LEAD-battery voltage vs. current

[Gunson]

Hallo battery

I am charging car-batteries with wind power and regular chargers.

I try to give the batteries as small charge as possible.

When I charge with regular charger the current is around 1-1.5 A when it reaches 14.00 V

After 24 h the terminal Voltage is 12.97.

A fully charged battery should be around 12.75. And the charge should be to at least 14.5 V to be fully charged.

Is it possible 1 A (11% of the original capacity) is too small current to bring the battery to 14.5 V?

So I figured a charger that cuts the charging at 14.5 V and delivers a small current would overcharge at a very slow rate. And that gives a higher terminal Voltage.

Anybody has some calculations for this?

    Best regards,

    Anders, Sweden

[dnix71]

I note you are in Sweden. Not exactly a warm place this time of year. Battery charging voltage depends on temp and whether the battery is being floated for occasional use, or is cycled daily. If it's cold enough, a fully charged flooded lead acid battery could be at above 15v.

http://www.powerstream.com/SLA.htm

Battery discharge capacity drops way off with temp, too.

[Gunson]

Thank you dnx71!

that was a nice link. I will tune up the charge regulator in the winter.

Still many thoughts about this though...

Would it be perfectly fine to set the charging limit at 14.00 V for the wind generator and fully charge it with a regular charger once in a while?

Any simple solutions or complex calculations are very welcome

Anders, Sweden

[wpowokal]

This might also shed some light.......

http://photovoltaics.sandia.gov/docs/BattIntro.htm

allan

[dnix71]

Why do you want to limit the output of your turbine to the battery? Are you using the excess for something else? Otherwise, yes, there is nothing wrong with stopping at 14 and doing the finish with something else.

[Gunson]

Thanks for another great link!

the batteries are never placed in below freezing point-environment.

Except of course the car's  battery. It's only -15 C now anyway ¤;-)

The reason I cut off the charge from the wind generator is because I don't want the batteries to get boiled. I'm not sure I understood your remark.

But I forgot the main question:  If I top off the battery and the current is only 1% or ½%, Could the battery get overcharged? And could this be why the terminal resting Voltage is above 13 V (after 24 h resting time, charge to somewhat over 14 V)?  

[kurt]

most likely you are seeing surface charge on your battery when you check the at rest voltage try putting a small load on it for a couple minutes something small like a 12v light bulb from a car burn off the surface charge then disconnect the load and check the voltage see where you are at?? mite also be that you are just floating your batteries at 14v long enough that they are charging if a battery is left on charge long enough at that voltage it will charge it just takes a long long time like days. allot of old sla chargers in ups's work that way because they are designed to float for months on end then discharge once then float for a long time again. most batteries in RE systems do not see that kind of use they are constantly getting charged and discharged so you have to charge them to a higher voltage to keep them working for a long time.

BTW as long as your batteries are the type you can add water to boiling them a little bit will not hurt them and actually they should boil some occasionally it helps them. just not to the extreme and do not let them get so low on water the plates are exposed or overfill so they spit acid when they boil.