RC Tank Warfare community hobby forum

Here's a question for you.

If I have a 7.2v 2000mah battery, how long can I have 10 x 5v leds connected to it before it expires? In reality they will not be on constantly, so whatever time you come up with will be extended considerably, I am just curious as to whether it would last a few hours?

The led's would require resistors but that's not a problem, though could I use one resistor and feed all of the led's from it?

Cheers

Rob G

Errrrrr a long time ?. Sorry Rob just couldn't resist that one
Alan

Hi Rob,

If these are similar to the Maplins CJ64U/CJ65V Kingbright LEDs (p763 of Winter 2009/10 catalogue) then as they each require 13mA then ten will take 130mA. So assuming your pack is in fairly good condition you will easily get 10 hours out of it (10 x 130 = 1300mAh) with some left over.

I've never used these regulated LEDs before, but I guess you _might_ be able to use a single resistor for all ten. If so, then it has to drop (7.2-5=) 2.2 volts at 130mA. Which using V=IR means you need a resistor of 2.2/0.130 = 17 Ohms.

The resistor will get a bit hot though and may burn out (W=I^2R) as it will eat up 0.130x0.130x17 watts ~= 300mW and most leaded resistors are usually rated 1/4 watt. For safety parallel up four 68 Ohm 1/4 watt resistors. Just wind their legs together in a 2x2 bundle.

Hope this helps.

Nige

Hi again Rob to make up for the earlier post one of the guy's posted this on the site which may be of some use to you. Sorry to say I can't remember who posted this up as they deserve the credit http://www.theledlight.com/ledcircuits.html" onclick="window.open(this.href);return false; . All I did was to book mark it. Best of luck with whatever you are planning ?.
Alan

Thanks guys, much appreciated.

Rob G

Heres another that may help
http://led.linear1.org/led.wiz" onclick="window.open(this.href);return false;

No help Rob ... but it begs the question WHY..................
Fleshy.............................

Its supposed to help with wiring diagrams and resistor values, on the warship forum i go on everyone raves about it, i aint got a clue cos i am thick, thought it may help