Re: Solar Charger Question

RST Engineering (jw) wrote:
I'm using one of those Harbor Fright 1.5 watt solar panels. Testing in the late October sun shows an open circuit voltage of 21.5 and a short circuit current of about 60 mA. Maximum power was at an output voltage of 12.7 and 38.5 mA...about half a watt. Probably double that in the noontime summer sun, but don't ever believe that a HF device will meet the published specifications.

My calculation shows that I can model this little rascal as a 21.5 volt voltage source with an internal series resistance of 220 ohms or thereabouts if that is what I want to do.

The recombinant gas "12 volt" battery I'm using likes to be taken up to 13.6, then allowed to self-discharge back to 12.6, then up to 13.6 again... .

I had originally planned on using a switching power supply to get the last milliwatt of power out of the little panel, but (a) the voltage is so close to the desired voltage that it seems a waste to go that sophisticated when a simple linear PNP pass using an LM324 as the error amplifier plus another section of the 324 as a comparator with hysteresis to shut the current off when the voltage hits 13.6 and then back on at 12.6. A 3-silicon diode reference to attempt to "track" the desire of a lead-acid battery to charge to different voltages summer and winter.

This is my first shot with a solar controller, so if anybody has any pearls of wisdom they'd like to lay on me before I start reinventing the Edison valve, I'd appreciate hearing from you in this ng.

Thanks,

Jim

Nothing wrong with the HD solar panel.

you will find the VOC and the ISC, as well as the R thevinin, changes dynamically with solar flux. If you are going to maj\ke a commmercail device and want to optimize the power pumped out of this or any cell. PLease contact me as our group has optimize the solar cell to battery, (or any other load) interface.

best regards,

Marc Popek

.

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