Using
a
Lithium-Ion Battery
For Old Engine Ignition

The battery pack with charger.
A while back, a friend gave me a practically new battery pack from a dead laptop computer.  The batery pack consisted of six Lithium-Ion AA size batteries.  The hookup was three series connected parallel battery pairs.

The other day, I dug the pack out and disassembled it.  The charger was part of the pack but, since I had no documention on it, I just removed the batteries and tossed the rest.  A bit of a study on the Internet educated me on the care and handling of these batteries.  The first thing I learned is that they do not charge like NiCad or other types.  They must be constant-current charged to roughly 4 Volts per cell.  At the point where the Voltage hits 12 Volts or slightly over, the charge should be discontinued.  They are not supposed to be constantly charged with a constant Voltage charger!  Doing so will destroy the battery and could cause them to explode.  Not good!

In my studies, I found that a good rule of thumb for AA size cells is to not exceed 0.5 Amps charging current.

Here's the simple charging circuit I've come up with.

Simple Li-Ion Charger.
Since the actual capacity of the cells I have is unknown, I'm playing it careful and charging them at about half the recommended current.  Because the cells are wired in parallel, the charging current for each one is 0.25 Amps.

In the circuit, I use a 126 Volt AC output wall wart that plugs into the charger box that is taped to the batteries.  When first plugged-in, nothing happens until the "Charge Start" normally closed button is pushed momentarily.  This causes the Schmitt-Trigger circuit to pull-in the relay and start charging the battery pack.  The light bulb, out of my box of assorted light bulbs is most likely a 6-Volt.  I chose it because it limits the charging current to  about 0.5 Amp. total.  In addition to serving as a ballast resistor, the light bulb gives a visual indication  when the battery pack is being charged.

The capacity of AA Lithium-Ion cells varies but can be as high as 4 Amp/Hrs.  Impressive!  The articles say that this type of battery shouldn't be completely discharged.  The minimum recommended  "stop use" Voltage is 3 Volts per cell.  They say the life of the batteries will be adversely affected if they are discharged below this point.

They also say that the batteries are happy to be stored at less than full charge, a nice change from NiCad and Gel Cell batteries.  I plan to cycle the charger after use then just let the pack sit on the shelf until I'm ready to use it again.  Then, I'll give it another charge cycle.  Since I'm not charging them to their maximum Voltage (4.2 Volts/cell), I think I'm safe with a charge cycle before storage.

So far, the pack will power my McVickerish engine for over 12 hours and the batteries are still making 11.6 Volts!  I may haul out the Jack of All Trades ignitor engine sometime and see how the battery pack does with that kind of load.  The instantaneous current is around 2 Amps.  I've got high expectations and will add the test results here when I have them.

If you are looking for a new Lithium-Ion battery pack, I'd suggest that you get one of the imported ones.  Some of the packs come with the charger and the price is around $20.  Look on Amazon or Ebay.
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If you have any comments, I'd be happy to hear from you.  I can be reached via email at this address:
[email protected]