Matrix "Multiplexing" with electromagnets, interesting behaviour

Question

I have an interesting behaviour with my electronics project. I am trying to do something like a LED array but with electromagnets instead. See the schematic below. I built the magnets myself by winding 5 meters of 0.3mm magnet wire around iron nails. I use relays for the switches. The diodes are rated for high currents.

When I pulse one of the top switches and one of the bottom switches together, I expect only one coil to get powered. BUT the interesting thing is that EVERY magnet pulses a magnetic field, just the one that SHOULD pulse has a more powerful field. I can feel that by holding a permanent magnet next to it.

Please can someone explain this to me, because I dont see how the current can enter the non-connected coils.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 1

Of course, permanent magnets are attracted to the iron with no current flowing. Iron is ferromagnetic.

If you don't have a more-or-less closed magnetic circuit, a lot of the field lines will go through the air and, if the cores (nails, in your case) are close then there will some effect on the nearby core when your coil is energized.

You should have diodes across the coils (in parallel), reverse biased, of course, to prevent the (high voltage) turn-off spike from possibly killing the series diodes.