The New Hotness

An octet of Eneloop AAA cells arrived, I wanted to measure their as-delivered charge (the package says “Factory Charged With SOLAR ENERGY”, so you know it’s good), and discovered I’d given away my AAA cell holders. You can actually get inter-series adapters on eBay, but what’s the fun in that? Plus, I didn’t want to delay gratification for a month; you know how it is.

Soooo:

AAA to AA Adapter - top - Slic3r — AAA to AA Adapter – top – Slic3r

It’s basically an AA-size sleeve that fits over the AAA cell, with a lathe-turned brass post conducting juice from the + terminal of the inner cell outward:

AAA to AA Adapter - parts — AAA to AA Adapter – parts

Not much to look at when it’s assembled:

AAA to AA Adapter - assembled — AAA to AA Adapter – assembled

The AAA cell fits deliberately loose, because this goes into a metal clip holding everything firmly in place for the battery tester:

AAA to AA Adapter - in use — AAA to AA Adapter – in use

The source code tabulates the sizes of several cylindrical cells, exactly zero other pairs of which have been tested; I expect most won’t work correctly. In particular, the table entries should include the contact button OD and thickness for each cell, so that I can turn out the proper terminal for each pair of cells. If I ever need a different adapter, I’ll beat some cooperation out of that, too.

Discovered I needed an adapter after breakfast, started testing cells after lunch. Life is good!

The OpenSCAD source code as a GitHub Gist:

	// Cylindrical cell adapters
	// Ed Nisley KE4ZNU April 2017

	//- Extrusion parameters must match reality!

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

	Protrusion = 0.1; // make holes end cleanly

	inch = 25.4;

	function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);

	//———————-
	// Dimensions

	OutCell = "AA"; // cell sizes
	InCell = "AAA";

	BottomClear = 3*ThreadThick; // shorten outer shell to allow base protrusion
	Terminal = [3.0,4.0,2.0]; // terminal: OD = nub dia, length = nub thickness

	NAME = 0;
	ID = 0; // for non-cell cylinders
	OD = 1;
	LENGTH = 2;

	Cells = [
	["AAAA",8.3,42.5],
	["AAA",10.5,44.5],
	["AA",14.5,50.5],
	["C",26.2,50],
	["D",34.2,61.5],
	["A23",10.3,28.5],
	["CR123",17.0,34.5],
	["18650",18.6,65.2]
	];

	Outer = search([OutCell],Cells,1,0)[0];
	Inner = search([InCell],Cells,1,0)[0];

	echo(str("Outer cell: ",Cells[Outer][NAME]));
	echo(str("Inner cell: ",Cells[Inner][NAME]));

	echo(str("Wall: ",Cells[Outer][OD] – (Cells[Inner][OD]/cos(180/NumSides) + 2*ThreadWidth)));

	Delta = Cells[Outer][LENGTH] – Cells[Inner][LENGTH];

	echo(str("Terminal OAL: ",Delta));
	echo(str(" … head: ",Terminal[LENGTH]));
	echo(str(" … shaft: ",Delta – Terminal[LENGTH]));

	NumSides = 3*4;

	//———————-
	// Useful routines

	module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes

	Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);
	FixDia = Dia / cos(180/Sides);
	cylinder(r=(FixDia + HoleWindage)/2,h=Height,$fn=Sides);

	}

	//———————-
	// Construct adapter

	module Adapter() {

	difference() {
	cylinder(d=Cells[Outer][OD],
	h=Cells[Outer][LENGTH] – BottomClear – Terminal[LENGTH],
	$fn=NumSides);

	translate([0,0,Delta – Terminal[LENGTH]])
	PolyCyl(Cells[Inner][OD] + 2*ThreadWidth,
	Cells[Inner][LENGTH] + Protrusion,
	NumSides);

	translate([0,0,-Protrusion])
	PolyCyl(Terminal[ID],
	2*Cells[Outer][LENGTH],
	6);
	}
	}

	//———————-
	// Build it

	Adapter();

view raw Cylindrical Cell Adapters.scad hosted with ❤ by GitHub

The original doodle:

AAA to AA Adapter - sketch — AAA to AA Adapter – sketch