18650 protected battery wont quit at 3.0 volts

[hoss1968]

I have aw 2900 mah protected cells and am using them in a fenix pd32. The batteries won't terminate at 3 volts, I just keep losing levels. After I take the battery out and check the voltage it is around 2.7. The batteries in my Maelstrom shut down at exactly 3 volts. Anybody have any idea what is going on with the Fenix?

[45/70]

Hi hoss. What levels are you running your lights at? The higher the current level (brighter), the earlier the lights will trip the protection circuit. The reverse is true when running at lower levels. In fact many protection circuits will not trip at all, at very low output levels. This is why cell protection circuits should not be relied upon. They are really there to prevent damage to the cell, not to remind you to recharge it.

Anyway, if your running the lights at different output levels, that may the reason there is a difference. Most protection circuits will trip between 2.5 and 2.75 volts, under load. And again, the higher the load on the cell when the protection circuit trips, the earlier the protection circuit will trip.

Dave

[hoss1968]

I am running it on turbo and when I lose the Turbo mode the battery is at around 3 volts then I pull it out and charge it.

[45/70]

Well, I'm not that familiar with the PD32, I haven't bought a Fenix since the L1P, L0P, and P1. The Maelstrom draws somewhere around 1A on turbo, but I have no idea what the PD32 draws. It could be that your just not draining the cell far enough for the protection circuit to trip in the PD32. Personally, if the cell is reading 2.7 Volts, I would try not to discharge the cell in the light any farther. Li-Ion cells do not take well to being deeply discharged. You can do it, but cell life will be extended by not discharging to such a low OC voltage.

Also, I'm not aware of any protection circuits that trip at 3 Volts. As I said, the protection circuit will trip at a voltage when the cell is under load, and most trip in the 2.50-2.75 Volt range. Apparently, when using the 2900's in the Maelstrom, the light's circuit voltage is reaching 2.50-2.75 Volts when the protection circuit trips, and this equates to an OC voltage of around 3 Volts. Sorry, as I said, I have no idea what the current draw of the PD32 is, but maybe it is less and thus is allowing the cell to discharge to a lower voltage.

Dave

[hoss1968]

OK I though they terminated at 3 volts. My 14500 that I use in my quark AA always trip at 3 volts so I assumed the 18650 would also. But at around 2.7 volts the Fenix pd32 only works on low and medium. So I just pull out the battery and charge it.

[Calcat576]

My PD 32 draws about 1 amp at max brightness.

[45/70]

My PD 32 draws about 1 amp at max brightness.

I checked the Amp draw of my Maelstrom last night, as I had never actually checked it. With a fully charged, older TrustFire 2500mAh cell, the light drew about 1.3A on turbo.

At about the same time as I was checking this, the thought occurred to me that these lights utilize a buck circuit, as I believe the PD32 does also. This means that once the circuit voltage reaches the Vf of the LED plus the driver overhead, the light is no longer in regulation, and the current draw from the cell begins to drop anyway.

My main point was that the voltage at which a protected cell's PCB triggers, is not the same as what the cell's OC voltage will read after the circuit has tripped. Depending on the type of cell, it's age and general condition, the OC voltage of a cell may be anywhere from close to the same as the protection circuit's trip point, at very low current levels, to as much as 0.5 Volt, or more higher, when the circuit trips at higher current levels. To add to this, the actual electronics of the light's driver can come into play, as well.

My best guess is that since the PD32 "looses levels" as the battery becomes depleted, a feature that the Maelstrom does not have, this allows the cell to be discharged farther, due to the decreased current demand at lower output levels. This, as I mentioned earlier, is a good reason not to rely on the protection circuit, as a cell can apparently be discharged to a much lower level, in the PD32. And again, I'm not saying you can't do that, but cells will last a lot longer if deep discharging is avoided.

Dave

[hoss1968]

Thanks Dave you have been a lot of help. I always check the voltage of my batteries and I rarley let then get below 3 volts. I was just testing my new AW cells to see how well the protection worked.