Quote:
Originally Posted by JRMichler
Get a DC-DC converter for 13.8 volts and put in an alternator ON/OFF switch. Lead acid batteries like about 14.3 volts (varies slightly depending on temperature) to be fully charged, and about 13.8 volts for a sustain charge. Too much voltage is bad for the battery, it converts the water into hydrogen gas.
Turn the alternator on about once per week just to make sure it still works and to top off the battery.
It takes almost a full kilowatthour of power to put enough heat into an engine to do any good. That's enough to drain a good sized deep cycle battery.
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Hmm... Thanks JRMichler. That would work. And yes, I was thinking of 2x 50w pad heaters on both gearbox and engine sump, left switched on overnight. That does add up to about 1Kwhr. Yes, probably not a suitable use for a battery. But leaving the car 'plugged in' overnight could charge the aux battery and warm the engine.
Probably best then to use mains voltage pad heaters reather than 12v ones. It would be nice if a large solar panel could provide enough charge in the battery for the pad heaters but that's probably too much to expect, and in any case that would mean the battery is exhausted by morning, which is the opposite of what you want. But a plug-in overnight thing would work. Even in (the cool, British) summer there should be some gains from starting the day with a warmer engine and gearbox.