Project super electromagnet - Page 1
Forum section: electronics / beginners

author: Maranto
author_rank: Contributor
timestamp: March 10, 2025, 05:56:40 pm
content: I have a project in mind, perhaps already built by others, premise, it is very difficult to obtain an electromagnet that has a high magnetic field (>2T) and high frequency, for this reason I thought of using two electromagnets, in which the first electromagnet transfers by induction high frequency or high field to the second electromagnet, this last one having the opposite property (high field or high frequency). I'll explain better I can have two cases: 1. the first electromagnet with magnetic core, with high field (2T) and low frequency (20 Hz), transfers the power by induction to the second electromagnet with air core, this second electromagnet would take the high field and low frequency, but would increase the frequency through an external capacitor, and therefore the second electromagnet would have high field and high frequency, that is, take two electromagnets, one with high field and low frequency and transfer these characteristics to a second electromagnet (in air) which would take the high field and increase the frequency with a capacitor, and finally have the second electromagnet (in air) with high field and high frequency. 2. Or do the opposite, that is, the first electromagnet (magnetic core) with high frequency and low field and transfer these characteristics to the second electromagnet (in air) which would increase the field through more windings. Here is which of the two possibilities is the most feasible? The project is very similar to a transformer except that there is no common magnetic core since the magnetic core has problems of losses at high frequencies and high fields while an aura core does not, that's why I thought of combining the characteristics

author: langwadt
author_rank: Super Contributor
timestamp: March 10, 2025, 06:02:29 pm
content: To get 2T with an electromagnet just for short while, you'll need alot of power and watercooling

author: TimFox
author_rank: Super Contributor
timestamp: March 10, 2025, 07:13:29 pm
content: How much volume (m3) is required for that highBfield?2 T is a common field in human-body MRI with superconducting solenoids, but they are expensive.Of course, ramping the current from 0 to full value quickly will be fought by the system self-inductance that depends on that volume.

author: mtwieg
author_rank: Frequent Contributor
timestamp: March 10, 2025, 08:47:12 pm
content: I don't think you (or most people) grasp how strong a tesla really is... the thought of a 2T field oscillating at 20Hz is... well let's just say I don't want to be in the same room.Wondering if you've tried estimating the forces acting on these two magnets in close proximity to each other.

author: hamster_nz
author_rank: Super Contributor
timestamp: March 10, 2025, 09:01:56 pm
content: "but would increase the frequency through an external capacitor"How does the 20Hz field excite the secondary's coil+capacitor, which is tuned to a much higher frequency? Both the capacitor and coil are a (mostly) a linear component, so no frequency conversion can occur.

author: coppercone2
author_rank: Super Contributor
timestamp: March 10, 2025, 09:10:25 pm
content: for a sense of scalehttps://www.holmarc.com/PC_based_water_cooled_electromagnet.php

author: Maranto
author_rank: Contributor
timestamp: March 11, 2025, 01:13:11 pm
content: Quote from: hamster_nz on March 10, 2025, 09:01:56 pmgood morning, then I'll take care of the calculations of the dimensions of the magnetic core, I think around 80 cm x 15 cm2. I can also use an induction field of 1.5 or 1 tesla, that's not the important thing, I just want to know which configuration is the most advantageous, the 1 in which there is the coil with high field and low frequency or the 2 in which there is the opposite? as you said it is difficult for two untuned coils to exchange energy, that's why in my opinion choice 2 is the most suitable. the principle is very similar as I already said, to that of the transformer in which the primary coil "drives" the secondary coil. so in this case if the first coil has high frequency and low field and transfers by induction to the secondary coil, the latter will therefore have high frequency (20 khz) and low field (mT) but how do I increase the field? by increasing the turns or connecting it to an independent generator that supplies ampere? (the secondary coil will have an air core so as to have no field and frequency limitations

author: Maranto
author_rank: Contributor
timestamp: March 11, 2025, 01:15:13 pm
content: Quote from: TimFox on March 10, 2025, 07:13:29 pmgood morning, then I'll take care of the calculations of the dimensions of the magnetic core, I think around 80 cm x 15 cm2. I can also use an induction field of 1.5 or 1 tesla, that's not the important thing, I just want to know which configuration is the most advantageous, the 1 in which there is the coil with high field and low frequency or the 2 in which there is the opposite? as you said it is difficult for two untuned coils to exchange energy, that's why in my opinion choice 2 is the most suitable. the principle is very similar as I already said, to that of the transformer in which the primary coil "drives" the secondary coil. so in this case if the first coil has high frequency and low field and transfers by induction to the secondary coil, the latter will therefore have high frequency (20 khz) and low field (mT) but how do I increase the field? by increasing the turns or connecting it to an independent generator that supplies ampere? (the secondary coil will have an air core so as to have no field and frequency limitations

author: CaptDon
author_rank: Super Contributor
timestamp: March 11, 2025, 01:30:25 pm
content: A transformer will not cause a frequency change, your capacitor/coil idea causes no frequency change either as another poster has already stated!!! MRI machines rely on nearly supercooling the electromagnet windings with liquid helium. The input power to the electromagnet would burn it up without the cooling. Operating any such electromagnet at any alternating field even one or two Hertz would first off probably tear the machine apart and secondly would generate inductive reactance causing a drop in current and field strength. Your logic is flawed and unsupported by your suggested theories. What is your desired outcome? You won't generate magnetic fields in the Tesla range with air core coils!!

author: Maranto
author_rank: Contributor
timestamp: March 11, 2025, 01:42:23 pm
content: Quote from: CaptDon on March 11, 2025, 01:30:25 pmno, as already said, the procedure is different from a transformer, yes there are two coils, but the first one has a magnetic core to overcome the limits of the air coil, and the second one will have an air core. the first coil will therefore have a ferrite core and generates a field of 0.5 tesla at 20 kHz, it transfers the power by induction to another coil a few millimeters away, this second coil will have a frequency of 20 kHz (like the first one) and a field of 0.5 tesla, so to increase the field of this second coil (given that it is with an air core, what should I do to increase it from 0.5 tesla to 1 tesla? increase the turns? or connect it to a 20 kHz oscillator and greater current?

author: joeqsmith
author_rank: Super Contributor
timestamp: March 11, 2025, 02:38:36 pm
content: I attempted to construct an EPR spectrometer for the fun of it. The first problem to solve was sorting out a way to get a high magnetic field. In my case, I limited it to less than 0.5T. I didn't require a low field and ended up using a combination of a fixed magnet and a electromagnet to achieve the required field strength. Some EPR systems will use a secondary coil in the path.First experiments used a voltage source which was dismal. Even at these low fields, cooling fans wouldn't hold the coil temperature stable enough so the field strength would drift. I later changed to a current source which improved it but ended up having to chop the field to compensate for the drift. Real systems will embed a sensor in the field and close the loop but I never took it that far.

author: TimFox
author_rank: Super Contributor
timestamp: March 11, 2025, 02:54:14 pm
content: By the way, 2 T is a practical limit for iron-core electromagnets, since the highest saturationBvalues are just over 2 T for iron-based alloys.Pure iron and pure cobalt saturate around 2.15 T, and Fe-Co-etc. alloys reach about 2.3 to 2.4 T.In grad school, we used 49 Fe, 49 Co, 2 V alloy for electromagnets.

author: Maranto
author_rank: Contributor
timestamp: March 13, 2025, 10:41:15 pm
content: Quote from: joeqsmith on March 11, 2025, 02:38:36 pmsorry if I give you a repeated answer, I did the calculations, I calculated that the voltage induced on a coil with 1000 turns and length 40 cm immersed in an electromagnetic field of 0.8 tesla and freq. 5 khz has a voltage of about 195 volts, so doing other calculations on the field generated by the secondary coil gives me a value of 0.7 tesla, but I calculated that the primary coil has a magnetic core while the second does not, so the results are contradictory, that is, how does an air core coil with only 1000 turns, which is immersed in a field of 0.8 tesla, and create in turn by induction a field of 0.8 tesla (incorporate it) seems too saturated to me, what do you think?

author: Maranto
author_rank: Contributor
timestamp: March 13, 2025, 10:41:52 pm
content: Quote from: TimFox on March 11, 2025, 02:54:14 pmsorry if I give you a repeated answer, I did the calculations, I calculated that the voltage induced on a coil with 1000 turns and length 40 cm immersed in an electromagnetic field of 0.8 tesla and freq. 5 khz has a voltage of about 195 volts, so doing other calculations on the field generated by the secondary coil gives me a value of 0.7 tesla, but I calculated that the primary coil has a magnetic core while the second does not, so the results are contradictory, that is, how does an air core coil with only 1000 turns, which is immersed in a field of 0.8 tesla, and create in turn by induction a field of 0.8 tesla (incorporate it) seems too saturated to me, what do you think?

author: mtwieg
author_rank: Frequent Contributor
timestamp: March 14, 2025, 11:53:24 am
content: Your description of how two coils would work together to change field strength and/or field doesn't make sense. Maybe try showing a circuit schematic.Quote from: Maranto on March 13, 2025, 10:41:15 pmHard to check your math without more info. For example, an air core solenoid with length of 40cm, radius of 10cm, and 1000 turns and an air core will require around 290A to generate a field of 0.8T. The inductance of that coil will be around 86mH. At a frequency of 5kHz, the impedance will be 2700 ohms. So the voltage required to create a 0.8T field oscillating at 5kHz is780kV, not 195V.

author: CaptDon
author_rank: Super Contributor
timestamp: March 14, 2025, 01:47:20 pm
content: 290 amps at 780KV, yes, calculate that power!!!! Getting a field approaching 1T in an air coil is just imaginary dream stuff. What is your practical use for such a high field in a small air core coil??? Play with the numbers all you want but you won't get that kind of field strength in an air core coil without tapping most of the Hoover Dam output. It takes cryogenic cooling and optomized core material in MRI machines. There are some specialized transformers who's core flux approaches 1T but again the core is very optomized and the flux lines are kept tight within the core. Sounds like you need a $25 million dollar government grant to prove the non-feasibility of your air core idea!!

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: March 14, 2025, 03:15:43 pm
content: Quote from: CaptDon on March 14, 2025, 01:47:20 pm226.2 MWThis one only needs 23.5 MW

author: TimFox
author_rank: Super Contributor
timestamp: March 14, 2025, 04:16:52 pm
content: Quote from: CaptDon on March 14, 2025, 01:47:20 pmAt the start of medical MRI machines, there were air-core magnets (usually four-coil Helmholtz construction) that applied 0.15 T (1500 gauss) to a roughly 50 cm diameter patient volume. That required a DC supply of about 250 A at 250 V. The 6.4 MHz NMR frequency had excellent penetration into the conductive patient, but less SNR than the higher fields of 1.5 T superconducting magnets.

author: Bud
author_rank: Super Contributor
timestamp: March 14, 2025, 04:52:18 pm
content: Prove your concept with 0.001T . There is no need to gigantize. Report here if it worked.

author: langwadt
author_rank: Super Contributor
timestamp: March 14, 2025, 04:56:06 pm
content: Quote from: Maranto on March 11, 2025, 01:42:23 pmso it is a transformer

author: johansen
author_rank: Super Contributor
timestamp: March 14, 2025, 07:52:21 pm
content: Quote from: mtwieg on March 14, 2025, 11:53:24 am290 amps in a 86mH coil is 3600 joules of energy stored, which is approximately correct for the energy stored (3200) joules in a .8T volume of length 40cm and 10cm radius, but it does not include the energy stored in the magnetic field around the outside of that solenoid. if your numbers are correct, and they might be, then only 400 joules of energy is stored outside the coil. (3200 joules at 290 amps is a 76mH inductor..within the margin of error for air core inductor calculators) (hamwaves.com puts it at 81mH)anyhow atat 5khz that's 18 megawatts of energy flowing, which is not entirely consistent with 290*780,000 volts. so i'm wondering how you did your calculation on the volts and amps.

author: Maranto
author_rank: Contributor
timestamp: March 16, 2025, 10:54:21 pm
content: Quote from: mtwieg on March 14, 2025, 11:53:24 am

author: Maranto
author_rank: Contributor
timestamp: March 16, 2025, 10:55:21 pm
content: Quote from: CaptDon on March 14, 2025, 01:47:20 pmyes you are right, I am only reading your answers now, but I had redone the calculations considering the inductances and not the simple calculation of the turns, given that there is the core in air, and the voltage induced in the coil with the core in air is very low due to the low inductance and with the high frequency, it decreases even more, so you are right, however I apologize for having posted such a stupid question on this forum