Hi all, this is mostly a continuation of CD's solar battery charger thread. I was thinking of using a power zener as a shunt reference... but this has some problems. I think #1 is that as the zener sucks up the power it will warm and go up in voltage... which is exactly the opposite of what I want. So how about a zener turning on a power npn. I think someone mentioned this idea in the previous thread, but I couldn't find it in a quick rescan. Maybe the TL431? Anyway I drew this,
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npn across the rails, with base feed by zener and some series diodes and maybe led and ?10 ohm base R. Then two or three diodes from base to emitter to protect b-e when it turns on. And maybe a collector resistor. ~50 ohms 3-5 watts I'd like the shunt to turn on at 13.5 Volts at room temp. with a negative tempco.. less voltage at high temp. I'd like some knob (pot) to tweak the voltage. I was thinking if I used diode connected transistor (as part of diode chain) I could put a little bit of R in the c-b connection... that seems like a beta dependent tweak. Which might be OK if beta goes down as the temperature goes up.
Oh boy, I think I'm liking the Darlington idea. On hot sunny days, I want this to reduce the float voltage...with D's, I've got two b-e voltages going down with temperature increase of the pass element. (one man's thermal runaway is another's control :^) George H.
That tempco is kind of accidental, but maybe you can make it work. I'd suggest a more deliberate circuit, maybe like my bang-bang thing, with a proper temperature sensor.
Seems like overkill, though. How about a solar panel and a diode?
There's three phases to be considered: firstly, if the battery is not fully charged, is the unlimited current into the terminals (assuming a solar cell source won't need limiting) phase. Second, when the battery reaches full charge, change to a 'float' constant-voltage-limited state. Third, every night will interrupt the solar power source, so a low-drain 'wait' phase will interrupt charging.
The 'float' state is to be entered when the (possibly temperature-dependent) fully-charged voltage threshold is detected, and occasionally re-checked during solar-power interruptions (once a day is often enough, so that's easy).
For an indicator, I'd like to see a moving-needle meter, with 10-15V expanded scale, which will only cost a few microamps (a photographer's light meter only has a few cm^2 of solar-cell to run it).
I dislike the power zener idea, because it could fail shorted, and it can be more expensive than, say, an eight-pin microcontroller.
A full, elaborate system would include a switchmode for low-solar-cell voltage boost charging, and an ambient temperature sensor. And, a minimal system is just a solar cell with backflow-prevention diode.
Oh I bought and tested a solar panel... it needs a voltage clamp... or a bang-bang switch thing... that's how my 2 amp charger works bangs between 12.9 and 14.2 V Oh could also make a with opamp and pass element. (I think that was your first circuit.. with optional hysteresis)
So I got my small riding lawn mower battery... ~1/3 the size of a car one. I fully charged it. And then hooked it up to the solar panel. It got to 14.4 V (at ~100mA or so) and I stopped. It's possible this panel would work fine with a bigger battery. Most the batteries I'll be charging are not attached to modern cars. There is no drainage (except internal), till I turn the key/switch.
George H. I'm going to try the zener thing.. I still need a voltage tweak. ~300mV or so. (+/- one Schotkky)
You do you. But thanks. This is only the float charge... ~13.5 V According to Bat. U. it needs less temperature dependence. (Max I for panel is 200mA.)
"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."
Maybe, maybe not; my old bike light used an alternator to charge the lead-acid
6V battery, and the first battery lasted over a decade, though the rectifier was a voltage doubler (12V nominal output). While the bike's moving, the battery cools just fine.
A 1 square foot solar panel generates as much electric power as the heat of a 3x3 inch bit of direct sunlight onto the battery. Free air may suffice to keep it cool.
Current, after it performs the charging chemisrty, evolves hydrogen and oxygen and blows up batteries. Modern SLAs have catalysts to recombine modest amounts of gas back to water, and a relief valve for extreme cases. That's why we don't have to keep adding water like we used to.
A small current, around enough to overcome self-discharge, won't hurt a good battery.
It's basic that a small solar panel can't make much power. Power cooks things, not voltage.
Yup, but you'd be surprised how much power these solar panels can generate. The one I have is only A4 size, but if orientated correctly will supply 10W on a sunny day. And with a Voc of nearly 22V. If you leave that connected with one rectifier diode on a "fit and forget" basis, it *will* cook the battery in short order. I think it's just semantics over the exact meaning of "cook" which seems to be the issue here.
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"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."
BTW, I breadboarded your design today and it looks promising. Cheers! --
"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."
On Saturday, 6 March 2021 at 19:12:21 UTC-8, snipped-for-privacy@highlandsniptechnology.com wrote: ...
... Not quite true - in both lithium-ion and lead-acid battery chemistries higher terminal voltage causes unwanted chemical reactions that don't occur at the same power level when the battery terminal voltage is lower.
Lithium-ion in particular is very sensitive to overcharge, even storage at high SoC activates irreversible side reactions.
Semantics again. I'm not talking about 'cooking' it thermally but rather 'boiling' the electrolyte. Cue big argument over the exact meaning of "boiling" in this context. ;-)
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"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."
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