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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 17th Jun 2020, 6:06 pm   #1
G6Tanuki
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Default NiMH cells - good and bad.

I get through quite a few NiMH AA cells: everything seems to use them. Testgear, small portable-radios, VHF/UHF walkie-talkies, calculators, cameras, wireless-headsets, GPS units, the Ferret-finder, my wireless keyboard/mouse....

Over the years I've tried different brands/capacities. It seems that the lower-capacity ones will handle a lot more charge/discharge cycles than the higher-capacity ones.

In a way this balances itself out because the lower-capacity ones _need_ more charge/discharge cycles to deliver the same number of Coulombs to their working-load.

In the photo you see some upright Energizer 2000mAH cells (which seem OK) alongside some Uniross 1300mAH cells of two designs - the ones in the green cases must be at least 20 years old and are seemingly indestructible!

Lying down - dead - in front is an Energizer 2450mAH cell. I've found these to be desperately short-lived and would not buy any more of them.

I recently re-celled the battery-pack for my little Yaesu VX150 VHF radio with RS own-brand tagged 2000mAH cells, they replaced Yaesu's 20-year-old 700mAH cells. I could have spent more and got higher-capacity cells but my direct experience suggested that higher capacity would probably mean shorter life.

What brands/capacities have you had success - or failure - with? And in what applications?
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Old 17th Jun 2020, 8:22 pm   #2
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Default Re: NiMH cells - good and bad.

I've been buying "Tronic" branded AA & AAA rechargables from LIDL, some are now 20 months old, in regular use, licence free radios in the house, head torches, bedside world band radio. No failures yet, or reduced capacity, if anything they're lasting longer than when first used. About 3.99 for four, so doesn't take long to break even. Prefer regular alkalines in keyboards and mice.

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Old 17th Jun 2020, 8:30 pm   #3
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Default Re: NiMH cells - good and bad.

I've been using the Lidl 'Tronic' ones too. I've had them for several years with no failures - in fact, they don't seem to have deteriorated at all, though I'm expecting that to change as the charge cycle count increases. They are low self discharge. I use them in lots of things - everything from a garden radio to a beard trimmer.

I also use the Poundland ones, which seem OK but have very low capacity.
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Old 17th Jun 2020, 8:40 pm   #4
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Default Re: NiMH cells - good and bad.

Today, whilst charging my AA Eneloops I saw that one them was no longer taking a charge. I only bought them a few months ago and I've only recharged them once. I thought Eneloops were supposed to be good.
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Old 17th Jun 2020, 9:02 pm   #5
andrewn
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Default Re: NiMH cells - good and bad.

I've been using eight Kodak 750mAH AA cells in my r/c car transmitter. That is a very low capacity for a NIMH AA cell but they seem to hold their charge well. Normally the transmitter is used every week at a race meeting. Since lockdown has stopped the racing I haven't charged them for several months and they still have a good charge. The benefit of the low capacity is the light weight and I can conveniently use a plug-in 50mA charger. Previously with high capacity cells I had to remove the cells and charge four at time in a high-current charger.
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Old 17th Jun 2020, 11:30 pm   #6
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Default Re: NiMH cells - good and bad.

I think consumer NiMH cells all use low self discharge technology now. Eneloops pioneered this of course.
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Old 18th Jun 2020, 12:15 am   #7
Andrew B
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Default Re: NiMH cells - good and bad.

I have Lidl Tronic AA and AAA cells, not had one go duff or low capacity yet.
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Old 18th Jun 2020, 10:20 am   #8
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Default Re: NiMH cells - good and bad.

Ah, but what charger do you use?

I think that can make a big difference to their life.
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Old 18th Jun 2020, 10:45 am   #9
poppydog
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Default Re: NiMH cells - good and bad.

I have got 2 or 3 lidl rechargeable AAs here that are not good. The suspects seem to be fully charged before all the others that are on charge at the same time, and loose their charge a lot quicker than the rest when in use.
The rest of the lidl ones I have here have performed very well.

I have got a couple of those small AA/AAA Uniross intelligent chargers that I use to charge them with.

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Old 18th Jun 2020, 11:18 am   #10
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Default Re: NiMH cells - good and bad.

To be honest I have never had much luck with rechargeable batteries, they don't actually work in most of my kit, I suspect it's down to them being 1.2V rather than 1.5V. I found a pack of AAA rechargeables in the workshop the other day, I bought them a couple of months ago for something, then forgot about them, they had corroded and leaked terribly despite being brand new, iirc they came from Home Bargains.
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Old 18th Jun 2020, 7:16 pm   #11
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Default Re: NiMH cells - good and bad.

I repacked a couple of large batteries with rechargeable AA 2200mAH NiMH tagged batteries that I bought in 2001. They are still going strong today after multiple charges. They are used in a Roberts R707 which we use as our kitchen radio.

They are no-name green sleeved.

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Old 18th Jun 2020, 8:56 pm   #12
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Default Re: NiMH cells - good and bad.

Hi

It's well known that unused NiCd cells can go short circuit due to tin whiskers. I think the same can apply to NiMH cells too.
I have some new NiMH cells in AA and C sizes (new oldish stock actually) that appear to be SC. Would it be worth trying a capacitor discharge across them to clear the short? What's a suitable value electrolytic to use and at what sort of voltage? I was thinking of using a 1000uF electro with it charged to about 20V. Does that sound reasonable?

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Old 22nd Jun 2020, 5:17 pm   #13
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Default Re: NiMH cells - good and bad.

I also have been totally satisfied with the Tronic AA & AAA rechargeable cells - less so with the 6LR22 or whatever they are called today (9v PP3). My best ones of those have been Duracell.

With regard to charging, I have three different chargers. A Uniross "Wallwart" one, a Tronic fast charger and Nitecore Digicharger. I tend to only use the Tronic for 6LR22s because they are charged at a slow rate which I would feel happiest with. The Nitecore is my favourite, partly because it will charge AAs & AAAs at different rates.
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Old 22nd Jun 2020, 6:23 pm   #14
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Default Re: NiMH cells - good and bad.

Quote:
Originally Posted by Philips210 View Post
Hi It's well known that unused NiCd cells can go short circuit due to tin whiskers. I think the same can apply to NiMH cells too.
I have some new NiMH cells in AA and C sizes (new oldish stock actually) that appear to be SC. Would it be worth trying a capacitor discharge across them to clear the short? What's a suitable value electrolytic to use and at what sort of voltage? I was thinking of using a 1000uF electro with it charged to about 20V. Does that sound reasonable?
I don't think it's a *tin* whisker effect....

Someone I know who had a couple of the NiMH battery-packs for his 'professional' power-tools go 'a bit numb' as he put it - so he stuck a couple of wires stripped from 2.5mm T&E into the battery-pack connectors and 'flashed' them across a 24V tractor-battery.

it didn't make any difference. If anything it made things worse. Then I pointed-out the 3-year-warranty advertised for the particular brand of power-tools. A quick phone-call (during which the 'flashing' event remained discreetly un-discussed) and he got several new battery-packs delivered to his workplace the next day. They didn't even want the failed ones back.
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Old 23rd Jun 2020, 12:23 pm   #15
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Default Re: NiMH cells - good and bad.

Quote:
Originally Posted by G6Tanuki View Post

I don't think it's a *tin* whisker effect....
Hi,

I think you're right. I misunderstood the chemistry involved. Metal dendrites would have been a more apt statement.

I have successfully revived short circuit NiCd cells by zapping them with a charged electrolytic capacitor as in the case of clearing tin whiskers in AF1xx series transistors.
What I wondered was to try the same method on NiMH cells. Would it be safe to do so? Has anyone tried this method and was it successful?

Regards,
Symon
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Old 23rd Jun 2020, 10:22 pm   #16
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Default Re: NiMH cells - good and bad.

I'm looking in to this myself at the moment. For years I've a dozen or so NiMH AA cells lying around but no charger to use with them. I don't recall buying any of them so I've no idea where they came from, but they're various brands. I bought a little Ansmann smart charger which measures capacity and has a 'refresh' mode which will charge cycle cells until their capacity stops increasing, to rejuvenate old ones.

I only started investigating the old cells today, but the results are already interesting. A rather unambitious old 'GP' 1300mAh cell held 1150mAh on its first charge cycle, which amazed me. Less impressive was a glossy Ansmann 2100mAh cell which could only manage 359mAh before the charger gave up on it!

Bear in mind that these are all cells which have been lying in a box for at least 5 years.

Chris
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Old 24th Jun 2020, 1:09 am   #17
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Default Re: NiMH cells - good and bad.

I haven't bought any hydride cells recently, but have been looking a sub-C NiCds for a Bosch drill. There's factor of almost 4 between the cheapest and the most expensive. Is that true for NiMH? The original drill battery lasted 19 years and it's generic replacement is deteriorating after just 2 .

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Old 24th Jun 2020, 8:58 am   #18
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Default Re: NiMH cells - good and bad.

NASA has chapter and verse on all rechargeable battery technologies for space applications. Google a few terms. From NiCd's to the modern day.

I can't find the NASA paper I recall reading about deep discharging NiCd's, putting a shorting strap across the terminals and storing at a low temperature (I seem to recall at -20C).

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Old 24th Jun 2020, 9:46 am   #19
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Default Re: NiMH cells - good and bad.

Quote:
Originally Posted by cmjones01 View Post
I bought a little Ansmann smart charger which measures capacity and has a 'refresh' mode which will charge cycle cells until their capacity stops increasing, to rejuvenate old ones.
Could you provide a pointer to that charger? Sounds interesting.

Mike
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Old 24th Jun 2020, 10:11 am   #20
cmjones01
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Default Re: NiMH cells - good and bad.

It's an Ansmann Powerline 4 Pro, image attached of it in action with a motley assortment of cells. I paid about £11 for a not-quite-new one on allegro.pl (the big auction/trading site in Poland). They seem commonly available on line. So far I'm impressed, and I think it will save a lot of time and money in keeping cells in good shape and weeding out the duffers.

Chris
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