MC-E U2 emitter swap question.

[flip]

I have an older Surefire U2 head that I combined with a SF A21(I think) for a 1 x CR123 bodied light. I am running 1 RCR123 in this. I'm not thrilled with the tint or output from this head so I'm thinking emitter swap.

Will this setup handle an MC-E emitter swap okay? I found someone to do the swap for me but I'm not sure that 1 RCR123 will handle the load. Opinions?

 

[Justin Case]

Most likely, the RCR123 will be asked to discharge at much higher than 2C, which is undesirable.

The older U2s used a boost driver to run a Lux V. Swapping in an MC-E probably means roughly at least a Vf of 6V at whatever actual drive current the U2 driver delivers.

Let's assume as an example that the drive current is about 700mA. If we assume that the RCR123 runs at 3.7V, the boost driver has to boost the voltage from 3.7V up to our assumed Vf of 6V. That's a ratio of 6/3.7 = 1.6. Even if your driver is 100% efficient, the RCR123 will have to deliver at least 700mA * 1.6 = 1.1A. If the driver is really more like 85% efficient, then the cell has to deliver 1.1A/0.85 = 1.3A. Since the true capacity of RCR123s is closer to 500mAh under typical flashlight current draw conditions, vs the advertised 750mAh, you are looking at a potential discharge rate of about 2.7C.

You'd be better off using an IMR16340. Those are rated up to 8C discharge rate (over 4A).

 

[flip]

Thanks Justin.