~MT-G2~ Pocket Monster (hard way moding SK98) now VIDEO preview

I feel I am missing the explanation of how you are giving it enough current to need the copper heat transfer parts. From the Cree site, 3 A at 6 V. There doesn’t seem to be enough 7135s and maybe not enough batteries for that.

Um…it’s still making ALOT of heat the MT-G2 emitter is what 2x-3X the size of the XM-L and the SK98 just doesn’t have alot of meat to absorb all that heat…copper will pull it away, and then dump it into the aluminum pill, aluminum pill to body, and all it can do at that point is just get hotter and hotter and hotter, these flashlights just don’t have the mass or surface area to convection that heat away…unless you consider the palm of your hand a good heatsink

If you look, he has stacked 18350’s, pushing 8.4v at full charge, thru the regulator (this is why he put the voltage divider 200ohm resistor and zener as to not smoke the ATtiny13)

Per the MT-G2 spec sheet:
The thermal resistance of the MT-G2 LED is 1.5 °C/W, so at 18.5 W the junction temperature (TJ) will be approximately 82 °C

6v at 3A is 18 watts…so he has 179.6F worth of heat in his hand…that is plenty hot to make me want to drop something that hot pretty quick

I am still missing something about how the MT-G2 is driven to its rated current, or why an SK-98 can’t handle less than that.

It is overdriven with total of 12 AMC 7135 rated to 350mA each. Theoretically they should give mi 4.2A on high but I’m reading 4.48-4.52A. 7135s basically don’t ask for voltage as long as emitters Vf is close to input voltage. In this case 8.4v and under load input voltage drops under 7V so 7135s doesn’t need dissipate more than few hundreds miliamps. Copper is added for keeping led performance for longer period…

Ok. Thanks. Somewhere above I missed four of the 7135s.

That explains so much, I am so glad you wrote that concise chunk of data. I can really use it. Thanks.

Nice explanation on the heat issue WarHawk. I need to remember how to do that.

I think many of us here build/mod our lights to have high modes way beyond what the host can handle continuously. I like to have the ability to blast out light if needed. I usually only need high for a second or two. Lows are the best modes for me as I like to see outside of the spill with my remaining night vision. So a light like this is what I strive for. Unfortunately, you can't give/.sell these types of lights to anyone but fellow flashaholics. Well, you shouldn't, that is.

Hahah yeah… gotta love the blast of absurd light some of these tiny modded lights can do.

My modded Sunwayman C20Cs, one with 3 amp MTG2 and the other with Comfychair FET mod and triple XPG2 emit so much light that if you hold the lens against your hand and turn them to max, your skin feels burning hot after just a few seconds. It’s fun… but could be awkward if it turns on accidentally in your pocket.

The MTG2 makes me especially nervous…. 15 minute runtime at max power, no automatic stepdown, can probably set pants on fire from either the beam or how hot the head will get. And to top it off as a 2-cell li-ion light in series it could explode if run too long if one cell depletes faster and then gets reverse charged by the other.

I’d planned to make an alternate driver for the MTG2 using Comfychair’s FET mod + zener diode + DrJones Lumodrv…. but I’m thining I’ll hold off on that. This host might be just a tad too small.

Well it’s a cross between my two hobbies, flashlights and vaping [nothing new really and it’s really basic electronics math]…vaping we deal with watts or heat energy, pulling volts and current thru a teeny wire, flashlights…same critter but we are concerned with pulling volts and current thru a light emitting diode (yeah it generates light rather than heat UNTIL you start pushing it WAY over it’s rated current limits) and we really don’t concern ourselves with watts…till you start pushing em REAALY hard, then you have to take into consideration where all that heat energy is going to go and figuring out the most effective way to move it away from the emitter because heat + LED = very very bad

Simple electronic math…but now we know why when you push a emitter rated for 3A max…why the thing gets more heat out than light, and things get rather warm…fast :wink:

This is also why I really like the STAR V1.1 firmware automatic throttle…you have a 2 min wide open blast out the light/heat turbo [it is configurable as well]…but then it automatically steps back to approx 50% PWM…effectively halving the original heat pumping blast of light, but the beautiful thing about cree is they are MORE efficient at lower power levels…so even cutting the power by 1/2 doesn’t reduce the output of the light we see by half…but it does chop the heat

Few days ago I was going back home from night ride with my bicycle in 2 am and I stopped by on local skate park to light a cigarette and play with mt-g2 sk98 a bit. Two minutes later crim police came to frisk me. I presume that they thought that I was waiting somebody for drug delivery or vice versa. After frisking and 10min of shining around with his 9led flashlight in order to find if I dropped something on the ground policeman asked me what’s that flashlight that I have. Luckily, last mode used was high :bigsmile:. After turning it on suddenly the child was awakened in him, he was absolutely blown away by the sheer output that was coming out from such a small flashlight and keep playing with it for couple minutes till his hand starts burning .After few minute chat they let me go. Two days later I was going to patrol station for cigarette tubes at 2:30am and on the way back traffic police stopped me ( nooo not again :expressionless: ). They were wondering what am I doing in the middle of the night with backpack. I showed them package of cigarette tubes and showed them store receipt. One of them asked me what am I doing in free time and I showed him my mt-g2 sk98. The first and only thing he noticed is the brand “ultrafire”. He showed me his ultrafire zoomie from ebay and asked me what is special about mine and I told hem that it’s full custom light and that I mod them in in free time. In his mind there is no way that flashlight that is smaller can be brighter than his bigger one. He turned on his and then turned on mine to compare. Last mode this time was low and his reaction was: “mine is a bit brighter, your’s not bad for its size ”. I told him that it’s on the lowest mode and that it can change mode by halfpressing the switch and only first time fast double halfpress… He was surprised with power and I saw jealousy in his eyes . “What batteries are in yours? Mines are empty ” he said to me. I said him: “unscrew the tailcap and check it out”. He saw two cells and thought that that’s the reason why is mine so much brighter than his. He started unscrewing his tailcap, took out his “empty GTL 5000mAh” cell and started putting in my two cells in. “No no no no, you will burn your light ” I said to him. He didn’t believe me and continued. I told him that I’ve warned him and that I’m not responsible for the failure. One big flash and his driver was dead, probably emitter too :bigsmile: . Big disappointment :_( … I said him that I can repair his flashlight because I have spare parts. His ego was wounded, he couldn’t accept my offer. After some chat he let me go home. I laugh all the way to home, what a night… :bigsmile:

MOD UPDATE: High was too low, low was to high J) . Yesterday I took some measurements and saw that I have spare room for four more AMC7135s on the battery side of driver. I stacked two 380mA chips from Qlite driver and replaced nanjg MCU with Qlite MCU. Moonlight mod on mt-g2 and 5 amps on high with well spaced mods in between. Now I am satisfied :slight_smile: .

Stellar mod! I’m jealous with your skills. :expressionless: 5A now? Must be very hot.

Thx! My skills are very limited but I learn relatively fast. And yeah… BAH, HAH (bright as hell, hot as hell :stuck_out_tongue: )

PH_Oton, that is great to hear. Sounds quite sweet. Getting stopped and searched by cops for no apparent reason is a bit unnerving. Great stories. Thanks for sharing them.

WarHawk wrote:

Per the MT-G2 spec sheet:
The thermal resistance of the MT-G2 LED is 1.5 °C/W, so at 18.5 W the junction temperature (TJ) will be approximately 82 °C

I guess I didn't look close enough last time. Will you please tell me how you get to 82°C? I'm assuming you factor in ambient temp, but I would figure that would be no more than 30°C additional at room temp.

Of course being out a lot at night makes you get stopped and also makes you like flashlights. Nice story.

I am not clear on how many 7135s you were able to fit in.

Just found the data sheet and went from there…I didn’t factor anything…calculated watts and temperature per watt, not scientific in any way.

My math could also be WAY off which it definitely looks that way…DOH

W = A × V

W = 5A X 8V (for stacked batts)

40 = W
So 1.5C/W = 60C…not 82…herp derp

Honestly…looking back at it…I have NO IDEA how I came up with that number… :confused:

That is 40 watts if the 5 amps and 8 volts happened at the same time. The batteries have internal resistance, so the voltage drops as the current increases. Maybe 40 W heat, but not 40 W light.
Beautiful work.

i think you figure the watts the emitter is putting out?

using the voltage forward of the emitter at the amperage you are feeding it… times the amperage (usually a tail cap reading, close enough)

in this manner? an xml emitter, running 3.5 volts at 3 amps… is 3.5 x 3 = 10.5 watts… so, we call that a “10 watt flashlight”

likewise, the run of the mill smaller emitter, getting fed by a 1 amp generic driver? is 3.5 volts x 1 amp = 3.5 watts… so that gets called a “3 watt flashlight”

or i could be wrong about this, wait until someone with more experience confirms or denies it…

i have a 12 volt driver feeding a 1050ma driver… but the driver is putting out around 3 volts to a small 1 amp rated emitter…

3 volts x 1 amp = 3 watts…

on the logic that you use the battery voltage? i would say my setup was 12 volts (battery) x 1 amp driver = 12 watt light (its not, lol)

Exactly 16. First I thought I can stack only 4 more on the emitter side of driver but then I realise that I can stack 4 more on the battery side of driver because I’m using button top cells and I have spare room between cell and AMCs .
I will post photo today.