Passive Car Battery Trickle Charger

Cursitor Doom · 2021-02-28T12:11:00+00:00

Gentlemen,When you don't drive much any more it's handy to keep a battery toppedup so you don't find it flat on those infrequent trips to the shopsand whatnot. Something that can be fitted and forgotten and requiresonly sunlight for power. Here's what I've come up with so far; justwondering if I've overlooked anything.... I'm not a designer and it shows; I know that. -- "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

Feb 28, 2021 Last reply: 5 years ago 173 Replies

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Liz Tuddenham 5 years ago

I've made up a little 'confidence' indicator circuit:

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The voltage drop across the 1N5001 is sufficient to turn on the transistor whenever a current of more than about 100mA is flowing. The green LED indicates that a) the panel is sufficiently illuminated and b) it really is connected to the battery, rather than just generating enough voltage but perhaps disconnected without the user knowing.

The dark reverse current is around 1mA and it all fits inside a (slightly butchered) IEC connector.

~ Liz Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk

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George Herold 5 years ago

I could measure no leakage current... I put a 1 k ohm R in series with panel and 12V battery. On the 200mV scale it read -000.01(0) maybe 10 uV... 10nA. This was at room temperature I think it should leak more if it's blazing hot out. (should I stick it in the oven?)

It's not at all clear to me that the ~200mA max current can hurt my smaller batteries... but I'm going to make a voltage limit with a 5W zener and some other diodes/ transistors... Maybe with a series Schottky

George H.

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Liz Tuddenham 5 years ago

With the older batteries that had inspection holes, the excess energy was dissipated splitting up the water into hydrogen and oxygen. A battery left on prolonged trickle charge would need to be checked and topped up from time to time.

Modern batteries don't have antimony in the lead grids, so gassing doesn't occur below the voltage corresponding to fully charged. That means that as long as the maximum charging voltage is strictly limited, there should be no gassing or water loss throughout the battery's lifetime. In turn, that means the manufacturers no longer need to provide any way of checking the individual cell and topping up the lost water.

If you put them on a trickle charge that leads to a rise in cell voltage and gassing, no matter how gentle, they will eventually 'boil dry' and fail. There is nothing equivalent to the gas recombination action of sealed nickel-cadmium cells which would protect lead-acid batteries against water loss; even sealed lead-acid batteries have strict limits on charging voltage.

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bitrex 5 years ago

The shortest route from western Michigan where my cousin lives to Rhode Island cuts through Canada, nice trip prior to Covid when they let you do that. Cuts a 14 hour drive down to just over 12

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George Herold 5 years ago

Great, so what's the maximum charging voltage? I've got a AC powered charger. On the 10A range it cycles between 14.2 and 12.9V. (When the battery is charged.) I'm checking the 2A range. It's about the same. I don't think my 0.2A panel can get it above 13 volts. (This is charging the smallest lawn mower battery.)

George H.

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