Tag: M2

Under ordinary circumstances, a fuseholder mounts in a square-ish panel cutout, but there’s no convenient panel to be found in the repurposed GX270 case. So now there’s a holder for the fuseholder stuck to the side of the power supply inside the case:

The square tube covers the entire fuseholder, with the quick-connect tabs protruding from the back, to provide enough surface area for the double-stick foam tape.

Looking down into the solid model, you can see the reduced width near the back end:

The black fuseholder contains a 5 A fast blow fuse, which should be entirely adequate for normal operation. In the event that a wire breaks loose and contacts the metal shell surrounding the whole chassis, it will pop instantly. That won’t disable the power supply, but it will remove line voltage from the entire motor controller chassis.

Remember that the source power line goes to the center QC tab, thus burying the always-hot contact deep in the fuseholder.

The OpenSCAD source code:

// Fuseholder mount
// Ed Nisley - KE4ZNU - August 2014

//- Extrusion parameters must match reality!

ThreadThick = 0.20;
ThreadWidth = 0.40;

HoleWindage = 0.2;			// extra clearance

Protrusion = 0.1;			// make holes end cleanly

AlignPinOD = 1.70;			// assembly alignment pins: filament dia

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

//----------------------
// Dimensions

Shell = [25.0,25];						// outside = bezel size + some stiffening

Mount = [17.3,15.7,21.0];					// mount section = slight compression in X
Base = [13.5,15.7,17.0];					// clearance over crimped contact

OAL = Mount[2] + Base[2];

//----------------------
// 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);
}

module ShowPegGrid(Space = 10.0,Size = 1.0) {

  RangeX = floor(100 / Space);
  RangeY = floor(125 / Space);

	for (x=[-RangeX:RangeX])
	  for (y=[-RangeY:RangeY])
		translate([x*Space,y*Space,Size/2])
		  %cube(Size,center=true);

}

//----------------------
// Build it

ShowPegGrid();

difference() {
	translate([0,0,OAL/2])
		cube([Shell[0],Shell[1],OAL],center=true);
	translate([0,0,Base[2] + Mount[2]/2])
		cube(Mount + [0,0,2*Protrusion],center=true);
	translate([0,0,Base[2]/2])
		cube(Base + [0,0,2*Protrusion],center=true);
}

Given the fragility of ferrite toroids in general and slit toroids in particular, a touch of up-armoring seems sensible:

The solid model includes a toroid shell with roughly the right curves:

That puts a nice rounded shape on the bottom of the armor, not that that makes much difference:

The central hole passes a 4-40 brass, nylon, or stainless steel screw. Most of the magnetic field stays within the ferrite and, heck, this isn’t a crazy-sensitive analog application, so even an ordinary steel screw shouldn’t cause any particular problems.

The rectangular (not pie-wedge) slit barely passes the Hall effect sensor.

I’ll pour some clear epoxy over the toroid, with tape masking the ferrite core and sealing the ends, to immobilize the windings. That sounds like a good idea after calibration and suchlike.

The OpenSCAD source code, which should be sufficiently parametric that I can crank ’em out for all the other toroids large enough to accept a screw:

// Toroid coil mounting bracket
// Ed Nisley - KE4ZNU - August 2014

Layout = "Mount";			// Coil Mount Build Show

//- Extrusion parameters must match reality!
//  Print with 4 shells and 3 solid layers

ThreadThick = 0.20;
ThreadWidth = 0.40;

HoleWindage = 0.2;			// extra clearance

Protrusion = 0.1;			// make holes end cleanly

AlignPinOD = 1.70;			// assembly alignment pins: filament dia

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

//----------------------
// Dimensions

ID = 0;												// subscripts for cylindrical objects
OD = 1;
LEN = 2;

Coil = [10.25,23.50,8.3];							// wound toroid core

SensorThick = 2.0;

BaseThick = IntegerMultiple(1.0,ThreadThick);		// baseplate under coil
WallThick = IntegerMultiple(1.0,ThreadWidth);		// walls beside coil

ScrewHoleDia = 4.0;									// allow alignment slop around 3 mm / #4 screws

//----------------------
// 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);
}

module ShowPegGrid(Space = 10.0,Size = 1.0) {

  RangeX = floor(100 / Space);
  RangeY = floor(125 / Space);

	for (x=[-RangeX:RangeX])
	  for (y=[-RangeY:RangeY])
		translate([x*Space,y*Space,Size/2])
		  %cube(Size,center=true);

}

//----------------------
// Basic coil shape

module CoilShape() {
	
CornerRadius = min((Coil[LEN] / 2),((Coil[OD] - Coil[ID]) / 2))  / 3;
MidRadius = (Coil[ID] + Coil[OD]) / 4;
HalfX = (Coil[OD] - Coil[ID]) / 4 - CornerRadius;
HalfY = (Coil[LEN] / 2) - CornerRadius;

echo(CornerRadius,MidRadius,HalfX,HalfY);
	
	color("Goldenrod")
	render(convexity = 2)
		rotate(180/20)
			rotate_extrude(convexity=3,$fn=20)
				translate([MidRadius,0])
					hull() 
						for (i=[-1,1],j=[-1,1])
							translate([i*HalfX,j*HalfY])
								circle(r=CornerRadius,$fn=24);
}

//----------------------
// Mount

module Mount() {

	difference() {
		rotate(180/20)
			cylinder(h=(BaseThick + Coil[LEN]),d=(Coil[OD] + 2*WallThick),$fn=20);
		
		translate([0,0,-Coil[LEN]])							// make screw hole
			rotate(180/6)
				PolyCyl(ScrewHoleDia,3*Coil[LEN],$fn=6);
			
		translate([0,0,BaseThick + Coil[LEN]/2])			// set bottom curve
			CoilShape();
			
		translate([0,0,BaseThick + Coil[LEN]])				// clear out top
			CoilShape();
			
		translate([(Coil[ID]/2 + Coil[OD]/2),0,0])
			cube([Coil[OD],SensorThick,3*Coil[LEN]],center=true);
	}
}


ShowPegGrid();

if (Layout == "Coil") {
	CoilShape();
}

if (Layout == "Mount")
	Mount();

if (Layout == "Show") {
	Mount();
	translate([0,0,(BaseThick + Coil[LEN]/2)])
		CoilShape();
}


if (Layout == "Build") {
	Mount();
}