

If the tail lights are on a 10 amp fuse and your boot warmer draws 15 amps then you're going to blow out the fuse for sure. Especially at a cold start for the heater. Heaters have lower resistance when they're cold. Once they warm up the resistance goes way up.

If you don't know the amperage, perhaps you know the wattage. To calculate amps when you know 12V and (for example) 120W you divide the wattage (W) by the voltage. 120W ÷ 12V = 10A. And if you have a 10 amp fuse and suppose the tail light is drawing 2 amps, 10+2=12. You're going to blow out the fuse. Probably not instantaneously, but it will blow soon enough.

#### Tonyr1084

Joined Sep 24, 2015
8,006
My editing is good reason why I should read the entire post before I start opening my mouth. Makes me look foolish when I do that.

Anyway, like I said, the voltage probably varies with engine RPM. You'd have to test the voltage at idle and at near max RPM's. Then you can figure an average for voltage. But still, it's the wattage that is the critical factor. At 12V & 2.5A the wattage would be 30W. A thermostat could help, but it would need to be isolated from any drafts, otherwise it will think the temperature is low and may continue to call for heat.

It's not so straight forward a project. Good luck with your venture.

#### bassbindevil

Joined Jan 23, 2014
838
The simplest option would be 12V incandescent bulbs inside the boots. Maybe inside a protective cage of some kind to avoid breakage or singeing.

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