reverse runtime calculation

[Kristofg]

Due to the lack of specs found on a flashlight package, I am left wondering if the led involved is a one watt or three wat version. It is a luxeon dome and runtime is stated as 10 hours on 4 energizer C cells.

Are my calculations correct in stating the following:
rechargeable C cells contain +/- 4000 mAh, so non-rechargeables should contain at least the same amount.

4 batteries * 4000 mAh / 10 hours = 1.6 Ampères

1.6 Ampères * 1.5 volts = 2.4 Watt

Thus, it would be a 3-watt luxeon?

Can somebody perhaps tell me the runtime for a 1 watt and 3 watt luxeon on 4C cells?

 

[chesterqw]

i think it is a luxeon III. there is no such thing as one watt or three watt version. i can drive a lux III to 8 watts and call it the 8 watts version.

so anyway, i think it is a real LUX III as,for the 4AA version, it is a lux III.

 

[Erasmus]

1.6 Ampères * 1.5 volts = 2.4 Watt

Four cells is 6V, not 1.5V. Or am I wrong? :)

10 hours can be the peak output, the time where the brightness plot is nearly flat and before it starts to dim significantly.

 

[Kristofg]

Four cells is 6V, not 1.5V. Or am I wrong? :)

10 hours can be the peak output, the time where the brightness plot is nearly flat and before it starts to dim significantly.

Good point. I supposed they were in parallel, but they might be in series. But then the voltage would multiply by 4 and the Amperage would be divided by four, resulting in the same wattage.

 

[Erasmus]

Good point. I supposed they were in parallel, but they might be in series. But then the voltage would multiply by 4 and the Amperage would be divided by four, resulting in the same wattage.

True :) I guess it's a LuxIII then.

 

[drmaxx]

Are my calculations correct in stating the following:
rechargeable C cells contain +/- 4000 mAh, so non-rechargeables should contain at least the same amount.

I thought that C cells have more somewhere around 7000 to 8000 mAh? But might be wrong.

4 batteries * 4000 mAh / 10 hours = 1.6 Ampères
1.6 Ampères * 1.5 volts = 2.4 Watt

The calculation is somewhat unusual but principally correct:
Energy in 1 battery = 7000 mAh * 1.5 V = 10.5 Wh (= 37.8 kJ of energy)
4 batteries = 4 * 10.5 Wh = 42 Wh
Power: 42 Wh / 10 hours = 4.2 W

 

[Handlobraesing]

Due to the lack of specs found on a flashlight package, I am left wondering if the led involved is a one watt or three wat version. It is a luxeon dome and runtime is stated as 10 hours on 4 energizer C cells.

Are my calculations correct in stating the following:
rechargeable C cells contain +/- 4000 mAh, so non-rechargeables should contain at least the same amount.

4 batteries * 4000 mAh / 10 hours = 1.6 Ampères

The cells are connected in series most likely. You don't multiply the Ah together.

1.6 Ampères * 1.5 volts = 2.4 Watt

Thus, it would be a 3-watt luxeon?

Can somebody perhaps tell me the runtime for a 1 watt and 3 watt luxeon on 4C cells?

There's no simple answer. You have to measure the current yourself. Different design drives the Luxeon at different current.

If you want to test the runtime, the easiest way is to use a cheap analog volt meter, watch and a webcam. Connect the volt meter across the battery assembly and get the volt meter and the watch in the frame on a webcam.

Runtime is the time from start to until the voltage starts coming down suddenly.