Archive for January 22nd, 2013

Hall Effect Current Sensor: Winding and Armoring the Toroid

Winding a slit ferrite toroid poses no challenge, so putting 25 turns of 26 AWG wire on it didn’t take long at all:

F50-61 toroid - 25 turns 26 AWG

F50-61 toroid – 25 turns 26 AWG

However, a ferrite toroid doesn’t take kindly to being dropped and I figured that a slit toroid would crack under a stern look, so I decided to wrap some armor around it. A small squeeze bottle offered a cap just slightly larger than the winding, so I used that slitting saw to cut off a suitable ring.  The first step was to grab it in the 3 jaw chuck and align its axis parallel to the spindle:

Aligning bottle cap in 3-jaw chuck

Aligning bottle cap in 3-jaw chuck

I wanted to cut off a slightly taller ring, but the clamping screw on the saw arbor just barely cleared the chuck for a 5 mm ring. I jogged around the chuck jaws to cut two slits in the cap that eventually joined near the back:

Slicing ring from bottle cap

Slicing ring from bottle cap

That was about 1000 rpm, no coolant, and slow feed, but also a totally non-critical cut in plastic.

I put a snippet of foam rubber in the slot, put the ring on a Kapton-covered build platform from the Thing-O-Matic, filled it with hot-melt glue, gooshed the toroid in place, and waited for cooling. Trimming and cleaning out the slit produced a hideously ugly, but (I hope) much more durable assembly:

Slit ferrite toroid - with armor

Slit ferrite toroid – with armor

I’m reasonably sure I didn’t crack the ferrite while cleaning out the slit; that hot-melt glue is tenaciously gummy stuff!

Now, to find out whether it actually works…


, ,