"Mark" wrote in news:1156735487.090872.131750@
74g2000cwt.googlegroups.com:

I'm wondering, would one of these things fully charge a discharged
*big* bank of lead acid batteries, like 500AH capacity? It'd take 20
days or so, but could it do it without harm? Would the gentle charge
rate stop sulphation during the 20 day charge? A half dead lead acid
battery sittin' around for 20 days would sulfate up with *no* charging
going on. And could 1.5 amps drive the batteries up to 14.2 volts?

Never tried such a thing - tiny charger, big batteries.


No harm at all. This charger completely shuts off when the red led comes
on at 14.2V and doesn't come back on again until the cell voltage drops
to around 13.2V. The charge you get is very deep, penetrating the plates
very nicely.

Nothing stops sulphation, a natural occurance no matter what you do. To
greatly reduce sulphation, the cure is to never discharge the battery
below 50% of capacity. The bigger the battery's capacity, the less
you'll be discharging it, so it sulphates (or sulfates??) less. It will
only sulfate when when the lead sulfate in suspension gets saturated
enough the ions form crystals that gravity falls out into the bottom.
You leave your car battery "half dead" all the time...short trips, moving
the car, the fans running long after you've shut down the engine drawing
30A cooling the radiator, the headlight delay shutdown drawing 20A so you
can get inside for many minutes. The recharging, even at the slow rate,
will cause the ions in suspension to stay in suspension.

If this little charger had no automatic shutdown, I'd never suggest
leaving it charging 500AH batteries as it would overcharge them,
eventually...after that 20 days.

One of the benefits of very slow charging is it never heats the
electrolyte. The batteries, here in the South, are kept too hot in the
first place inside an engine room at 120F with the boat sitting in the
sun. Slow charging keeps from exascerbating the problem.

You must also consider any discharging loads like bilge pumps that cycle
on and off when you're not in the boat, before you consider if this
little battery charger is a good idea. If you're charging at an average
current of 1.5A and the loads are averaging 2A, that isn't going to work
and you'll arrive at the boat with dead batteries, ruined. The poster
that started this, I assumed, has a boat on a trailer with everything
shut down. If you forget one good light, the charger will not recharge
and may even lose the battle, killing the batteries....not good.

--
There's amazing intelligence in the Universe.
You can tell because none of them ever called Earth.