Robert Bruninga via EV wrote:
What happens when you might forever overcharge a CAR battery with 30 mA (during daylight).
Most car batteries are flooded (i.e. not sealed). If you continuously charge them, once they reach "full" they simply convert the excess charging current into heat and gassing.
Both are bad for the life of the battery. The heat shortens its life. The gassing slowly vents away all the precious water (which can't be replaced on modern "sealed" car batteries because the vent caps are glued on).
On the other hand... most cars have dozens of "vampire" loads that are always on... clocks, odometers, radio presets, keyless door entry, alarm systems, that phone charger that you leave plugged in all the time, etc. It's likely that these are already drawing more than 30ma.
So, a 30ma (peak) PV panel probably can't overcharge the battery. Even a panel that delivers 100ma peak in full sun still probably can't do it, because it's long-term average is still less than the "vampire" loads.
I added an unregulated solar panel that typically produces only 30 mA to a very remote cabin car battery deep in the woods. The charge rate will give a 2 hour per week use of the lights. But what happens if no one uses the cabin for months? NiCd's can absorb such small overcharge, but I assume Lead Acid will everntully be dried out?
The easy way is to measure the battery voltage. If it's under 13.5v, you're not overcharging it. Even 13.8v isn't too bad (see my earlier post).
OK, now add in the fact that for maybe an hour a day, the sun will directly hit the panel and the charge will be 500 mA
Now 500ma probably *is* enough to overcharge it. Especially if this is a battery in a cabin in the woods, and *has* no always-on vampire loads.
The simplest solution is to buy or build a zener-lamp regulator. Nothing but a light bulb and zener diodes. When the PV panel tries to overcharge the battery, the lamp just lights to "burn off" the excess.
http://www.sunrise-ev.com/LeesEVs.htm#zenerlamp -- "IC chip performance doubles every 18 months." -- Moore's law "The speed of software halves every 18 months." -- Gates' law -- Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
