Run Times

[houndlegs]

Hi all
Can someone please tell me if i have this correct.I want to get some idea of run time for this system.
2 MCE running at 500ma each ( so my nFlex will be drawing 1a).
If i use a battery with 1mah will it last for 1 hour, and a battery with 2 mah, 2 hours and so on.....
Or do i have it all wrong and theres some formula i could use to work out run times?

Cheers
Phil

 

[matt303]

The current taken by the driver is not the same as the drive current to the LEDs, it will be the amount of current needed at the battery voltage to give the power used by the LEDs plus a little bit for losses in the driver.

e.g. (approx values for driving something like 2 Cree Q5s)

2 x LEDs at 700mA with a Vf of 3.4V each = 4.76W

4.76W / 14.4V (example battery voltage) = 330mA from the batteries without the losses in buck driver taken into account.

The MC-E LEDs have 4 LED elements which if driven at 500mA have a forward voltage of around 3.3V so that's a total of 13.2V per MC-E if all the elements are driven in series. Two of those in series and you are pushing towards the top of what the nFlex can drive and you'll be needing a 30V battery.