Core Material for Induction Coils / Transformers

Discussion in 'Homebrew and Kit Projects' started by KK4NSF, Oct 13, 2020.

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  1. EI7KS

    EI7KS Ham Member QRZ Page

    Try to get a (old) toroid transformer (50/60Hz) from which you can remove the existing wiring easily , subsequently replacing it by what you want to do . I am sure the core will suit a demo with variable frequency up to 400 Hz or higher.

    Note : For training purposes I have an old toroid transformer having removed the secondary winding but with the 230V winding intact.
    When adding a secondary of insulated wire say 10 windings , the trainee is asked ,how many winding are on the primary.

    The transformer is then connected to 120 or 230 V -AC (or lower voltage)and the primary and secondary voltages measured from which the number of primary windings can be calculated . It is all very basic,but useful learning for novices.

    So, when you come across an unused toroid transformer , (for example at a junk sale or rally ) get/keep it and use it for a future project .
    Personally , I have a sacred collection .

    Frank , EI7KS
  2. W1VT

    W1VT Ham Member QRZ Page

    Silicone Steel Sheet Metal Plate Core For Speaker Audio Transformer Divider DIY

    ebay listing from China but already cut into small pieces.
    Last edited: Oct 14, 2020
  3. KK4NSF

    KK4NSF Ham Member QRZ Page

    thanks for the tip. However, I tend to avoid both eBay, and direct-from-China products.

    I think I've located some material that will work and will be testing it later today.
  4. K6BSU

    K6BSU Ham Member QRZ Page

    I once made a spark coil for a "low voltage" hit-miss engine. Consists of just an inductor. I used about 20 8"-long pieces of soft iron coat hanger wire for a solenoid core. Probably not the best iron core but it had enough inductance to spark inside the engine cylinder.
    N1OOQ and KK4NSF like this.
  5. KK4NSF

    KK4NSF Ham Member QRZ Page

    OK.... results of my tests:
    I made three cores, one out of a solid piece of Vim-Var core iron, .5" diameter x 6" long, a second one the same size made out of a bundle of soft iron rebar tie-wire, and third made of mild steel rod. Using the same coil, driven by a 12v power supply, a 555 timer / driver, and an amp meter. I measured three things: the strength of magnetic force, the current draw and the residual magnetism after the current was turned off.

    The units of measure used were:
    for magnetic force: Nuts. (N) -the number of 4-40 steel nuts that the magnet would pick up, on one end stuck vertically into the box.
    for residual magnetism: Remaining Nut (RN) the number of nuts remaining stuck to the magnet after current was turned off.
    Current draw- amps

    The idea being that the strongest magnet for the lowest current draw would be the most efficient. (R to Amp Ratio )

    The average results from multiple tests are as follows:
    Mild Steel Bar- N= 33, RN= 14, A= 3.38
    Vim-Var- N=46, RN= 0, A=3.55
    Bundle of Rebar Tiewires- N=52, RN=1.4, A=2.99

    While far from being scientifically perfect, the results do seem to indicate that the wire bundle has the strongest N:A ratio, which seems to indicate lower losses. The Vim-Var had the least residual magnetism (RN)... and the mild steel bar was the worst.

    So, there you have it. For this particular project, I'm going to use the "bundle of wires" design.
  6. K6BSU

    K6BSU Ham Member QRZ Page

    You should first paint each wire before bundling them all together. The idea is to prevent circulating currents through the wires. There can be no circulating current if there is no electrical conduction between wires.
    KK4NSF and AD5HR like this.
  7. G4COE

    G4COE Ham Member QRZ Page

    That Induction interrupter circuit brings back memories-:

    As a small kid I was given 'Shocker toy', this toy basically a buzzer with a sliding rod inside the core that had a overwind and coupled to two hand grips, a metal tube connected to the overwind via wire of course, although this worked of a 6V lantern battery I think it was ....... was rather shocking, you could have four or five people holding hands in a circle and the end pair held one of these handgrips.

    Which reminds me no special transformer required..... just a good ol' car alternator did me just fine making it into a buzzer by using a relay switching itself produced massive big spark's - think of that if the output was coupled to a tuned circuit...! No doubt a modern switching FET would do better. A local ham about 500 yards away as the crow flies complained of a racket on his radio.

    KK4NSF likes this.
  8. G0GSR

    G0GSR Ham Member QRZ Page

    This whole thread does.
    As a child, I was given most parts for an induction coil.
    The bundle of soft, iron wires with the primary winding already wound, an "interrupter" and a home made "condenser".
    I never did get enough wire to wind a proper secondary though... it needed far more turns than I realised at the time.
  9. W1VT

    W1VT Ham Member QRZ Page

    Sparklers, also known as fireworks, are made on thin soft steel rods.
  10. K1APJ

    K1APJ XML Subscriber QRZ Page

    Years ago, there was a book that gave a detailed account of building an induction coil, seems like you bundled up the wires and heated them in a fire and let them cool slowly. Might have been one of the Alfred Morgan books, or " The Boy Mechanic" or something similar. I'll look around.

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