Simple electronics question: AC -> DC

That all depends on the specification of the strip heater. If they are mains AC strips then probably the easiest way to get them working is to use an inverter connected to the battery, but this isn't very power efficient.

I would then supply the battery with solar power:

Depends on how much heat you need, this is the safest method if you don't know much about electronics.

Regards,

Bob

Batteries are an expensive way to produce tiny amounts of heat.

You're better off to burn fuel to produce heat, or use solar energy. There are several designs of both active and passive solar heaters.

If you need heat at night you might get something like an "Aladdin" kerosene lamp - it is a non-pressurized mantle lantern that produces the equivalent of 75 watts of light, and about 2,000 BTU of heat.

Aladdin style lamps were invented 100 years ago and have been in continuous production since. They are somewhat harder to find in developed countries - but still available.

Less than 2,000 BTU and something like a catalytic hand warmer(s) might work - good enough for something like an incubator in a cold room.

Beyond that, one of the kerosene space heaters, or propane heaters.

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[snip]

Possibly. But it probably wouldn't be any use even if it did, read on...

Yes, current flow through a resistor (i.e. anything with resistance) produces heat. The element itself is a resistor in that sense. However, it's a resistor sized to provide the appropriate heat output power (Watts) with mains voltages. 12V is 1/10th or 1/20th of the voltage it is designed for. Power is related to voltage and resistance by the formula:

P = V^2 / R

Resistance is constant as we're not changing the element, so with 1/10th the voltage power will be (1/10)^2 or 1/100th what it would be on the mains. If it's a 240V heater power will be 1/400th what it would be on the mains. 1/100th or 1/400th of an already low heater output would be of no practical use.

There may be heaters out there suitable for your purposes (ones designed to run off 12V power); I'd suggest looking at RV/mobile home/caravan/boating suppliers. Another option (though probably not a cheap one) is 'dew heaters', designed to gently warm telescope lenses/mirrors to stop dew forming on them.

Tim

Probably. But it might be way more efficient to leave the tap running a bit while you are there, and possibly insulate the pipes.

Water needs a huge amount of energy to cool down. Suppose the incoming water is at 5 degrees C (9F above freezing).

A D cell has a capacity of about 15 watt-hours.

A liter of water at 5 degrees C has 20kJ energy more than at 0 C. (9 degrees difference in F). 15 Wh = 54 KJ.

Where I live, 3 liters of water is cheaper than a D cell. But when the water gets closer to freezing, you need more and more of it.

Thomas

If the water is free leave it running.

Otherwise use pipes that are resistant to freezing and insulate well.

I can't conceive of any reasonable battery that can supply the needed power for more than a brief time.

Thanks everyone for your replies.

I didn't know this would be such a big deal - a kerosene heater and insulation for the pipes will probably be the easiest.

HOWEVER....

In searching for a DC heater, I came across this 12-volt blanket:

I am wondering what would happen if I connected this right to one of those 12 volt lantern batteries.

I am asking this mainly out of curiosity about electronics / electricity.

Would it drain the battery really quickly... perhaps give off an hour of heat before the battery is completely drained?

I realize you would only be guessing without knowing some of the parameters of how it is wired. But a guess is all I'm looking for.

Thanks.. Stephanie D.

..... "Car Cozy"

Draws 'just" 4 amps of power = dead battery in 60 seconds or less.

10 hours = 40 VA, so a car battery would work but you'd need to charge it twice a day or so.

Quote: "... A heavy duty, deep cycle Marine battery at Sears. It is about 84 amp/hours and weighs in at 53 pounds!"

You want to haul that sucker in and out? Now if you could hook up a solar or wind system to charge it - but you'd be better off to build a large solar water heater and use that for various purposes. A big one will work in Scotland in winter but you need power for a pump if you can't get the tank above the collector.

Well they can put a few amp hours into a D cell size battery these days. But unless you have some overpowering reason, this is not going to be economical. Generally speaking, using electricity to produce heat is wasteful. You can get more heat, cheaper, from burning fuel.

If your in a space craft, deep mine, deep cave, or under the ocean - electricity may be the best option.

The tailgate blanket is only marginally useful. A better quality blanket would probably be more useful in that application. In a car you have a battery that is good for 20 amp hours (unless you put in a deep cycle battery) and that energy has to come from somewhere (like running the engine)

It might be just the thing for a cold-blooded girlfriend trying to sleep in the rear seat on a long trip - but a polyester comforter would work better at a lower cost.

Did you catch the "Sorry! On Back-order until 1/22/04 ?" Hmm,

3004?

I drive a motorcycle and found "battery heated, electric socks" worthless. I only needed the heat on long trips, and the battery wasn't up to the task for long.

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