Re: Use of solar cells for inflight recharging


Dave Sinclair wrote:
Does anyone have any recommendations on the appropriate
solar cell technology for in flight recharging of sealed
lead acid batteries? Ie Eg what's the recommended
regulator technology - is it normal to shunt the solar
cells when the battery voltage rises at full charge
to prevent overcharging? This seems a little strange
to me (ie you allow the solar cells to discharge at
high current through a shunt thereby dissapating the
full wattage of the solar cells rather than increasing
the series impedance in the charging line).

Any recommended manufacturers
of regulator/shunt units? Any recomended panel suppliers?

The main issue for in-flight solar charging is where do you put the dog
goned panel? Rigid panels can only be put inside the cockpit, so a
thin, flexible panel. These are available, but at a jaw-dropping price.
A reasonable alternative to solar charging is to use a bigger battery
(or more of them). You can still charge with solar, but it is on the
ground. That is how I keep my batteries charged in my DG400, and it
really makes a BIG difference. I used to charge them while I was
assembling using the car. The battery voltage would indicate that they
were charged (13.9 V), but they weren't. I would really find this out
if I had any difficulty starting and had to crank more than usually. At
times I would have give up and pull my car over for a jump start (not a
pleasant task when you are by yourself!). Now I have no problem
cranking, even if I have to crank it a lot. And I have plenty of
reserve capacity to start it again after I have landed from a 4-5 hour
flight. And these are 3 year old SLA type batteries. I use a 20 W panel
with a solar charge controller. No need for a fancy MPPT type, because
I have plenty of time to charge the batteries. It is a PWM controller
with anti-sulfating circuitry (I have previously posted the source of
the panel and controller).

Some year I am going to locate a higher engery density battery in the
SLA form factor, such as a lithium-ion or a nickle-metal hydride. But
so far no luck. You can have battery packs made out of individual
cells, but they are VERY expensive and come with no warranty.

Tom Seim
DG400
Richland, WA

.

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