Luminus SFT40 test

I do not understand how the electronics work, my modifications are based on trial and error. I have broken more flashlights than I have been successful. I’m sorry if I don’t understand much but languages ​​are not my thing … anyway I try to learn by reading forum members like you

By the way Pacolux, what is the value of the sense resistor in the 8A driver for KW CULPM1.TG?

The sense resistor is the lowest value, biggest size resistor onboard, and is in series with the driver's output (with the emitter). This is something you may already know. In the above picture, right next to the negative or black wire. It is an R0-something, but what is that something?

Just curious. Given its switching nature, I'd like to know how good is the sense resistor stage in such driver.

R010. Will this driver turn up the current by stacking resistors? I say it because for example in this Convoy driver6V 9,75 | Controlador XHP70.2 para una celda it does not

stacking resistors = additional sense resistors in parallel, it is understood?

People always talk about sense resistors, this should imply that a voltage is measured over the resistor and a feedback-loop is in place which makes the current constant. But in many drivers a fat low-value resistor in series with the output is talked about as sense resistor but it is not sensing anything, it is simply a dumb current limiter, and if nothing else happens in the driver, the current will go down with the voltage of the battery.

Not sure which one is the case in this driver.

The link is wrongly done.

I'd be wondrous if people would steer from using the more limited simple post editor, and everything would be editor-unified, but this is another story which involves sb56637; it's not an straightforward task to convert quotes between editors.

Is it this XHP70.2 driver you are speaking of?

So what did you did with it? :-D

This driver is a switching, boost type driver. Technically speaking, these driver types are the ones which actually pull current. Others like this or that don't pull current from the battery, they just regulate or accurately limit the flow of current from the battery to the emitter, as they are regulated variable load devices.

These driver types or switching converters are usually designed with a power output in mind. The XHP70.2 driver claims 4800mA of output at the voltage of a 2S emitter (“6V”, or about twice that of a more standard 1S emitter like the SFT40 in this thread). I am sure it does it. However, bear in mind this already is a lot of power, and this driver will actually pull or try to pull a very high amount of current from the battery for it to be so. Let's do some math:

Pemitter = Vemitter × Iemitter = 6.5V × 4.8A = 31.2W

Pdriver = Pemitter / ηdriver = 31.2W / 0.9 = 34.6̅W ≈= 34.667W

Where P is power, V is voltage, I is current, and η is energy conversion efficiency (values used for voltage at the emitter and efficiency stem from XHP50 emitter tests and buck and boost driver threads).

I can't find any cut-off voltage in the driver's advertisement (bad practice), so I'll presume 3V. This means that, when the battery is discharged, the driver will pull up to Ilowbatt = P / Vcutoff = 34.6̅W / 3V = 11.5̅A = 11.556A for high mode, and with a full or close to full battery it may start from Ihighbatt = P / Vhigh = 34.6̅W / 4V = 8.6̅A = 8.667A.

And why did I use just 4V as voltage from the battery when the battery is full or nearly? Well, because there is resistance in between (battery, springs, a switch, etc.).

So, it is safe to say that such 4800mA “6V” or 2S boost driver requires between 8.5A to close to 12A from the battery to work in high, and depending on battery state of charge and other parameters like actual efficiency and etc.

Advice: take out that driver from the flashlight you stuck it inside Pacolux, undo the ;-) shenanigan you did and restore its original sense resistor, and be done with it.

I say shenanigan because I feel you probably reduced the original sense resistor a lot. This is like taking a stock car to a tuning centre, and expecting its engine to deliver twice or thrice the horsepower just by reprogramming the control box. LMAO!

I do not mean to say that reducing the sense resistor won't work, but you have to understand what are the potential limits. I once built an SK98 with an H1-A boost driver among many major modifications (pill, switch and shaved XHP50 emitter). Emitter was driven at 4.2A maximum or so (I stuck an R050 over the stock R025 sense resistor, if I'm not mistaken), this is because the boost converter is limited to around 10A of input. I still have it by my side.

The H1-A which is sold now uses an 1.5μH inductor, this reduces its efficiency (they cheaped on it). Initial versions like mine employ a 2.2μH inductor.

Many drivers? Not that ;-) many. Drivers which use low value resistors as voltage droppers are the least sophisticated, and usually super-cheap. You may find them in seedy flashlights, and also in some retailers (example: 2600mA 2-Mode LED Flashlight Driver Circuit Board @ FastTech). As a curiosity, I remember a driver I found in an SK68 flashlight, it was a low current output boost type driver which allowed the torch to work with AA cells (alkalines, Ni-MH, etc.), but it also handled li-ion cells. I am fairly sure that the sense resistor was used as a voltage dropper/current limiter in the latter case.

Fri, 08/27/2021 - 17:12

I reflowed my FT03 with an SFT40 and I think I have a new favorite LED. Current measures 9.63 amps with the HLY cell that came with the light, so I probably wouldn’t put a higher current cell in it. I dont have any way to measure the intensity so I can’t give any numbers on that but it looks impressive.

Lurker turned into a new poster here. I live in China and I just got a 4x SFT40 Jin Heng JKK80 light. The light runs on 3x 18650 and the seller claims 28A max current draw.

Small black dots have already appeared on top and bottom emitters while a bigger black dot is on the right one. The left one so far looks perfect.

While unfortunate, because it is a 4 emitter flashlight, there is nothing I can see in the beam. I’m just wondering if the emitters will stay this way or get worse? I ran it on turbo a few more times after the black dots appeared (2 minutes at at time for about half a dozen times) but the black dots don’t seem to be expanding or increasing in number. I can live with the black dots as long as the emitters don’t get worse.

Not sure, but may be a contaminant or particles causing the black dots. Hope it's not the high amps.

On Ali, this JKK80 claims SST40.2 LED's, interesting. I haven't seen/heard of SST40.2's yet, because we are pretty sure the SFT-40 is a domeless SST-40 new (2nd) generation part.

Did you get a "blue" output on max/turbo? If so, it could have damaged the LED's. I'd be surprised if a stock 3 cell/4 LED light this could happen but it's possible I suppose. Are the springs doubled up or bypassed, or better than average quality?

I wonder if it’s from left over flux or other contaminate that wasn’t cleaned off. Someone else posted about this in the Convoy thread

Tom E - You bet me to it

Have you heard of SST-40.2's yet?

Fairly certain that’s just the same that’s currently being used. The gen 1 were burning the bond wires at 8.5A, but no reports of this happening in the Astrolux FT03 with bypasses at over 9A. I was told a couple years ago that the FT03 was using the gen 2

Ohhh, true - could be right there. From the pic on Ali, it does look like a standard SST-40 we all know now. A domed SFT-40 would have the same bond wires as the SFT-40 I'd assume.

Thanks guys, no blue output - hopefully it’s just contaminants. I’m a little reluctant to open it up again since the flashlight originally had XHP 50.2 emitters but I decapitated them and took off all the phosphor with it.

I live in Shenzhen and I sent it back and the seller Old Jiang (the guy’s name and owner of Jin Heng) replaced my board with 4x SFT40s for 98 yuan.

So I guess it’s bad news… I took it apart and used some compressed air on the leds. It seems like the black spots are from the emitter itself (see the clearer picture below). I actually don’t think the emitters were overdriven much but don’t have a great way to test. They should have received 7amps at the most while SFT40s are rated for 6amps.

The SFT40s should be from a quite new batch since Old Jiang from Jin Heng just had them restocked. Do you guys think it will get worse? I ran it for a few more times on turbo today without more damage. Although my batteries are no longer fully charged.

you have to clean with cotton buds and isopropyl alcohol, pressing hard without fear. Before mounting the reflector, look at the LEDs with a magnifying glass to make sure that there is no trace of anything left.

I’m afraid of damaging the phosphor layer. I also don’t know what I’d be actually removing since I’m 90% sure the black spots were not there before running turbo. Anyone else try Paco’s method?

Had some flux left on the LED which caused a burn mark, used a microfiber cloth and scratched away at it, worked without any issues afterwards.

I’m afraid of damaging the phosphor layer. I also don’t know what I’d be actually removing since I’m 90% sure the black spots were not there before running turbo. Anyone else try Paco’s method?

the match has a nice silicone coating on top even though it may not look like it