# DIY Snowmobile seat and hand warmers getting too hot

#### ryansnowmobile

Joined Nov 29, 2016
10
I am building a second seat for my snowmobile and in doing so i am adding 12v 10 watt hand warmers and a seat warmer. I belong to a snowmobile forum and after discussing it with the higher ups we figured it would be easier to just run 12v AC power straight from the power source off of the stator. this worked perfectly except that now the hand warmers are getting too hot. what do i do. i have practically no knowledge of electronics/circuits. ill attach my best attempt at drawing this wiring for anybody who wants to help. the hand/ seat warmers are supposed to get 12v 10 watts of power. i'm fine going over that but is there a way to maybe vary the power they get to adjust the heat? part of the problem s that the stator at idle will produce 12-14 volts but once the rpm increases it can go from 12v to close to 30v. Thanks for any help

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#### GopherT

Joined Nov 23, 2012
8,012
You nailed the problem with using unregulated power. You have some options. Size your heater element for 20 volts or so. Then it will keep you a little warm when at idle but that is ok since you are dressed for a windy ride. Also, when you go faster, you could use the extra heat. I would add two heater elements in series and you will get a fraction of the power. It sounds odd to a beginner but...

Compared to one heater,
-You would get double the heat putting two in parallel

- You get half the heat by putting two in series.

for the two-in-series option, you can add a switch that disconnects one (by-passes one) to go back to your current situation on cold days.

#### ryansnowmobile

Joined Nov 29, 2016
10
That is so perfectly simple thank you very much!
Now in series will one hand warmer get hotter than the other? or is that nullified by the use of AC current?

#### crutschow

Joined Mar 14, 2008
25,135
Now in series will one hand warmer get hotter than the other? or is that nullified by the use of AC current?
No.
If they are equal in resistance, they both will dissipate the same amount of heat when connected in series.
Makes no difference whether it's AC or DC.

#### ryansnowmobile

Joined Nov 29, 2016
10
Alright i have the general idea i think. now how do i execute the parallel to series shift? right now i have the 2 seat warmers in parallel and the 2 hand warmers in parallel and then those two wired in series. like attached.

i went and wired it up as shown and it seems not to be warm enough. hardly could feel the warmth. at revs it would be better but im worried the current setup wouldn't be enough. is there a middle ground?

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#### GopherT

Joined Nov 23, 2012
8,012
Alright i have the general idea i think. now how do i execute the parallel to series shift? right now i have the 2 seat warmers in parallel and the 2 hand warmers in parallel and then those two wired in series. like attached.

i went and wired it up as shown and it seems not to be warm enough. hardly could feel the warmth. at revs it would be better but im worried the current setup wouldn't be enough. is there a middle ground?
My motorcycle grip warmers take about 5 or 10 minutes to warm up when I'm holding them with gloves (effectively insulating them). Longer if left in open air. You don't want more or they will feel really hot when holding them with gloves for 20 or 30 minutes. If you smell roast pork, they are too hot.

If it doesn't prove to be enough, there are switches (simple PWM or various feedback systems like PID or Fuzz logic) that will let you control like a thermostat. How far do you want to go with this?

#### ryansnowmobile

Joined Nov 29, 2016
10
ok.

Not that far. Unless its cheap... I should add to this that i've only paid ~$7 per warmer set shipped and$2 on some sleek switches.

If the thermostat types are cheap i don't care about doing some work to get it installed. But i don't want to put more than \$15-20 into this project and I still have to paint it.

#### ryansnowmobile

Joined Nov 29, 2016
10
How about a potentiometer. currently doing some research into it. could i get one that would do they kind of load that id need it to? and how do i calculate how big of one i need?

#### GopherT

Joined Nov 23, 2012
8,012
How about a potentiometer. currently doing some research into it. could i get one that would do they kind of load that id need it to? and how do i calculate how big of one i need?
What is the resistance of the heater?

What is the rated wattage?

#### ryansnowmobile

Joined Nov 29, 2016
10
12v ac @ 10 watts for 2 heat pads in parellel

#### ryansnowmobile

Joined Nov 29, 2016
10
i think that makes the resistance like 14.4?

#### GopherT

Joined Nov 23, 2012
8,012
i think that makes the resistance like 14.4?
So they are 10 W stock (12V). Run it up to 30V and you still have 14.4 ohms you end up with 2 amps and 60Watts!

Are you sure you can't just use regulated power? It keeps everything much easier. Even with a potentiometer, you'll get cool at idle and hot at higher revs. Not a desirable situation.

#### ryansnowmobile

Joined Nov 29, 2016
10
How do i set up the regulated power? I have a dc regulator on the sled but i was advised that the dc is not a good way to go. from the snowmobile forum "You really want to run this off the AC side. The DC can handle it, but it just won't work as good and will most likely burn out the DC line."

#### GopherT

Joined Nov 23, 2012
8,012
How do i set up the regulated power? I have a dc regulator on the sled but i was advised that the dc is not a good way to go. from the snowmobile forum "You really want to run this off the AC side. The DC can handle it, but it just won't work as good and will most likely burn out the DC line."
Ok, then we'll see what we can do. Motorcycles can handle it just fine on the DC but I don't know how sleds are setup.

Where are you located?

#### ryansnowmobile

Joined Nov 29, 2016
10
Like where i live?
if so NY

#### SLK001

Joined Nov 29, 2011
1,548
Like where i live?
if so NY
Gee... If there was only a way that we could get people to put where they are from in their profile!

#### GopherT

Joined Nov 23, 2012
8,012

#### GopherT

Joined Nov 23, 2012
8,012
Gee... If there was only a way that we could get people to put where they are from in their profile!
He added it! It may have even been there from the beginning and I missed it.

#### ryansnowmobile

Joined Nov 29, 2016
10
I added it while perusing through the site and bouncing around. And i believe 2 wire.

#### GopherT

Joined Nov 23, 2012
8,012
I added it while perusing through the site and bouncing around. And i believe 2 wire.
Ok, the simple solution is to get a dimmer switch from the hardware store. These are different than simple potentiometers (rheostats), because a dimmer will turn off for part of the AC wave to control power.

Put it in a junction box from the hardware store and get a proper wire clamp connector. Sleds and cycles vibrate and wires become abraded if not restrained properly. Ask your friendly hardware store guy for advice on parts. I hope you have the space for a single junction box. It will be easy and cheap.

My only concern is that your 2.5Amp application at 10,000 rpm (about 150 HZ) may be more than the triac in a dimmer can handle - normally they run at 60 HZ.