LED duration

TB2 · Post by **TB2** » Wed Apr 26, 2006 11:50 am

I have Bandai's 1/35 Batmobile (Batman Forever) which lights up with a single blue LED. I plan to enter this in contests, so I'd like to have the LED on for at least three hours during judging, preferably about six in total over the duration of each contest. It's powered by three 1.5 V watch batteries; how long can I safely leave it on before it fades/dies? Would heat be a concern over a few hours? It's enclosed in the model but I believe there's some "breathing room" there. Thanks.

en'til Zog · Post by **en'til Zog** » Wed Apr 26, 2006 2:27 pm

That depends on just which watch batteries you are using. To get an idea of how long they SHOULD last, take the Amp Hour rating given for one battery, and divide it by 0.020. That's the AH rating of the battery (if given) divided it by the current drain of the LED which should be 0.020 Amps or 20 mA.

If you can't find the AH rating of the batteries, you can use the old "Turn it on and see when it dies" method.

HTH

3D-builder · Post by **3D-builder** » Fri May 05, 2006 6:30 pm

Can you fit 1 AA 1.5 volt battery in your car or base if it has one? You won't have any heat issues with the LED there is no filliment in there, they draw no real forward voltage.Part of the reason they last so long ,you could power one LED probably for days with a bigger cell like a AA just don't forget your resistor because your LED will be working off miliamps.Hope some of this helps,
Regards,

Michael

paraclete1 · Post by **paraclete1** » Sat May 06, 2006 9:48 am

I modified my B-9 LIS robot with LEDs (in parallel) and 2 AA batteries, and it lasted several days. One of the LED's flashed and while it wasn't very bright, it flashed for over a year from the same batteries. I didn't use a resistor either and it didn't overheat the LEDs. However, it most likely shortened the life of the LEDs. But for my experiences, LEDs and batteries have worked fine for most of my modeling needs.

Now, having said all that, I have had some LED's heat up to the point of burning my fingers. So be careful when working with them.

Don

jwrjr · Post by **jwrjr** » Sun May 07, 2006 11:07 pm

The trick allowing you to run a led off of a battery with no resistor works because the battery has an internal resistance. That varies with the battery. Do NOT try this with an AC adapter ... unless you like to see leds get very hot and/or explode. I mean that literally.

paraclete1 · Post by **paraclete1** » Mon May 08, 2006 7:09 am

I've run LED's off AC adapters as well with no noticable problems, but it was for a short duration. It probably is still a good idea to use a resistor. But now my curiosity is up so maybe I'll do some experimenting... in a Fire Proof Location