Assistance selecting controller for ? solar panels.

[Lgboro]

I have secured at no cost to me a couple of solar panels that were the power for a Weed Eater VIP Robotic Solar Mower that I believe was sold for a short time around 1995 and sold for around $2000. The panels came from a local hardware store that I work at part time and appear to have never been used as a mower. As in the picture below the back of the panels are covered in foam and I have not been able to locate any specs or other information on the solar panels. The individual solar cells that make the panels are 4" x 4" and have 17 per panel.




I did an open circuit voltage test in a filtered sun (its been foggy and cloudy all week in eastern NC) and got 8.2 volts. How would I go about matching a suitable controller for these panels without knowing any specs on expected output? I have been looking at a Morningstar SS-6-12V as I can get one delivered under 50 bucks but I'm not sure if that might be a good choice or are there other controllers that might be more suitable.

[brian_bp]

At 8.2V open circuit (although not in the most intense sun), I assume that the two panels will be combined in series to get a suitable charging voltage.

With 544 square inches of cells (in two panels, if I did the math right) the total capacity might be around 30W peak, with a peak current of perhaps 2 amps. Just about any controller has the capacity for this output and will work... so it seems like a matter of picking one which is not excessively large, and deciding how much to pay for nice features.

The Morningstar SunSaver SS-6-12V is 6 amp (lots) and 12V (correct for the battery, assuming the usual 12V battery) PWM model - a big step better than my basic on/off controller.

The SS-6L-12V model would add the "LVD" feature, which is a low-voltage disconnect for the load: it disconnects loads from the battery if the battery voltage goes too low. That doesn't really have anything to do with controlling the charging of the battery by the panel, but is a possibly valuable battery-protection convenience feature.

For more features, the Morningstar SunSaverMPPT is a maximum power point tracking design, which would get some more power out of the panels, for increased controller cost.