DIY Lithium battery packs

[gbb]

For you guys that like to DIY your lights....its getting to that time of year again...

I use a double Cree setop on the front with an Enix 15v 2.2amp Lithium battery, nice and compact, sits nicely in the saddlebag. As luck would have it, some laptop batteries use 16850 3.75v lithium cells, the same basis as the Enix pack.
Ive stripped an old laptop battery (carefully, lithium cells need respect) and found half the cells were ok voltage wise, the other half dead.
So, 4 cells arranged the same way as the Enix, a bit of soldering and a lead and plug...free Lithium battery..

Enix and homebrew battery completed...
http://i146.photobuc...oto/lithium.jpg

Another view of it under construction...
http://i146.photobucket.com/albums/r269/gbb_photo/DSCN0603.jpg

Used it extensively last winter, still going well.

Photobucket I'm going to go elsewhere...the problems i have with that site, took me ages to upload these photos....

 

[Wobblers]

How do you charge your Li-ion batteries? Li-ion cells need to be monitored individually whilst being charged to prevent individual cells becoming overcharged - that's something you definitely want to avoid (unless you like fires!). You'll most likely find that the Enix battery pack contains a protection circuit which does just that. I would not charge Li-ion batteries in series without that protection especially with older cells, as in your case, which may no longer be properly matched and more likely to experience problems on charge.

 

[gbb]

How do you charge your Li-ion batteries? Li-ion cells need to be monitored individually whilst being charged to prevent individual cells becoming overcharged - that's something you definitely want to avoid (unless you like fires!). You'll most likely find that the Enix battery pack contains a protection circuit which does just that. I would not charge Li-ion batteries in series without that protection especially with older cells, as in your case, which may no longer be properly matched and more likely to experience problems on charge.

This did occur to me but at the time i was interested, i did some research on Candlepower forums (they have a subsection on cycle lighting) and there was no mention of protection. I may be taking a risk, i dont know, but the packs been recharged a good few times with no heat problems.

Incidentally, i get 4 hours runtime with two cree leds and its still running even then.

Charging...i use a Mascot 16v Li-on charger (from RS components) 3 stage charging with overcurrent
protection.

You got me thinking now...i may do some more homework.

 

[gbb]

Hmmm, McWobbles made me think.
IIRC, when i researched this, these particular cells have inbuilt protection..individually. That made me think it was ok. Now i'm not so sure.
More research and i havnt found any info on joining them in series without further protection. (i cant find anyone who has done this build at all)
It may be the charger takes care of it, but maybe isnt good enough with hindsight.

I think i'd suggest you do NOT try his at home. Going to stop using it until i can verify its safety.

Shame really, this configuration works really well with Cree setups and the like.

 

[Davidc]

A few years ago I saw a Li-ion laptop battery burst into flames - I wouldn't take the risk!

Soon we'll have NiZn batteries in Europe, which have the same energy/weight and slightly better energy/volume than Li-ion, with slightly worse impedance. They are supposedly safe to crush, hammer nails into, and burn, so much better suited to DIY packs.

 

[02GF74]

Hmmm, McWobbles made me think.
IIRC, when i researched this, these particular cells have inbuilt protection..individually. That made me think it was ok. Now i'm not so sure.
More research and i havnt found any info on joining them in series without further protection. (i cant find anyone who has done this build at all)
It may be the charger takes care of it, but maybe isnt good enough with hindsight.

I think i'd suggest you do NOT try his at home. Going to stop using it until i can verify its safety.

Shame really, this configuration works really well with Cree setups and the like.

you should use what is called a blanaced charger - this has connections to each cell and charges them indivually to overcome the porblems listed below.

I have one, off ebay for about a fiver from Taiwan. search for mystery charger.

ok, seven quid for this baby:
http://cgi.ebay.co.uk/Mystery-7-4v-...0383820393?pt=UK_ToysGames_RadioControlled_JN

 

[Wobblers]

you should use what is called a blanaced charger - this has connections to each cell and charges them indivually to overcome the porblems listed below.

I have one, off ebay for about a fiver from Taiwan. search for mystery charger.

ok, seven quid for this baby:
http://cgi.ebay.co.u...ioControlled_JN

That's the safest way to recharge lithuim ion batteries. Your charger, gbb, simply applies 16.8 V across your battery and assumes there's electronics built into the pack to make sure each individual cell get a balanced charge. A battery pack will become unbalanced when one cell becomes fully charged before the others. Since the others are still charging, this cell will become overcharged, and that's something you need to avoid. Battery manufacturers specify that cells should never be charged above 4.25 V.

The good news is that the cells from the laptop battery will be good quality ones so that there should be little variation between cells (hopefully). You can check this if you have a digital multimeter. When charging your pack, measure the voltages of each cell - if they're different by 0.02 V or more, I'd only charge the pack with a balancing charger.