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I am designing a project that will require about two dozen smallish electromagnets (larger than in a relay but much smaller than used to activate car door locks). They will be powered by a battery bank in an RV, so 12 vdc and the equivalent of about 4-8 car batteries in parallel. I have not chosen the electromagnets yet, so part of what I am deciding is what voltage rating to look for.

I used to be an electronics technician in the USMC, but all my work was in low-voltage signal shaping, where power use played almost no part in the way the circuits worked. I assume the serial vs parallel math is different when powering electromagnets is involved.

Here's the question: Would I be better off arranging these electromagnets in series or parallel? Would the actual current coming out of the batteries change much at all when the electromagnets are doing the same amount of total work either way?

By the way: These will only be in operation for about a second, every day or so. They are to release catches that hold things closed.

Naturally, parallel will be better for later troubleshooting. Should I just get 24 12vdc electromagnets, arrange them in parallel, calculate the total current, size my wire accordingly, and consider it done? Are there any other concerns I need to consider?

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  • \$\begingroup\$ USMC - this is an international site and references to local organizations is not understood by the majority. Who you worked for once is probably irrelevant too. \$\endgroup\$ – Andy aka Sep 13 '15 at 9:03
  • \$\begingroup\$ If they are only to operate for a second or so per day, it sounds as if there's no need to operate them all at once. If you can arrange or guarantee that only one or two operate simultaneously, that reduces the wire size you need. \$\endgroup\$ – Brian Drummond Sep 13 '15 at 10:38
  • \$\begingroup\$ Andy, if you don't know what the United States Marine Corps is, and you find who I worked for irrelevant, then why did you say anything at all? Lots of "local organizations: are internationally known. Besides, the organizations one has worked for gives some clue as to the type or scope of work one has done. In the USMC they train you to perform a very narrow set of tasks. There were many electronics tecnitians who did not know how a capacitor or transistor worked. Only how they affected the circuits they worked on. \$\endgroup\$ – GrantRobertson Sep 13 '15 at 15:46
  • \$\begingroup\$ Brian, operating the units separately will require separate wires on the power side (they could use the same ground). Considering the distance separating these things, that might be more expensive in the long run. They do have to operate in pairs, so that wouldn't be as much extra wire as 24 separate connections. Then there is the cost of the control circuit. The power switching components could easily eat up any cost savings in wire. Mostly I am just checking to see if the math is different for electromagnets compared to simple resistors. \$\endgroup\$ – GrantRobertson Sep 13 '15 at 15:58
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ORIGINAL ANSWER:

If you connect 24 twelve volt electromagnets in series you'll need 288 volts to drive them properly, while if you connect them in parallel you'll need only 12 volts, which you already have, so it seems like parallel is the way to go.

EDITED ANSWER:

Since you've changed streams in mid-horse, it seems a little clarification is in order.

For identical cores, the strength of the electromagnet will almost totally depend on the product (ampere turns) of the current through the coil times the number of turns wound about the core.

What that means is that if you have a core with a single turn wrapped about it and one ampere through the winding, (one ampere-turn) the strength of the magnetic field generated using that configuration will be identical to one generated by two turns wound about the core with half an ampere through the winding, which is also one ampere-turn.

Next, responding to your response to @Brian Drummond's comment, the steady-state math is no different for an inductive load than it is for a resistor since it all boils down to the resistance of the coil,

However, where the rubber meets the road, the impedance of the coil has to be accounted for when power is first connected to the coil, as does its inductive kickback when power is disconnected.

Then there's the resistance of the winding to consider, and all of a sudden the power required to generate the required magnetic field rears its ugly head.

Do you want to pursue this further?

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  • \$\begingroup\$ Going further with the thought experiment, you'd then have to get a switching supply to boost the 12 volts up to 288, and then (neglecting the efficiency of the supply), you would end up pulling the same current out of the battery, just like you (the OP) asked. \$\endgroup\$ – gbarry Sep 13 '15 at 7:33
  • \$\begingroup\$ In my question, I stayed that I am still determining what voltage rating to use. If I put the electromagnet in series, I would not use 12v units. Though, I doubt .5v units would be strong enough to accomplish the task. My question is: would 24 .5v units in series have the same current draw as 24 12v units in parallel if the electromagnets were otherwise spec'd out to perform the same work? \$\endgroup\$ – GrantRobertson Sep 13 '15 at 15:30

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