Making use of old Lithium batteries

Most of us have got some lithium-ion and lithium-poly batteries/cells lying around, if only old cellphone batteries. I also have a nice little 'free sample' Li-poly I won in a Varta competition and some two and four cell batteries (paralleled) from broken 'power banks'. I get given the job of recycling all the WEEE stuff round here!

I bet most of us don't make any use of these due to the lack of a suitable charger, as these are often fitted internally to the appliance the cells came from. If cells are heavily discharged, the internal chargers will often refuse to charge them and the whole thing may get junked.

Making your own charger is demanding, as if overcharged lithium cells can catch fire, or worse. They need a charger that can monitor cell voltage to within 1%. Making a charger that can pre-condition an over-discharged battery is even more challenging.

So, good news!

I got a little (very little, it's a SSOP - silly-small outline package) chip from CPC for about a fiver. Add a 500 mA 5V supply, 2.2uF and 4.7uF capacitors, an LED and a resistor and you've got an intelligent Li-ion charger that will apply a gentle precondition charge below 2.3V and charge at 500mA. It includes a temperature sensor to reduce charge and stop it overheating itself.

You can add one or two switches to select 500 or 100mA charge and 4.1V or 4.2V endpoint.

The beast is a Maxim 1811:

**LINK**

It is making a good job of 'regenerating' a two-cell pack from a 'power bank' that was just flashing 'error' when connected up, presumably as the cell had dropped to less than 0.5 volts.

A most impressive chip, I think!

Neil

Edited By Neil Wyatt on 12/09/2014 19:34:59

I used to reinvigerate mobile phone batteries that would not charge due to the cell voltage falling below charging threshold by applying a larger voltage I.e 12 v but limited current about 100ma from a wall wart type psu for a few seconds, once the voltage of the cell pack was raised above the charging threshold the battery could be replaced in the phone and the normal charger used.

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.

Les, it may be a different issue - Dell have a horrible little extra contact that establishes a 1-wire communication between laptop and battery pack. If the wire breaks you can run the charger but the battery won't charge and slowly fades away and dies.I tried a BIOS update and switching off charger monitoring

You end up paying for a new charger AND a new battery if unlucky. I only fixed my Dell charging lead a few days ago.

Neil

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

Hi Neil,
The laptop worked with the new (Clone. ) battery pack bought on Ebay. On the subject of chargers my brother in law had his TomTom destroyed by a faulty lead on the in car charger. The power lead has a third wire for sensing the voltage at the plug that plugs into the TomTom. This wire fractured so the voltage regulator did not have the feedback signal so it was outputting close to 12 volts rather than 5 volts. The addition of one extra resistor at the charger end between the output and the sense wire would have prevented this from happening.

Les.

Hi Peter

Zapping Nicads is very different. I'm sure 100mA is 'brutal' in the context of a deep-discharged Li-ion!

Neil

The charging of Ni-cad's is a minefield as users tend to 'Top up' the batteries and this sets up a,'Memory condition'. This then lowers the capacity of the Ni-cad pack until it only lasts an hour or so. All Ni-cads should be discharged to 1.1V per cell and then given the longest charge possible, then discharge it again and recharge. We do this 3 times and gain some good discharge times. Individual cells in a pack need to be checked but it is not always a reliable method. We also replace individual cells in packs (7A/hr rating) I have seen Ni-cad packs re-charged off a car battery in 5 mins for model plane flying but they get very hot and you need special batteries to do it. Once had a 12A/hr battery explode on an overnight charge which opened out the metal casing like a football.

Lith-Ion cells have no memory problems and can be topped up as needed but care taken as to temperature over time. Special chargers are needed and as Neil says have temp. cut off and voltage sensing.

Back to rejuvenating Ni-cads, i read at one time that the method was to put a voltage in the reverse direction which would burn off the spikes (Dendrites) Momentary contact was enough but that was in the day when Ni-cads cost a lot of money but now they are fairly cheap so maybe not necessary. If you are going to store Ni-cads then either fully charge them or drop the cells to 1.1V per cell. We replace 100+ cell packs a year that are used on Surveying equipment and then disposal becomes a problem where specialist handlers charge £100 for 1 to a 100 old cells to take away. No wonder they are just dumped in the waste. Which of course is illegal. We make sure they are discharged using a heavy resister and then solder a wire between the + and - contacts. Again I have seen the old cells thrown in a bin and catch fire!

Clive

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

Ian, what polarity for the capacitor zap? Plus to plus or the other way round? Or does it not matter?

Mike

Mike T.

Positive to positive. The idea is to put a heavy charging current into the cell.

Neil,

I was replying to your comment re shorting Ni-Cds. I have no experience of Lithiums other than of replacing them when capacity is very low.

Peter G. Shaw

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

Its to burn out the dendrites. I have often done it, when a cell is 0V, zapping it immediately gives .6V or so, so charging can begin. I tend to use 1000 MF at 50V, makes quite a splash!. I don't think it does the cap much good either .

Frank

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 expertise with old TV sets was knowing exactly where to whack the thing, and how hard, to cure the particular fault!

I think most domestic TV owners in those days had a knack of doing the job on their own set, I know my Dad did.

Edited By V8Eng on 13/09/2014 20:16:22

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

R the 35000 uf cap, no polarity quoted, it's just to burn off the whiskers.

Ian S C