Passive Car Battery Trickle Charger

How big is the panel?

On a UK February day and a nominal 12W panel you would be lucky to put more than a couple of Ah into the battery even on a good day. Mid summer you might need to stop charging once the battery voltage gets too high. Adding 8Ah every day might be a bit too much even for a lead acid cell.

Most lead acid batteries can tolerate trickle charge rates of C/100 almost indefinitely.

--
Regards, 
Martin Brown
Reply to
Martin Brown
Loading thread data ...

There are 36 cells in series and they are silicon technology, so that would indicate a battery voltage of 0.6 x 36 = 21.6v would be needed in order to pass any significant forward current through them. I tested up to 20v and got no more than a few milliamps; perhaps there would have been a sudden increase if I had tested to a higher voltage. With a simple direct 12v system, there is no need for a diode at all as long as there is a sufficient number of cells in series.

If you start installing a control unit to optimise the energy transfer or to control the charging rate, then there is a definite need for a diode to prevent the control circuitry from loading the battery during darkness and to protect the control elements from reverse voltages. I also take the point from the other contributors: the diode which was already installed was probably to give continuity for series-connected panels.

I've tested the panel this morning to see how it responds to dull, murky overcast conditions. Laid horizontally inside the van above the dashboard, parked facing away from the sun direction and in an allyway between two two-storey buildings, it gave 16.5v off-load. That means that for any reasonable level of daylight, it definitely isn't going to be draining the battery and may possibly be contributing a small charging current.

--
~ Liz Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
 Click to see the full signature
Reply to
Liz Tuddenham

[Editor's hat on.]

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.

[Editor's hat off.]
--
~ Liz Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
 Click to see the full signature
Reply to
Liz Tuddenham

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

--
~ Liz Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
 Click to see the full signature
Reply to
Liz Tuddenham

te:

bit

ely

or

't

s
e

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.

--
Bill Sloman, Sydney
Reply to
Bill Sloman

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.

--
~ Liz Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
 Click to see the full signature
Reply to
Liz Tuddenham

for

wasn't

vious

n the

,

SW

ed

rs

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.

--
Bill Sloman, Sydney
Reply to
Bill Sloman

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.

Reply to
George Herold

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.

--
Regards, 
Martin Brown
Reply to
Martin Brown

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!

--
~ Liz Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
 Click to see the full signature
Reply to
Liz Tuddenham

e

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

Reply to
three_jeeps

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.

--
John Larkin      Highland Technology, Inc 

The best designs are necessarily accidental.
 Click to see the full signature
Reply to
jlarkin

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...

10 pn diodes would give you about -20mV and then...? A diode connected transistor is about twice the tempco of a 'normal' diode. So how about 6 (or so) transistors and a 3 watt zener picked to give a reasonable voltage...

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

Reply to
George Herold

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

Reply to
John S

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

Reply to
Cursitor Doom

'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

Reply to
Cursitor Doom

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

1995, so more of the cars that I have dealt with have had much heavier gauge exhaust systems (and longer ones fin many cases as well). Alternators generally don't give remotely near their full output until they reach at least 2K RPM, with wide error bars on that figure, and during the time from which I draw my direct experience more than a few of them didn't produce enough at actual idle (700-900 RPM) to charge in anything like 10 minutes, depending on the level of discharge. Fast idle, though, would significantly change that situation if you live somewhere cool enough for the engine to idle faster. I almost said 'engage the choke', but that was mostly over even when I was finishing up working on them. I've had to boost any number of batteries where they had been left idling for extensive periods of time and they didn't have enough left for a cold start afterward. Usually on big Detroit Iron, they had terrible alternators at low speeds. As I recall, the newer alternators do a better job of charging at lower RPMs than the older ones, and since the computer on the current generation monitors the voltage, it can increase the idle speed to quickly charge up the battery. I had thought we were talking about older collectable cars and trickle-charging and such anyway, I wasn't originally even thinking about newer ones.

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

Reply to
Gone Postal

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

Reply to
Cursitor Doom

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.

Reply to
bitrex

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

Reply to
Cursitor Doom

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.