Re: (ET) Dave Roden battery lesson

[poweredbysun <jimlynch poweredbysun com>]

>         What is "tapping the pack"?
It is when you run wires off part of the bank to get lower
voltages. For example, the 12 volts for the lights on the
original elec-tracs was tapped off two batteries in the 36
volt series bank. The 18 volts for the lift motor was tapped
off at another point. Using a DC to DC converter to convert
the 36 volts from the bank to a lower voltage will be more
expensive, but it will draw equally from all batteries instead
of drawing a few batteries lower than the rest.
>         How do you "equalize"?
Over time, some cells will become less fully charged than others.
The traditional method of correcting this is applying an equalizing
charge, where the voltage is run up to slightly above the fully
charged voltage and held there until all the batteries have reached
the same voltage. If this is not done, the batteries that are not
fully charged will quickly "sulfate" coating the plates with a layer
of non conductive sulfur which will permanently reduce their capacity.
When some batteries have permanently reduced capacity, the few that
are carrying the load will quickly be used up. So, equalizing charges
are important if regulaters are not installed on each battery to
ensure they are charged and discharged equally. Equalizing charges are
especially important when the bank is tapped. The elec-trac chargers
seem to run the voltage up higher than fully charged when they are left
running for an extended period of time. This seems to me to be
equivalent
to an equalizing charge, though I'm not an expert.
>         What is "gassing"?
The chemical process by which electricity plates lead back on the plates
during charging is not 100% efficient. Some of the water in the battery
is electrolyzed to hydrogen and oxygen gasses. This bubbling is said to
help mix the electrolyte and is said to be good for the battery.
Hydrogen
gas at 4% or greater concentration in air is an explosive mixture. The
water that is "used up" by gassing must be replaced or the electrolyte
will fall below the level of the plates and they will be damaged.
>         Are VRR batteries something some of us may be using?
High tech batteries are a lot more expensive than Sams golf cart
batteries.
Their possible advantages of high discharge rates, lower weight, etc.
are
perhaps not so important in the lawn tractor application. For
competetive
tractor pulls there might be distinct advantages under some conditions.
Good luck,
Jim Lynch