I seem to get into a pattern with my Suncontrol board, and I don't like it.
Let's assume the battery powers my setup successfully through the night, with about 35% capacity left at sunrise. Temperatures are below freezing. Thermistor is connected to the board and sitting next to the battery.
As soon as the solar panels catch the first sun the solar input light and the charging light (red and yellow) come on. Shortly thereafter the green light comes on as well, and the USB output gets cut off. I can only get it to switch on again by unplugging the solar cells from the board and then cycling the output switch.
It's as if the board tries to start charging and then realizes it's too cold to charge, and instead of just stopping the charging it shuts the output down as well.
My expectation would be that the output would stay on as long as the battery voltage is above the threshold (seems to be 3.43V for my case) regardless of what the charging circuitry is up to. (The attached chart mentions "capacity" - I define 4.10V as 100%, and 3.43V as 0%. Crude, but works for me. "Contribution" is the amount of wattage supplied by the solar panel compared to the wattage consumed by the load)
Two solar panels in parallel, with 10 1W zener diodes 6.2V across the leads (to be replaced by a single 10W diode).
Same issue when using only one panel.
Would be happy to get suggestions on how to avoid that morning shutdown if possible.
Last Edit: Dec 12, 2018 7:23:47 GMT -8 by lbendlin
Interesting question and problem. We haven't seen that, but we don't normally operate with the thermistor installed, so we haven't seen that.
The only way the USB would shut off if the battery voltage goes below about 3.4-3.5V (3.43V sounds good) Something in your system is pulling the voltage down below that threshold, guaranteed (or at least very likely).
As just an idea, adding a 1000uF cap on the Solar Panels (there are holes for it on the board), might stabilize this problem. It sounds like a pulse of noise coming from somewhere that jerks the battery voltage down.
I don't understand the right side y axis on your graph. What is that?
If you can, send a voltage curve rather than your approximated capacity. We use a similar estimate for battery capacity.
I eliminated the thermistor as well as the Zener bank as the source for that behavior. Even with both out of the equation I still see the yellow AND green LED lit and USB output off whenever the solar panel is plugged in. I think I may have just fried the charging circuit with my pre-Zener experiments. I have ordered a new board. If that doesn't fix it then the whole setup goes back into the bin...
the right side axis shows "Contribution" - the amount of wattage supplied by the solar panel compared to the wattage consumed by the load. If the solar cell provides the same energy that the load consumes this will be 1 (ignoring the amount of waste produced by the circuit, as well as the battery current flow direction). As I mentioned, crude. But you can see that at times of good insolation the panel produces roughly 8x the amount of energy that's needed by the load.
I replaced the Suncontrol board and haven't seen that behavior any more, however I now also have a single 10W Zener and your solar panel balancer board. Plus, we're officially at the worst possible time for insolation (solstice etc) so I can only really say for sure once we see the sun again for appreciable amounts of time. Fingers crossed...
It looks like that on the picture but is pretty small IRL. I'd say 8mm in diameter.
From what I read about Zeners with the bank of 10 you always have the risk that they don't have the exact same characteristics, and that the weakest of the bunch has to carry the brunt of the current (and might fry?). No such danger with a single diode.