P60 Drop in driver question.

Ok guys, maybe someone can help explain to me what is actually happening in this scenario.

I built a new P60 drop in for my bored out Surefire 6P. I am using a standard OP p60 reflector with the small thin walled brass pill. The led is an XML2 U2 1D that I reflowed to a copper Sinkpad, and I am using this 3-10v 1 mode buck driver from KD. So, I threw everything together, tested it out on the bench, all is good. Measured ~1a with both 1 and 2 cell configurations, on fresh 4.2v cells. I put it in the host with the same 2 IMR 18350 cells I tested it on the bench with, and BAM all of a sudden, its WAY brighter, but overheats in roughly 5 seconds. Volt meter is now reading 1.8a with 1 cell, and 2.5-2.8a with 2 cells. I take it all apart and see that the bottom of the reflector has obviously grounded out on the negative post of the LED.

So, I got to thinking, what if I pot this sucker, and see if I can prevent it from over heating. I crammed a thick thermal pad from IO, in the driver side of the pill, and filled the leftover gaps and all over the driver with Arctic Silver thermal adhesive. I then applied some Arctic Silver MX4 thermal compound on the reflector threads. I tightly wrapped the drop in with copper foil, and threw it back into the host. Fired it up, and so far, no over heating issues. I let it run for 10 minutes straight now, without a single hiccup. The host get pretty darn hot though, unless I am holding it in my hands.

Anyway, I guess my question is, is this safe? What is really going on here? It seems as though it’s in a direct drive state, but it runs fine on 2 cells? Did grounding it out, somehow bypass any resisting circuitry that may have been on the driver? I’d like to play with it for a while, and see how it does. I build 3 of these drop ins, so I am not too worried if it dies. Also, I would really like to know what kind of power this XML2 is really seeing. Is 2.8a current draw at 8.4v alot? What would this be in terms of wattage? Sorry for all the noobish questions.

Shorting the leads will do that. You should use an isolator disk.

Wondering why you’re using 2x18350.

Well, I wanted a drop in that was versatile in my non bored Surefires. I can now use a 17670, 16340’s and even plain ole cr123’s if that’s all I can find. However, I am using the 2x IMR 18350’s at the moment, because it’s bright as all get out! I will probably just use this drop in with an 18650, and keep it grounded out. It’s almost 2 amps with one cell, so it’s still fairly bright.

Either way, that still doesn’t answer my question. What is going on with the driver by shorting the negative lead?

Even though it's no longer regulating because of the short, all the current still has to go through that tiny little inductor coil with the super skinny windings. That inductor is acting as a resistor and limiting the current to a survivable level.

Ah, I see. So would it be unsafe, or unwise to use it in this condition? I am not worried about regulation per say. I generally keep a close eye on my cell voltages. Plus, I could always use protected cells.

Thanks comfy

I would not use it like that. The inductor is being severely overloaded and long-term it could either burn out or, worse, melt the coating on the magnet wire and turn from a poor conductor into a really good conductor (at which point the LED goes 'poof').

Haha, fair enough. It’s not even close to being practical in this state anyhow. It draws way to much current from multiple cell configurations. I would be looking at like a very limited run time, even if it weren’t at risk.

Thanks again!