23 v solar charger for 12 v systems

Gentlefolk,

A couple of weeks ago I picked up a solar charger to keep a seldom-used truck battery topped off. It is a Coleman charger and seems intended for the purpose, but the info supplied with it is sketchy at best.

It produces 23v at 2 watts in full sun.

How does shooting 23 volts of current into a 12 v automotive system work? It seems to me something would be getting fried. Do I write this off as a lost purchase, since I have no 23v DC anythings?

The solar charger has two types of connectors - standard clips and a plug that goes info a power port. My thought was to use the power port connector, but then I wondered about the 23 volt issue.

Thx!

Depends on the size of the battery... your solar panel voltage will drop to the voltage of the battery and deliver ~0.2A if it's a 2w panel. I don't think it's possible to overcharge any battery >50Ah with 0.2A of current. Try it but keep an eye on Battery Voltage... If it rises >13.2v you need a charge controller but those are typically <$10 for one that size...

Other issue is most more modern cars shut off the "power port" aka cigarette lighter" after a period of inactivity. Heck...heck my 2005 mini did this, so "battery matainers" don't work if plugged in there.

ZippyNH said:

Other issue is most more modern cars shut off the "power port" aka cigarette lighter" after a period of inactivity. Heck...heck my 2005 mini did this, so "battery matainers" don't work if plugged in there.

Click to expand...

The '98 F250 is one target. It has a "cigarette lighter" and next to it a "power port". Instructions with the charger say to use the "power port".

The other target is a late-80s Bronco. 1988 I -think-.

My main concern was pushing 23 v through a 12 v system. I guess from what I read here, if nothing is running, no harm to the battery? I can see electrical choas if the engine is started with 23v flowing back thru the system and the instructions DO say in NO uncertain terms to NOT have the charger plugged in when starting the engine!

Duplicated post. Delete.

nwdiver said:

Depends on the size of the battery... your solar panel voltage will drop to the voltage of the battery and deliver ~0.2A if it's a 2w panel. I don't think it's possible to overcharge any battery >50Ah with 0.2A of current. Try it but keep an eye on Battery Voltage... If it rises >13.2v you need a charge controller but those are typically <$10 for one that size...

Click to expand...

The charger drops output to the voltage of the battery?? Is this by virtue of some electrical law or some intelligence built into chargers? As I said, the instruction with this $25 piece of Chinese engineering wonderment was very limited.

The battery produces 750 CCA, what this means in terms of amp hours I have no idea.

TDIfor said:

The charger drops output to the voltage of the battery?? Is this by virtue of some electrical law or some intelligence built into chargers? As I said, the instruction with this $25 piece of Chinese engineering wonderment was very limited.
The battery produces 750 CCA, what this means in terms of amp hours I have no idea.

Click to expand...

When Do I need a charge controller?

Yes; this is how solar panels behave. Think of the output like a garden hose... voltage is pressure, amps are current. If the battery can accept the current output then voltage won't rise... 0.5A is pretty low. It would be like dropping your garden hose in the backyard; you're not gonna flood the neighborhood that way. You're not gonna exceed ~14v on the battery if you're only pushing 0.5A.

The voltage output of a solar panel will match the battery it's connected to. That's why we need sophisticated electronics to maximize the output... but using a small one to trickle charge a battery is fine if you're not aiming to squeeze every mw out of it.

I have a 10kW array on my roof that outputs ~30A and 350v = (10kW). If I connected it directly to my 48v backup battery I would only get 32A (Isc) and 48v = (1.5kW) current doesn't rise... voltage just drops. Using a charge controller I can increase the current so I'm getting 208A at 48v.

Long story short, the panel is current limited to 200mA which will not overcharge a car battery. Just make sure there is a diode installed so it cannot discharge back though the panel.

Thanks, all.

Not pretending I am getting the mathematical relationships, never claimed to understand electricity -but battery won't go boom, that was my main question. Thx!