As housing for heater use metal cans of coffee. It should have a diameter of about 10 cm and a height of about 20 cm Cardboard Bank, for example, from under the chips, is not suitable as a vessel made of plastic or any other material. Drill out the housing a few dozen holes with a diameter of about three millimeters.
In the bottom of the can drill a hole under the arm, which can be used U-shaped metal item from the children's designer. Secure the bracket and at its opposite end, place the bayonet socket car bulb brake signal. It needs to be exactly in the middle so the bulb does not touch the walls of banks.
In the side wall drill a hole of larger diameter. It insert a bushing of insulating material through which pass two wire cord with a cross section not less than 1 sq mm. connect it to the cartridge. In a cartridge, attach the 12-volt light bulb 25 watts.
Close the lid of the jar. To break the cord include 2 amp fuse. Pre-charge in a ventilated area regular car battery using the standard charger. If it is not used for a long time, periodically recharge it. Once in the cold period, disconnect the power supply, connect the battery to a homemade heater. He warmed up in about ten minutes. Don't keep hands on it for too long to not get burned (remember how heated on the radiator: keep your hand while it tolerates heat, then removed, and after some time the tray again). Do not hold on the heater near flammable items do not use in atmosphere with flammable gases and mists.
Battery voltage monitor periodically with a voltmeter. If it falls below 10 volts, immediately shut off the heater, otherwise the battery can permanently malfunction.