Cree XM-L2 direct to 18650 Only 3.4 amps?

Flashlight Modding and DIY Parts
1

I hope I’m not going to embarrass myself again with another question that has a blatantly obvious answer that I’ve overlooked. :open_mouth:

I’ve tried a couple of emitters tested separately to rule out a fault with one of them.

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XM-L2 E6B3 connected directly to a Panasonic NCR18650B fully charged and they’re only pulling 3.4 amps.
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As soon as I connect the multimeter the current shows around 3.3 amps and then it rises and stabilises at around 3.4 amps.

I made sure that I kept a sharp eye on the current so I wouldn’t fry them.
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Shouldn’t I be getting somewhere in the region of 5 amps? I have short, thick leads on the multimeter.

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With the same 18650 cell used in a Shadow JM35 the current at the tailcap is just over 5 amps.
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I’m confused?

2

I asume your batteries are charged to 4.2 volts. The next thing to do would be to check the voltage at the led while it was lit up. It could just be voltage sag only allowing the led to draw the 3.3 amps.

3

Ahhh, thanks for that MRsDNF. :wink:

4

there is some great info in this thread about DMM resistance…https://budgetlightforum.com/t/-/4405
I believe it is the resistance in your meter leads preventing the XM-L’s from reaching their full potential.

5

Thanks for that Dallas, it was an interesting read. :wink:

It does make sense to use the original leads that were supplied with the multimeter, also to take some reading’s before you start modifying.

6

Probably in this case it’s not the ammeter, as it measured another light at 5A without issue.

Thermal sag is what I’m thinking. Probably running hot and Vf changes.

Still, this discussion had me thinking about ammeter resistance. I have to start trying out inductive ammeter. (I have one, never used it due to lesser precision on it.)

7

Yep, the voltage sag. :wink:

The reason I tested the emitter connected directly to the cell was because of the problem’s I’m having in increasing the current by adding 7135 chip’s to a Qlite driver.

I added four 7135’s yesterday and I’ve had a fair bit of practice now so I can get them soldered on easily. All the soldered joints look neat, I’ve checked the continuity and made sure I haven’t applied too much heat yet despite this the current increase is much lower than expected, very frustrating when you’ve taken your time.

I’ll take some more measurements.