R123A on incandescent bulb?

if i want to use r123a in a SL TT 1-L, SF 6P, SL TL-3, what kind of resistance i can use to simulate the original voltage?

It's not quite that simple. R123s and CR123s are not replaceable 1 for 1. The voltage coming off a CR123 is pretty much 3V, whereas the voltage from a R123 is anywhere from 3.8 to 4.1 or so. If you put a R123 in a SL TT 1-L, there's a good chance you'll give something in there a really bad day (i.e. cook something).

The SL TL-3 is a 9V rig so you might be able to use 2 R123s with a dummy battery spacer. The voltage in that case would be under 9V and the bulb would live to shine another day. It would be around 8.something which is good enough to run most 9V bulbs. I haven't tried this combo, but in theory it should be okay.

The SF 6P is a different matter. The P60/P61 LA in it is intended for 6 volts. With the Surefire you can do one of two things. The first would be to get a Pila 3.7V LA, trim the spring, a use 1 R123 with a dummy battery spacer. The second and probably more fun choice would be to use 2 R123s and get a P90 LA. Don't even think about a P91 the protection circuit in the R123 cells won't allow it to happen.

Hope this answers your question. If not, hop over to the search page and there are plenty of other threads with the same questions.

thanks for the help

i have in mind of don't change the original bulbs. does exist some formula for calculate the resistance?

for example: 4,2v batt with X ohm resistance = 3v batt

You can figure it out with by calculating loop voltage drops, but you need to know the current the lamp likes first. Then with good old Ohm's Law you can figure out how much the resistor would have to eat up. The problem is that the twin task light has 2 types of lights in it so that if you calculate the safe level for the incandescent bulb, the LEDs are probably under driven… or is it over. Too tired to think about it.

On top of that, you'd be throwing power in the resistor, which in itself isn't a problem, but the heat that it generates is. You will need to sink the resistor to a heat sink of some kind. That's assuming that the size you'll need will actually fit inside the light somewhere.

I have run two R123s and a dummy cell on my TL3 and it shines. Only the runtime is a bit short with about 15-20 minutes ( on two 550 macells ). I have also tried running a Pila 168 on my TT2 - the LEDs lights up fine but the incand bulb was very dim due to low voltage. I 'll risk a TT1 bulb and try again /ubbthreads/images/graemlins/blush.gif

Best of luck.

you can change the bulb to 4.2 or 7.2 volt for use with r123.