Dont run down protected 18650 in U2 style!

hi guys, i just completed a runtime for the U2 EWJ light on www.lightreviews.info (i also redesigned it to remove the frames as advised )

seems thats AW's protected cells wont kick in early enough in low current drain lights like this one. mine went all the way down to 2.5V, below the safe operating 2.8V

www.lightreviews.com is down, buddy.

sory it's .info, my bad just updated url redirect, takes a few mins to go live

I don't get it, this sounds like a battery problem not a light problem. Maybe a bad protection circuit in the battery?

Did the light cut off at 2.5 volts? From my readings on CPF it seems that that 2.5 volts can be a cut off voltage for LiIon batteries. I have inadvertantly run some of my LiIon's below 2 volts and have not seen any damage as a result. In fact my wife using a KL1 and two RCR123's, unprotected, ran it down to 1.06 volts per cell. I quickly changed out RCR's for a protected 17650, as she does not know how to monitor LiIon's.

Bill

Some low protection doesn't cut off until 2.5v, but the voltage should jump back up to 3.0v when you take it off load. If it doesn't, it has been damaged to some extent (at best, its life has been shortened).

If a cell goes below 2.0v it should be considered irrecoverable -- recharging it is highly inadvisable as it could overheat and blow.

@ Byggeren

Yup, its partially the battery's problem that it doesnt cut off at 2.8V. It's also the light's problem because the regulation board continues to draw a constant low current after initial regulation drop out.

The battery is supposed to shut off when it gets too low. In fact, it should show 0 volts until it is recharged. It has nothing to do with the flashlight.

oh ok, well anyway thats wat AW told me. He said low current drain lights will will only make the circuit kick in at 2.5V but regulated lights will be ok.

yeh i know, it basicaly sounds like the protection circuit isnt working as it should and cut off at 2.8V

LightScene said:

The battery is supposed to shut off when it gets too low. In fact, it should show 0 volts until it is recharged. It has nothing to do with the flashlight.

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It will show 0 volts because the LVC has kicked in. It won't give a voltage until you reset ithe LVC by putting a bit of charge into it. It is a matter of debate what that low setting should be, and for best battery cycle life I personally think 2.5v is too low. It is just not good for the battery's life to run it down that low.

x2x3x2 said:

oh ok, well anyway thats wat AW told me. He said low current drain lights will will only make the circuit kick in at 2.5V but regulated lights will be ok.

yeh i know, it basicaly sounds like the protection circuit isnt working as it should and cut off at 2.8V

Click to expand...

Now I understand what you're saying about low drain, and it is kind of surprising.

Under load, the battery will typically drop 0.5v. If the battery is under full load, the LVC will kick in at the low point, which if it is 2.5v means that the battery will recover that 0.5v back up to 3v. So all is OK.

However if the battery is being drained at a very low rate, say <0.1C, it is not really under a load so it could actually drop right down to 2.5v before the protection kicks in. This can easily happen with LED lights on very low settings. It is not good to drain Li-Ion cells so low. It is not dangerous, but it will shorten the life of the cell.

What CAN be dangerous is overheating during charging afterwards, so the battery should be watched carefully for this.

In my experience a light with a buck circuit (or even a direct drive light) will allow the cell to keep dropping until it is putting out almost no light before the protection circuit kicks in, but a light that uses a boost circuit will typically cause the protection circuit to kick in much sooner either due to the voltage sagging under the higher load, or due to the current exceeding the maximum that the circuit will allow.