From: TacticalTruck@aol.com
Date: Sat Feb 23 2002 - 06:08:02 PST
In a message dated 2/22/02 10:56:38 AM, amnon@deltaforce.net writes:
>This may be a stupid question, but why can't one just run wires from one
>battery to get 12V?
Let me quote from "Battery Equalizer Application Notes" by Mark Endres,
Project Engineer Sure Power Industries, Inc.
"The 24V system normally consists of two-12V batteries connected in
series, with a 24V alternator providing power. It seems the most logical
place to to obtain 12V power is the junction between the two batteries.
However, a problem arises if the system is constructed in this fashion.
"Consider the situation when the engine is off (alternator is not
generating), and 12V power is used. Load current comes only from the 12V "low
side or A" battery, none of which is being furnished by the top or "high side
or B" battery. After a time, the 12V loads will discharge the "A" battery
while leaving the "B" battery charged up. Since the "B" battery has not been
discharged it will not need any electrical current to recharge it; however,
the "A" battery will.
"When the engine is started and the alternator furnishes current to the
load and to charge the "A" battery. All the current now flows throught the
"B" battery, since it is in series with the load and "A" battery.
"When this happens, a condition exists where the "B" battery overcharges
because it does not need recharging, and the "A" battery does not get the
charge it requires. Charging current for the "A" battery is impeded by the
already charged "B" battery and reduced by the amount of current that flows
to the load. Even if there were no load at this point, the same problem would
exist due to the imbalance of the battery charges.
"When operating the system in this manner, the life of the batteries is
dramatically shortened. The "A" battery fails prematurely because lead
sulfite builds up on the battery plates, reducing the capacity. The "B"
battery fails when its electrolyte "gasses" and evaporates and damage occurs
to its plates and separators in the dry battery cells as a result of ov
ercharging. Failure time can be as short as a few weeks for heavy 12V loads.
"If there is no 12V load, a 24V system with a two battery "stack" can
operate well without an equalizer. However, the batteries must be of the same
type and age. Without a battery equalizer, current draw from one battery and
not the other will cause an imbalance. This imbalance accumulates over time.
Because the effects of the imbalance are cumulative, battery degradation
occurs even with very small loads, such as a radio, clock or small lamp"
The paper goes on to describe how their converter/equalizer works and the
benefits of their system. Again, I have some new surplus 25 amp units for
sale for $150.
Jeff
TacticalTruck.com
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