U2 thermal regulation?

I'm not sure if this is the same problem KDOG3 experienced with his U2. At the behest of a member here, I did the following experiment with my U2:

1) Set digital egg timer to countdown from 10 minutes.

2) Set U2 to highest level.

3) U2 starts to flicker and then turn off on its own within those 10 minutes. A little past 5 minutes on the average.

4) After the U2 flickers and shuts down, I use the tailcap switch to turn it off and back on. Light comes back on to highest level.

Is it possible that these new U2s have some sort of thermal regulation? This U2 would only get warm to the touch. I remember an earlier U2 I had could stay on until the batteries were completely drained and the body was hot to the touch. Any ideas?

It can't be thermal because my L4 and L2 will get SCORCHING hot when left on and they don't shut down. My U2 by comparison, will only get warm to the touch (the larger head helps dissipate heat better). If the U2 shut down from overheating, then the L2 and L4 would be practically unusable. I have done extended runtime tests w/ my U2 without any issues. you have a problem w/ your light, I'd reccommend calling SF and sending it in. This specific issue seems to be a more recent problem. This is the third recent post I have seen referencing this.

Sorry about the defect, that's frustrating, especially w/ such an expensive light. I hope you get it ironed out quick. If you can wait to get a trouble-free U2, I think you'll find it well worth it. My favorite light.

Thanks SCBlur. Looks like a call to Surefire is in order.

pm sent.

grnamin said:

This U2 would only get warm to the touch.

Click to expand...

Sounds like it got too hot and failed. Another U2 would not stop running, and the body would be very hot. It's a safe bet that your LED has a worse connection to the body of the flashlight.

So far, my experiments point to bad batteries. After the light would start to flicker and then drop to a lower level or shutdown altogether, I would then take each battery and test it in a KL1 + Vital Gear FB-1 setup. One battery would still be good, while the other would either drop the KL1 to a lower level or wouldn't work at all. Trying another set of batteries. BTW, all of the batteries I've used so far were SF123s.

Uh-Oh! When the same thing happened to me, I tried 3 different set of batteries, 2 sets of Surefires, and 1 set of batterystation. The problem would still occur. Yikes dude, I think your's might be toast. Is this the Duracoated one? SF might not repair it because of that....

My current will stay on just fine, even when it gets downright hot.

KDOG3, fortunately, it's not the Duracoated one. I'll call SF tomorrow to request a repair or exchange.