well i know flat tops are cheaper, but i dont currently own any, if i did of course i would.
how does it fit? isnt the tube only for 18650?
I modified the 18650 to 26650 adaptor that came with the ft03, by cutting the ribbed slats out with a narrow chisel… But i have ordered a couple of 21700 to 26650 adaptors from AX, the nice solid white one that came with my MF01mini - 3.86€ 5% OFF|Hohe Qualität 21700 zu 26650 Batterie Converter Weiß|Tragbare Beleuchtung Zubehör| - AliExpress
The modified 18650-26650 adaptor works OK but doesn’t look great. I also have just put the 21700 in ft03 with no adaptor and that worked fine also - fully functioned.
i see…iirc, the 700 in 21700 is the length right? meaning 70mm? so thats way more than the button top 650, which i measured it last night at 670 ish. so i guess if your 700 can work, then this should be no problem.
Exactly, 70mm, which i assumed, because i don’t own BT 650, that it must be longer then 650 BT… You should be good!
ok thanks a lot! thats very reassuring!
I’ve got three FT03 and the newer ones have bigger springs and I cannot fit a 21700 without crushing the springs. I would double check if you are not sure.
I’m in the process of getting a custom tube made for 21700 and maybe after new year I will have some 21700 tubes available.
well im not planning to use 21700 anyway, i just need it to fit button top 26650, which is about 1-2 mm longer than flat
I found my notes on the spring sizes, the springs sit on head driver board and the flat tail cap board, so the tube length + springs = available battery length.
These sizes were taken with springs compressed, but not crushed hard enough for the coils to overlap. You can gain a fraction of a mm more by crushing the springs but you risk damaging them.
First edition (black) FT03
Tube length 76.9mm
Tail spring 4.7mm high when compressed
Head spring 3.0mm high when compressed
Max battery length = 76.9 - 4.7 - 3 = 69.2mm
Blue (later) FT03
Tube length 77.0mm
Tail spring 6.12mm high when compressed
Head spring 3.0mm high when compressed
Max battery length = 77 - 6.12 - 3 = 67.88mm
My Samsung 40T 21700 measures 70.3mm so just fits in the black with some spring crushing, but no way fits in the blue one.
So I would say you have 2-3mm extra to play with for a button top. I would go max 68mm.
wait how can you tell if its first edition or later? is it just by colour? i have the black one, but i just bought it recently, is it still first edition?
Sorry, I didn’t mean to cause confusion. I just meant the first production run, I guess they just use whatever springs they have handy at the time. The new springs are thicker than the old ones which mean they compress less, but maybe have lower resistance?
I would assume that all current lights use the bigger springs giving you less available length.
oh ok, well that would make sense in my situation then, 67mm sounds about right
The springs seemed to have one more turn and maybe thicker wire
maybe its the angle, but the black one looks longer since it has more space in between
It is longer when uncompressed, found my original spreadsheet:
wow thats some meticulous data. how did u measure all that down to fraction of a mm?
this light isnt designed to run 21700 they are too long.
I bought my FT03s (sbt90.2) last month and run Samsung 40t without a problem, springs not crushed battery now dented, also run p42a as backup battery.
My ft03 I bought this March and tried to put 40t in it, no problems. Although I run efest 26650 4200mah in that usually. The different springs was something I never noticed and wasn’t aware of
It looks a bit wobbly, but the results were repeatable and I would say reasonably accurate!
Set the probe on the circuit board then zero the gauge and work out the compression by watching until the spring coils touched.
I would expect the springs vary by batch, some will fit 21700 fine, some might be tight. From my own measurements I won’t be using a 21700 without the longer tube I’m making for it.
damn, that is some professional setup