Calculating runtime?

MrNaz

Enlightened
Joined
Jul 20, 2006
Messages
244
Location
Melbourne, Australia
3.7V battery, 880mA
3.7Vf LED

One DD LED from one battery with a 350mA AMC7135 board gives you about 2.5h runtime.

Now, lets say I have 3 LEDs and 3 batteries, configured like in the first diagram here:
https://www.candlepowerforums.com/threads/201392
I actually just built this:
http://static.mrnaz.com/tmp/driver_cleverness.jpg

How do you calculate the runtime? I have 3 batteries, and 3 LEDs, so there was a proportional increase in energy use and energy supply, but here I see a total of 880mAh x 3 batteries = 2,640mAh. Current use is still 350mA, so now my runtime is 7.5h? That can't be right, surely?

The same number of LEDs and batteries, connected to one driver each would give a total runtime of 2.5h. So by configuring them this way, I get 3x the runtime for free? I can't see a fault with it, but I have Homer in the back of my mind saying "Lisa, in this house we obey the laws of thermodynamics!".
 

Packhorse

Flashlight Enthusiast
Joined
Nov 29, 2007
Messages
1,912
Location
New Zealand
You have wired the batteries in series so you triple your voltage but the mah capacity remains unchanged at 880mah.
 
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