On 2020-09-12, The Natural Philosopher  wrote:
> On 12/09/2020 01:59, Robert Riches wrote:
>> For some
>> applications, (Wahl series 4000 shavers, for example) a NiMH cell
>> of the same physical size can replace the original NiCD cell, (as
>> mentioned) the original charger still (at least the old
>> high-current type) works, and the NiMH provides about 3X the
>> shaves per charge compared to the original NiCD.
> Be very careful of this. Fast chargers for nickel cells use the delta
> peak detection - a fully charged nickel cell will show a DROP in peak
> voltage as it reaches full charge. This is detced to switch the fast
> charger off.
>
> The drop  is far smaller on NiMH and sometimes not enough to switch the
> charger off..not good.

No fancy end-point detection in the chargers for that Wahl
shaver--just a transformer (as measured by wall-wart weight), so
no big difference in behavior between the cell types.  IIUC, a
lot of NiMH cells contain a catalyst that shunts off excess
charge.  It's been at least a few years of charging about every
20 days, so I'm guessing my cell (purchased from Mouser) has the
catalyst.

--
Robert Riches
spamtrap42@jacob21819.net
(Yes, that is one of my email addresses.)

--- SoupGate-Win32 v1.05