Calculating runtime?
02-23-08, 12:35 AM
#1
Senior Member
Thread Starter
Join Date: Jul 2006
Location: Oakland, CA
Posts: 1,300
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
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
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
Zoom zoom zoom zoom bonk
Join Date: Sep 2006
Location: New Zealand
Posts: 4,624
Bikes: Giant Defy, Trek 1.7c, BMC GF02, Fuji Tahoe, Scott Sub 35, Kona Rove, Trek Verve+2
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 551 Post(s)
Liked 722 Times
in
366 Posts
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.
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
Senior Member
Thread Starter
Join Date: Jul 2006
Location: Oakland, CA
Posts: 1,300
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
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
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.
