use Solar Sunroof as a trickle charger for battery

notorious · #1 15th February 2014, 05:33 PM

I'm going to install solar sunroof soon into my D2 and I was thinking to install an additional switch somewhere in a car to choose between 'normal fan mode' and 'trickle charge' mode.

That additional switch will allow me to to connect solar battery directly to the following device manufactured by CTEK that basically converts any DC power source including solar cell power into a relevant charging voltage.

http://www.ctek.com/gb/en/chargers/D250S%20DUAL
http://www.ctek.com/Archive/ProductP...%20DUAL_EN.pdf
http://www.ctek.com/Archive/ProductM...%20DUAL_EN.pdf

What you guys think?
What can be wrong with this idea?

P.S. Power rating of FL D2 sunroof with 4 courses of cells is 33,6 Watt.

Delboy · #2 15th February 2014, 10:23 PM

I'm not familiar with the solar panel sunroof but from what i ahve seen on other threads its not a complicated device and combined with the charger you shown i don't foresee any problems with it working.

PsYcHe · #3 16th February 2014, 10:15 AM

If it puts out enough power, then I don't see why you couldn't splice a charger in with a switch.

ainarssems · #4 22nd March 2015, 12:16 PM

I have been thinking about this a s well. Couple things to consider is that panel wattage is rated as maximum so it will be for direct sunshine in middle of hot clear summer day when the sun is shining perpendicular to the panel and panel needs to be clean as well. Also panel itself will be deteriorating as well depending on the panel it will loose 0.1-0.8% a year.

So today I decided to measure actual volts and amps going to the fan. It is a clear day with lots of sun but it is at a fair angle and cold. So my measurements were 2.7 Amps and 3.7V which is roughly 10W You would need DC-DC converter to take it up to 14V which makes it 0.64 amps at 90% efficiency. It should be enough to keep the battery charged but unrealistic to charge it up from flat. This was measured on PF 3 row panel so for FL you might get 30% more power.

Also fan is not connected directly to the solar panel, there is DC-DC converter already in the sunroof so to increase efficiency you could hook up battery charger directly to the panel but would be a bit tricky to run extra wiring.

notorious · #5 22nd March 2015, 01:31 PM

Thanks Anairs. Very useful information.

ainarssems · #6 22nd March 2015, 02:21 PM

And now couple of hours later sun is a bit lower and angle not so good it measures 1.9A and 2.6V or approximately 5W