I really like the form factor here, and the handle is big enough for a 21700 cell. It has a twist to zoom, which is useful for my job (the zoomed-in beam makes a great pointer!).
What’s a good choice for LED & driver? Groups are not important - a High-Mid -Low split is fine. I’d prefer to err on the side of caution here, as this is my first mod. I’m a novice solderer
Talking about replacing the 3 * AAA battery holder with a 21700 cell.
The theoretical diameter of an AAA battery is 10.5mm, that gives you at least 22.6mm of space.
So the diameter of the body is probably big enough to offer accommodations to a 21700.
But the length of an AAA is 44.5mm, and that’s where you need some kind of a caliper.
Because you need the full lenght of the diameter.
Depending on what you want to do a caliper might not be needed.
Try inserting a 21700 into the tube and see how much extra length sticks out. If the light uses typical zoomie construction you might be able to recover some internal space at either end of the tube by shortening the pill and/or tailcap. Recover enough space and a 21700 might fit.
If that still isn’t enough, the only option would be to add some kind of battery tube extension. That’s hard to do well without machine tool experience.
I’ve modded a couple Gearlights successfully (push-pull heads), but not the twist one so I dont know what the inside looks like.
As far as squeezing a 21700 in there, honestly you don’t really need a 21700 since an appropriate led won’t be driven much harder than a good 18650 can muster. It’s not really worth finaggling a 21700 into the space. Plus the lack of heatsinking (unless you add more like I did) restricts you to maybe 10w total output?
A good LED for these? I like the round die 5050 size, so like the LMP5050 from Convoy or any of the masses of Chinese clones. You could also go SFT-25R.
Driver. Go with a 3v 17mm Convoy 5A buck driver. Or if you increase the heatsinking, the 8A is nice too.
In most twist zoomies, the twisting action comes from interlocking ridges on the top of the body and bottom of the head. It is often possible to convert a twist zoomie to push-pull simply by filing off those ridges.
I did this years ago. Unfortunately I don’t have any photos. I used a set of rounded needle files to manually grind off the ridges.
It’s pretty obvious what to do once you take apart the light and look inside. You don’t even need to file off the ridges on both the head and body. Just filing them off one part is enough.
The biggest problem is going to be heat.
Since there’s no aluminum under the MCPCB, the heat from the LED is only transferred through that 1mm or so of aluminum around the shelf.
With a powerful driver the LED will get hot enough to melt the solder that attaches it to the MCPCB.
I’ve modded lights with hollow pills with no shelf in the past. They can easily withstand 3-4 Amps of current without the driver wires popping off the star.
Just make sure to replace the aluminum star with a copper one. And generously slather Arctic Silver 5 thermal paste where it meets the pill.
Get a few real pennies, not crappy “zinkies”, and sand 'em absolutely flat, solder them into a stack.
Depending on the diameter of the shelf, you might need to file around to press-fit into the hole flush with the ledge. Or heat the Al, chill the Cu, drop it in fast, then Let Thermal Expansion/Contraction Be Your Friend™.
The driver wires are closer to the edge and thus probably better heatsinked than the LED. The real issue with 3-4A of current heatsinked through just a PCB is not just potential desoldering, but the rapid loss of performance and premature emitter death. LEDs performance is already very sensitive to whether the board is made of Cu or Al; removing the heatsink will make a much, much bigger difference than changing Cu to Al.
Third, obtain a supply of copper disks, then turn them into a small shelf. Amazon.com
Fourth, get this LED, which should pop right in. LMP W5050SQ3 LED - Convoy flashlight I may need to fit the LED & shelf first to get the alignment right.
Driver is probably just press fit. Heat should not be needed to remove it.
Try pushing it out from the front with a toothpick. If that doesn’t work, you could insert an awl and tap it out by banging on the back of the awl with a small hammer or side of a wrench.
Now you have a solid shelf vs a ledge.