Hey everyone, First post here
Just a few questions
How does everyone pick their flashlight drivers (ignoring size),?
How can you tell if a driver will work for multiple LEDs?
Do you always run a LED at max current e.g. Cree XHP50 J4-1A says max 3 amps would you always run @ 3amps for max brightness (ignoring heat output) and if so how would this affect LED life?
Thanks:)
It depends what you’d like to do or what your host is capable of.
- decide which light/host you either have or which one you are planning to purchase (-> sizing up driver, MCPCB/1S or nS battery setup)
- see which emitter can fit on what MCPCB/which emitter you’d like have and what driver is available for this application
- combine the two - i.e. DD FET +1 for XM-L2 or triple Nichia 219C (just an example)
(- see whether all subsequent parts are available for the build, i.e required lenses, reflectors, …)
- you can estimate the outcome of your build with existing builds on BLF or based on calculation/experience; this doesn’t have to be 100% accurate but it will give you a ballpark figure for…:
i.e. if it is too much of a pocket rocket you could downsize the driver or estimate another build.
Just my .02 cents, this is roughly how I do it and I hope to hear more from the pros here.
edit: WELCOME TO BLF!!!
I always do constant current.
None of this FET direct drive “fade over time” and “max output only with fully charged battery” nonsense.
Umm this seems a familiar thread, wonder if you’ve posted it elsewhere….
Respectfully I’d suggest you are maybe missing the point or not really understanding how they work. At the very least I struggle to believe you have used such drivers, as they work perfectly well. And unless you are plotting output on a graph your eyes are unlikely to really see the difference by and large.
I understand perfectly well how they work.
When in direct drive, the current the LED will take is dictated by the forward voltage, which drops quickly on lithium batteries.
So if you want a certain LED to run at 6 amps max, in direct drive it will only run at 6 amps for a few seconds or minutes as the voltage from a battery drops rapidly.
It is better to use a higher voltage battery pack and a constant current driver that keeps the 6 amps constant until the battery is completely depleated.
It’s even worse actually…
To limit the maximum current drawn by modern low Vf LEDs on a DD FET driver, the electrical path is often not optimized to the max and / or batteries with a not so low internal resistance are used.
So as a result a light with DD FET driver will perform no better and possibly worse than a constant current driven LED light which has an optimized electrical path (spring bypasses, fat switch, 18AWG wires, real high drain (low internal resistance) batteries) when the battery is partially discharged.
In other words, i’m not a fan of DD FET drivers either.
But, it’s a lot of fun none the less in my S41S XP-G3, because it’s crazy bright !
…but only when the battery (VTC5) is freshly charged…
…and i don’t think i should bypass the springs either…
No, you are wrong about CC driver
If the Vf too high for battery to supply 6A, the CC driver in this case won’t help, and the brightness will be not constant
Unless you use buck boost driver, but that’s a different story
I enjoy the DD FET nonsense 
A constant current driver takes a battery with a voltage higher than the LED Vf and regulates it to provide a constant current.
So if your LED uses 7v at X current, you might use a 2s battery providing 7.4-8.4v and the driver will regulate it down to 7v in order to deliver the X current it is designed for.
Since it is constant current, it won’t matter if the LED needs 7.0v or 6.5v or 6.0v for X amps, the driver will regulate the voltage to deliver exactly X amps.
Some drivers will take a lower voltage and boost it up to achieve the constant current, those are called boost drivers instead of buck drivers.
I think you have a lot of research to do on how LED drivers work and what Vf and CC is.
I like consistency and predictability, too. I’d rather limit a light to 2.1A or 2.8A as long as I know the donk can handle that power indefinitely, vs cooking it with a fresh cell but knowing it’d handle things fine if half-spent, etc.
And after hating those 3×AAA lights with multiple LEDs that start off bright but fade constantly ’til you get sick of dim light, I don’t want an 18650 or 26650 light to do the same.
That includea DD FET drivers and parallelled SM ballast-resistors in the driver.
Gimme stacked 7135s any day…
as i said, boost/buck driver is a different story, i dont see any DD buck/boost driver, because the voltage is regulated-> the current is regulated
let take a look at some 7135*8 driver
for example, the current of xpl-hd led at 3.8V is 3A( example, not exactly), what if your battery’s voltage is 3.6V, then the output can’t be regulated
7135 ftw
You don’t need to stack them if you use a massive PCB
uses different criteria for choosing a driver. If you make an effort to understand each point of view then you’ll end up with a better understanding of where each type makes sense to use. Constant current drivers if they have good efficiency are great for providing stable output for a long time but are severely limited on total output/driver size whether boost or buck whereas FET DD drivers can deliver enormous currents with very small driver sizes so it all depends on what you want or need. “That’s what the lower modes are for” was a common phrase used by FET DD protagonists responding to run time criticisms. Now that there are hybrid drivers that combine regulated constant current with FET DD turbo levels it’s less of an issue but people still have their preferences and can get pretty excited over them.
Like this driver for click switch lights, http://drjones.nerdcamp.net/h17f.html one of my favorites!
Naw, I never actually stack them. Don’t want them cooking any more than I want the LED cooking. Meant that just as slang for parallelling them.
Ideally, I’d want a single beefy FET used in linear mode to regulate current. But that’d probably mean a low-side / P-type FET, and some sense resistor. Not much saving vs the 0.15V drop of a 7135.
As for multiple LEDs, if they are in parallel you can use the same driver that you might use for one led(with the same voltage) the current will be shared between the LEDs. If they are in series then the driver must have an output voltage sufficient to drive the sum of the led voltages(referred to as Vf). Since Vf is dependent on current you need to know the current you wish to drive at to figure the total Vf.
Thanks for all the replies, Just trying to pick a first flashlight for modding, i have alot of experience with modding incan flashlights but no experience with LED (been lurking for a few weeks)
Go for a light that takes a pill. The older C8 (type I) that has a brass pill is nice and easy to mod. 20mm LED star, 17mm driver, you’re done.
The WF-502B (or ’501 or any that takes P60/P90/D26 pills) is also easy to mod. Love the ’502, one’s my EDC, and you can make a dozen different pills (NW, WW, 1-mode, 3-modes, domed, dedomed, XM, XP, white/red/green/UV, whatever) and swap pills for variety, vs building/having a dozen different lights.
It’s a lot easier working on a pill, vs sticking fingers and soldering-irons down the hole of a light with integrated shelf. For a newb, it’s perfect.