Some random rules about charging lead-acid batteries:
1. You should not attempt to charge more than one battery at a time from the
same source. They will develop a race condition, because of inherent
diferences in each battery. Most chargers for multiple batteries have a
circuit known as a charge equalizer, that compensates for this condition.
2. Two or more batteries can be charged from the same supply, if they are
isolated by diodes. These diodes (sort of a check-valve for electricity),
are the main component in isolators that can be purchased from marine supply
stores, and truck stores that cater to fire departments, telephone companies,
and other utilities who require two batteries per truck, that charge
separately, but can be paralleled for expedient starting.
3. All diodes, regardless of their voltage or current rating, have an
inherent voltage drop of 0.7 (zero-point-seven) volts. Whatever voltage
setting that is available at the input (anode) is reduced by 0.7 volts at the
output leg (cathode) of these isolators.
4. A maintenance charge of 1 to 3 amps should be sufficient to keep good
batteries up to par, in temperate weather. 25 amps is way too much current.
You will cook your batteries. (You will never see a truck's ammeter at that
reading for more than a minute or two, if that long.) This current
recommendation assumes that all parasitic loads are removed. These are loads
that are caused by moisture and insulation breakdown in the vehicle, along
with devices such as alarms, clocks, etc. (Disconnect the positive cable, in
other words.)
5. Commercial chargers have a circuit that will limit, and ultimately reduce
to almost zero, the current presented to the battery. The internal
resistance of a lead-acid battery increases with its charge condition, which
is a self-limiting feature. This is another reason not to try to use a 25-amp
supply.
6. Automotive batteries lose half their potency at 32 degrees F. They lose
3/4'ths their potency at 0 degrees F. While this fact has nothing to do with
charging, it is recommended to take the batteries indoors during extreme low
temps, to aid the charging process.
7. Do not set the batteries on a cement floor, or bare earth. Place them on
wood or other insulating material. This will prevent currents from leaking
over the case of the battery.
8. Place a piece of heavy duty sponge rubber under any battery that is in
service. The reduction of vibration will extend the life of the battery.
9. Put on your safety glasses, when connecting, disconnecting, or messing
around with, batteries, even if they do make you look like a nerd. Better to
be a seeing nerd than a blind tough guy.
10. Loosen the caps. Wear gloves.
These comments are offered in good faith. I expect to hear unpleasant remarks
from the experts. Flame suit on. Fire at will.
A P Bloom
www.M35products.com
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