Battery Runtime Calculation

[Goldigger]

Hi,
Apologies if i have posted in the wrong place.
I have put together 3 Seoul P7's wired in series driven by a Konlux 2800 driver + BOOM P7-S reflectors. I ran these of a 12volts mains adaptor with the p7's attached to a heat sink.
I think the Konlux 2800 driver drops 2 volts, so i get 10volts shared by the 3 leds 3.3 volts at 2800mah/8400mah? I know the leds require 3.7 - 4.2 volts max each.
They ran fine and didnt get to hot, the driver stays nice and cool. I plan to put this in a suitable host for a dive torch. The part that i am not to sure on is how much runtime i will get from a battery.
My options are a 12volt 4.5ah, 12volt 9ah or a 13.2 volt 4.5ah pack.
Please can somebody advise me how to work this out?

Is the following correct? is this total runtime? how much could i expect it to run at full brightness?
P led = 3 x 3.7V x 2.8A = 31.08W
Battery = 12.0V x 4.5Ah = 54Wh

Let's say efficiency is 95% for the driver.

P in = P led / Eff = 31.08W / 0.95 = 32.7W

Therefore Runtime = Battery / P in = 54Wh / 32.7W = 1.6 hours



Thanks in advance

 

[DM51]

I'll move this to the Batteries section for you.

 

[SilverFox]

This must be a cross post.

I just posted in the other thread.

I will close this one and we can continue the discussion in this thread.

Tom