Surefire P90 in a G2 with 2x LiFePO4 cells

First off, hello, this is my first outing into the incan section of CPF.

This post was going to be a question, but as I started to write it, I realised that it was about time for me to start taking some of my own risks and doing my own tests.

So, I put a Surefire P90 in a G2 (with aluminium head, not nitrolon) and used 2 x LiFePO4 batteries.

My questions were going to be, will it....

A: Not work, the P90 needs the full 9v, or at least more than 2xLiFePO4 can offer.
B: Work.
C: Something else will happen that I haven't thought of.

Well, I tried, and it worked, but I'd appreciate it if anyone has anything to offer as advice.
Is it a good idea, and if it's a bad idea, why?

Thank you

The P90 will work with two 3.7v rcr123s, what is the the voltage of the LiFePO4? I should also mention not to use a P91 with such small cells.

Nominal voltage 3.2v, LifePO4, bought from AW on the MarketPlace.

What's the voltage off the charger, and how do they hold under load?

I wouldn't really know how to explain it, but there is a discharge graph from 0.5A to 5A in post#2 of the sales thread. The only extra I could offer is a quote from AW....

"RC people have been discharging PO4 cells routinely up to 10C without any problem to the cells"

http://www.cpfmarketplace.com/mp/showthread.php?t=125353

EDIT: Voltage off the charger is 3.7v

It is probably dimmer than it would be with the third cell.

The way incandescents work is if the voltage sags it isn't as bright. I'm sure you've seen it in your house, the voltage drops and the lights dim.

Probably going to be dim and will drop off rapidly. I'm not sure, but I'd think that you may get a better beam from overdriving a P61 bulb with 2 LiFePO4s... not sure if it will blow but regardless you're going to have terrible runtime either way.

Hi Niconical!

As it turns out, there aren't really any tactical lamp assemblies with a design voltage that pairs well with any number of LiFeP04 cells. CR123s operate ~2.2-2.5V into the load of a tactical lamp, LiCoO2 cells (regular li-ion) runs around 3.7V give or take, a pair of 3.7V cells takes the place of 3 CR123s nicely, but a pair of LiFeP04 cells comes somewhere in-between. You can't really drive the P90 very well, and can't really drive a P60 type lamp very well either as it will likely blow the bulb. The LiFeP04 cells are best used in those LED lights that don't tolerate 3.7V cells very well

Eric

Look here for rechargeable configurations http://candlepowerforums.com/vb/showthread.php?t=161536

edit nevermind... I thought it was a Surefire 9P and not a G2.

Well, a summary.

The P90 used with 2 x LiFePO4 (6.4v total) instead of 3 x CR123A (9v total) is a more yellow light. It runs about 20% less bright than with 3 x CR123A, but that's a rough figure based on a cheapy lightmeter. I got about 20 minutes of useful light before each LiFePO4 hit around 2.5v, so it was time to pull them. It could have gone a while longer and still been voltage safe for the cells, but it was already starting to get quite dim so wouldn't have been much use.

So, all-in-all, I'm happy. An easy way for me to run an incan light, and more importantly, it didn't cost anything to setup and won't cost anything to run.

Did you continue with this experiment to see how long the bulb lasted?

Running it that much lower a voltage ? This thread is from 2008 and I bet he never blew the bulb yet if he continued running it that low.

It's since been found in practice that Lifepo4 cells can directly substitute in anything that runs off 3,6,9,12,etc volts respectively. I would not have hesitated to try running it off 3 lifepo4 cells.

I'm surprised. A p90 is designed to be run on about 7.5V or so. Three lifepo4 would be at least 9v. That's a significant overdrive

Isn't the P90 a 9v 3cell bulb?

Yes but the cr123 cells drop to 2.5v a cell at the load of a p90. So total of 7.5v. 2xrcr123 would also be around 7.5v. 3x lifepo4 would be 3.2x3=9.6v. Very overdriven. It would almost certainly poof.

Almost forgot about this.

Bare in mind, in that size format, a lifepo4 cell is going to sag pretty hard also.

I have a small 2 cell nitrolon copy that I run lifepo4 cells off of no problem.

The bulb is rate 4.8v 1.1a. Fresh cells sag down to 2.65v with this bulb.

Again, I wouldn't hesitate to try it.

Ok. Didn't realize the 16340 size lifepo4 cells were that bad