Hi Neil,
Thanks for the link. I also use cells removed from a faulty Dell laptop battery. All of the cells worked OK so the fault must have been the charge/ discharge monitoring electronics in the battery pack. The cells were type 18650 and I now use these in LED torches. One other point about this type of cell is that none of the ones I bought on ebay (From several different sellers.) came close to the rated capacity. The ones removed from the laptop pack had more capacity.

Les.

That's a bit brutal Howard! I've used a dead short to bring nicads back to life, for a while.

Back in the 1970's, K C Johnson in Wireless World published his findings on rejuvenating NiCD cells. Essentially, Johnson found that unless NiCD's were worked hard, the manufacturers life could not be reached, as lightly loaded cells would internally form metallic spikes which ultimately would cause the cell to be internally shortcircuited. Johnson's method of rejuvenation was to connect the cell across, eg, a 12V car battery via a suitably rated bulb. This caused a much higher current to flow which, with luck, would melt the spike. Howard's 100mA is quite low by Johnson's standards although I seem to recall Johnson based his rejuvenating current on some multiple of the cell capacity, eg 5C.

Shorting the cell may achieve the same objective.

As Johnson says, if a cell is shortcircuit, then you have nothing to lose by trying it. The danger is that too much current may cause the cell internal connections to melt and hence ruin the cell permanently.

On a personal basis, I have done this on NiCD's, but as you say Neil, it's only a short term solution. And there are some cells which have refused to work even after an unlimited short blast from the car battery.

Incidently, this idea is only suitable for cells which are short-circuit to an ohmmeter. An open-circuit cell cannot be rejuvenated.

Regards,

Peter G. Shaw

On the subject of zapping nicads..
One design ..published…used raw mains rectified and gated with 50 Hz 10 nS pulses for as long as a push button held down…
The pulses were generated by xor gating the sniffed incoming mains…54 F series gates if I remember. .
….still seems scary to me

Restoring Nicads, the ARRL (American Radio Relay League) "Hints and Kink" book suggests that a 35000uf electrolytic capacitor be charged to 12 volts, then discharged across the cell, it may need zapping more than once. I'v used this meathod to wake up the cells in a battery drill.

Ian S C

A very important thing to note about nicads…when fully discharged they can inadvertantly suffer cell reversal…that is charge with plus where you expected minus…happens in multicell packs where one cell in pack gets reversed….
Even used to do this as a joke at college. ..imagin the fun when some AA battery is reversed..and left lying about ….oh it is to laff…..bit like charging a cap off mains and leaving out on bench….

Peter.

Thanks. I was not sure whether Ian SC's capacitor zap idea was to burn off the dendrites or to restart the charging process.

Mike

The voltage of lithium cells when fully discharged can fall below that required for the internal charger to start a charge cycle. A quick way to get the voltage up to the point the internal charger can take over was indicated in my original post. As the higher voltage is only applied for long enough to get the voltage up, usually a matter of seconds rather than minutes, it is unlikely to affect the cells in an adverse way. Lithium cells, even small ones can generate high current so pushing 100 ma through for a few seconds is less brutal than throwing the cell pack away.

When I worked for BT there was an unwritten rule called "percussive adjustment", if some mechanical device was proving to be reluctant to take the adjustment procedure, a quick look round for peeking eyes, then clout it with something heavy usually caused the offending device to cooperate.

Occasionally big sticks do work. Old fashioned valve TV's being a classic example – who (of us oldies) haven't used ones hands to to slap the thing into submission then scarpered while it was still working?

The life of Ni-Cad's is quoted as 500 charge and discharge cycles, I got into trouble one day by telling a customer that detail and he got onto the MD who called me in to answer about it, expecting this I pulled the manufacturers data sheet and stuck it under his nose and he read and then apologized , as he did not know that detail. One of the reasons was the warranty system we ran which covered the Ni-cads.

All the customers were referred to the data about full charge and discharge cycles and I started a nice line in discharge devices with an audio tone when the cells reached 1.1V and to start charging the cells. Now we no longer sell Ni-cads to power theodolites as all our batteries are Lithium and very small compared to years ago and inside the theodolite.

Clive

Edited By Clive Hartland on 13/09/2014 20:30:20

Hi,

You can purchase a ready made single cell charger on the auction site, it has mini usb socket and soldermpads to put your own connection wires, best of all it costs around £2.

I use it with some 1850 cells removed from old laptop batteries, I leave it charging over night.

I post some links if anyone's intersted.

As would re seating the bottles…but then duff connections aren’t confined to valves machines…but semiconductor stuff doesn’t ..generally…see the same temperature cycles as valve gear or have heavy components in sockets.