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I'm looking at making a quick disconnect battery that is attached with magnets. It looks like most magnets have a coating for abrasion and oxidation protection but no mention of conductivity.

Is it possible to coat the magnet in a dielectric then a conductive coating and run current through as a sort of battery connector? Would you even need the dialectic?

usernamechecksout
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    Hm, while you certainly can make some contact either way, you really would need to explain why that approach would be even comparable to using well-proven contacts (which solve the whole reliable contacting and release dilemma you get) that you just secure mechanically with a magnet. – Marcus Müller Dec 17 '19 at 20:40
  • This is for a quick swap system for a battery that only weighs 10g and normally has very small connectors that are difficult to work with and can take 20 seconds or more to fiddle with. It would also allow for easy balance charging for multi celled lion batteries. The batteries only last about 2 minutes each so swapping frequently is required. – usernamechecksout Dec 17 '19 at 20:42
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    It's a battery: good connections are paramount, and will not be achieved without proper contacts. pressing two conductive surfaces together does not make a reliable, low-ohmic connector. You really need a good metal contact – these exist and are cheap. Copper coating doesn't do! It will oxidize!The idea of fixing these with a magnet is great, but really, don't try to make the magnet surface be the contact. – Marcus Müller Dec 17 '19 at 20:47
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    There ARE magnetic connectors out there that just about snap into place by themselves if you bring them close to each other. But they don't rely on the magnet itself to conduct. I am not sure if any are small enough for your needs. It is definitely an interesting idea and I am glad you asked about it. – user57037 Dec 17 '19 at 20:48
  • https://www.amazingmagnets.com/t-plating_options.aspx Ni-Cu-Ni coatings exist but does not solve other issues for current density and contact pressure, size , fit , adhesion to SS electrodes. – Tony Stewart EE75 Dec 17 '19 at 20:50
  • Thanks for your answer Marcus. Copper probably wouldn't be the way. The other problem is getting a good connection from magnet>pcb. I think if the magnets were not flat and more of a dimple in crater approach it would work better. – usernamechecksout Dec 17 '19 at 20:51
  • Plenty of drones and model aircraft have slide-in battery docking implemented with quite ordinary miniature connectors and some additional molded pieces for fixturing. – Chris Stratton Dec 17 '19 at 22:25
  • If you were going to do this, a brass coating would be far better than plain copper. But a different method altogether would be even better. – Hearth Dec 18 '19 at 00:32

3 Answers3

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Most neodymium magnets have a nickel based coating. It is pretty conductive anyway. Give it a go. I have a pile of magnets and a battery next to me so tried it, and it worked...

Think carefully if it's for a product, but for a home project, why not!

David Molony
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  • I'm looking for about 10 amps through anywhere from 14-100mm^2 of contact area depending on what's possible here with a higher performance coating. The problem isn't whether it would work but if it would be efficient. – usernamechecksout Dec 17 '19 at 21:38
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    @usernamechecksout So why did you ask "Is it possible..." if the problem "isn't whether it would work"? You should take the time to write the proper question from the beginning. Edit your question and add all of the information you gave in your comment. – Elliot Alderson Dec 17 '19 at 21:46
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While it might be possible to get a results using the coating on a magnet for connectivity, it would seem a real unknown at 10 Amps. Trying to over-plate the surface would seem like an excise in futility as you'd have almost no control of the contact surface.

I'd suggest that you build your batteries with Pogo pins on the terminals and simply use the magnet to provide the contact pressure you need to compress the springs. Most Pogo pins are limited in the current they carry because of the conduction thorough the spring, so you need multiple to supply 10A. For example: enter image description here

Those above are rated at 2A. Clearly you could pass more current but would be advised to have at least 4 for each terminal.

Perhaps more engineering but more capable are spring loaded self wiping contacts such as this:

enter image description here

Here the current rating is 9A so it's easily possible that this would provide service at 10A for your 2 minutes.

I'd normally consider Mill-Max for reliability, but they are higher cost and usually specified at about 3A peak per contact.

Jack Creasey
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Homopolar motors bank on the fact that a neodymium magnet has a conductive outer layer.

enter image description here

https://en.wikipedia.org/wiki/Homopolar_motor

Aaron
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