I had a car battery on my desk to charge it, I have since noticed a patch of wet on the desk which on cleaning up revealed a battery shaped mess of the surface.
Is this normal? I didn't notice anything spewing out of the caps on the top so wondered if it was condensation which had become acidic or something.
Rick
It's not normal. If it's not a self maintenance battery then the caps should be removed when charging or you get gaseous pressure build of hydrogen gas which can damage the battery or cause an explosion. the acid has probably leaked out of the bats weakest point under pressure. When it's charging the electrolosis generate hydrogen gas from the cathode.
Not that I'm saying you are wrong but doesn't that mean you should remove the caps after starting your car so the alternator charging the battery cause the same problem?
The charge is regulated by a more sophisticated system when in the car; this is done either by electronics within the alternator, a separate charge control unit, or via the ECU. This will prevent, or at least reduce significantly, any risk of over-charging as the charge will reduce to zero when the battery is fully charged.
Bog standard chargers just rely on the back emf from the battery reducing the charging current. There will still be some charge continuing even when the battery is fully charged, so it will gas to a greater extent.
Chris
Certainly on older cars, I was under the impression that the alternator just typically held the supply voltage at constant voltage so as to achieve constant voltage charging (battery is charged until terminal battery voltage rises to meet the charging voltage and thus charging ceases). 2.3V per cell being typical, hence 13.8V regulated voltage out of the alternator. I could go and dig out my copy of Horowitz & Hill if you want... :-)
Can you still buy such devices? Mine is getting on for ten years old but cuts off totally when the battery is charged.
Not on most modern chargers they're regulated nowadays, same as an older alternator
Didn't realize "The Art of Electronic" was that well known and popular! I had the first edition, bought in 1981. Its treatment on the traditional as well as the unconventional circuit techniques was very much appreciated. I don't consider it a textbook, more a compilation of insights from perhaps two nerds (One later became a professor at MIT). What was valuable was its collection of some hard-to-find, unorthodox circuitry, which may well be unique. Pity there wasn't a second edition.
Lin Chung
Oops....first printing, not first edition.
Indeed. It's probably as cheap in mass production as a large series resistor...
I hope my solar panel trickle charger is not causing gassing. I leave it connected (through the cigarette lighter) whenever I'm not driving. Tod
In the UK, you'll be lucky if it causes charging ;-)
Chris
The output of any solar charger is so low that they barely blance the alarm system drain. All they do is slow the natural discharge down.
Err.. There was! Second edition came in 1989 (mine was printed 1994).
Mathew
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