Rooting around in the fascinating stuff at the bottom of a draw labelled 'Engineering - Junk Miscellaneous'. Delving amongst the delightful...
Li-ion chargers, searching for a good one
I have a pair of rechargeable CR123 lithium ion cells for my rather fine Zebralight head torch. An older version of this.
If you want a wide even beam head torch with no appreciable ‘hot spot’, this is a good one – great for seeing around inside a building or tent. Not so good for looking down narrow paths between hedges as it lights the hedges more than the path. Tiny and light weight, it needs CR123-style cells.
If a bit more of a between-hedges beam is needed, this H51 is good, although it needs an additional strap to stop it nodding when if running.
Anyway, lithium ion cells need to be treated well, especially while charging.
To re-cap on many many articles: the traditional 3.6V (cobalt or manganese – rather than the roughty-toughty iron phosphate) types – need charging:
At constant-current (CC, value proportional to cell nominal capacity. 0.7C good, 1.0C max) terminating at a terminal voltage of 4.20V.
Followed for a limited period of 4.20V constant-voltage (CV) charge to put in the final 30-ish% of capacity.
Because of these constraints, there is no way to hurry the process and minimum charge time is always close to three hours. By missing the CV stage, this drops to two hours, but the cell will never be fully charged.
4.2V is chosen to get as much charge in the battery as possible without room temperature cycle life dropping below around 600 cycles. (Less with high temperature use, and deep discharge (3.0V good, 2.7V acceptable, 2.5V bad news).
Charging at 4.3V crams a little more into the cell, at the expense of life, which may go down to tens of cycles.
Charging to 4.1V only gets 80% of full charge, and cycle life goes up to thousands.
The above are rough figures – the ‘Battery University‘, thoughtfully provided by Cadex, has a lot more.
By the way, never charge at all if the cell is blow 0°C, unless it is specifically designed to be used like this – Don’t guess on this one, they can catch fire – as can cells charged at over 4.3V.
To charge my rechargeable CR123s (warning, most CR123s are non-rechargeable primary lithium cells) I bought a charger, and discovered that it was set to 4.3V. Reading blogs, the set voltage varies from unit to unit.
So I bought a different one, which seems to charge to 4.1V sometimes, and higher other times.
So I bought another – a Nano (Google CR123 nano, quite a few people do them – although they may not all be the same thing) which worked brilliantly with a nice 4.2V CV stage. It is not fast, but I can leave it overnight.
The only limitation is that there is no automatic termination of the CV charge.
And that it broke down – I read that if you pull them apart, there are some internal contacts that can be bent to make it better again.
Does anyone make a CR123 charger that charges at somewhere between 4.1 and 4.2V consistently and reliably? Preferably with automatic CV charge termination.
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