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For example, are there inductors with values in terms of kH or even MH? 1 H inductors are not all that easy to find.

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    \$\begingroup\$ A quick google came up with an MRI magnet being only 6H, I'm surprised it's as small as that! This isn't really a physics question, it's an economics question. With a large coil of very fine wire, you could make a record-breaking inductance, that was totally useless through having very low SRF or high resistance, just to break a record. \$\endgroup\$
    – Neil_UK
    May 4, 2017 at 9:38
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    \$\begingroup\$ @Mr X .Would it be interesting to know what the highest Q inductor is ? \$\endgroup\$
    – Autistic
    May 4, 2017 at 11:12
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    \$\begingroup\$ I have seen some large values attained using gyrators (I cannot recall the exact values but certainly in hundreds of Henries and perhaps more). \$\endgroup\$ Apr 10, 2020 at 15:35
  • \$\begingroup\$ Whenever you find it, put two in series. \$\endgroup\$
    – user253751
    Jul 12, 2020 at 19:48
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    \$\begingroup\$ I think gyrators are cheating. They are inductor simulators, not real inductors. If gyrators count, then an open circuit also has infinite inductance. \$\endgroup\$
    – user253751
    Jul 12, 2020 at 19:48

6 Answers 6

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The largest inductor ever known to me was Fermi National Accelerator Lab's Tevatron magnet. If memory serves it was 1000 Henries running continuously at 1400 DC Amperes. Energy storage must have been right around 1 GigaJoule. They had a "quench resistor" designed to burn off the energy in case the magnet would develop an open circuit. The resistor (designed by my boss!) could be seen from space on Google Maps until not long ago.

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  • \$\begingroup\$ Thanks for the answer! That's pretty much exactly what I was looking for. \$\endgroup\$
    – Mr X
    Apr 8, 2018 at 2:42
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    \$\begingroup\$ BTW, do you have any links to the huge "quench resistor" used? \$\endgroup\$
    – Mr X
    Feb 27, 2020 at 23:22
  • \$\begingroup\$ Designing such a resistor was a question from my time as an undergraduate. \$\endgroup\$
    – D Duck
    Apr 15, 2021 at 8:49
  • \$\begingroup\$ I recall calculating similar numbers for the specs of the magnets in ITER. That was quite a long time ago; ooh, I wonder if they have actual test data now?! \$\endgroup\$ Jul 5 at 4:28
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What is the largest inductance value ever attained(in Henry's)?

The magnetic permeability of free space is 1.2566370614…×10−6 henries per metre and the universe is pretty big. "What" you might possibly say and I would say that radio waves (and light) are carried vast distances between far-away galaxies so this "inductance" is being used to convey energy we can see and detect therefore it exists.

Between earth and the sun (93 Million miles or 150,000,000 km) I estimate the inductance to be 188,000 henries.

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    \$\begingroup\$ Interesting. The Solar system is only 150 times more inductive than a ABB transformer? \$\endgroup\$
    – Paul Uszak
    May 4, 2017 at 12:17
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    \$\begingroup\$ @PaulUszak given that inductance is proportional to turns squared, that should not be surprising !! \$\endgroup\$
    – Andy aka
    May 5, 2017 at 15:48
  • \$\begingroup\$ I wonder what the capacitance and resonant frequency is? ?365.25 days≠ (not ;) \$\endgroup\$ May 11, 2017 at 23:55
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I can't compete with the Universe (that's cheating anyway), but it's fairly easy to buy 25H inductors for power supply smoothing. The audiophile guys do this all the time for their valve amps.

Inductance is a way to transfer power from one bit of metal to another. So look at transformers. Clearly power rating is closely related to inductance. I can't find concrete evidence of anything bigger than 1200 MVA, but see this Wiki page. It lists the largest inductance at ~1300H for a 3000MW transformer. ABB do some large ones.

So we need another question: What's the biggest single transformer, and what's the power /inductance equation?

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    \$\begingroup\$ I've never heard of [large] inductors for PSU smoothing (unless it's a constant current one). Why/how would it be used instead of a large capacitor? \$\endgroup\$
    – CL22
    May 4, 2017 at 12:47
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    \$\begingroup\$ @Jodes They're better than just large capacitors, and certainly were in the heyday of valve technology. It's a sentimental throwback but works. See angelfire.com/electronic/funwithtubes/3_Simple_Power.html , valvewizard.co.uk/smoothing.html , and ebay.co.uk/itm/… if you want to buy one. \$\endgroup\$
    – Paul Uszak
    May 4, 2017 at 13:02
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    \$\begingroup\$ Instead of CRC rectified-ripple filters, use CLC. The very oldest radios used the L to also provide the flux field for the loudspeaker instead of expensive ALNICO material. \$\endgroup\$ May 4, 2017 at 15:19
  • \$\begingroup\$ @analogsystemsrf i remember those... I wonder if anyone tried to make a 100kFarad LiPo Battery into a 100kHenry inductor with a power TIA. (transvestite amplifier) \$\endgroup\$ May 12, 2017 at 0:01
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Not sure about those but I just measured the inductance of a Tesla Model S rear drive AC inductance motor and it's somewhere between 20H and 25H across one phase. I got 23H but it was a really rough measurement. This means it would be around 70H for the 3 phases.

It's not the largest admittedly, but it's interesting to me so I thought I'd add it as a real world thing.

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    \$\begingroup\$ But the three phases aren't one inductor unless they're in delta and you open the loop. You might be interested in my answer to electronics.stackexchange.com/a/487353/73158. \$\endgroup\$
    – Transistor
    Apr 10, 2020 at 15:14
  • \$\begingroup\$ Tesla Model S rear drive AC inductance motor is delta format \$\endgroup\$
    – Graham
    Apr 10, 2020 at 15:56
  • \$\begingroup\$ @Transistor how do you exactly define the motor inductance? the inductance seen across 2 connections, the coil inductance of a single phase or some way i didn't think of? \$\endgroup\$
    – diegogmx
    Apr 10, 2020 at 16:40
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    \$\begingroup\$ @diegogmx: Good question. I would only have to consider it from the point of view of power factor correction. For PFC we quote the capacitors in kVAr per phase so I imagine a motor would be specified in the same way using the P-N voltage and phase single phase current. \$\endgroup\$
    – Transistor
    Apr 10, 2020 at 17:08
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I had a small signal step-up transformer made once (~3 cm diameter) that had about 250 H secondary inductance.

That goes to show that you can achieve ridiculously large inductances by just winding many turn on high permeability cores. These inductors won't be able to handle a lot of current before saturating, so they are mostly useful for low frequency signal transformers.

Consider a slightly larger core with 1 mH permeance. Then you wind 100,000 turns on it. Its inductance will be 10 MH. I suppose it would be approx. the size of a large cooking pot (~30 cm). The reason this isn't done, is that there are no use cases for such inductors.

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Signal transformers can go quite high, thanks to the extreme permeability of certain materials: permalloys and some nanocrystalline types being the most important today. The catch: you don't get much flux, so the signal level and magnetizing current are both very low.

Offhand, I have a UTC (United Transformer) O-1, an audio transformer specifying 50kΩ secondary, 30-20KC (it's old enough to predate Hz, that's "kilocycles"), max level 8dBm. It's packaged in a metal can (cylinder) about 2.2 x 3 cm (D x H). With a 100kΩ source impedance, I measure -3dB (implying equal reactance) at about 5.3Hz, or L ~= 3000H.

If we make some assumptions about the core, say Bsat ~ 1T, Ae = 30 mm^2, then the signal level of 8dBm corresponds to 17.8Vrms into 50kΩ, and this voltage at 30Hz requires about 4.4k turns \$\left( N = \frac{V_\textrm{rms}}{4.44 B_\textrm{sat} A_e F} \right) \$. (It's quite fine wire I'm sure; DC resistance is 3.7kΩ, probably in the range of 44-46AWG?)

(Aha, which is not at all a bad guess: I measure saturation at almost exactly the specified level. They said 8dBm and they meant it!)

Note this means an inductivity (AL) around 150µH/t2, no small feat for a spool of magnetic strip.

There are probably some (custom / boutique) audiophile transformers, or inductors* even, that have been made with similar or higher values. I recall Turner Audio specifying some 150H chokes in one design, or maybe they were even more; I wouldn't be surprised to find an additional order of magnitude or two somewhere else.

*Inductors being the more impressive, as they have to tolerate some DC bias, so can't draw advantage from high-μ materials, and real (considerable) energy storage is in play. Note my transformer saturates at a mere 30µA.

Also worth a look: anything with high voltages. Neon sign transformer; power line sensing (potential transformer); historical examples perhaps (25Hz, 16.67Hz used to be used for power, and still are in some places!); etc.

Also, if you don't mind that it requires an external power source to operate, arbitrarily large inductances can of course be synthesized by active circuits.

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