Float charge 12v car battery?

See

For good results the float voltage needs to be accurately controlled, and temperature compensated, and there needs to be an occasional equalisation charge, which is presumably why cheap chargers stuff the battery up in fairly short order.

Sylvia.

I don't know off the top of my head, but if I wanted to do it I'd first try to find some of the magazine articles covering car battery charger projects and see what figures they went by for the "float" charging mode.

That "Battery University" website might also have some useful info.

Though I imagine that most people who need those battery trickle chargers do so more due to the power drawn by the electronics in a rarely used car than the battery discharging by itself. I'm not sure to what extent it will help for storage.

The LED driver will probably be constant current. For a car battery, you need a constant voltage. Sources vary, but between 13.5v and 13.8v should be fine for a float charge.

Peter

Thanks Sylvia.

Cheers Peter. I have a couple different LED drivers that do both CC and CV (adjustable). I might whack it on at 13.7 and an amp for now (unless Sylvia's link says otherwise).

Thanks Kev. I'm worried because I was in a similar situation a decade or so ago and kept the 'spare' battery for a year or so. When I went to use it again it was dead as a doornail and I couldn't get it to take a charge again. I have a bit of info now so off to read Batteryuniversity site...

A good way to destroy it.

Pick up battery charger designed for purpose and one a week, use 10% of capacity then recharge it. I forget the voltage, but lead acid batteries need to be charged at an optimal voltage and they need exercise to keep them fit.

I fed it 13.8v and an amp and after a few hours the charge it was taking dropped gradually to 0.25A so I'm assuming that it's topped off.

Thanks to all for the input.

If you have a solar panel Oatley Electronics sell a nice little regulator kit for around $25 which is ideal for the purpose.

I have a solar car battery float charge thing about the size of a car sun visor I got from Jaycar a few years back (I don't shop there any more) but with that thing plugged into the cigarette lighter for a couple of weeks the battery actually got flatter! (In the car I have the cigarette lighter is always connected regardless of key position.)

I don't suppose you could give me a link to the Oatley thing? I'm in NZ so shipping would probably be prohibitive but I'm curious. I've cut the regulator off the Jaycar panel and just the panel outputs 24v in sunlight. I'm not sure how many (milli)amps it will deliver though, haven't tested that yet.

Cheers,

You can download the notes but not the schematic IIRC. The less common components, with the exception of the PCB, should all be available through AliExpress if you can dig up a cct from somewhere.

The original was published in Silicon Chip but Oatley have since modified it considerably.

I've no experience with the vehicle sun screen solar panel you purchased from Jaycar, but the basic battery charger/solar panel regulator they were selling comes set to SLA chartging and you need to change it to output for wet cells if that is your type of battery.

the solart panel probably didn't do anything as the panel was't in optmal conditions, aka facing north and perpendicular to rays from full sun. also a good change that being in a closed car in full sun, the output was limited by thermal load.

You've posted the OCV(open circuit voltage), What is the SCC(short circuit current)?

I don't know my meter only goes up to 10A and the fuses aren't cheap.

Thanks John.

Which is what I get out of a 120watt full solar panel, so it would have to be incredible if something the size of a car visor got anywhere near it. Stick some "resistance" in the circuit at first.

You don't need to measure the current. Load the panel with a wire wound resistor (22 ohm ought do) and measure the voltage when it's facing the sun. Ohm's Law being the clue.

Don't hang about too long as the resistor is likely to get very hot.

Power (which is what you really need to know) = V^2/R.

Yeah I mis-read, checking the newsgroup quickly. I thought he meant SCC of the battery!

Thanks. I mis-read when checking the newsgroup quickly. I thought you meant SCC of the battery! I'll check the solar panel when I get a chance. It's 'stored' so might take some finding.

Also we've not had any really sunny days here for a while.