More battery charger, voltage shunt reference.

Voc is not useful. 10W is how much it will supply at noon on the equator on a clear day. If you connect it to a 12V battery, it will not deliver

10W because 12V is below the mpp of the panel.

I encourage you to put the panel and battery outside on your best sunny day and measure the current into the battery. Then multiply the current times voltage and see how much power the panel is delivering.

"For a few hours a day" is not the same as "fit and forget" though, John! The experience I had with the HD Land Rover battery was due to me fitting and forgetting the A4 size panel with only an inline diode. --

"Andrey Semyonovitch really was rather stupid; he attached himself to the progressive cause and 'our younger generation' from enthusiasm. He was one of the numerous and varied legion of dullards, of half-animate abortions, conceited, half-educated coxcombs who attach themselves to the idea most in fashion, only to vulgarise it and who caricature every cause they serve, however sincerely."

- Fyodor Dostoevsky

I wanted to and normally would have, but for some curious reason I'm unable to run LTSpice on the box I'm currently using. The O/S really doesn't likws client, hence I'm having to use an ancient version of Free Agent for news - a bit galling when I have the latest paid-for version. :( I'm using a one meg for the feeback resistor; seems to work fine with that value. I initially tried using the first resistor I could find:

68k but that didn't go down well at all, probably due to me uisng a 200k variable in place of the pair you showed on the battery's side of the diagram for breadboarding convenience (although I think I'll run with a variable/preset one for the final version - probably inserted between two fixed resistors to narrow the adjustment range down to something more sensible.) It's a better solution than the one I came up with that would have ended up with over 40 diodes used up. :)

--

"Andrey Semyonovitch really was rather stupid; he attached himself to the progressive cause and 'our younger generation' from enthusiasm. He was one of the numerous and varied legion of dullards, of half-animate abortions, conceited, half-educated coxcombs who attach themselves to the idea most in fashion, only to vulgarise it and who caricature every cause they serve, however sincerely."

- Fyodor Dostoevsky

The size of the battery (A-Hours) being charged compared to the solar panel matter here. Assuming there is sun of course.

It isn't the power input that does the harm it is driving the terminal voltage above some absolute threshold that makes cell gassing much more profuse. I'm not convinced that toy solar panels can even do that.

But I was taken aback by the very high open circuit output from mine even in cloudy skies it was 22.6v peak voltage and 15mA output shorted.

CD is being imprecise when he says cook. I'm not at all convinced that the sort sold for topping up car batteries can really do them any harm. In winter mine can only increase the time between needing to put the battery of the (presently) unused car on charge. In summer it works.

Mine could in theory manage peak 1A charge rate if perfectly aligned to the sun tapering off with cos(theta) for any misalignment. I can't see it really bothering a 40Ah car battery except maybe in the tropics.

It probably does make sense to have something to take the edge off the peak current forced through a fully charged SLA though. Relying on the catalyst to sort things out will lead to premature failure.

It is excessive cell potential that does the damage when you are forcing more current through an already fully charged unit.

The algorithm for this is very simple: If the battery voltage goes above

13.5V, break the path between panel and battery. If the battery goes below 13.5V, connect the path between panel and battery. Your choice on the amount of hysteresis. The smaller the hysteresis, the more frequently the switch opens/closes.

This is the idea behind JL's bang-bang controller. It is inherently stable. I have used bang-bang controllers in certain applications since the early 1960's.

JL might be persuaded to produce a spice schematic for simulation if he is asked politely.

Right I was looking for a means to tweak the 13.5 Volts... I've got a string of a zener and several diode drops. (The diode string is for thermal compensation... reduce voltage at higher temperatures.) More or less R in the string should do the trick.

I understand JL's idea. It doesn't have to be bang-bang, a controlled pass element would do. (Since this is not high current) I should try that way also...

George h.

Yeah I don't need that... I was trying to do this w/o the opamp... show my awesome transistor level design skills. :^) (that last bit is meant to be irony.) George H.

Er, it's not a "toy" panel and neither was it marketed for keeping car batteries topped-up. I know the sort you mean, but mine's got a lot more 'grunt' behind it. Cue argument on the precise meaning of "grunt" in this context. A lot of elastic terms in use here: grunt, boil, cook, fry.... :-) --

"Andrey Semyonovitch really was rather stupid; he attached himself to the progressive cause and 'our younger generation' from enthusiasm. He was one of the numerous and varied legion of dullards, of half-animate abortions, conceited, half-educated coxcombs who attach themselves to the idea most in fashion, only to vulgarise it and who caricature every cause they serve, however sincerely."

- Fyodor Dostoevsky

JL's design does allow for tweaking. All you need do is replace the two fixed resistors on the battery side of the diagram with a variable or preset resistor of some sort, with the wiper going off to the op-amp input. Obvs there's a lot of energy lurking about in that area, so I'd stick a fuse inline to the battery+ terminal, perhaps in series with a diode to deal with reverse polarity connections, shorts and so on. --

"Andrey Semyonovitch really was rather stupid; he attached himself to the progressive cause and 'our younger generation' from enthusiasm. He was one of the numerous and varied legion of dullards, of half-animate abortions, conceited, half-educated coxcombs who attach themselves to the idea most in fashion, only to vulgarise it and who caricature every cause they serve, however sincerely."

- Fyodor Dostoevsky

Anybody can do that.

Prove it.

You could do it for yourself in about 5 minutes flat! I assume you ARE familiar with Spice? I've been using it for *years* and I'm just a hobbyist. --

"Andrey Semyonovitch really was rather stupid; he attached himself to the progressive cause and 'our younger generation' from enthusiasm. He was one of the numerous and varied legion of dullards, of half-animate abortions, conceited, half-educated coxcombs who attach themselves to the idea most in fashion, only to vulgarise it and who caricature every cause they serve, however sincerely."

- Fyodor Dostoevsky

What, you can't?

I can do it, but not in 5 minutes. How do you simulate a solar cell? How do you simulate a battery? The battery is easier, just a voltage source with internal impedance and an internal "capacitance" (or time constant).

Hey, I invested several minutes of my incredibly valuable time to scribble and photograph and post that schematic. Almost over-cooked the bread pudding. I've done my share.

Please show me. It won't take you more than about 5 minutes and I would be very interested in how you create a solar panel source as well as a battery load.

Good excuse, chicken.

I've done it before but I would love to see your approach to simulating the solar panel and battery.

But it's child's play, man! You're not stupid so you're trolling, right? As I said to John earlier up the thread, I'm unable to Spice anything currently due to O/S incompatibilities. Just model the battery as you described with a low internal resistance and the solar cell you can set as a voltage source to sweep from 0 to 22V. Someone else here posted the typical closed circuit current of these panels. Check it out it's a cake-walk. --

"Andrey Semyonovitch really was rather stupid; he attached himself to the progressive cause and 'our younger generation' from enthusiasm. He was one of the numerous and varied legion of dullards, of half-animate abortions, conceited, half-educated coxcombs who attach themselves to the idea most in fashion, only to vulgarise it and who caricature every cause they serve, however sincerely."

- Fyodor Dostoevsky