Nichrome wire gauge

[ystumtec]

Hi, Great work here: a really creative use of low-cost/readily available materials!

I'm about to put together a system based on your work, and have a couple of questions: 1) What gauge nichrome wire did you use? Maybe you say this somewhere, but I couldn't find it. 2) I can't get either the STL or STEP files to load into FreeCAD or other viewers, any ideas? I'm planning on integrating your release into my own PCB, so I'm probably not going to use them as they are, but it would be useful to see how you laid stuff out. 3) Did you do any playing around with super-caps or other ideas for getting nice big current pulses through your nichrome? I'm planning to use my main system battery to power the release mechanism as well, and would like to use a relatively small (low current capacity) battery and a super-cap seems like a reasonable idea to give a decent high-current pulse without getting the battery close to its limits.

Great ideas in here and thanks for sharing them,

Mark.

[WildSpyAdmin]

The CAD files are for the housing, not the PCB. Gerber files for the PCB are available under the Production folder.

We did initially experiment with supercaps, but they just didn't have enough current to do the job. Not in the device form factor we required back circa 2010ish. They may be viable now for other applications though.

The nichrome is somewhat finicky, and it took a bit of experimenting to find something that worked as desired. Unfortunately I don't think that particular type/brand is available any more but the gauge should be 32 AWG.

[ystumtec]

Thanks for getting back to me. In the meantime I put together and field tested my own design based on your idea. Just in case someone else picks up on this in future here are a few details of my rig: 1) I Used 0.3mm nichrome wire bought on eBay. I also experimented with 0.1mm, but it makes a really fast fuse :-) . 2) For long endurance logging (tracking deer over a year) I am using 2 x 18650 lithium ion cells in parallel mounted in PTH clips directly on the PCB assembly (potted inside the 3D printed housing). 3) To heat the wire I use a series of short pulses (about 75ms repeated 10 times in 1 second) through a n-channel FET rated at 5.5A as a low-side switch. This lets the wire get red hot, without burning through it. 4) My nichrome is fed through two vias in the PCB spaced 8mm apart and then drowned in solder to make the (mainly mechanical) connection. Solder doesn't really stick to the wire, but seems to make a fairly good electrical connection nonetheless. 8mm is too short really, but constraints of my design led to that. 5) In V1 I trapped the nylon line between the PCB/nichrome and a piece of my 3D printed housing, which worked ok, but sometimes the line would cut but get stuck to the plastic in the print and the collar took a long while to drop. 6) For V2 I'm trying making a loop in the nichrome with the nylon monofilament fed through the loop. Lab tests look good, field tests in the near future. 7) I tried a 5F supercap for heating the wire, worked ok, but the 18650s work fine, so sticking with those. 8) The PCB has a "nubbin" (about 15x15mm) with the holes for the nichrome in it which slides through a slot in the housing to allow the wire to be attached and the monofilament fed through after assembly of the main housing.

[WildSpyAdmin]

For our collar use we had an acrylic plate to sandwich the nichrome and fishing line. It's detailed in the journal article, but here are some 3D renders to give you an idea.