Results: Testing XM-L, MC-E, SST-50, and XP-G emitters **Updated**



If you have a shot of the driver board, or just the part # off the chips on it, you can tell how it works.

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He is correct in that this is in error:

"Run in series, you have to have a resistor that will run the wattage of the light"

It doesn't because the resistor doesn't have to have the same voltage across it as led Vf.

However, your main problem is that putting a resistor in parallel will lower the equivalent "resistence" and therefore not really lower the current much through the emitter. IOW, you'll mostly just heat up that resistor.

Thank's Match! So the general consensus is the XM-L should be driven between 2.4-3.2A for optimal results current/lumen/heat ratio.

I find the KD 2.8A driver the best for the job even if it works at 2.8A for a dozen min or more then drops gradually as Vbatt drops.

We really need some decent buck/boost drivers for cheap!

And for higher voltages 8.4V with few memory modes also!

Good job as usual Match!

Awesome job Match! I think that pretty definitively settles all that nonsense :P

Page 13 for this? Never!

Good work Match. There were similar tests by someone on CPF. People definitely need to pay attention to this thread. Needs a sticky to get the word out. No reason to excessively overdrive XM-Ls. Maybe a catchy title like the CPF one. Something like "Overdriving XM-Ls diminishing returns and loss"

I'd just like to point out that tailcap current is normally not what actually even goes into the driver unless it's a twisty light. Most tailcaps offer significant resistance, this has less of an effect on regulated drivers but with the Manafont 3 mode it has quite a big impact. My L2p tailcap consistently lowers the actual current by about 0.5A from what I read over the tail cap but not through the actual tail switch. The basic L2 switch lowers current a little bit more again.

So, if you read 3.6A on the tail while using the DD manafont drop-in, once you put the tailcap back on the led will probably only see 3.1A of it.

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Great information in this thread, I'v wondered when XM-L would simply start to overrev.

3.25A looks to be a realistic ceiling.

I registered because of this thread,..thanks

Welcome to BLF, Orbital!

Regarding resistors in series vs parallel

In a normal situation - lets call it a DD circuit.

Series - will add a resistance to the whole circuit, reducing overall current draw. Since current passing through each component in the series circuit is the same, the LED will be receiving reduced current draw.

Power in watts is the current multiplied by the voltage drop across each component. The emitter will drop between 3-4V depending on what it is, and what current flows, the resistor can drop any voltage depending on its value.

Parallel - The resistor is effectively independent of the LED because current can flow both "circuits"; the LED or the resistor. Remembering that current draw is determined by the resistance of each circuit, the LED will draw its own current, the resistor will draw its own current and will not affect each other.

With an ideal power supply, the resistor will simply draw current, and make heat. The LED will also do its own thing, as if there was no resistor. So essentially all thats happening is that more power is being drawn

This changes however in a Current Controlled circuit. If your circuit is able to run in regulation, and has enough voltage excess, the 'better' way to reduce power to the emitter is to put a resistor in parallel with the emitter, because the total current flow is limited to X amps. A resistor in parallel will in this case be dividing the current.

A resistor in series will be increasing the total resistance (voltage drop) of the circuit if driven by a constant current driver, and will increase the power draw at the battery end to deliver the same current output. So in that case we will be pushing the same current through the emitter and the resistor. We will effectively just be creating more heat in the resistor, with no reduction in current to the emitter.

The only reason why this is confusing is because we are using current controlled circuits, it reverses the ideas sometimes. This is an example where it can be sometimes counterintuitive. Like for example, when I want to measure the current output of these drivers, I just select the amps setting and short out the driver (only TRUE CC drivers) with the DMM. This short has a very low resistance and normally lets lots of current through, but in a TRUE CC driver it will effectively be drawing almost no power to maintain those 3A. If the driver is not a true CC driver, it will let more amps through and possibly die..

On the other hand open circuits are destructive to TRUE CC boost drivers, with the boost voltage potentially rising very high and killing itself.

And thanks match for the datapoints! Invaluable data!

And thanks for the linear scale graph brted - looks beautiful how all those datapoints line up soo well, thanks to match

First post now updated to reflect testing of the cree MC-E emitter. Test procedure was performed exactly like the xm-l.

Post is now sticky'd for easier reference.

p.s. - Welcome Orbital! Glad to be of assistance.

Folks,

Testing complete and up in the first post for the SST-50. Thanks again goes to BobK for providing the emitters for testing. From the results it's clear that the SST-50 is still alive and kicking in applications above 4 amps.

Great work, Match! I really appreciate the effort as do, I'm sure, we all!

Great work. Very useful also for mod with hard driven emitter. Thanks Match!

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thanks Match

Will there be a test for SST90?! Thank!

Match, thank you for your valuable information with these tests. I have had a 3-4 XML build swirling around in my head and this thread is rich on information. It also answered my curiosities on the SST50's. I know the thread is a bit dated now, but hey, I'm the "new guy". Im guessing that similar info is at cpf but it seems I can hardly stand looking over there for more than 5 minutes at a time.

Have you done a "pop" test for giggles on a XML?

Also something else I would like to see charted- temperature on a smaller given heatsink say after 5 minutes being ran at 2.4A and the same test at 3A.