DD P7 and Li-ion

[cd-card-biz]

Guys, I would like a confirmation that this is "OK" before proceeding.

I want to direct drive a P7 using one of AW's protected C-cells.

Is it OK to just run the finished light until it goes out? Will the protection circuitry in the C-cell prevent over-discharging? If so, is this generally accepted as being OK? I only use protected cells in all my lights.

Thanks for any information.

Edit: Sorry for the double post! Mods please remove.

 

[MWClint]

single level DD p7 lights will be noticeably dimmer before you hit the 2.7v cutoff in the protection circuit. when it dims, thats a better indication of "recharge me now" than letting the battery cut out. it's ok to let it hit the protection cutoff once in a while, but really, if you want to prolong your cell life, dont rely on it.

for the first few uses, get an idea of how long the light will hold decent
brightness and see what voltage remains in the cell. then you know, "ok i can
run this light on a full charge for x minutes down to y volts"

once a li-on begins to dim.. there's really not much life left in it. most can
only take a couple more minutes before banging the protection circuit.
so it's pretty easy to avoid on a DD light. harder to tell on a regulated or
dimmable light. in those cases, you really do need to pay attention to runtime.

 

[lowatts]

Will the protection circuitry in the C-cell prevent over-discharging? If so, is this generally accepted as being OK?

The built-in protection is against severe damage, not intended for routine use. The best thing would be to run the light and test with your multimeter every few minutes. When the cell reach 3v hot out of the light is a good stop point (it will recover back to around 3.6 IIR no load) to stop, though opinions vary on the best exact cut off point.

 

[monkeyboy]

This is not a good idea with direct drive. Since the current is so low before cut-out, the battery voltage does not bounce back to a safe level (over 3.0V). This is something that AW mentioned himself.

It probably won't kill the cell as long as you put it back on the charger straight away but it could damage the cell in the long run and potentially be dangerous to recharge. Incans and regulated LEDs are OK since final current is not so low. As MWClint mentioned, you should get plenty of warning before the cutout.