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Author Topic: Battery recharger for Alkaline cells (AA / AAA)  (Read 418 times)

sheddyian

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Battery recharger for Alkaline cells (AA / AAA)
« on: September 07, 2017, 11:46:46 PM »

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

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burakkucat

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Re: Battery recharger for Alkaline cells (AA / AAA)
« Reply #1 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).
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sheddyian

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Re: Battery recharger for Alkaline cells (AA / AAA)
« Reply #2 on: September 08, 2017, 12:25:03 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).

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
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tickmike

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Re: Battery recharger for Alkaline cells (AA / AAA)
« Reply #3 on: September 08, 2017, 10:38:41 PM »

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).
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:


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sevenlayermuddle

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Re: Battery recharger for Alkaline cells (AA / AAA)
« Reply #4 on: September 08, 2017, 11:07:43 PM »

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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sheddyian

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Re: Battery recharger for Alkaline cells (AA / AAA)
« Reply #5 on: September 09, 2017, 10:20:22 AM »

It's a commercially available charger, branded "Watts Clever" that claims to safely recharge Alkaline cells - so I'm not just connecting Alakalines to my power supply and hoping for the best  :-X

I concurr with the point about cost - when rechargables were expensive (and lower capacity) I think this option made more sense.  With good quality (eg Eneloop) Ni-Mh cells holding 2500mAh or more, and keeping their charge for a long time, there's much less of a need for recharging Alkalines.

That said, I've had some pleasing results of boosting near-dead cells (some I'm still using, eg the bathroom lamp) but I've also had some leak on me afterwards.  No explosions (yet).

Ian
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sevenlayermuddle

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Re: Battery recharger for Alkaline cells (AA / AAA)
« Reply #6 on: September 09, 2017, 06:53:29 PM »

Nit-picking perhaps, but the fact it is commercially available does not mean it is safe.   I can think of several products that are available, some made by big brands, yet I remain unconvinced by their safety.   It does however mean you have somebody else to blame if things go wrong, which is always nice to know.

If you don't mind me deviating off topic, the latest thing to worry me is led light bulbs.   They run much cooler and so, compared to indandescents,  the theory goes, not much risk of setting fire to the lampshades.  But they also contain various small electronic components that can occasionally fail, and failure mode may involve a small flame.   These LED bulbs are enclosed in a plastic (not glass) 'globe' which in turn catches alight, dripping burning plastic onto whatever sofa/carpet/bedspread lies beneath.   I believe they have been identified as the cause in a fair number of serious house fires.  I do still use led bulbs, but I'm more careful about making sure they are not left on when unattended. :o

Apols for deviating, if it annoys you I'll happily edit. :)
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sheddyian

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Re: Battery recharger for Alkaline cells (AA / AAA)
« Reply #7 on: September 09, 2017, 11:47:51 PM »

It's an interesting deviation of discussion.

LEDs run cooler = less fire risk
But contain circuitry that can fail = potential fire risk
plastic globe dripping melting plastic

I agree with 1st point, hard not to agree.
2nd point .. well, that could apply to any circuit anywhere, couldn't it?  Your phone, your TV, your microwave oven, your modern toaster.  How often do they catch fire?
3rd point, re melting plastic - if it's built to current EU standards, then it shouldn't and MUSN'T do this.  Any plastic enclosure should be self-extinguishing; it should not sustain fire.

That's not to say dangerous non-compliant LED lamps don't exist; but those made under an EN or EU standard ought to be safe under normal usage.

Basically, buy wisely and don't believe all the nonsense you read in newspapers :)

Ian


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sevenlayermuddle

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Re: Battery recharger for Alkaline cells (AA / AAA)
« Reply #8 on: September 10, 2017, 12:03:36 AM »

My phone, like my microwave oven and my TV, all sit on MDF benches.   Half inch thick  MDF may combust, but it would take more than a lick of flame from an overheated resistor, so I do not worry.

In contrast, an LED bulb might be suspended over soft furnishing which obviously, might easily be ignited.   If you trust politicians who are supposed to govern safety standards, be they EU, UK, US, whatever then all is well, you have nothing to fear.  Personally I prefer to make my own assessments.    :)
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