This is a magnetic phone charger. It's a USB cable that plugs into a standard 5V phone-type charger. The magnetic "plug" has a (+) center-pin and a (-) round metal as the ground with a magnet behind it. The receiving load-side "socket" mirrors the power-supply plug by having a spring-loaded (+) center-pin and also (-) metal ring as the ground with a magnet behind it. Has no (D+/D-) data lines, only power.

Unfortunately, (with some deliberate effort) I have discovered that the physical design DOES ALLOW for an inadvertent short-circuit by having the "plug's" center-pin touch the round ground metal of the mating "socket" while at the same time it's own round metal ground touching the center-pin of the "socket".

I can protect the receiving load circuit with a diode, or a MOSFET, or other common reverse-current/voltage protection. But is there any way to prevent the power-supply itself from getting shorted out? The 5V power-supply/charger can be anything, since this is just a USB cable.

The only way I can think of protecting a connected 5V power supply/charger (let's assume it does not have one built-in) is to somehow channel away/absorb the short-circuit current somewhere on the receiving load side of the circuit by offering a lower path of resistance, while also making sure that the load-side of the circuit is not damaged either.

What say you?

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    \$\begingroup\$ Something is wrong about your assumptions. A short-circuit on the supply side does not lead to a current that needs to be shunted/absorbed away from the load. It creates a high current that overloads the supply. Carefully draw the schematic of the components with a wire indicating the short-circuit connection, and see where you have currents flowing. \$\endgroup\$
    – nanofarad
    Mar 3, 2021 at 5:28
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    \$\begingroup\$ The load will not be damaged if the supply is shorted. The load will not even be aware of the short-circuit, and will be totally unable to do anything about it. Let the supply fend for itself. It is pretty rare to send a supply out into the world that can't handle a brief accidental short-circuit. \$\endgroup\$
    – user57037
    Mar 3, 2021 at 5:42
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    \$\begingroup\$ If you produce a short on the supply side with the plugs, there's nothing your load can do about it. You need to redesign the plug so that shortcuts become impossible. \$\endgroup\$
    – PMF
    Mar 3, 2021 at 5:49
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    \$\begingroup\$ @TommyS Since you are using magnets, have you attempted anything with axial self-aligning magnets? (Concentric alternating cylinders, for example.) With several alternations (more is better), it gets almost impossible to make them mis-align. (Have a look here. I just searched to see if someone was already doing this for you.) \$\endgroup\$
    – jonk
    Mar 3, 2021 at 5:50
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    \$\begingroup\$ The protection for the supply MUST be in series with the cable before the short circuit. Something like a fuse or PTC or electronic over-current detection back at the supply is the best way to do it. There just isn't a way to do it at the load. The load will never know that the supply has been shorted. \$\endgroup\$
    – user57037
    Mar 3, 2021 at 5:56

1 Answer 1


It appears you want to do something with the load side circuitry to protect the supply from overcurrent caused by shorts in your magnetic connector. As stated in the comments, you can't. It is not physically possible. Possible options that would allow you to continue using this connector include installing a PTC fuse or similar circuit in between the power supply and the offending connector, or ensure you're always using a supply that can handle shorts.


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