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How long does the battery last when not in use?

A flashlight with no charge is not much use. If I throw this in a bag, how long could I reasonably leave it without using/recharging and still get some use?

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Self-discharge: reduction of the battery capacity when no current is

flowing to an external circuit.

Self-discharge is minimal, at under 10% per month.

Self-discharge is affected by the storage temperature and by the depth of charge. The nearer the battery is to the fully-charged state at the time of storage, and the higher the ambient temperature, the greater will be the decrease in capacity. When a fully-charged lithium ion rechargeable battery is stored, it ordinarily loses about 10% of its capacity in three months; however, this is a small amount compared withthe self-discharge in rechargeable batteries with alkaline solution such as nickel cadmium and nickel metal hydride batteries.

2-3-2 Long-term storage characteristics

When batteries are stored over a long period, depending on the battery state and the storage temperature, in some cases irreversible deterioration may occur and the battery will fail to hold a charge even after recharging. Deterioration is not observed in batteries in the discharged state, but the greater the charge in the battery, the more

pronounced the deterioration after storage. Also, the higher the storage temperature, the greater the deterioration tends to be. For these reasons, lithium ion rechargeable batteries should be in the discharged state when stored for extended lengths of time, and it is desirable that they be stored in a low-temperature environment.

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The voltage regulator can be turned on either by pressing the button, or by the CPU raising PB0 (physical pin 10, "pin 8" in Auduio-eze).

You can see this being controlled in the code, look where the modes are changed. You'll see

digitalWrite(DPIN_PWR, HIGH);

For all the modes except MODE_OFF, where it's

digitalWrite(DPIN_PWR, LOW);

So, when it's off and you press the button, that powers the CPU. It initializes and changes the mode to one which latches the power on using the statement above. When you turn it off, DPIN_PWR is turned off, so the voltage regulator turns off as soon as you release the button, and battery draw drops to almost nothing.

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Can't be 100%, because the first "Open Source light" isn't yet Open Source, so there's no schematic to confirm.

But, it seems that when with the standard code, when off, the voltage regulator is turned disabled. In that state, it consumes around 2 uA. The only other thing connected directly to the battery is the charge controller, which draws about 0.1 uA when not in use.

So, a 2400 mAh battery should last about 130 years. :-)

(self discharge is the limiting factor - the battery should last as long in the flashlight as it would on a shelf)

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That definition seems to describe the discharge characteristics of a battery that isn't connected to anything. Since the back switch of the Hexbright isn't a true power on/off switch, I would assume that there's some current draw from the microcontroller at all times since it has to monitor whether the switch has been pushed.

Hmmm, just found this... The project log/documentation says:

''2011/11/14U26: Ultra-Low power off mode in which only the leakage current of the LED Driver, Voltage Regulator, and Li-Ion charge controller will be present

2011/06/22C: The FLEX has a bit of a draw. The switch is not for power, but watched by the microcontroller.''

So if I'm reading those correctly it does seem that there is some "negligible" current draw when the HexBright is turned off...


Dave B.

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Christian did specifically state that we don't have charge-level monitoring specifically because it would introduce a constant power draw, even when off. So, while I understand what you're saying, I'm not sure it's true.


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Mike: So this device is in some sort of "sleep" mode when off, and not plugged in? Out of curiosity... how does this happen? I would have thought that we'd see some odd register-banging to go to sleep when commended OFF, and NOT on USB. It seems to wake immediately when I press for ON again.

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The current is low enough that I wouldn't trust a cheapie DMM to measure it. Just the same, I removed the battery from my hexbright, set my bench power supply to 3.7v, put the DMM in "20µA DC" mode, and got a measurement of 0.08 (i.e., 80nA) with the hexbright "off". Not definitive, but together with MikeS's datasheet diving, battery self-discharge is clearly dominating over leakage current in determining "shelf life" of an unused flashlight.

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Scott will be eternally grateful.
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