Thanks Paul!
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Originally Posted by paulgato
The starter motor will be drawing 100+Amps. Any DC/DC step-up converter I might use to get the battery voltage up to the alternator output voltage of 14.5v is only going to output 30 Amps at the very most, more likely between 10 and 20 Amps, so I don't think the starter motor will 'see' a significantly increased voltage. If you start a car with the headlights on, they often dim as the starter turns...
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Agreed. I didn't account for the fact that a booster of approx 30-40A capacity couldn't possibly power a starter.
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As far as the headlight dimming goes, ... It's common to find a significant drop there which can be removed by feeding the headlights direct from the battery via thick cable and a relay triggered by the existing wiring to them. (The stock wiring is usually too thin ... The same MAY be true of the wiper motor, although I haven't measured that yet.
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My experience, in which the 12V lead acid deep cycle really only could power headlights for about 1-1.5 hours effectively, was based on my experience in the Civic. Originally it had too-thin headlight wiring, with too long of a run also. Early in my ownership of it, I remedied that with heavy gauge leads directly from the battery to relays, and more heavy gauge leads to the bulbs. I used the deep cycle battery with that improved wiring configuration.
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I would forget the fuse ratings. Headlight bulbs use about 55w, or about 5Amps. One 10Amp converter should be adequate for each bulb.
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Good point. I like that.
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... One thing to watch out for is that they usually don't have a common ground or common negative. That means that you have to isolate both the positive AND the negative outputs from the vehicle's chassis and from the rest of the car's wiring...
Using DC/DC converters to feed power into the WHOLE of the car's electrical circuit however is not so complicated as the only place where you have to carefully isolate a negative from the chassis is between the donor battery's negative terminal and the DC/DC converter. The output negative from the converter can be connected direct to the chassis as long as the input negative is not. I hope that makes sense. As I say I have not yet used one of these converters so take anything I say for what it's worth!
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Thanks - I wasn't aware of this. My past setup used a chassis ground for the battery. I'll need one additional wire for battery - to booster -, but that is very doable.