Thanks DBC. Looks like you have yourself a real nice light there. The emitter measurement at the led is no different than taking a measurement at the tailcap. Remove the earth wire to the led and run it through the meter and back to the led. You know that you really do need a lathe. When is it coming?
OL. I have it on good authority that Buddy the white dog was black before this flashlight shootout.
Wonderful pictures! And a nice mod!
Looking forward to emitter current measurement. :)
pulling a lead from the emitter and having to solder it back on just for that reading? Doesn’t the tail cap reading say enough? That 32mm copper star on thick aluminum with a 1/4” of copper underneath it sure makes it difficult to solder a lead!
If you think it’s worth getting that number, I’ll consider it. But really, what’s it going to tell us that 4.05-4.15 at the tail doesn’t say? I suppose I’d also have to run it in Voltage configuration to see what the Vf is at x amperage reading while I was there, right?
I’m still new enough at all this that when I get a build done and it works I’m scared to mess with it in fear it’ll fall off the cliff it’s been perched on the edge of.
With my limited testing and experience you will probably get between half and two thirds the current reading at the led compared to the tailcap which has something to do with the higher forward voltage. You get a lower current measurement than you would if you had an XM-L led in its place.
I’m not sure if you have seen this thread.
to really get an estimate on how many lumens it’s putting out is to take an amperage and voltage reading directly from the emitter?
Here’s some more numbers for the numbers freaks…start at 91.1º and in 5 minutes it’s at 133.3º. Pulled cells, top cell showed 109.9º at the positive end. The host was sucking heat from the head at an alarming rate, which is why I pulled the cells immediately. It get’s hot, it spreads it, but man it’s bright for that 5 minutes! 
Cells went down from a freshly charged 4.20 to 4.03.
I looked earlier and didn’t find it and got distracted. Sorry bout that. Try reading this thread and I believe you’ll find the answers or the people that have them.
Ah thanks! And no problem. I forgot 7135s don't have the 6v limit like the MCU, but they are all about how much voltage they can drop before burning up. Now I just need to think about how that zener diode and resistor work to drop the voltage to the MCU. I'll have to break out my "Electronics for Dummies" book again.
And I got 6.42Vf on high. So those 12 7135 chips are scrubbing 2V between em, before taking sag into consideration. Not any worse than a 4.2V cell running a 3Vf emitter with 8 chips.
I’m told the chips DO have a 6V limit, the MCU has a 5V limit.
I also got some crazy numbers taking amperage readings, but can’t believe em so won’t even post em. Ultimately I ended up with a last tail reading of 4.41A, taken the way I always take tail readings. I’ll leave it at that. I will say though, like I did on the other thread where all this is being discussed, this K3 pointed at the ceiling lights up the room better than my S2200, even better than my Elektrolumens Triple XM-L2. And for me, for this little light to do that, that’s saying a lot!
Edit: I set up the Canon G1X in my bedroom, limo tint on the windows and specially made “room darkening” blind drawn tight. (The blinds are narrow with the cord cuts also as tight as they can be made, custom fitted to the window frame to allow minimal light to pass) Aperture priority with aperture on 2.8, ISO on 800. A test exposure took 1 second. The Elektrolumens Triple XM-L2 pulling 8.48A pointed at the ceiling exposed at 1/10 second. Same point for the Solarforce S2200 on Hi, exposed at 1/15 second. Again, same point for the K3 exposed at 1/20 second. The camera shows the K3 is clearly brighter than my other monster lights!
i think the zener limits the voltage to the MCU, but may be wrong... i always thought a zener was used to have a low voltage cutoff, but i dont really know much about this stuff, maybe they can be used in reverse
did you stack the zener and resistor, or remove the stock parts and replace them?
put the resistor in the polarity diode’s place (removed the polarity diode)
So the 7135's do have a 6v limit (too lazy to pull up data sheet on my phone)? Will they just not last as long pushing 8.4v minus sag?
A voltage measurement is only a measure of a potential difference between two points in a circuit. The current-carrying part of the 7135 never sees the 8.4v input voltage, as it has no connection to the positive side of the power circuit, only to the LED- and GND. The voltage between those two points is only 2v.
The zener/resistor mod takes care of limiting the voltage for the MCU and the voltage the MCU applies to the Vdd pin on the 7135.
The zener diode is a controlled leak in the power supply to the MCU. Being installed 'backwards' between the MCU's power pin #8 and ground, any voltage above its rated voltage is 'leaked' away to gnd, so a 4.3v zener will work like a pressure regulator or a bleed-off valve and maintain voltage on that line at... 4.3v. If the voltage applied is less than the rated 4.3v, the zener will block current flow like a normal diode.
The ~200 ohm resistor is there to limit the current available to be leaked away through the zener. Without the resistor the zener would either burn up or waste too much battery power.
Appreciate the explanation. Loving the modded K3! Hot little demon that it is…
In trying to take amperage measurements at the emitter, I took a close look at my stacked chips. The tail numbers I’d gotten previously seemed low at 4.05-4.12A. Seems like one of the chips I added wasn’t making a good connection so I made an attempt to add solder to it to see if I could regain that chip. And it seems to have worked! I’m now getting a solid 4.40A reading, even off not-quite-so-fresh cells. No flickering numbers, easily repeatable 4.40A. The numbers add up to 4.56A at 380mA chips, but I understand the ratings aren’t usually correct and 380’s tend to run a bit lower while 350’s tend to run a bit higher. So this makes perfect sense now and all seems to be working as it should.
Also added some thermal paste around the copper slug in the pill to help it make contact with the sides better. And as mentioned I added a copper plate on top of the chips.
I’ll get the cells charged up fresh and run the heat test again, see if there’s any visible difference in the amount of time it takes to reach Hot!
Oh, and you're aware that's a faux-copper MCPCB with a dielectric layer, right?
So I might just have to implement my plan and take it a step further, make a pillar atop the heat sink to bring that dead phoenix back up from the ashes. And here I was thinking they did something right! That’s it! I’m not buying another Solarforce light no matter what! This week.
Thanks for letting me know.
<—-goesoffgrumblingandcursingunderhisbreath,swearingvengeanceonthepennypinchingtightwadsthatunderdesignflashlightsforaliving
And where’s the best place to buy Noctigon pads for MT-G2?
Had I known that the “copper pcb” was of that variety, I’d never have glued it down! Now how am I gonna get that bad boy outta there? Do you know what bin the MT-G2 is? Like, does Solarforce use the 5000K PO group emitter? Is that one readily available? Cause I’ll flame that one out of there if I have to! Hate liars, and that bogus copper board is a blatant lie! OTOH, it does make a ton of lumens, so a change would only make it better, right? This is the side of modding that gets exasperating…
Thank you very much for a very detailed and in-depth experience of the K3. Sure looks like a must-have :)
Strip the pill down to just the pill & star, blow hot air from the bottom, lift the LED off. Then pry out the MCPCB.
IOS is the only source for Noctigon, it's their own house brand.