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Background

I have an application that requires an electromagnet (either 5v or 12v) to be powered on for long durations of time (up to a few hours). While looking for one online, I was having a hard time finding one that could be powered on for more than 7 minutes without incurring damage. I have seen some access control magnets (although they are larger than my need), but they did not have info on durations.

Questions

There are a few things I would like to understand about this:

  1. Is there a way to modify an electromagnet (restricting current, ect.) to allow it to be run for longer periods of time?
  2. Does the strength of the magnet come from the voltage or the current draw? And is the damage over time caused by the current draw or the voltage?
  3. Are there electromagnets on the market that can be used continuously / how do they maintain continuous power?
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  • $\begingroup$ 2. voltage pushes current through a load ... higher voltage is able to push more current ... current flowing through a conductor creates heat ... higher current creates more heat $\endgroup$
    – jsotola
    May 7, 2023 at 4:18
  • $\begingroup$ Access control magnets are designed to be continuously on. $\endgroup$
    – Transistor
    May 7, 2023 at 9:27
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    $\begingroup$ there exists a type of permanent magnet that can be electronically switced from contained (magnetism is inside housing) to external (acts as magnet) these do not need to be powered between states. $\endgroup$
    – joojaa
    May 7, 2023 at 11:15
  • $\begingroup$ Can you please add to your question, why you have this requirement? What‘s the application? Thanks $\endgroup$
    – MS-SPO
    May 8, 2023 at 5:27

3 Answers 3

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Similar answer to @Phil Sweet and comment by @joojaa it seems and similar sector too as I work in horticulture. The solenoids we use for battery-operated irrigation controllers have a latch mechanism: a permanent magnet keeps the solenoid in the open position rather than having to hold it, then the polarity is reversed to close the valve aided by a spring. Power is only required for the open/close pulse.

https://www.tlxtech.com/articles/latching-solenoid-basics

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Using the terms "continuous duty solenoid" provided a number of results which may be of value to you. A solenoid is an electromagnetic switch. When the coils of the electromagnet are energized, the mechanical component of the switch causes the contacts to close (or open) allowing for current management at higher voltages than the energizing circuit (typically).

In a vehicle starter environment, the duty cycle is quite short, but in an electric vehicle the duty cycle is continuous. The components are engineered for the increased duration of operation. Two of our EVs operated the contactors in excess of ten years, not continuously, of course, but for periods in excess of two hours, with no difficulties.

Many solenoids are encased in a metal housing, making access to the electromagnet challenging, but that is not always the case and you may find a suitable candidate for your purposes.

Waytek Wire web page presents useful information regarding selection between relay, solenoid and contactor, the latter being the continuous duty type of device. It is referenced in the linked page that a contactor frequently is configured to reduce the current flow once the circuit is energized, as the power requirement is higher to pull the electromagnet than it is to maintain the position.

Contactor image from above linked page:

Contactor

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  • $\begingroup$ Good point about dual coil solenoids. The classic example is a diesel engine fuel solenoid that has a continuous duty hold coil powered from the "run" switch position and a high-powered, short duty cycle pull coil powered by the "crank" switch position. The pull coil is more than ten times as strong as the hold coil, and will burn out quite easily when trying to crank a hot, vapor-locked diesel. $\endgroup$
    – Phil Sweet
    May 7, 2023 at 13:34
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As others have said, you just need to buy the proper type with a continuous rating. Confusingly, there are two types of continuous ratings - indefinite and not indefinite, which I can't explain because I don't know what the difference is. (As it happens, I am building a replacement for a 3 port 2 way solenoid valve that uses a continuous solenoid for "left port" and a spring return for "right port". Deere wants about \$1200 for the valve that switches soap bubbles to either the left or right side of a pesticide sprayer, so I'm building my own for about \$100.) Below is a snip from the specs of the valve I'm going to use.

enter image description here

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