Automobile battery charging

Usually the car has a 15A fuse on the cigarette lighter circuit. If you buy a pre-wired lighter "plug" or hack one of an existing device (e.g. laptop charger or cellphone power) the true current limit is probably the skimpy wiring attached to the plug (maybe a few amps!) At least some of these plugs have integral non-replaceable fuses at a few amps, and some have solid-state circuitry built into the plug which will get in your way!

Tim.

In most cars, it is possible - the cigar/cigarette/aux-power outlet usually has a fairly direct feed to the battery, often through a fuse of its own.

The max charging rate would depend on the vehicle. You'd need to check the fusebox and/or the owner's manual, and find out what sort of amperage fuse is used for this feed and whether the owner's manual says anything about the safety of doing high-current transfers through this outlet.

The contacts in these outlets are sometimes quite rugged and robust, and are sometimes pretty wimpy - the latter in cases where the outlet is intended as a low-amperage auxiliary supply for laptop PCs and tape players, and not as an actual cigarette lighter.

Trickle and float charging, at rates of up to a couple of amperes, is probably going to be safe. There are some solar chargers, intended to provide a low-level float charge for vehicles in storage, which work this way. I believe that there are some line-powered chargers, good for a couple of amps, which are used to recharge or float batteries in cold climates to make sure that they're in good shape to start the car when the morning temperature drops below zero.

I would not stick a cigarette-lighter connector on the wires from a stand-alone fast-charger and plug it in... a continuous flow of 20-30 amps is probably quite a bit more than this outlet ought to be asked to handle.

The allowable charging current would be somewhere between 5 & 15 A, depending on the wiring in the car and your adapter.

On many cars, thie outlet is disconnect from the battery if the key is OFF. You could switch it to ACC, but this might turn on more things and draw more current than you were able to pump into the system, which would make this a losing proposition.

I once modified a car just so I could do this. I had to reconnect the lighter jack to a fuse that was hot all the time.

----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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