sizing solar panel

Udo,

When our Club's Orion arrived it apparently chewed through batteries at
a high rate. After some time, we found that the spec sheet for the
diode installed to protect against reverse polarity had a huge 1.2V drop
across it.

As a result, the charger wasn't charging to anywhere near full capacity
because the battery only saw 12.6V when the charger saw 13.8V.
Accordingly, it appeared as though the instruments were drawing much
more current than they were. It took quite a while to find the real
problem.

Does this fit your case?

In the course of troubleshooting, we also found the interesting fact
that the cheap $20 SLA chargers (usually a sealed black plastic box from
China) have target voltages which varied from 13.3V to 15.8V for the
sample we tested. 3 out of 5 were around 15V.

My DG has a factory fitted diode in the system with a 0.3V drop. The
manual specifies that a charger charging to 14.1V is needed to charge
the batteries completely. I suspect that a number of the debates on
batteries on this forum are related to diode voltage drops. My
electronic guru pointed out that ALL diodes had a forward voltage drop
and some are quite large.

Graeme Cant

Udo Rumpf wrote:

If I want to maintain a 12 volt 7amp/h Battery with a solar cell panel
what rating would I need during flight, if after 4 hrs I wanted to have
a usable, not full, charge in my 12 Volt battery.
Right now, my as good as new battery is useless after 4 hours.
and what size would the panel be?

Udo