Charging battery via cigarette lighter socket

[abar]

Hi,

I'd like to connect a 12v solar battery charger to my 2006 Subaru Legacy without running extra cables from the engine bay. Unfortunately, the cigarette lighter socket is isolated from the battery via a relay, which is energised when the ignition is in the ON position.

I've been considering opening up the relay and putting a diode across the poles so that charge can flow from the cigarette socket to the battery when the ignition is OFF. The diode would be shorted out when the ignition is on and therefore behave as normal when running normally.

The standard fuse would protect the socket, and the relay could be returned to normal/replaced, if required.

Does this sound reasonable? I'm normally a bit gun-ho, but I don't want to fry the electrics.

Cheers,
Adrian

[Steve_D]

Sounds OK to me but then I'm not an electronics person.
However, I believe you get a volt drop (2v ?) when passing through a diode which may be too much for a solar charging system.

If it were me I would just hard wire a Halfords 4 socket cigar extension lead up under the dash so its permanent live and ready for anything else you want to plug in....mobile charger, sat nav, airbed pump, etc.

Steve

[Mr2Mike]

A silicon diode will give around 0.5-0.7 volts drop, depending on the exact diode and the current it's passing. A Schottky diode would give a somewhat lower drop, maybe 0.3v or so. Either may slightly reduce charge current depending on the open circuit voltage of the solar panel.

You could of course wire in a second cigarette lighter socket (possibly hidden under the dash) connected to a permanent 12v feed via a suitably rated fuse,

[abar]

Thanks for your help. The solar panel (Sunsei) produces 15.5v so the voltage drop shouldn't be a big issue. Having said that, I think you're right, a fused cable to the battery will probably be the easiest solution.

For anyone that's interested, I found a set of Subaru wiring and bodywork PDF's at this site: http://www.subaru-car.ru