How to compute runtimes for various LEDs/Batts

Hi everyone,

I'm trying to figure out how to approximate runtimes for various LED and battery combinations. I'm having trouble figuring out what kind of runtimes to expect from various P60 drop-ins.

Example:
Cree XP-G @ 1.4 amps using a 18560....vs. same LED but a 17670

I don't know enough about electricity to figure this out, and I'm unsure where to look for the proper numbers for specific LEDs.

Thanks.

Approximate run time = (cell capacity / current draw) x.80

(2.4Ah / 1.4A)x.8 = 1.37h

This should probably be in the battery section, but kramer5150 pretty much summed it up.

If you wanted to get more accuracy, something like this

http://www.kenworster.com/ledcalc/

Would give you a better estimate

What are some of the accepted values for the different LEDs? I think XPG was 3.2?

This is only a rough estimate, but

Convert to watts, then calculate:

Guessing that your XP-G has a Vf of 3.2v (won't know until you measure), and you say the current is 1.4A (assuming that's at the tail). 3.2v x 1.4A = 4.48W


Now, say you're using an AW 2600mAh 18650. Calculate to WH 3.7v x 2.6Ah = 9.62WH, then divide battery capacity by emitter wattage: 9.62 / 4.48 = 2.15 hours. Reduce this by driver efficiency. Say (roughly) 85%: 2.15 x .85 = 1.83 hours or 1 hr. 50 min.

An AW 1500mAh 17670 would be: 3.7v x 1.5Ah = 5.5WH

5.5 / 4.48 = 1.23 hours. Reduce again: 1.23 x .85 = 1.05 or 1 hr

How do you account for batteries in series? Just add the mAh(1)+mAh(2), v(1)+v(2)?

Im doing the trueblue mod https://www.candlepowerforums.com/posts/1205794&postcount=21, what method can I use for resistors assuming the LED is regulated from a single level driver?

Some really good info here, thanks guys.

red02 said:

How do you account for batteries in series? Just add the mAh(1)+mAh(2), v(1)+v(2)?

Click to expand...

V1+V2 is correct. The Voltage potential of 2xRCR123 cells in series is 8.4V.

However the mAh capacity of the series pair is equal to the mAh capacity of each cell. So a pair of RCR123 cells in series is 500mAh (for example).

red02 said:

How do you account for batteries in series? Just add the mAh(1)+mAh(2), v(1)+v(2)?

Im doing the trueblue mod https://www.candlepowerforums.com/posts/1205794&postcount=21, what method can I use for resistors assuming the LED is regulated from a single level driver?

Some really good info here, thanks guys.

Click to expand...

Here's some good info to help you find needed resistance:

Click here

Thanks for the help everyone, much appreciated!