Magnets and Printed Parts Make Quick-Disconnect Terminals

The Apple MagSafe power connector is long gone from their product line, but that doesn’t mean that magnetic connectors aren’t without their charms. It just takes the right application, and finding one might be easier with these homebrew magnetic connectors.

We’ll admit that the application that [Wesley Lee] found for his magnetic connectors is perhaps a little odd. He’s building something called Linobyte, a hybrid art and electronics project that pays homage to computing history with very high-style, interactive core memory modules. The connectors are for the sense wire that is weaved through the eight toroids on each module, to program it with a single byte. Each connector has a 3D-printed boot that holds a small, gold-plated neodymium magnet with the sense wire soldered to it. A socket holds another magnet to the underside of a PCB. The magnet in the boot sticks to the PCB and makes contact with pads, completing the circuit. We know what you’re thinking: heating a magnet past the Curie point is a great way to ruin it. [Wesley] admits that happens, but it just makes the connection a little weaker, which works for his application. The short video below shows how he puts them together.

We can think of a couple of ways these connectors would be useful, and we really like the look of the whole project. It’ll be interesting to see where it goes, but in the meantime, brushing up on how magnets work could be fun.

[via r/electronics]

19 thoughts on “Magnets and Printed Parts Make Quick-Disconnect Terminals

  1. Be careful soldering neodymium magnets, if you get them even mildly hot they loose their magnetic properties. You could solder on ferrous metal and use the magnet in the center, but if a lot of current flows weird things may happen. If it gets warm it may lose it’s magnetism and fall apart and if it gets a high current pulse, it may want to jump. Perhaps the safest thing to do would be to modify a normal connector like a db25 but remove the screws and epoxy magnets onto both ends to hold them together, far enough away from heat and lectrisity for the lecttric and magnetic not to interfere with each other.

    Cool idea though. Very cool. Got me thinking.

    1. I’d prefer adapting a piece of pre soldered copper foil (ie wire soldered to strip of copper foil first then) crimped suitably (and carefully) round the (somewhat brittle) magnet with maybe a touch of neutral cure silastic too, that way one can’t lose connection reliability from it being too loose :D
      Magnets certainly very useful, so it surprises me it took so long for industry transition as in oldie db-9 PC serial connectors to approach any sort of USB type unpolarised connector with magnets. I’m attracted to using them in all sorts of places and would induce others to think likewise… Thanks for posting, cheers.

      1. I suggest soldering to a piece of nickel strip (like the one used to join battery cells) and glue the magnet on one side of it with a thin layer of glue. The other side can be magnetically attached to anything easily. Nickel is ferromagnetic and of good electrical conductivity.

        1. Hmm, well I don’t see this not being as effective as crimping copper around the magnet due to external selection of low resistivity materials for carrying current…
          ie. Copper more conductive than nickel and more conductive than the magnet. In any case crimping copper around the magnet means far less current through the magnet which might have raised its temperature towards the Curie point otherwise. Hence my point about the silastic as it buffers any physical stress/shock so the ostensibly fragile NdBFe magnet far less likely to facture if one were a bit enthusiastic with crimping. If you don’t have copper then sure use nickel as a secondary option, though the issue of Ni being ferromagnetic doesn’t matter here either way as the magnet sufficient in that regard it’s the source of attachment.
          Just in case there is some misunderstanding when I refer to crimping, I would make a rectangular tab of copper just wide enough that it surrounds the magnet and to avoid stress on the magnet crimp the edges only. One could be a bit more careful by first pressing the copper around the magnet with the silastic and let that set before crimping and you don’t need me check silastic either, just a smear is ok as it reduces chance of vibration if the crimp force relaxes over time…

    2. For some reason, soldering neodymium magnets seems to work fine in practice though. I’ve done it for the z-probe wire in my cnc, and years later it still works fine and the solder has stayed on – while I’ve had to redo the epoxy that I added as strain relief. Perhaps it loses a bit of magnetism, but not that much that it would matter.

      1. Maybe that’s because neodymium magnets are so overpowered that even with some magnetism lost they are still useful.

        I once baked some tiny neodymium magnets in an oven at about 170C (I intended to remove them before baking the cookies, if you ask :), and they became noticeably weaker afterwards, but still stronger than same-sized ceramic magnets.

      2. They main thing is that part of the magnet doesnt reach curie temp, so some residual magnetism is left. Also, there is still another magnet behind the PCB, which attracts the soldered one.

  2. I made a magsafe-like connector for the touch-probe on my CNC mill. (I was worried that I might turn on the spindle with the probe fitted, of course I never have).
    I wanted two poles, so I used ring-shaped magnets (which are readily available).
    I actually just pressed the magnets in to the housing, trapping wires in intimate contact on the edge.
    In the centre of one terminal is a brass plug for the second terminal, which makes contact with a spring-loaded contact in the centre of the other (like a home-made pogo pin).

    1. Does an alligator clip clipped on to a magnet that is then stuck on the side of the spindle count as a connector? If so this is what i use for my probe when leveling pcb’s. Only one carbide engraver was lost when the corrosion on the side of the spindle exceeded the conductivity of the magnet to spindle connection.

      The alligator clip holding a magnet also works great when you don’t have a battery holder for 18650 cells and want to make a quick connection with not much current flow.

  3. I used to do a lot of work with piezoelectrics which have a depoling temp. like magnets where the effect is progressively lost with time above the depoling temperature, and we soldered to them in a similar fashion with very little effect loss from soldering. Our depoling temp was around 80c which is a bit lower than neodymium of 100c, for common grades. Blob of flux on piezo, blob of solder on iron, light touch to tin the piezo, more flux to cool blob, new solder on iron, heat up tinned wire, touch the wire to the blob on piezo, isopropyl to cool and clean.

  4. I came up with the idea of using neo magg battery connectors some 15 years ago and have been using them in my projects ever since. The advantage is that now I can use any sized battery be it AAA, or AA or C or D cell to power my led light projects or radios or whatever and changing batteries takes only seconds. In my original design, you do NOT ever want to solder to the neo magnet because first, it is only plated and that plating is not very strong and can come off under tension, (ask me how I know) and the temperature required for a good solder connection degrades the magnetic properties greatly…they are still magnets, but much weaker. I have videos on how I made my earlier design on my youtube channel. The way I build them now is to simply solder a good connection to a steel washer the same diameter as my magnet, the magnet holds the steel washer tightly and then I install that into a rubber ring and pour epoxy to fill the top side. The connection stays good under tough circumstances and the assembly is small, (About .250″ diameter) I have sent these to many folks all over the country and many people have built their own now and I see them on their projects. When I first used them in a video, I had many comments about how the magnetic field would block energy flow and that these could not possibly work and they must be fake, etc. Gotta love the youtube comments section.

  5. Another old trick for cheap low voltage quick connects where the last half ohm or hundred millivolts doesn’t matter is to use sewing snap fasteners (Press studs, poppers or rivets (not pop-rivets) are other things ppl call them.)

    They come in either rivet-on or sew-on varieties. The sew on ones have been known to take solder. The rivet on ones may, but may require setting with the proper riveting tool in order that they press together correctly, some allowance being made for deformation in setting.

    They can also be used glued-on for fastening small hatches and access panels.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.