Originally Posted by

**mdocod**
Hello Ti-Force,

Convert to watts, then calculate:

LED@3.4V X 882mA = 3W

3W / 0.9 (regulator efficiency) = 3.33W

17670@3.7V X ~1500mA = ~5.5WH

2xRCR123@7.4V X 550mA = ~4WH

(I'm using realistic capacity values considering the expected load here)

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17670: 5.5WH/3.33W = 1.65H or about 100 minutes.

2xRCR123: 4WH/3.33W = 1.2H or about 70 minutes.

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Realistically speaking, the buck driver will have some over-head voltage requirement, and may not operate at full output through the discharge on a single 17670, which will translate to longer run-times with diminishing output. This can not be so easily calculated unless we know the exact Vf at the desired drive level and the over-head requirements of the driver. Also, the driver efficiency will likely vary across the range of voltage input, but for rough calculations 90% is perfectly acceptable IMO.

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Hello sfce,

For CR123s, we have to de-rate them pretty heavily for the higher expected loads. I think we would have to assume around 2 amp loads at the cells to achieve 2.8A at the emitter. This would de-rate the cells to around 2.35V and maybe 1000mAH. That makes a total of about 4.7WH to work with, and you'll probably be consuming at least 10-12W or more,

20-30 minutes run-time would be a rough estimate after factoring in regulator efficiency loss.

Eric