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Reviving 'dead' PP3 NiMH?

Started by Terry Pinnell October 20, 2015
Some of my PP3s steadfastly refuse to recharge. Neither in my
'intelligent' nor basic chargers. Despite being years old, I'm
reluctant to dump them. Any tips from others who have managed to bring
these back into service please?

-- 
Terry, East Grinstead, UK
On Tue, 20 Oct 2015 08:58:57 +0100, Terry Pinnell wrote:

> Some of my PP3s steadfastly refuse to recharge. Neither in my > 'intelligent' nor basic chargers. Despite being years old, I'm reluctant > to dump them. Any tips from others who have managed to bring these back > into service please?
They likely developed thin internal shorts into one or more elements, this happens often in NiMhs. Like other NiMh cells you can attempt to "zap" them a few times with a short high current/voltage pulse, such as a big capacitor discharge, until all thin shorts are gone and the charger sees them as chargeable again. It usually works, especially well on single cells (D, AA, etc), but don't trust that battery anymore as it will develop a short again one day.
On Tue, 20 Oct 2015 08:58:57 +0100, Terry Pinnell wrote:

> Some of my PP3s steadfastly refuse to recharge. Neither in my > 'intelligent' nor basic chargers. Despite being years old, I'm reluctant > to dump them. Any tips from others who have managed to bring these back > into service please?
I know the old nicads had internal shorts (an actual 0 volts or a millivolt or two, measured at the terminals). I'd recover them with a large cap 100,000 uf charged to 25-40 volts then zap them and read the voltage. There'd be a few tenths of a volt indicating that the short was gone. But if these batteries of yours have been siting around in a discharged state you may get them working by zapping them but they will never perform anywhere like they did when new.
 default wrote:
> > > I know the old nicads had internal shorts (an actual 0 volts or a > millivolt or two, measured at the terminals). I'd recover them with a > large cap 100,000 uf charged to 25-40 volts then zap them and read the > voltage. There'd be a few tenths of a volt indicating that the short was > gone. >
** I found connecting a good NiCd cell in parallel with a shorted one did the trick - with minimal risk. Shorted cells in a pack you cannot access is more difficult to fix and in a 9V battery near impossible.
> But if these batteries of yours have been siting around in a discharged > state you may get them working by zapping them but they will never > perform anywhere like they did when new.
** Old NiMH cells are not prone to shorting, but simply lose capacity and can self discharge in a day or so. ... Phil
default <default@defaulter.net> wrote:

>On Tue, 20 Oct 2015 08:58:57 +0100, Terry Pinnell wrote: > >> Some of my PP3s steadfastly refuse to recharge. Neither in my >> 'intelligent' nor basic chargers. Despite being years old, I'm reluctant >> to dump them. Any tips from others who have managed to bring these back >> into service please? > >I know the old nicads had internal shorts (an actual 0 volts or a >millivolt or two, measured at the terminals). I'd recover them with a >large cap 100,000 uf charged to 25-40 volts then zap them and read the >voltage. There'd be a few tenths of a volt indicating that the short was >gone. > >But if these batteries of yours have been siting around in a discharged >state you may get them working by zapping them but they will never >perform anywhere like they did when new.
Thanks both. Zapped them all yesterday and most are at least now charging. But I note your cautionary warnings. Only intend to use for old stuff in the shed. -- Terry, East Grinstead, UK
On Wed, 21 Oct 2015 10:13:42 +0100, Terry Pinnell <me@somewhere.invalid>
wrote as underneath :

>default <default@defaulter.net> wrote: > >>On Tue, 20 Oct 2015 08:58:57 +0100, Terry Pinnell wrote: >> >>> Some of my PP3s steadfastly refuse to recharge. Neither in my >>> 'intelligent' nor basic chargers. Despite being years old, I'm reluctant >>> to dump them. Any tips from others who have managed to bring these back >>> into service please? >> >>I know the old nicads had internal shorts (an actual 0 volts or a >>millivolt or two, measured at the terminals). I'd recover them with a >>large cap 100,000 uf charged to 25-40 volts then zap them and read the >>voltage. There'd be a few tenths of a volt indicating that the short was >>gone. >> >>But if these batteries of yours have been siting around in a discharged >>state you may get them working by zapping them but they will never >>perform anywhere like they did when new. > >Thanks both. Zapped them all yesterday and most are at least now >charging. But I note your cautionary warnings. Only intend to use for >old stuff in the shed.
Rechargeable PP3 were always expensive but we have here Hibrio/Eneloop/already charged type PP3 which have low self discharge character, and they have been fully reliable even when left to totally flatten in equipment at times. Ocasionally Lidl (UK) have these at 2.99 ea which is a very good price even compared with eBay, but you have to be careful not to get the non ready charged type which is what you have already! C+
On Thu, 22 Oct 2015 07:50:18 +0100, Charlie+ wrote:

> On Wed, 21 Oct 2015 10:13:42 +0100, Terry Pinnell <me@somewhere.invalid> > wrote as underneath : > >>default <default@defaulter.net> wrote: >> >>>On Tue, 20 Oct 2015 08:58:57 +0100, Terry Pinnell wrote: >>> >>>> Some of my PP3s steadfastly refuse to recharge. Neither in my >>>> 'intelligent' nor basic chargers. Despite being years old, I'm >>>> reluctant to dump them. Any tips from others who have managed to >>>> bring these back into service please? >>> >>>I know the old nicads had internal shorts (an actual 0 volts or a >>>millivolt or two, measured at the terminals). I'd recover them with a >>>large cap 100,000 uf charged to 25-40 volts then zap them and read the >>>voltage. There'd be a few tenths of a volt indicating that the short >>>was gone. >>> >>>But if these batteries of yours have been siting around in a discharged >>>state you may get them working by zapping them but they will never >>>perform anywhere like they did when new. >> >>Thanks both. Zapped them all yesterday and most are at least now >>charging. But I note your cautionary warnings. Only intend to use for >>old stuff in the shed. > > Rechargeable PP3 were always expensive but we have here > Hibrio/Eneloop/already charged type PP3 which have low self discharge > character, and they have been fully reliable even when left to totally > flatten in equipment at times. Ocasionally Lidl (UK) have these at 2.99 > ea which is a very good price even compared with eBay, but you have to > be careful not to get the non ready charged type which is what you have > already! C+
I second the low self discharge batteries. With others, especially in a pack, it seems I'm never sure of the charge remaining, and trust is everything when you are away from home.