Luminus SFT40 test

This 8A “12-groups/biscuit” buck driver at Convoy (marketed for the Osram KW CULPM1.TG or White Flat 4040 2mm²) is also suitable for high powering this SFT40 led (better than for the CULPM1.TG, imho). It's pricey, though.

I'd prefer a universal, high efficiency regulated high power boost-buck driver. A regulated boost-buck driver always ensures the full drive current independently of battery voltage or state of charge (for as long as the input voltage is above the minimum, that is). This way you wouldn't need to care about angry blue overdriven emitters, or always fully charged batteries to get maximum performance. But well…

Does Simon will offer L21A with SFT 40..

This host goes very well with the SFT40. Host L80, Mantaray driver with a stacked R020 resistance and 20AWG cables, 2 20AWG derivations. With the amperimeter clamp I measure 11A and according to my measurements (which can be a bit high) 2620lm and 670,000cd

What’s the reflector inner diameter and bezel outer diameter on that L80?

Nice numbers anyway

Bezel 76mm, Reflector I think 69.5mm x 55mm depth

Mantaray driver with a stacked R020 resistance? What I can remember from having seen it in AliExpress somewhere, the Mantaray driver you are speaking of uses an R015 sense resistance, and claims up to 7A of output. With these figures it is easy to infer that maximum sense voltage is Vsense = Istock × Rsense = 7A × 15mΩ = 105mV.

Technically speaking it is a linear driver or regulated variable load driver. Uses a MOSFET or MOSFETs as variable resistors, and a sense stage to “feel” the flow of current and do its job.

These drivers are set for a particular current. When current goes through them, they sense it in their MCU thanks to its sense resistor and operational amplifier. This allows them to regulate in a sort of conscious way.

The key with these is to adjust the sense resistor value properly, if required. When you change the value of the sense resistor in the driver, you can obtain the new maximum current value by using Ohm's Law. Also, additional sense resistors in parallel add current to the limit. The limit for the stock driver is I = Vsense / Rstock = 105mV / 15mΩ = 7A, this is explained above when calculating the maximum sense voltage. Now, with an R020 in parallel with the stock R015, we have to add: I = Vsense / R020 = 105mV / 20mΩ = 5.25A. All of this being said, Pacolux's Mantaray driver with both an R015 and an R020 in parallel as sense resistors will now allow up to 7A + 5.25A = 12.25A to the emitter before using their MOSFETs to throttle the output and protect the emitter from overcurrent in doing so.

All of this being said, Pacolux is overcooking its SFT40 emitter. I think 7A is plenty for this emitter. If you really need to add something using this driver, I'd use an R100 for 1.05A extra, 8.05A total. This is toast enough. Please consider that not all emitters behave exactly the same, and that one must be sure that the driver fully meets the claimed specifications, because if not final maximum current figures can be different. To illustrate this I was recently setting up a custom S21A with SST-20, using a Convoy 12-groups driver I received months ago as replacement for a recalled defective unit: presuming 60mV sense and R020 plus R050 sense resistors in parallel the unit should have attained 4.2A, but I finally got 4.7A (variations in sense resistor values also matter). Check this here, among other things related to obtaining correct measurements with these driver types when using power supplies.

Does your L80 have a donut hole with a domeless Led? Tried mine with Culpm1, Cslpm1, Cslnm1, also dedomed Xhp50.2. The results for all of them = donut hole :’

With the original SST70 I had a donut hole visible to several meters, with this SFT40 has nothing and no rings in the crown

in English is corona or crown?

Corona :+1:

Exactly, I’m talking about that aliexpress driver with a detection resistance R015.
I like that my LEDs work hard, maybe 8A is enough but I can see a difference of almost 400lm between this Pioneman and a Mantaray host C8.2 with Driver 8A by Simon and SFT40. Actually with the Stock Mantaray driver I can not read more than 6.6a on the clamp as with the 8A driver for Simon Culpm1 I can not read more than 7.6 with my AMperimetric clamp UNI-T UT210E.
I also did tests by downloading a bit the battery to verify that the LED was not saturated, with the battery at 4.15V 9,3A it and about 100lm less than with the battery fully charged and 10.8A

I just realize that you get a perfect reflector, Kinda jealous though :’

This is mine:

those details should not harm anything

Sensing resistance is the more appropiate term, detection and sensing do have different semantics. By the way, are you using DeepL to help you with this? ;-)

Concerning these matters, every time you mention some important part it is important to post a link with specifications. This is very helpful, namely for people who have never heard something about it.

¡Buf! :facepalm:

What is this Pioneman?

Mantaray host C8.2, had seen it before. Apparently a great C8 type host with 26650 tubing. Can't say anything else about it.

So you tell me that you are using the not very correctly marketed 8A driver for KW CULPM1.TG with the Mantaray C8.2. 0K.

Do you know that such driver is a switching buck driver? I guess when Simon ordered this 8A driver, due to the high current output the driver manufacturer decided to use a switching topology to minimize heat dissipation, increase efficiency and etc. This is nice.

However, since it is a switching driver, as a rule measuring the current at the tailcap or using a clamp meter to measure the current will not give you the current at the emitter. Because of it being a buck driver, it only pulls what it needs from the battery.

As an example, let's say the Vf of your SFT40 is ≈3.4V at 8A, this is 27.2W at the emitter. For the switching driver to be able to deliver this, it needs this amount of power divided by its efficiency at max or in high for this to be possible, let's say 27.2W / 0.88 = 30.90̅9̅W at the input presuming 88% efficiency in these conditions. With a fully charged battery and optimized current paths, the driver may be receiving ≈4.1V at the input, and so it would only pull ≈7.54A in these conditions. If you slightly discharge the battery, you will be able to measure more current with the clamp meter. If you continue discharging the battery the measured current with the clamp will at some point top out and then start going down, because eventually the driver will not receive enough input voltage for it to be able to deliver enough voltage to the emitter for it to receive 8A…

Addendum moral: with switching drivers you can't use the “tailcap current” or clamp current as a measure of what the emitter is receiving. This is incorrect. Period.

I am fairly sure that this buck driver delivers 8A at the emitter for as long as it receives enough input voltage, or this is what should happen according to its architecture.

And sorry, but I'm not going to continue with this. You need to understand how the different drivers you are using actually work, how the flashlight internals behave, and etc.

Something I've for example done in the past, and a very wise thing to do, is to buy a pair of these drivers as test devices for a proper review, submitting them to HKJ, a professional tester and the owner of It's all I'm going to say. ¯\_(ツ)_/¯

Have a nice day.

Wed, 08/25/2021 - 23:13

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