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Battery recharger for Alkaline cells (AA / AAA)
sheddyian:
Not a great deal of sheddy activity here recently, for those who know me, but thought I'd mention this bit of tinkering.
Late last year I got (mostly out of curiosity) a battery charger that claims to recharge alkaline cells. It can accept AA and AAA cells.
I was a bit sceptical (partly why I got it) but it's... well, not bad, with caveats. Recharging is probably the wrong word to use here, it's maybe better to describe the unit as rejuvenating alkaline cells.
The more discharged your alkaline cells are, the less you'll be able to rejuvenate them.
(from experience) some cells will start leaking after you've charged them; it may not be apparent for a few days.
Some cells won't charge at all, even if they're not completely dead.
I had a wheeze where I thought I'd get free cells from the recycling points in most supermarkets. I helped myself to a few handfuls of old (and sometimes already leaky) cells from there.
Some of them did recharge/rejuvenate.
More surprisingly, some of them weren't very flat to begin with. People seem to throw out quite reasonable cells that just work with no problems.
To reduce the risk of cells leaking into equipment after rejuvenating, I test the cell beforehand, put it in the charger, test it afterwards (if it's not improved much it gets sent to the recycling). If it's taken a charge, it gets put in a cardboard box for a week or so. After that rest, if it's not started leaking, it's probably ok, so goes to the "good" pile after one final test on a battery tester.
Ian
burakkucat:
Interesting. Hmm . . . :hmm:
I remember from many years ago (probably late 1960s or very early 1970s) when the concept of "dirty DC" recharging/rejuvenating of primary cells was described in one of the popular (i.e. mass-market) electronics magazines of the time. It was, basically, a very simple concept . . . just a half-wave rectifier shunted with a suitable value wire-wound resistor. Looking via an oscilloscope it appeared as an AC current with a DC offset -- similar to the "ringing" current of the PSTN (but without the cadences).
sheddyian:
--- Quote from: burakkucat on September 08, 2017, 12:07:20 AM ---Interesting. Hmm . . . :hmm:
I remember from many years ago (probably late 1960s or very early 1970s) when the concept of "dirty DC" recharging/rejuvenating of primary cells was described in one of the popular (i.e. mass-market) electronics magazines of the time. It was, basically, a very simple concept . . . just a half-wave rectifier shunted with a suitable value wire-wound resistor. Looking via an oscilloscope it appeared as an AC current with a DC offset -- similar to the "ringing" current of the PSTN (but without the cadences).
--- End quote ---
I don't know the mechanism involved here, sadly. I can vouch that it works (up to a point). example :
I have a battery operated PIR light over the basin in the bathroom. If you just want to wash your hands when it's dark, it's enough to see by - it switches on when it detects movement. It's LED, but as it's running the PIR and light sensor all the time, it runs down every 3 or 4 months and needs new batteries. It had stopped working because the batteries were flat. I put them in the rejuvenation for a few hours until complete, put them back in the light and it lit up brilliantly. I've since repeated this once more. Still working.
Testing cells before and after usually shows a reasonable increase in cell voltage (and those that don't show this I put into recycling).
Ian
tickmike:
--- Quote from: burakkucat on September 08, 2017, 12:07:20 AM ---Interesting. Hmm . . . :hmm:
I remember from many years ago (probably late 1960s or very early 1970s) when the concept of "dirty DC" recharging/rejuvenating of primary cells was described in one of the popular (i.e. mass-market) electronics magazines of the time. It was, basically, a very simple concept . . . just a half-wave rectifier shunted with a suitable value wire-wound resistor. Looking via an oscilloscope it appeared as an AC current with a DC offset -- similar to the "ringing" current of the PSTN (but without the cadences).
--- End quote ---
I tried that before the price of re-chargeable batteries come down, seemed to work ok but you have to watch how much current you put through them or there might be a loud bang. :lol:
sevenlayermuddle:
I'm honestly not sure of the physics behind recharging a non rechargeable cell. It might appear to work, but is it dangerous? I simply do not know, but I'd recommend suitable research before trying it out.
Not quite the same, but in terms of 'theoretical risks'... I once accidentally connected a small tantalum electrolytic to a 6V supply from 4 AA cells, with wrong polarity. That carries a theoretical risk of explosion, so what happened? Within a few seconds there was a column of smoke. By the time I'd focussed on it, and just about had time to think "Ah, wrong polarity" there was a 'pop' and a substantial flame, leaping from the capacitor.
If you have done the research, and satisfied yourself it is safe, then fair do's, it is an interesting experiment. :)
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