I am trying to come up with the best possible battery operated heat source to heat a blanket. I want it to last for 3 hours or a football game... I have a working prototype but it doesn't put out enough heat. Any ideas?

 

Was it not putting out enough heat or was the fact the blanket is exposed to the air and loosing too much heat that way? What kind of batteries are you using and what kind of elements? I suspect a bit of the first and the fact you're probably not driving the heating elements near what they are rated at. Just too many unknowns to make any judgement on.

Other than that is the blanket made up of one big element connected across the battery or smaller sections across the battery? I might to help break it up into smaller pieces so you have more voltage across a smaller segment than trying to put the battery across the whole thing.

 

Can you make one for less than US $35?
http://cozywinters.com/shop/12v-heated-blanket.html

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Ron

 

I wonder how much current it uses.

Now all you need is a huge lead acid battery to connect it to.

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The one I linked to draws 4 amps. For a 3 hour game, you'd need at least a 12AH ,12V battery. I guess a big rechargeable lithium battery would work, but I think you would have to buy the charger also, and they would be expensive and hard to find. An SLA that was large enough would probably weigh at least 10 lbs.

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Ron

 

A human consumes about 2,000 calories in food per day.
That's 2,000,000 heat calories/day
That's 8,400,000 joules/day
That's 97 joules/sec
The human generates 97 watts of its own.
The blanket only generates 48 watts.

Warm clothing can help keep you warmer than that particular blanket.

 

You do have a point but that blanket will do a better job of keeping your extremities warm and 48W of extra heating power is actually quite significant.

Also, you could just put it on the seat so you don't have to sit on a cold seat.

An SLA battery is probably the best thing for the job and is also handy as you can easilly charge it in the car.

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But toting it into the stadium would be a drag. The effort would give you a good start on keeping warm, though.
I have a 6V, 12AH SLA that powers my Minelab GP3000 metal detector, and it weighs 5 pounds. 12V, 12AH will probably weigh 10 lbs (I haven't researched this to see if it is true ). 12AH will probably not be enough, if he wants it to run continuously at 4A for 3 hours.
Maybe he could have a really long cord, and leave the battery in the car. Better yet, just get a set of really long jumper cables, and run it off the car's battery.

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Ron

 

The cord on my vacuum cleaner gets pretty warm. You could carry about 20 of them in a bucket to keep you warm at the game.

My propane barbeque gets hot. You could carry one to the game.

My wife is hot. She is from Spain. Get one. But she doesn't like games.
My dog is also hot. Get one. My dog loves playing games.

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Uncle $crooge

 

Toting it into the stadium will provide extra warmth.

 

I sort of hit on that theme too, in that same post.

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Ron

 

Focus on the thermal properties of the blanket. Retained heat does not require current. Maybe use thinsulate or similar.

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It's probably for his wife or girl friend so he'll end up having to carry the heavy battery.

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Whisky flask, nuff said

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