Bike Forums > Calculating runtime?
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 02-23-08, 12:35 AM #1 BikeManDan Senior Member Thread Starter     Join Date: Jul 2006 Location: Oakland, CA Bikes: Posts: 1,300 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 1 Post(s) Calculating runtime? I don't know why I have so many problems with these calculations but I cant get my numbers straight So say that I want to run 3 Cree LEDs at 350mA from a 14.8V 4.4AHr, what kind of run time is that? Appreciate the help
 02-23-08, 12:56 AM #2 znomit Zoom zoom zoom zoom bonk     Join Date: Sep 2006 Location: New Zealand Bikes: Giant Defy Composite, Trek 1.7c, Avanti Circa, Nishiki SL1, BMC GF02 Posts: 3,488 Mentioned: 2 Post(s) Tagged: 0 Thread(s) Quoted: 70 Post(s) Roughly 15 to 16 hrs: Method 1 LEDs are around 10.2v total. 14.8v/10.2v = 1.45 * more volts than needed 4.4Ah/0.35A = 12.6 hours 12.5 * 1.48 = 18.2hours Minus 20% for driver losses, around 15 hrs. Method 2 At 350mA a led is burning around 1.1w... total 3.3W Your battery has 14.8V * 4.4Ah = 65Wh(watt hrs). 65Wh/3.3W = 19.7h Again minus 20% for driver losses = 16hrs.
 02-23-08, 03:02 AM #3 BikeManDan Senior Member Thread Starter     Join Date: Jul 2006 Location: Oakland, CA Bikes: Posts: 1,300 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 1 Post(s) I appreciate you taking the time to explain something so simple. I think I got it now, thanks Seems like I should step it up to 750mA 3.7V per LED * 3 = 11.1V driven 4400mAh / 750mA = 5.87hr 5.87 * (14.8V / 11.1V ) = 7.82hr 15% loss = 6.65hr Not bad at all. Can finally put my halogens to rest Last edited by BikeManDan; 02-23-08 at 03:13 AM.