"Double Clicking" Protected Li-Ion...What happens?

[LuxLuthor]

I have this light which uses 2p-4S x P-14670 cells to power a special Carley 43W bulb, and puts out a blazing 1500L. It works great with single click.

Then I have this 4S smaller 1.5D size FM Maglight which will also power the blazing bulb, but you have to double click it to bypass the cell protection. I tried this a few times, and it does work, but I realized I really have no idea what is happening at the Li-Ion cell/PCB level with this double clicking.

Does anyone know what/how the protection circuit is being bypassed by the double click, and what problems if any this might lead to? I suspect the other way to avoid the PC double click is use unprotected cells, but that isn't a great solution either.

 

[DonShock]

You aren't bypassing the protection circuit, you are just keeping the current surge below the level where the protection kicks in. When you first light off an incandescent bulb, it is cool and thus has relatively low resistance. So when you first light the bulb, you get a very high current draw which can trip the protection circuit. When you do a very short click, it starts lighting the bulb and heats it up slightly. But it's not on long enough for the current to spike high enough and long enough to trip the protection. When you click on the second time, the bulb has heated up slightly so it has more resistance which limits the current draw to within the protection circuit setpoints.

 

[LuxLuthor]

Interesting. Thanks.

But then what causes the shortened battery life down to the 500 cycles that FiveMega said in this post? I was assuming it must do some kind of cellular damage independent of the PC bypass.

 

[DonShock]

I think that was in reference to the earlier discussion regarding the fact that the cell discharge would be in excess of the max recommended rate of 2C, not that the double click was needed. Since the 14670 cells were rated for 1100 mAH, 2C would be 2.2 Amps. By discharging the cells at 2.9 amps as mentioned, you are exceeding the rated capacity and thus will shorten the life of the cells. Of course the double click and the overdischarge are somewhat related. If you were staying within the capacity of the cell, the double click probably wouldn't be needed.

 

[LuxLuthor]

OK, that makes sense...he was answering about the double click, but referenced the reduced cycles related to the excess current draw.

Something struck me about "bypassing the protection circuit," and I just didn't want to assume things with these cells, but the more I understand these nuances, the more secure I am feeling about what to do and not to do.

Thanks very much again, Don!