Hi Chris
On (08 Dec 96) Chris Harper wrote to Roy J. Tellason...
 CH> I doubt any single average deep cycle battery could deliver 3KWH for any
 CH> length of time without suffering increased wear, and I intend to hook
 CH> several in parallel to reduce the load on any single battery. I may have
 CH> that pack run into a couple common car batteries, which will handle 
urge
 CH> needs, and be replenished by the deep cycle pack.
 CH> The car batteries would handle not only surge demends, but would take 
he
 CH> main charge from the panels, as the charge would vary with clouds 
assing
 CH> and such. The car batteries would act similar to an extremely large
 CH> capacitor, in effect, to smooth out the load (either inbound or 
utbound)
 CH> for the deep cycle batteries, which would handle the main storage.
Very interesting but I think there is a flaw in the theory. I assume the
circuit would be passive ie no switching of the auxiliary auto batteries, you
would have these closely paralleled to the deep cycle units.
The flaw seem to be this- the energy given out by the battery will depend on
the voltage drop forced at its terminals. Yes, a heavy surge would be 
rovided
mainly by the auto batteries and the deep cycle units would take it easy and
not contribute much. If the surges were a considerable part of the duty cycle
so that substantial energy [watt hours, rather than watts] was necessarily
being pumped into the tired auto batteries from the deep cycle batteries, 
hen
there would be a penalty in losses because charging/ discharging produces 
eat
inside the battery, and the kwH of heating energy would be a waste and not be
available as light/ TV/ radio whatever you wanted to supply.
Secondly, as the reason for using deep cycle batteries, is because we wanna
run these flat fairly often, and in that case the paralleled auto batteries
running flat in unison would be injured and wear out rather fast.
Solution? Think about a smart paralleling circuit that isolates the auto
battery, before its terminal volts run below [say] 11 volts for more than 30
secs. See what is done in some RVs so that the starter battery, is not
compromised by what the refrigerator takes from the "hotel" battery on board.
There is no need to "protect" the deep cycle battery from momentary overload.
But, if you want to hold the volts up close to 12v during heavy overloads,
then the auto batteries would certainly help.
Cheers...ALEC
... Life is one long process of getting tired
--- PPoint 1.92
---------------