Single-Stack Parallel Serial Battery Cartridge

Background
While it's common to find serial and parallel battery carrier setups which place the component batteries next to each other, I needed a parallel carrier that would fit inside of a slender Mag C body. Reason being, a WelchAllyn superbulb I was planning to run had 2x123 voltage but a sky high current demand of 3.85A. Clearly, a single stack would not last long under these conditions. What I needed was a 2x2x123 setup. Having passed on the Mag 1D GB and liking the form factor of the 3C better, I decided to make my own single-stack parallel serial carrier. While this design is for 2x2x123, it can easily be generalized to any number of cells.

Parts List
* Battery tube: Bristoltherm CPVC hot/cold water pipe, 7/8"OD, 3/4"ID. This pipe is near perfect for stuffing in 123's and I use it for all my 123-in-C mods
* Battery cartridge conductive end caps: 5/8" metal hole plugs
* Battery positive contact pads: 6 x 9/16" fender washers
* Battery negative contact pads: 6mm flat washers
* Spring loading: 3/8" x 1-1/8" x 0.041" 9lb compression spring
* Stack separator plate: 3/8" acrylic sheet
* Circuit wiring: 20 gauge high-temp insulated wire
* Miscellaneous: soldering iron, sandpaper, Dremel, mill file

Procedure
1. Machining the separator plate
I traced out the shape of the pipe cross-section and rough cut with a hack saw. The acrylic separator plate will fit into a slot cut into the pipe. Finish to size using a mill file. A Dremel was used to grind out shallow recesses to accommodate the battery contact pads. Here's what it looks prior to gluing down the contact pads.


2. Building the positive and negative contact pads
I chose the 6mm washer because it fits perfectly into the recess at the negative end of the 123 battery. I chose the fender washer because it provides a large, robust contact patch for the battery positive nipple. I used a diamond bit to grind out channels on the backsides of the two washers to allow me to solder the circuit wiring flush with the washer surface. This would allow me to create a flatter separator plate-contact pad unit. Solder on the wiring. Leave plenty of excess length so the wiring can be adjusted as needed for 2x2, 2x3 etc. I applied a thin layer of JB-Weld epoxy to the recesses, dropped in the washers and clamped it together with a vice grip to set overnight. The finished sandwich was only 4.3mm thick.


3. Building the battery cartridge conductive end caps
These are the end caps on the cartridge which make electrical contact with the Mag tailspring and switchbody spring. I chose the 5/8" hole plug because it is a perfect fit for the ends of the CPVC pipe. Take the endcaps and open the retaining prongs a bit to get some working space. Take the compression spring and cut one in two. Solder one onto the inside of the hole plug. This is the negative cap which sits behind the rear stack. For the positive cap, solder the half-spring as before. Afterwards, solder a fender washer to the top of the spring. This makes contact with the nipple of the top battery in the front stack. I'll add here that all electrical contact points are sanded, cleaned and treated.


4. Machining the cartridge tube
Measure the total length of batteries, the thickness of the separator plate/contact pads, and the spring length of the end caps. Subtract 2-3mm to allow for compression. Cut a slot in the middle of the the cartridge tube to allow insertion of the sep/cont assembly. No photos as this is a dull step.

5. Assembly and testing
Insert the sep plate/cont pad into tube slot. Feed in batteries. Insert end caps. Here is a shot of the completed cartridge. I tested continuity with some used up Duracell CR213s. Replace with fresh SureFires, drop the battery cartridge into a Mag 3C and you're ready to rock. If so inclined, one could also load in two Pila 168S li-Ions and run it on rechargeables. When my WelchAllyn bulbs come back from Carley, I'll be back to post comparative beamshotz against some other superbulbs as well as tried and trues like the KPR112.



And there you have it. A way to run parallel-serial in a single stack torch.

Wilkey

Restored 12/21/06

Wilkey,

That's a clever and neat way to obtain a parallel configuration. I like its transportability from one battery tube to another. I presume that you wrap the wires around the tube in a helical fashion before inserting it in the flashlight.

The stack separator plate is an especially nice implementation. Was it difficult hollowing it out without punching through the acrylic?

I have questions about the battery cartridge conductive end caps. I don't recognize the 5/8" metal hole plugs. Would I find these at Home Depot? What are they normally used for? Evidently they grab the inside walls of the PVC, but it's not clear to me how that happens.

Nice work. /ubbthreads/images/graemlins/thumbsup.gif

Paul

Paul,

The wires get wrapped around the tube a few times. However, I think that I will probably trim them since I have no forseeable need for anything other than a 2x2. I was considering running the WA01111 on 2x3 but I'll probably be selling off those bulbs.

I used a HSS cylindrical bit and just nibbled away on a firm surface. No problems with cracking. 3/8" is pretty thick in some respects.

The metal hole plugs were bought at Lowe's although I imagine HD would carry them as well. I think they're used to plug unused holes in electrical boxes and such. The prongs press against the inside of the CPVC tubing and hold through friction. The 2mm compression against the end springs is sufficient to maintain battery contact yet insufficient to cause any significant backing out of the end caps. One could use a lower pound rating spring but I could not find one that fit the bill exactly. Weaker ones were too narrow to be stable or too wide to fit between the prongs. One could make the grip a bit more sure by grinding out a small ring just inside the edge of the tube for the prongs to grip.

This is a specialized mod to be sure. I don't expect it to garner much use outside of a very few specific applications but at least it shows that it can be done relatively easily.

Wilkey,

Thanks. I know what plugs you mean now.

This cartridge is a great solution for the WA 01274. <font color="red">** CORRECTION: (1183, not 1274) **</font> I look forward to your reports of testing. In particular, I'll be looking for what the size of the hotspot is and the angle of the cone it subtends.

I see you have a new meter. Are you having fun with it? /ubbthreads/images/graemlins/grin.gif

Paul

Paul,

I don't really know how to use the meter for doing much more than 1) voltage checking of batteries and 2) continuity for blown bulbs. It's fine for a cheap meter.

The WA01274 seems to be running well on 4x123 so I think I'll leave it that way. The WA01183 is the real bulb of interest here. The unstated benefit of such a parallel arrangement, of which I know you are already aware, is that you double the amp-hour rating of your battery stacks. Perhaps a llittle more due to the decreased internal resistance/current draw (see? I've been listening /ubbthreads/images/graemlins/wink.gif).

I'm quite excited about being able to do some comparative studies of the filament size versus hotspot size and shape of various bulbs.

Wilkey

Ha ha. Yeah, I slipped a few neurons there. I know perfectly well it's not the 1274. I was thinking 1183 but typing 1274.

I also am excited about your upcoming studies. "Throw" and "gain" and "beamwidth" are not ideas that we yet pay much attention to when playing with Superbulbs. My objective has been raw, naked lumens. And sometimes that's not enough.

Paul

I did something similar awhile back, but it was not as elegant. I was running a single stack of 2 123s and could only use 3v or less (madmax converter). I was very limited in space, as this was already a 123 flashlight, so I needed something very thin that would lay right alongside the batteries so they would still fit into the light. My solution was two thin brass pieces (made of .01" shim stock) and a wood separator. Same idea though.

Nice work! /ubbthreads/images/graemlins/thumbsup.gif