Please see the attached photograph of the component:

enter image description here

My guess is that it is a solenoid, but I am not sure. If it is a solenoid, I would really like to use it. The problem, however, is that I do not know anything else about the component. There are no part/model numbers or any identification of any kind on the component.

In a situation like this, how do you go about putting a mysterious component to use. I generally don't throw away things simply because I don't know what they are, and am sure I could use this for something.

  • \$\begingroup\$ Why do you like to use it? It is a solenoid. \$\endgroup\$ Commented Jan 11, 2013 at 4:29
  • \$\begingroup\$ Some kind of bell perhaps? \$\endgroup\$ Commented Jan 11, 2013 at 4:30
  • \$\begingroup\$ @ChetanBhargava Sorry, what do you mean? I don't like to use it, I would like to use it. \$\endgroup\$
    – capcom
    Commented Jan 11, 2013 at 4:37
  • \$\begingroup\$ @capcom What I mean is why do you have to use an unidentified component and for what use? \$\endgroup\$ Commented Jan 11, 2013 at 4:45
  • 3
    \$\begingroup\$ @ChetanBhargava Well, that's the fun. Once I know what it is, I can think of something creative to use it for. I can understand why that may seem odd though, but I'm a tinkerer, and enjoy such activities. \$\endgroup\$
    – capcom
    Commented Jan 12, 2013 at 0:55

3 Answers 3


It looks like an electromagnet.

Start with a DMM - check the coil winding resistance. From there, you can probably make some educated guesses about where to start testing using a benchtop DC supply. Slowly increase the supply voltage. Keep tabs on when it starts to get hot, and you've likely found its continuous current limit.

  • \$\begingroup\$ I tried that with a converted pc power supply. I tried 3.3V, 5V, and 12V. Nothing seemed to happen. I will check the resistance too. \$\endgroup\$
    – capcom
    Commented Jan 11, 2013 at 4:39
  • 2
    \$\begingroup\$ @capcom An electromagnet would produce a magnetic field, but you need something for it to act on. A small piece of ferrous metal, like a ball bearing or a altoids tin. Something to attract or push away when activated. Like this: img.directindustry.com/images_di/photo-g/… \$\endgroup\$
    – Passerby
    Commented Jan 11, 2013 at 5:02
  • \$\begingroup\$ Thanks, you were right, it is an electromagnet! I tried it at the three voltages from my power supply, and the magnetic force was strongest at 12V, as expected. Thanks, I'll definitely put this to use when the opportunity arises. \$\endgroup\$
    – capcom
    Commented Jan 12, 2013 at 0:52

After searching, I am quite certain it is a holding solenoid, similar to those used to hold doors open, or to lift piles of metal/cars at a junk yard. Compare to the pictures below. Near identical in operation as a linear solenoid (The push/pull rod type). You will need some ferromagnetic metal (like carbon steel - stainless steel will not do) to interact with it, or use a compass to verify it is working. Practical uses are to hold a door open. Impractical would be to make a miniature magnetic crane game, or scale sized scrap yard crane remote controlled car, or rig a dart board.

enter image description here Door Holder

  • \$\begingroup\$ You hit the nail on the head. It is an electromagnet. I remember making one in grade school by wrapping wire around a screw. Thanks a lot. \$\endgroup\$
    – capcom
    Commented Jan 12, 2013 at 0:54

Depending on what test equipment you have available, before you apply any power, you can test it's resistance, inductance or capacitance (probably the first 2 are most useful in this case since it looks to be a coil of some sort)

An LCR meter (Inductance Capacitance Resistance) is a great tool for testing unknown components such as this. I have a Mastech MS5308 (can be found for £133 on eBay) and can highly recommend it. For the price it is comparable with more expensive meters (from e.g. Agilent, BK Precision, etc) comes with proper 4 wire kelvin clips, 4 wire SMD tweezers, an isolated USB link and case.
It tests at frequencies of 100Hz, 120Hz, 1kHZ, 10kHz, and 100kHz (the more test frequencies the better - many lower quality meters only have a couple and do not test at 100kHz, which is the frequency most capacitors are tested at for the datasheet specs)
It has a minimum resolution of 0.01pF, 1nH and 1mΩ which is very impressive indeed, tests ESR (Equivalent Series Resistance), Q, DF, θ and has a sorting/tolerance mode you can use to quickly find parts that are out of rated tolerance. For comparison the Agilent U1731C only tests at 120Hz and 1kHz, and has a minimum resolution of 0.1pF and is over £200. Anyway, you might guess I'm extremely happy with mine, but have a browse around before deciding just in case I'm talking rubbish :-) )

Also, you could carefully peel a little of the covering away to reveal the windings (assuming it is a coil)

When you do apply power, preferably use a current limited bench supply and ramp up slowly. Try swapping leads around to see if this makes any difference (just in case there's a series diode hidden in there somewhere)

A function generator may also be of use, possibly combined with an amplifier in case it requires AC drive.

Having said all the above, it does look like either an electromagnet or part of a solenoid/relay assembly (but it could be a buzzer, or...)

  • \$\begingroup\$ Thanks for the awesome tips. I never heard of an LCR before, but now I really want to get one. It is indeed an electromagnet. \$\endgroup\$
    – capcom
    Commented Jan 12, 2013 at 0:53
  • \$\begingroup\$ @capcom - I added a bit more detail on LCR meters, also there's quite good discussion of various LCR meters on the EEVBlog Forum. \$\endgroup\$
    – Oli Glaser
    Commented Jan 12, 2013 at 4:44

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