Did you re-flash the firmware on the driver when you removed the R1/R2?
The firmware is the same firmware as the GT70 which does use the R1/R2 arrangement as far as I know, they just adjusted the resistor values for the lower voltage.
5% gain from removing the window is what Vinh said he got as well, so sounds perfectly reasonable to me.
Yep - forgot to mention I flashed Anduril2. Voltage readings are accurate, least in the ballpark. Anduril2 has voltage cal built in so not a worry.
Ok, that makes more sense. :+1:
What do you think - would a bypass on the spring under the brass cap help much? I'm think'n it might on these modded setups. It looks like a high quality, (beryllium?) spring but it's carrying a ton of amps through it. We are probably over 25 amps and thinking the output curve on the SBT90.2 is probably flattened out anyways (djozz LED test), so probably not much of a factor.
Hhmmm... Maybe it would help to hold higher amps for longer
On a setup like your trying to get every last lumen, it might help a little, but we are talking a very small gain if I had to guess.
For anyone else, I would say it is not worth it.
I don’t see it causing a noticeable gain and we are already at the point of diminishing returns on the SBT90.2 anyways.
I personally am not worried about it.
What's pretty cool about this FET driver setup is that we are probably pulling about 30 amps or so, think VOB measured 27 amps, but 30 amps equates to only 3.75 amps per cell.
Really 3500 mAh cells would be the best option to go with. From tests I've done with the Q8 in the past, the 35E's did pretty well. Was thinking of trying 25S's or VTC5D's but probably not much point.
I am finding measured variances on different cells. For example, I got some 30Q's from 2016 and they are showing their age. Coming off the charger, aging cells will drop fairly quickly to 4.18V/4.19V even though the charger is set to 4.22V. These cells are getting lower #'s then newer 30Q's on the GT90.
SONY cells seem to age/degrade quicker than Samsungs, at least it's been my experience with them. I've seen my VTC6's and VTC5A's and VTC5D's all degrade quicker than Samsungs.
I own over 30 lights, from mini to gt and ms18, the only light that kinda makes sense the light with a active cooling system.
I would have more lights but they are almost all the same, too damn hot and unable to sustain high outputs.
Build cooling systems for your lights instead of bypassing springs and modding to get them hotter.
Remember I said this.
The issue with cooling is that you either go with massive heatsinking like the GT4 for passive cooling and the GT4 is already at the limits of that.
Or you go with active cooling that is loud and annoying.
Active cooling can be improved but regardless of how it is done it will be really hard to make it truly weather proof over the long term since small fans simply do not play nice with real world grime/weather. It can work well in a lab environment though.
Having given a fair amount of thought to active cooling setups, there is room for improvement for sure but the cost would climb in a real hurry and the lights would loose practical uses with it due to increased size/weight along with it.
The best setup thus far I have come up with is a actively cooled design that gives up on weather proofing and simply makes the fan easy to replace when it fails. The cost for such a designs would be a lot more then existing designs to do it properly though. Like 2-3x the price.
I have one idea for a basic active cooled design that would net moderate gains but it only works with a specific flashlight setup. and would still be bulky.
Yea, but not the first one. As TA said, big $$$ and weight, or just settle for lower output levels.
A different approach, is a compromise with shielding the heat from human touch.
Ding ding ding, Been saying this quietly for some time as I usually get heavy push back for even suggesting that the thermal path should be compromised.
I did this to an extent with my EDC and love the results.
You know, this is what they do in commercial lighting. Doing it for years with old style bulbs but betcha they are doing the same thing with LED bulbs.
Hhhmmm. deja vu - think we had this conversation before? 
lol, yeah I think we have, there are a few others that agree with this mantra as well, think djozz is on this train as well.
It is not that complicated really, just reduce the temperature of the handle and let the areas designed for dissipating heat cook to within reason.
For a hobby project with a SBT90.2 I bought this 13cm COB heatsink, it can passively dissipate up to 65W the description says.
I never change my opinion 
, I still think that the GT should have been a box-design with a fat 15cm x 15cm flat heatsink directly behind the led 
LOL, I actually still think that is a good option for the GT4 style light (assuming that it would be manufactured properly, which has been the issue so far, no one I trust to do it right), the GT didn’t output enough heat to make that necessary IMO.
This is a review of the Astrolux MF05 Flashlight and it is compared to the GT90.
You cannot tell the difference in the video beam shots !!
The GT90 is on the left.
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You don’t really need to measure the LED temperature. The main reason for cooling is just so that you can hold the light without burning yourself. The actual LED can handle much more heat then your hand can. Over 200°C. The main point of cooling is just to prevent you from burning yourself.
You can get a rough idea of the wattage being put out by the LED just by calculating the voltage and amperage. I’m sure the SBT 90.2 is well over 100 Watts.
Heat sink with a large surface area like in the picture can work with a very small point source of heat if you use a good spreader such as an intermediary copperplate. Copper tends to spread the heat out very evenly.
Note, I’m not sure I interpreted what you asked correctly.
The reason for thermal stepdowns and cooling is not about user comfort. It’s about not burning the user and getting sued.
There is nothing baffling about flashlights being round and no active cooling. The explanation is super simple. The round shape is dictated by the reflector. It doesn’t make much sense to machine a square flashlights and put a round reflector in it. Square is harder to machine and has extra weight compared to a round flashlight.
Adding active cooling tends to double or triple the cost of the flashlight and reduces the reliability. It also tends to compromise it’s water resistance. This is why you very rarely see it. Nobody wants to pay the price premium for it.
The tongue was because at the very start of the BLF GT project a few years ago, I was sideways involved and suggested a box design with handle (including a crude design drawing) with the led directly on the radiator, like the COB heatsink above. That design was never followed, BLF was in favor of the classic style flashlight shape, which happened. I’m still grumpy about that because I still think I was right. 
About measuring the temperature of your emitters: I’m all for measuring everything, but it is not needed everytime. After following temperatures and performance of a number of flashlight builds, over time you develop a feeling for how to mount your led, thickness of material for heatspreading, and size of radiators. I.e. that 13cm radiator combined with a SBT90.2 on a 30mm copper DTP board at 20A, will be fine (btw it will be bolted to a 20x20x0.3cm aluminium plate which adds a bit extra surface area for heat to radiate away). My educated guess is that after 8 minutes the radiator will be fully heated up and in steady state, about 90degC, by which time the 21700 battery already will be two-thirds depleted so that the current will drop significantly. Let’s see after the build if I guessed that right 
LOL, I still think the box idea is a really good one, just for a different style of light. I have a few ideas bouncing around that would make really good use of it but sadly have not found a manufacture I trust to do it properly and done wrong it would ruin the whole concept in the eyes of manufactures.
Also agreed that it is not necessary to take detailed temperature readings for flashlights most of the time. First off with modern copper MCPCB’s the temperature of the shelf is pretty close to the temperature of the LED itself. Meaning you can get a really good idea of the temp with an IR thermometer on the outside of a light and modern LED’s are generally rated for up to 150c+, so it is highly unlikely you will be anywhere near that regardless.
Basically I have never had an LED die due to age, this is not a real concern for flashlights that would be lucky to get a few hundred hours of use with LED’s that are rated for 50k hours.