@rjkesler, a boost driver won’t work for this LED unless it’s in a quad setup for 12V operation.
A buck driver however would work just fine.
Happy to hear this…that’s what I was going for when the KR4 gets its new driver.
Quick sanity check. If I have a flashlight with triple SST-20 that draws 9,2A on turbo with a full battery… that means just over 3A per LED with low enough Vf to be replaced with 519A without issues right?
Based on djozz test a reasonable triple should be ok with decent heat path and MCPCB, etc.
The info you provided is not what is needed to determine that though. The type of driver, battery and LED determine a lot and then the rest of the resistance coming from things like springs/wires are like the icing on the cake.
If it’s an 18650 and smaller size FET driver it’s rare to see anything go above ~15A which would be a lot for this LED but still OK.
In your example SST-20 has higher vf than 519A so the 519A will likely draw more amps, how much more depends on the rest of the variables though.
Agreed with contactcr. Heat path is critical, and 519a has lower vf. Sst20 definitely more durable.
maybe… you could do a test and let us know 
imo, if you limit the max output to reasonable levels, below 1000 lumens, it should be fine… you could also limit power by setting a lower ceiling, and or a low thermal stepdown temp, and or by using a lower drain rate battery
fwiw, I use 219b in my FWAA… no issues… Im not someone that uses Turbo, especially not over and over again. I also use a 35C thermal limit… and I do not allow my light to get too hot to touch…
I look forward to your success! 
Talking about Wurkkos TS21 with stock re-wrapped 5Ah 21700 battery. Driver with FET. Just going through options for now. Mine must have used a pretty green batch of the SST-20, so needs a replacement.
I know, but the whole reason for asking is not to blow up 3 519As in one go
The guy in this link is doing it. He is selling them on Facebook, Reddit, and here… So there has to be a way!
Yes, I was wondering about it also, but mine failed 
I didn’t want to try again an replaced it already…
I don’t blame you, prisma. That’s why I haven’t got into that end of the hobby, yet. Just don’t have the time to be learning lessons like that… Having to learn other lessons right now!
I find curious how the usual way to make triples or quads is in parallel. This is far from being the best approach.
When you set leds in parallel there can be large differences in current distribution among the leds, this is because of their Vf differences. Just a small Vf difference is enough, you would need to test and hand pick the leds for “operation in parallel” to work really well.
For this reason it is a bad idea to push a lot of current (current approaching led limits in equal share) to a triple, while expecting it to handle it well. Let's say your leds in the triple blew up at 7A in independent tests, while your just built unregulated flashlight starts drawing up ≈18A when in turbo. In a case like this one, due to Vf curve differences quite likely one of the leds will share more current and blew up. There you have it.
The way to do triples or quads correctly is with leds in series (and of course boost drivers). This ensures all the leds receive exactly the same current (they're properly driven with regulation).
I don’t disagree with your points.
However, a high-current boost driver is hard. If you’re pushing 18A total to three LEDs, that’s a lot simpler and cheaper to do in parallel than to get a 6A/9+V boost driver. Space is also an issue - a FET driver could be 15mm and single-sided! But you won’t fit a high power boost in there.
Last, it’s really hard to find series MCPCBs these days.
I’ve been saying that, like, forever. I used to try stringing 5mm LEDs in parallel, only to have random brightnesses to each one.
So it’s either parallel with at least small ballast resistors to help smooth out the differences, or go for series arrangements.
But since COBs took off, no one thinks twice about parallelling just about anything together.
But if you can get LEDs from pretty much the same batch, you have a better chance of matching them. But people usually just reach for what’s in their parts-drawer. Worse, they’ll try mixing tints with completely different LEDs. “Oh, but they’re all blue, just have different phosphors!” Yeah, but still DIFFERENT LEDs from different batches with different characteristics.
Heads bleed, walls don’t, so I mostly stay out of it. If it works for people, even manufacturers, hey, great.
@multiple persons
Thanks for sharing your experiences.
I’ve let go of putting these in flashlights with a FET driver for the time being. And since I don’t have anything else suitable lying around, a triple 519a will remain something for another time. Which is totally ok considering I’ve been going on a emitter swapping rampage lately, so maybe not a bad idea to slow down and actually enjoy the results so far. And in the mean time a triple or quad in series with boost driver sounds awfully nice, so might as well do it good once the time comes.
Who is selling these again?
Got mine from Convoy, but I’m sure there are other places as well.
Btw, did anyone use these with a Carclo 10507? If so, is the result any good?
Clemence via Group buy on Telegram. There are forwarders in each continent so you just need to join the train.
Similar beam to LH351D. I think 10507 works fine with 519A’s.