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I am using a LightingWill Waterproof IP67 LED Power Supply to power a magnetohydrodynamic drive with a circuit diagram that looks like this:

enter image description here

The solenoids are wrapped around a bunch of iron nails as the core and the electrodes are copper tapes. The direction of current and magnetic field is shown in the circuit diagram (yellow is current, cyan is magnetic field). The whole apparatus submerged in saturated salt water. By the left hand rule, when electricity passed through the salt water, they should be propelled by Ampere force with the direction being perpendicular to the screen and out. However, when I connected everything and plug the power supply into the kitchen socket, nothing happens and there is no voltage inside the circuit.

I tested the resistance at the joints between the solenoid branch and the electrode branch and received a resistance at 0.01 ohm. When I disconnect my apparatus and just plug in the power supply, the voltage at the power supply output (the red and black wire) is 12 V, that means the power supply is working. So why didn't I get current into my apparatus?

I used 18 AWG wire for my electrode branch (this is the wire that also connects to the power supply) and 12 AWG wire to make my electromagnet solenoid (which is basically wounding wires around a bunch of iron nails).

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    \$\begingroup\$ Spend a lot more time drawing better diagrams! I think I see a current (cartoon character) and a magnetic field line (cartoon, again) but I don't see what you imagine to be the direction of the resulting force from these. I hope you are imaging either into or out of your drawing plane as the direction is the cross-product. But I've no idea what you think from that terrible drawing. Please spend some more time laying out the details of the design and what you expect to see happen. It wouldn't hurt any if you did a few calculations to work out the force, too. \$\endgroup\$
    – jonk
    Commented Aug 29, 2021 at 5:45
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    \$\begingroup\$ please do not crosspost engineering.stackexchange.com/questions/45815/… \$\endgroup\$
    – jsotola
    Commented Aug 29, 2021 at 6:14
  • \$\begingroup\$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. \$\endgroup\$
    – Community Bot
    Commented Aug 29, 2021 at 8:56
  • \$\begingroup\$ You need a much greater length of much thinner wire, 26 AWG perhaps, 1000s of turns \$\endgroup\$
    – Neil_UK
    Commented Aug 29, 2021 at 9:46
  • \$\begingroup\$ Could you tell me why though? Wasn't that the thinner the wire, the higher the resistance and less current? and less current means less magnetic field, right? \$\endgroup\$
    – Faito Dayo
    Commented Aug 29, 2021 at 16:21

2 Answers 2

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As Neil pointed out, you need more turns of thinner wire to increase the resistance. More resistance means you stay within the specs of your power supply unit's (PSU) current limit. When you exceed that, several things might happen depending on the unit. One would hope it would cause a fuse or breaker to shut it down. It might drop in voltage to keep supplying something while avoiding burning out. Or finally it might burn out. An supply like yours is usually designed to output constant voltage. Design your resistance for that voltage and about half its current limit.

12V=12.5A×0.96Ohm 0.96 MINIMUM to keep that power supply in spec. Aim for 1.92 Ohms

Another issue is the salt water environment. You need to make sure the current flows where you expect it. If the insulation is broken somewhere, you might end up bypassing your coils.

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  • \$\begingroup\$ Understood. But the connection between my wires for electrode and wires for my solenoid is above and out of the water container though? \$\endgroup\$
    – Faito Dayo
    Commented Aug 29, 2021 at 17:03
  • \$\begingroup\$ Check where your current is actually going. Ditch the electrode branch and see what happens. probably a short there sapping the solenoid. \$\endgroup\$
    – Abel
    Commented Aug 29, 2021 at 17:13
  • \$\begingroup\$ but the two solenoids are actually made from the same wire. So I am not sure what do you mean by a short. Do you mean the insulation broke and salt water got in contact with the wire? \$\endgroup\$
    – Faito Dayo
    Commented Aug 29, 2021 at 17:16
  • \$\begingroup\$ maybe try series instead of parallel if there is voltage at your psu terminals when the electrodes are gone but unit is still powering coils (indicating your psu is not quite dead even with your coils as they are) \$\endgroup\$
    – Abel
    Commented Aug 29, 2021 at 17:24
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    \$\begingroup\$ @FaitoDayo The point is that the resistance of the two solenoids is probably too low. have you measured it? If the resistance is less than about 1 ohm, it will draw too much current, and the power supply will shou down to protect itself. \$\endgroup\$
    – Simon B
    Commented Aug 29, 2021 at 20:28
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when I connected everything and plug the power supply into the kitchen socket, nothing happens and there is no voltage inside the circuit.

Let's remember that fact.

When I disconnect my apparatus and just plug in the power supply, the voltage at the power supply output (the red and black wire) is 12 V, that means the power supply is working. So why didn't I get current into my apparatus?

A likely explanation is that the power supply is overloaded when you connect it to your solenoid, the resistance of the solenoid being too low. The power supply is likely shutting down to protect against this overload.

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