I purchased a used J18 and J12 from a member, and have had different problems with both after just several uses. I talked to the member and he says they were both purchased from Fast tech. I’m posting a different thread since these issues are different from the other poster who just bought two J12s.
First the J18; This new light I was using outside for about an hour I think in 3x26650 King Kong mode, in the cold (did not seem to overheat) and it suddenly switched off. Now it will turn off on high suddenly after a few seconds. If I turn it off, going to medium or low will usually allow it to be on for longer, but it then turns off again. I can turn it off/on and get another few seconds to minute, depending on the mode, or cycle through to high again and get another few seconds. I’ve tried Trusfire flame 26650s and King Kongs in it with the same result, so it is not the batteries. I’ve also switched tailcaps from the J12 and had no improvement noted. Tailcap is dryish, worked fine for several uses of over an hour the first few times. I have another J18 working for about a year and have not encountered this issue, but I had not used KingKongs in it.
After this happened, I decided to use the J12 for a while in 2x26650 Trustfire config, and got a different problem. Also suddenly while using it, it turned off. I tried to turn it on again and it did for a little while, then went off again and I could not get it to turn on again…so I thought and put it in my pocket. When I got home I found the light was on, just very reduced brightness that you dont really notice unless you are focused on the ground right in front of you, or are in complete dark or looking at the LEDs. It has remained this way since, I can switch through the modes looking at the LEDs seeing the tiny brightness get reduced even more as I go to med and low and then back up for strobe. I’ve tried Trusfire flame 26650s and King Kongs in it with the same result. I’ve also switched tailcaps from the J18 and had no improvement noted. The previous owner used superlube on this tailcap and my first usages over about 30-60min 2-3x were fine.
Batteries are Trustfire Flame 26650’s 5000mAh that test fine with voltmeter, charge up fine and have been used reliably for several months previous. King Kong protected 4200mAh 26650’s are relatively recent, but have worked fine in my other lights without problem.
From the behavior I’m thinking the drivers are the problem… Anyone have suggestions on either situation? Has anyone run into this?