Passive Car Battery Trickle Charger

The rule is to print the expression in full the first time you use it, then abbreviate it, if necessary, after that. Also, abbreviations should have full stops between the words to indicate that they are abbreviations.

As long as you can get at the cells to top them up.

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Agreed. I'm putting together the March issue of the newsletter of rhe NSW b ranch of the IEEE at the moment - not that I've got many of the promised ar ticles yet - and my editors hat is near to hand. It will be my nineteenth i f it ever gets out, and with any luck one of the contributors will get cros s enough with me to volunteer to take over the job.

With a deadline approaching, I've been known to write the contributor's article myself and e-mail it to him with a note asking if this is what he would have said, if he had ever got around to it.

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Not an option with my contributors. It's mostly about what their particular chapter did. The only article I've got so far by a relatively young profes sor reporting a presentation about adding in-band signalling to low voltage DC distribution set-ups, and included the usual references to the Internet of Things.

Hmm OK, I'm not sure why I was worried about reverse voltage. Well I've got a panel on the way, so playing with it will help get my head straight. With just a little bit of light, can the panel discharge the battery? Every site I find says you need a blocking diode to stop the panel from draining the battery over night. (There is also talk of bypass diodes.)

George H.

I can't see a panel that can only source 600mA under optimum conditions ever really frying a 40Ah battery in the UK. It might make it lose some electrolyte from overcharging after a while though. C/100 is ~400mA.

The simplest and cheapest scheme that would probably be good enough would be something like a chain of 6x cheap 1A rated diodes in series with a 0R2 resistor and also with a trickle charging bleeder of 100R across 5 of the diodes. That way it always replaces current used by vehicle electronics (assuming a nominal 15mA continuous average load as a typical value).

The PV output can only supply diminishing current as the battery approaches its fully charged state. The other simple linear approach would be a voltage follower hung off a 14.1 or 14.3 zener diode.

I get the impression that most PV top up chargers just rely on a single diode to prevent reverse leakage discharge and the intrinsically high source impedance of the PV panel to limit short circuit current.

UK simply isn't sunny enough for over charging to be much of an issue.

If there aren't enough cells in series, that is a possibility, but with a 36-cell panel on a 12v battery I can't see what mechanism would cause that to happen. If there are fancy controllers connected to these systems, it could be the controller electronics that draw a lot of current.

I might install a simple indicator circuit that includes a diode, so that the volts dropped across the diode can be used to turn on a LED to let me know that charging current is actually flowing. It would all have to be small enough to fit inside an IEC plug body.

My van has a pair of 12v batteries in parallel, giving a total of 140 AH capacity, so if there is a mechanism that could discharge that lot overnight, I'm going to find some evidence of it pretty quickly!

e,

Late to the party and looks like a lot of other ppl have contributed. If you are looking for more fun, perhaps a design aimed at high-efficiency charging? Some years ago, I did a design based on maximum power point tracking charge controlling. First design used a TI MPS430 and a LT8490 buck boost regula tor. Another approach used a NXP MPT612 SoC. Yes, overkill for what you p robably want but I wanted something the provide an efficient charging and k eeping within charging guidelines for specific mfg batteries. Have fun

Don't sealed lead-acid betteries tolerate mild overcharging? They catalyze the hydrogen back to water or something.

The solar panel and a diode should be fine.

Oh an 'array' of diodes and R's as I(V) current limits.. that's fun. The thing I don't like about a current limit, is I've got 12V batteries of various sizes. ATVs and lawn mowers to trucks and tractors.

OK but for extra points you have to match the TC of the battery.. about -3mV/C (per cell) (Bat. Univ.. link above) So -18mV/C.... plus the series diode another -2mV. So -20 mV/C on the zener voltage ref side. Hmm...

George H. (Hmm does the tempco of the solar panel help? less voltage when it's hot.)

Yes, because it is a series string of diodes with the anode producing the + output. Therefore, as it heats up, the voltage drops.

Depends entirely where you are. If you're in the south east of England you have (or *had* until Covid) a layer of air polution in the sky which markedly attenuates the brightness of the sun. You will get far brighter sunlight in places like West Wales and N. West Scotland than you do in London.

--

"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

'fraid I've used every single one of those zeners up already. None to spare so it'll have to be the 5v regs which fortunately I have dozens of and rarely use anyway. --

"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

Yikes! My comment was solely intended as a reminder, not a proclamation or the final word! My information maybe rather dated, I was a auto mechanic until

Sorry I'm so terribly wordy and tend toward lecturing, I'm sort of obsessive that way and don't mean to be an ass.

Ray

Shame you don't, Bill! Like most folks here I could well do without the kind of 'help' you dish out. :-D

--

"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

Boosting is the only reasonable way to charge up a battery that's deeply discharged

A late-model car that doesn't come up within about a second of the engine-start command (keys are going away with the snows of yesterday...) has got something wrong with it I think.

In any event, the handful of mA that the panel sucks back off the battery in the hours of darkness is *dwarfed* by the quiescent current drain due to the typical car's immobiliser/sensors and whatnot (300mA typically IME). I like the old classic cars which don't drain anything when parked, other than what goes on inside the battery itself of course - but that's negligible.

--

"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 panel I used as the basis for this experiment is A4 sized and passes 5mA 'leakage current' in total darkness when in situ. A small amount compared to the 3rd of an amp or so the car's systems consume when parked up with the immobiliser and whatnot continuing to drain the battery for what might be an extended period (and typically is highly extended in my own circumstances). Measure yours when it arrives and let us know what kind of drain you get? --

"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