On (17 Nov 97) Jim Dunmyer wrote to Alec Cameron...
 > I hope the 50% makes sweet music now! Best "headroom" seems to
 > apply, when the panel open circuit voltage is twice the battery
 > voltage.
 JD> I think that HomePower Magazine had an article some time ago
 JD> that indicated a need for 18 or 19 volt-rated solar panels to
 JD> charge a 12 volt battery. It was significantly higher than the
 JD> nominal battery voltage, but not double. The reason for the
 JD> higher voltage was as you said, to make up for blocking diode
 JD> and regulator losses. You do need that headroom!
It's more than just that, and I wish I understood it. Voltage
depends on the state of charge of the battery. A full and equalizing
12 volt battery can get up to 15+ volts. Since voltage is just
"pressure", in order for the current to flow from PV to battery, the
PV voltage has to be higher than the highest battery voltage. And
there are bound to be not only diode losses, but line losses too.
Does that muddy the waters some more?
                        Ian
... Hockey Players are protesting the excessive violence in figure skating.   
 
... The primary use of conversation is to satisfy the impulse to talk. - 
George
Santayana
--- PPoint 1.96
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