Surefire Driver mod?

Anyone ever do a volts out mod to a KL4/LX2 Surefire LED driver? I have been wanting to use the stock driver out of those heads/ lights to drive an XML EZW LED but mine only put out 5.5 volts. That's not enough to drive the XML EZW or even an MCE decently. I did find one in a KL4 head of mine that did put out 5.8 volts and there was a huge difference in output but the XML EZW runs much better at 6 volts or even 6.3 volts.

I tried an RCR123 with a CR123 in one of the 5.5v SF drivers and did get 5.9 volts out but we all know not to mix chemistries or battery types. Two RCR123 and the 5.5v SF driver put out 6.5 volts but it gets pretty warm and I'm not comfortable at this point committing to that. Figured maybe one of you fellow modders might have already tackled this issue? TIA

The original KL4 driver is a constant current boost driver. You don't control voltage to the LED. I forget what the drive current is, but let's just say that it is 700mA. The voltage you get across the LED terminals, which is what I assume your voltage figures are, depends on the specific V-I characteristic curve for that specific LED. Every LED is slightly different. So for the one KL4 head, at 700mA, the LED forward voltage (Vf) was 5.8V. For the XM-L EZW, it was 5.5V for the same hypothetical 700mA drive current.

When you used 2xRCR123, you no longer were in a boost condition. Now Vbatt > Vf, so you were effectively in direct drive. That's why you measured a Vf of 6.5V. The drive current was higher than 700mA, giving you a correspondingly higher Vf. That approach is probably not a good idea. Although SF seems to build their stuff robustly, you still risk frying the driver.

What you are looking for is a constant current driver that has a higher drive current than the stock KL4 driver provides. You may be able to change out the sense resistors to achieve that. Or replace the driver with something else.

Outstanding! Thank you JC. I sort of figured on what you said but since so many have been modding SF heads/Lights it seemed like the obvious question to ask. BTW the driver I'm refering to is the 20342_A. It seems the older driver versions are the ones putting out about half a volt lower output. Again a big thanks!