That is all…
hehe, thanks for the encouragement guys.
Hopefully it won’t take too long to get this project up to a functioning state. I’m at the mercy of an unusually hit and miss chinese postal system at the moment as I’m sure you all know 
One thing I wanted to ask, is it at all possible to fit 4 18650s into a stock BTU battery tube? I don’t mean using the stock carrier but just whether they would fit inside the tube without having to enlarge it. By my calculations using the 50mm outside diameter quoted on the site and tube thickness of 4.45mm from a great review by “the” here on this forum (would be lost without that review btw) I should have just enough space to squeeze 4 cells in there. If anyone has a BTU shocker and would be willing to test the fit for me that would be awesome!
The reason I’m curious is that ideally I’d love to be able to run this light on either the battery pack or 4 18650s in 2s2p config depending on the situation. First hurdle to that would be the four cells actually fitting the tube, then making a new carrier for them, giving up all that lovely empty space inside and cramming the XLR socket extra tight into the tailcap. Not to mention making my driver wiring life a lot more difficult.
So please someone tell me that the cells fitting the tube is a pipe dream and allow me to make this a power pack only light! 
Cheers
Much as I would like to see that portion of the build, 4x18650s will not fit in a standard tube. Anyway the tube might not be empty 4 long, space to fit heatsinked drivers and pos lead to balance it, and a fan for cooling >)
45.0 mm inner diameter on the threads - 4 bare Sam 20Q's don't fit. The Vostro that takes a 4 cell carrier is 45.7mm inner diameter. So, the Shocker is really, really close but NG.
Damn… so close, cheers for having a look.
I guess the only option would be to ream it out a bit but it’s probably not worth the extra hassle.
You’re right xmint the space inside probably won’t be going to waste and certainly will give me many more options for assembly. Exploring active cooling options is certainly something I’ll be doing but hopefully I won’t have to add any extra lead weight for balance purposes. The XLR plug from the power pack alone weighs over 50g and it along with the fairly heavy cord hanging off the back of the BTU should be enough to balance out that heavy front end.
With regard to the tail cap on the BTU, to get at the rubber boot you have to screw out the center part of the back end with the 4 dimples right? I assume the inside of the cap is a solid piece plate with only a hole in the middle for the switch boot to pass through. Is this tailcap easy enough to disassemble or is the thing glue shut?
Cheers
Be very careful.
One thing I immediately noted was the use of an XLR for power.
I've seriously never ever seen an XLR being used for anything but low current signal-only transfer.
Yours might be different with the 15A rating and all, or yours might melt and cause shorts, fire and explosions.
If you're going for 100W from a 2S config, you'd be cutting it close to your rating.
If it were my project, I'd use XT60s or speakONs.
Batteries. Two homemade packs in series doesn't raise any alarm bells?
Single blocks will reduce headache immensely in the future.
You could possibly shorten the whole thing by a significant portion if you increase the drop from the rail.
In the end, it's your project, your call. Just throwing some suggestions out there.
All the best!
Thanks for the comments and you make some very good points.
Regarding the XLRs I believe they used to be implemented for high current power supply for speakers and such but not anymore. I only know I had some available, saw the 15A rating and felt the contacts and internals were reassuringly robust to back up that claim. No doubt a 15A rating and running it at the kind of currents I intend is cutting it fine so I appreciate you suggesting the SpeakOn connectors. Those look superb and exactly what I need. Will be ordering a couple to have a play around with. They may even make installation in the BTU easier since they are sightly narrower than the XLRs.
The packs look dodgy but they are in no way less safe than ones bought pre assembled. I’ve been building custom packs from individual cells quite a bit for very high drain Heli use and have never had a problem, as long as you’re careful to ensure no bad cells with different IRs end up in the mix and you regularly keep an eye on the health of each cell they will function just as safely (or dangerously depending on your view of Lithium technology ;)) as anything factory assembled.
That said these packs are only really intended for testing as I’ll be replacing them with a set of 2 or 4 of these at some point.
Still when dealing with lithium cells it’s best to be safe than sorry, and there’s a reason I want to build a temperature monitor/alarm into the pack and insist on having a quick disconnect power plug on the flashlight 
I’m not sure I understand what you mean with shortening the whole thing by increasing the drop from the rail. Can you elaborate?
Edit: Oh I think you meant removing the body of the BTU entirely, raising the handle higher and screwing the tailcap directly into the head. Right? That could be interesting. I hadn’t contemplated this till now because I was still hoping I could make this flashlight work on both Pack and 18650s but if that’s out of the question this may be something to try.
Not sure if the tailcap would thread all the way onto the head, BTU owners, would this be feasible?
Thanks again for the comments
Linus
Had to try it!
Yep it’s hilarious…this must be attempted!
The improvised riser is not based on something that exists in the real world but I’m sure I could find something that would fit the bill
Edit: Something like this would work perfectly
…and with an appropriate spacer it ever looks somewhat nicely proportioned!
What I really meant was placing to unprotected packs in series is quite iffy to us battery snobs. :)
Nice modelling work, btw!
I'm sure it's possible, if the spacer is designed correctly, for your BTU to still function as a 18650 flashlight. :)
Thinking about it, though the tube in standard form will not take a 4 cell carrier if you had machining facilities it could be made to do so.
The end cap from a FF4 fits the Shocker In fact the shocker’s battery tube is slightly bigger in diameter, so I would think that even after machining there should be enough metal left for reliability as there is in the FF4.
If the socket, plug and lead does balance the head that will be a bonus.
If you go down the active cooling path be interesting to see which way you go. I have been looking at a sandwich peltier and annular fan for one of my projects (a 47 yo space beam torch updated slightly LOL).
Yeah I wish I had the tools and the ability to machine, would make things a lot easier alright.
Another question for the BTU owners. If you thread the tail cap as far as it will go onto the head of the light i.e eliminating the battery tube entirely. How much of a gap is left to fill between the head and the front of the tailcap?
Assuming you can’t screw the cap on all the way because of that long threaded section on the head.
Peltier coolers are definitely fascinating. Maybe I can figure out some way of making one work here.
Cheers
I’m using an XLR plug in conjunction with a 13.1V LiPolymer pack to power an older Canon 1DsMkII camera that had a NiMH pack. The OEM pack is unreliable with some age on it, my external pack will run the camera for several days.
Of course, I’m not pulling the amps you’re looking at, but I’ve no issues with the plug whatsoever.
Nice work, love the renditions, can’t wait to see what you actually do. One of those would be fantastic in the Photography profession, on location lighting extraordinaire!!!
I’m just wondering… why use BTU? it is very heavy…
why not use Fenix TK75 instead? as it have a deep reflector too and can add more battery extender for longer runtime or more “juice” 
Well two reasons mainly.
1. I was offered the BTU host without leds/drivers for a very good price. So that’s what started this whole mess
2. I don’t have a Fenix TK75. Are you offering me yours? hehe :party:
But yeah, I know it’s probably not the ultimate choice for what should be a relatively light host+heavy battery pack combination but then again the extra mass has heatsinking benefits as well.
Looking at the Fenix, I love the extra cooling fin surface area, the BTU is sadly a bit lacking in that department.
Linus
Yes I think a good XLR will do fine even at those higher currents. In fact I know mine will work fine since I tested my power pack cable and connector combination last night.
At a constant 15A and 20A the connectors didn’t even get warm, and even if they did heat up a bit the plastic construction on the inside seating the connector pins is made of something I can’t melt with a 450°C soldering iron.
The 18awg cable however will make a nice hand warmer. It got up to 50°C after 4mins at 15A, with a drop of 0.68v across the cable when cold, up to 0.74v at the 4 minute mark.
Was hoping for better.
Massive waste of energy right there, really need to find a more suitable cable, at this rate it might actually be more effecient to boost the voltage from the battery pack to something like 30v and then convert it back down to 7.4v in the torch. haha.
Having said that you have to be careful you get a decent XLR for power, I think mine must have been designed for speaker use or something else that matches or exceeds their 15A max rating. With plugs that aren’t universally used for high power distribution the construction can vary quite a bit. I have another XLR plug that has very thin contact tabs inside not really designed for soldering wires to. And the plastic is not as heat resistant either, wouldn’t be comfortable using that one here.
I can certainly think of a few uses for this light when it’s done
If only! How I envy those that have a workshop these days :cowboy_hat_face:
The tail cap does not screw into the thread on the head (poetry :nerd_face: ) it is bigger! 
Oh, you see I wouldn’t have guessed that from the photos I’ve seen. Good to know, so it will require some machining to make this work. Thanks for the heads up!
Note to self: Always have flashlight host in hand before planning mod!
The cap is not that much bigger so it is a pain… hopefully it may be possible to get a cap from another light that would fit.
I do know a machinist who lives locally so getting something modified or a thread cut isn’t entirely out of the question, certainly finding parts that fit from other flashlights is an option but often I’ve struggled to find spares sold separately and buying a couple different flashlights just to use a part or two from them doesn’t feel right.
Not to mention that would leave me with another orphaned host that’ll require modding…vicious circle that!
Getting a new end cap to exactly your design would be the way to go! but I hope the price would not be too high as you know the bloke. I want a double length battery tube for my shocker, but the quote I got was stupid money.
Must admit the few times I have needed parts for modding lights, I have been lucky to have found suitable donors from jumbles/charity shops and boot sales. So never felt that guilty about nicking bits off them.
Never quite understood the reluctance of light manufactures in selling spare parts.