the largest inductor value you ever came accross in real life ? - Page 1
Forum section: electronics / projects

author: oz2cpu
author_rank: Frequent Contributor
timestamp: March 21, 2024, 09:52:47 pm
content: please tell me ?where and when and what project where you found the largest inductor value you ever came accross in real life ?the reason for asking is the Wayne Kerr Component Bridge B522 i just scored :-)really cool unit, but its range go to 500kHI also made a little video about it here :https://youtu.be/DpKalkZi4bU

author: CaptDon
author_rank: Super Contributor
timestamp: March 21, 2024, 11:59:49 pm
content: Ran into a large 10 Henry choke in a hard modulator for a very powerful radar. I think it was also insulated to 50Kv at sea level and 30Kv at 50,000 feet A.S.L. It was part of the pulse forming network and I think it was used to recover energy on the trailing edge of the main bang. The most 'Henries' I have ever seen was 100H at around 10 milliamps and was part of some weird audio circuit used in a Heising modulation scheme in a vacuum tube transmitter modulator. The A.M. modulation was done at low levels followed by several amplifier stages. It was military so it didn't have to be practical or even make sense!! As I recall, the plate supply was around 200 volts and the plate idle was about 150 volts at 10 milliamps and that was mostly due to the winding resistance of the choke. The choke was about the size of a 25V.A. transformer. If I remember this circuit was directly coupled to the screen grid of an R.F. amplifier stage.

author: jbb
author_rank: Super Contributor
timestamp: March 22, 2024, 01:10:53 am
content: It’s a bit boring, but the 600 Ohm telephone line isolating transformers have a magnetising inductance up around 10 Henries. No doubt they can only take a tiny bit of DC current before saturating.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 22, 2024, 01:17:12 am
content: Have heard of ~1kH used in some audio apps. That's pretty high impedance even at low audio range, so there's not a lot of applications beyond that.Not sure offhand what, say, a neon sign transformer -- or even more specialized, an X-ray power supply but before they used switching, just raw 100kV AC -- would be, but maybe not quite as high. Maybe the latter.Would imagine 10s or 100s KH would be easy enough with supermalloy or nanocrystalline, and just a lot of turns. Definitely not something you need ever day.Tim

author: ejeffrey
author_rank: Super Contributor
timestamp: March 22, 2024, 02:02:27 am
content: I used a superconducting solenoid in a cryogenic system. I don't remember the exact value, somewhere in the low 10s of henries. So in the same range as audio transformers, but with an operating current of 100 amps. You could apply 5 V to it and watch the current rise slowly.

author: TimFox
author_rank: Super Contributor
timestamp: March 22, 2024, 02:38:46 am
content: A 60-watt output transformer, with no gap in the iron, for push-pull tubes can have a primary (magnetizing) inductance > 200 H.

author: Wolfram
author_rank: Frequent Contributor
timestamp: March 22, 2024, 10:59:34 am
content: Quote from: T3sl4co1l on March 22, 2024, 01:17:12 amSmall X-ray transformers, like the ones used in dental X-ray heads, are likely in the hundreds of kH to low MH range, from the turns ratio and magnetizing current. Much less for small signal excitation though, as the permeability of transformer steel is very non-linear.Since the inductance goes with the square of the number of turns, it rises pretty quickly. 10k turns on a moderately sized ungapped PM core would already get you into the kH range. Nanocrystalline would offer an order of magnitude higher permeability, or reducing the required turns by the root of that, but winding 10k turns on a closed core is not trivial compared to on an open bobbin. There are also cut cores available to simplify winding, but I'm not sure how easy it is to get performance close to uncut cores.

author: PwrElectronics
author_rank: Regular Contributor
timestamp: March 22, 2024, 03:06:12 pm
content: We have some line reactors in some of the labs at work. Use them for some tests or as loads in 3ph inverter development. I am not sure what inductance values (they have taps I think) but physically, the steel cabinet housing them is a cube a little over a meter per side. 0000 cables are used for 3-400A RMS.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 22, 2024, 05:22:46 pm
content: Quote from: PwrElectronics on March 22, 2024, 03:06:12 pmThat'll be pretty low actually. Remember that for given voltage, current goes inversely with inductance. Let's see -- if that's 480V, and ignoring phasing for ballpark figures, 480V/360A = 4/3 ohm, L = (4/3) / (2 pi (60)) = 1 / (90 pi) = 3.5mH.Meanwhile, the peak current might be over 500A, or 0.5 (3.5mH) (500A)^2 = 453.6J, no small amount of energy storage.Let me see... something the size of a microwave oven transformer can store almost a J; this should need to be cuberoot(450) or 7.7 times larger on each side, or a core of say 15" stacked, 40" wide, 48" tall... or, yeah, a bit over a meter.Likewise, EHV feeders don't need to be too crazy, though I haven't seen any datasheets and can only estimate. For example, say a transformer for 500kV 100A, a modest 50MVA substation tapping off long distance lines. Say magnetizing current is 1% or 500kV/1A = 500kohm at 60Hz, L = 1.3kH. Big, but not up there.500kohm is also well above what you would need for most tube amplifier input (including phono) and interstage transformers, even if it drops to 1/3 that impedance at 20Hz. So like I said, not many applications that go higher; that's some serious choking!Tim

author: MarkT
author_rank: Frequent Contributor
timestamp: March 23, 2024, 09:28:39 am
content: Quote from: oz2cpu on March 21, 2024, 09:52:47 pmI suspect some gyrator circuit could win this title - if you allow synthesized inductance to count...