Surefire C3 with 1200mAH Li-Ion from camcorder pac

Just finished a two week field test on a C3 with P91 HOLA using 1200mAH Li-Ion rechargeables from a camcorder pack. This thing is impressive to say the least. Didn't want to pay for the high $$ shipping from Hong Kong for the Copia's so I went out an bought a camcorder battery pack and took it apart.

***Warning, do not do this unless you know what you're doing!!!!****

With that caveat aside, proceed with caution... Anyway the packs that are readily available uses the 18500 cells which is a bit fat for the C3. I proceeded to ream out the inside of the C3 to take the fatter (and higher capacity) cells. (The Copias are 16 or 17mm in diameter and have 1000mAH of capacity) Compared to using 3 SF 123's, I'm seeing less voltage droop on both the P90's and P91. That's surprising since the nominal voltage of the cell is 3.6V. That's good since the rechargeables will perform at least as good as the SF 123's. Best thing is that it's rechargeable. Runtime is comparable with the P90's. Haven't done the P91's since heat is an issue but I estimate it should be about the same as using non-rechargeables. I did not see any yellowing but then again I don't let the rechargeables discharge below 3V. I already have the Copia 9T kit so I use the charger to charge the cells. It doesn't terminate but at the end of charge at 4.25V, the current is less than 10mA so the charger does have *some* protection though I still watch the voltage carefully. Another advantage is the ability to top off anytime to get a very white light when you need it. Lithium Ion's don't suffer from voltage depression like the Nickel based secondary cells, and it's good not to discharge too deep anyway. I know this isn't a very sophisticated mod but in case anyone was interested, it's now been done.

CM

Are those cells without individual protection circuits?

Yes. That's why I presented the precaution above. I've been looking at a TI part that protects individual cells, it's thin enough you can mount it directly on the cell itself. I suspect that's what Copia is doing since their li-Ion are 2mm longer than the standard sizes.

How you deal with Li-Ion cells? I heard that soldering cells are dangerous. Are you just tape them together?
Many manufacturers have single small IC to protect Li-Ion cells but we need to know exactly parameters of cells or set?
What is your opinion?

Bob123,

Good question(s). I left the tabs on the cells from when they were in the pack just for the purpose of not having to solder to the terminal itself. As far as the exact parameters, you can reverse engineer the packs protection circuit to determine which voltage version of the protection ic to use. Mine uses a 4.3V cutoff. Your other option is to just not use any protection, however you MUST watch the voltage carefully. In the two weeks of testing I've done, I haven't had any problems. I try to recharge when the open circuit voltage is about 3.3V. That gives good run times between charges and offers reasonable margin from overdischarge. The light is also still *very* bright and white at this point. I have two sets that I rotate between so the light is ready for use any time. One set is the original cells from the Copia 9T kit that I bought. I figure 20 recharge cycles on these and they will have paid for themselves assuming a $1.25/cell price for non-rechargeables. Not too bad. Wish I'd have thought about doing this long ago. Now I don't think twice about using the P91's since it is now very economical to run, even considering the recent SF price drop on the 123's.