Surefire 2-Cell Rechargeable Solution

I accidentally got my greedy hands on a P61. Although I do not own a two cell light just having the P61 lying on my desk made me thinking. The thought process was like that:

- Hm, it needs 6 Volts.
- It puts pretty high draw on two primaries.
- Therefore there will be voltage sag.
- So it must be designed for less than 6 Volts.
- A single Lithium-Ion has less than six Volts.
- At a given voltage it most likely will be brighter than a P60.
- Gotta try it.

Result:

Running from one Pila 150S (not fully charged, 3.9 V) it draws 2.05 Amps. It is not as bright as a P90 driven by two Pilas. However it might be a nice rechargeable solution if driven by a single protected 17650/18650 instead of running a P90 off two unprotected RCR123s in two cell lights.

I hope this isn't old news.

I have used that combo with a Pila 168s and it works well except for the reduced output as you have stated. I have not used it for prolonged periods due to me not knowing if it is a good idea or not. I would also like to know if it is safe for long periods with a Pila 168s Li-Ion.

It sounds pretty safe to me. If the draw was too high the protection circuit would trigger. After all the draw is around 1.5C. That should not pose a problem.

I however do not know how the P61's lamp life is affected, if at all.

Reducing the voltage to a incadescent bulb has a few effects. It reduces light output, power consumption, efficiency, filament temperature, and increases bulb life. Halogen bulbs (which I'm fairly certain are the bulbs used in Surefires) are a slight exception.

During use, tungsten evaporates off the filament and condenses on the glass surface of the bulb. Halogen bulbs use a special fill gas in the bulb, which is chemically reactive. In short, it combines with the tungsten on the bulb wall, and then deposits it back on the filament. This can extend the life of a filament beyond what you would see in simlar bulbs with cheaper fill gases.

However, the halogen cycle only works if the glass surface of the bulb is hot enough for the halogen gas to react with the condensed tungsten. If you are running the bulb on a decreased voltage, this is not always the case. Thus, you will only see an increase in bulb life down to about 90% of the bulb's rated voltage. If the bulb is thermally isolated (i.e. heat does not conduct away easily), you may see bulb life continue to increase as input voltage drops to 70-80% of the bulbs nominal voltage.

As voltage decreases beyond that, bulb life won't get any better, but I'm fairly certain won't get worse either. You will have lower brightness and efficiency (lumen/W), and tungsten deposits on the glass may make your bulb seem dimmer over time, but the filament should last just as long, if not longer.

This is my understanding, in any case.

Is the beam still relatively white or does it yellow signifcantly?

btw: I've been using AW's rechargeable LAs for the 6P as well as the Wolf-Eyes 3.6V LA with a 17670. They both draw a little over 2Amps and the cells seem to be holding up so far. I've only recharged the cells approx. 4 times though and don't use the light for more than 5 to 10mins at a time.

Thanks for the insight C_H; I assume the bulb is driven at less than 80% spec.

PhotonAddict: The beam does yellow significantly.