Current question

I have two Ultrafire BJO8A lights using a single 14500. Using the same battery one has a current reading (tailcap) of 800 mA and one has a reading of 650 mA.

Is this just likely to be differences in individual emitters and drivers or could it be a good/bad connection problem.

I've read of some people spraying their threads with Deoxit or something like that. Is that just a CPF fetish :) or could cleaning the threads make that much difference?

This has nothing to do with the tail cap and switch since the readings are with the tail cap removed. I've wiped off the threads so there is nothing obvious to explain the difference.

Edit: After experimenting some more... the light with the higher current draw is dimmer than the one with the lower draw as measured with the light meter.

When I put the pill with the higher draw in the light with the aspheric the lux reading is less than when I match the aspheric head with the lower draw pill.

Would this be a combination of where the driver is less efficient but the emitter is more efficient (higher lux reading). Could the other pill with the higher draw have a more efficient driver and a less efficient emitter?

It's an odd outcome and it's very repeatable.

I even took a bare emitter reading from both lights and the light driven at 800 mA was dimmer than the light driven at 650 mA.

It could be losses in the light body which you can check for in part by exchanging the pills. Or it could be one sags more due to heat than another. You can then also check voltage across emitter to check it's not driver itself.

I did exchange the pills and it is in the pill. It happens right at start up as well so heat build up isn't an issue unless it's just poor contact of the emitter with the pill on one and not with the other.

How do I check voltage across the emitter? Pull back the white material (fabric) covering the pill and then put the probes on the + and - pad of the emitter while it's turned on?

Deoxit does work. Remember the Sky RAy SR3800? I had it on DD now.l I got 2.5A or some initially on all batts and i was intriguide, i expected it to be higher. I already cleaned all threads when i first got it like 2 months ago and it was ok.... More of de-oiling the light. heh...

I re-cleaned it now and wah la...nearly 5A on freshly charged Solarforce v2 2400s. Hehe....... I guess need to clean it regularly, i mean the Aluminum oxide and residue oil (can't seem to get it all off, even though i am using thinner/isopropanol). I guess the threshold was at 2.5A, with your 1A-1.5A XP-G it doesn't matter.

800mA vs 650mA. Sometimes if the emitter is not mounted correctly (very plausible with cheap lights), the heat might be hotter esp for 0.8A. In this case the heat is the limiting factor, not current. When emitter junction reaches past 120 deg C for most Cree stuff, it actually makes less lumens than at a slightly lower current. You can play with it on the LED calculator. As i have shown many times, there is life to XM-L @ 4-5A when sufficiently cooled as I have shown in my tests. (match's testing with a very big block does have a lot of heat mass but you need to wick more heat faster from the local junction and local metal mass, active cooling by creating a huge temp difference esp with latent heat of fusion is one of them).

Too bad, over here i can't take advantage of latent heat of fusion, and its always damn hot here!

Yeah. What you're going for is to isolate whether it's the emitter, or something behind the emitter. A higher voltage across the emitter I think would imply higher current given similar emitter bin, and what you would expect from higher draw. Ideally you want to measure the current across the emitter, but this isn't as easy.

The emitters may be different bins, or possibly one is damaged. If you could swap the emitters on the drivers then you could further isolate the problem. Of course if you do this then you may also be able to measure the current through the emitters. (Current - through; Voltage - across)

This is what happens when you start comparing things. "A man with one watch knows what time it is; a man with two watches is never sure."

Best of luck, let us know what you find.

Soldering is not within my skill set :) and even the white covering over the emitter is not looking easy to remove. I'm not sure at this point whether it's hardened paste or a white fabric but it's not coming up easily.

I've decided to leave well enough alone (not the choice I usually make by the way) :)

I put too much effort into getting two of these lights and changing out the switches and optics. The one with the lower current draw but greater brightness I'm using with the aspheric since brightness matters more there and with the TIR I'm using the less bright pill.

They are both supposed to be XR-E Q5 and there is no apparent damage to the emitter but who knows!