sizing solar panel

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

just did a search and I think I got it covered, still if some with
experience would like to comment please do.
Udo
"Udo Rumpf" wrote in message
. ..
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

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

To reduce voltage drop from a charger, when a diode is inserted, the diode
should be a shottky type diode. If 3 amps maximum current is sufficient, a
1N5822 will work fine. Those diodes are available at Radio Shack. Voltage
drop is about .3 volts.

In many cases, a "protection" diode is not needed when charging a system.
They simply prevent current from going the wrong direction when the charger
is not connected.

Solar panels may or may not require them. Many circuits show a diode in
series with a solar charging panel. The theory is that it prevents current
from reversing direction during darkness. In many cases, the diode is not
necessary and the instruction books are guilty of simply copying a circuit
without understanding it. The reason diodes are often not necessary in
solar panel charging systems is that the panel itself is a diode. I always
check with a ma meter, just to make sure.

I installed a 100 ma (.1 amp) panel on a friend's motorglider (no electrical
charging system or starter) and it has charged the battery for over a year
with no problem. He is an occasional user and not a contester, nor does he
fly many hours at a time.

If you consider a 12 volt storage battery as being fully charged at about
14.2 volts and unusable for your purposes at 12 volts, you can consider the
stored power available pretty much as a straight line with 14.2 as 100% and
12 as 0 %. That means that when the voltage is 13.1 volts, you have 50%
power available. Batteries, both rechargeable and non-rechargeable may
expect the voltage to go below 12 volts to achieve the rated amp hours, so
if 12 is your minimum, you may need to de-rate your battery. The
manufacturer should have a graph showing the actual capacity
available with the maximum and minimum voltage you have in your electrical
system.

Colin

In many cases, a "protection" diode is not needed when charging a system.
They simply prevent current from going the wrong direction when the charger
is not connected.

Not connected to the AC power that is. When the charger is not connected to
the battery, current would not flow because there is no completed circuit.
Still early.

Colin

"Udo Rumpf" wrote in message
:

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



Udo,



Most battery manufacturers consider their battery to be depleted at
around 10-10.5 volts. I usually switch to my secondary battery when the
primary depletes to around 11.2 - 11.5V. I also agree with other
posters here that unless you have a transponder or something you should
not be drawing anywhere near 1.1 amps typically. In situ measurements
may be called for.



Larry

Although I have never measured it, I recall the average current drain for my
Becker transonder is only a couple hundred ma. The reason is that only
pulses are sent out and the average power consumed is pretty low.

Colin

COLIN LAMB wrote:
Although I have never measured it, I recall the average current drain for my
Becker transonder is only a couple hundred ma. The reason is that only
pulses are sent out and the average power consumed is pretty low.

Not everyone has (or can afford) a Becker transponder. A Terra will
happily consume several times that amount. And, try measuring the drain
from the encoder at altitude, particularly if it's one with a heater...

Marc