Homebrew Transformer

Far more common when someone needs a custom transformer, is to find one that's the same sort of specs, take it apart, and rewind it. That gives you the core material and the rest. There have been plenty of articles on such things in hobby magazines over the years.

At the very least, if you want to build a transformer, you ought to take a commercial one apart to see what's involved.

Michael

How about buying a spool of iron wire? Preferably insulated in some way. Then you form the wire into a coil, looking something like an overgrown toroid core. Bare the two ends of the iron wire and bond them together, solder would probably do. Then wrap your windings around that. Putting your winding wire onto a spool that you can easily move around and around the core as you unspool it onto the core will probably be necessary.

The insulation on the iron wire is to reduce "eddy current" losses.

I vaguely remember guidelines like that.

"Don Taylor"

• WARNING !!

This is a completely insane idea.

FORGET IT !!

....... Phil

Winding transformers is a bit of a 'black art' or indeed 'black science' perhaps and it's certainly not as simple as you seem to think. . On account of the safety implications I have to discourage you from doing this until you understand the safety principles used in winding them.

It used to be possible to get 'transformer kits' that had prewound primaries btw.

Graham

You're an idiot who's seriously dangerous.

Graham

Ive seen "cores" made using insulation hangers.....small "sticks" of iron used to push up against insulation between floor joists to hold the insulation up....you can lightly spray them with laquer to insulate the rods from each other before making a bundle....

Ive also heard you can make your own "E" and "I" laminations from ordinary sheet metal....take the sheetmetal and burn it in a fire.....cut the laminations from that....the burning supposedly does something to the metal ...makes it perform better.....not as good as silicon steel but better than just ordinary unburned steel.

There should be some resources on the net concerning homebrew power transformers....at least there used to be in the late 90s early

2000s....

used to be a whole "book" online about it.

The easiest thing to use for the core are E-I laminations which are readily available. You can even take apart an old transformer and re-use the core. The size of the core depends on the power required and there are many rules and guidlines on this depending on core loss, heating, leakage flux, noise and other issues. If you start with a scrap transformer of known wattage, use it as a guide.

There is NO SUCH RULE that a primary should have 6-8 turns per volt. The primary windings should based on Faraday's law and is dependant on the operating voltage, the desired flux density (Bm) and the core area (Ae). The equation is: Np = Vrms * sqr2 * 10^8 / (2*Pi*f*Ae*Bm) where Np = number of turns, Vrms = primary AC voltage (rms), f = minimum frequency (Hz), Ae = effective core area (cm^2), and Bm = maximum flux density (gauss).

Typical small transformers should operate at between 10Kgauss and 15Kgauss using standard silicon steel transformer laminations. Bob

"Bob Eld"

** Errr - there is, actually.

The rule is for common magnetic steel laminations ( not GOSS), for 50 Hz operation and for a 1 square inch cross section. It is understood that the number of turns varies in *inverse proportion* to the core's cross section.

For a GOSS toroidal core, the number can be reduced to 4.5 to 5 turns per volt per square inch.

The rule is based on standard commercial practice and typical *off load* I mag figures.

Even lower numbers apply when the transformer will always be operated under full load.

....... Phil

Why? It sounds like the kid wants to try building a transformer.

He clearly didn't say "I want to buy a transformer" He clearly didn't say "I want to use the parts from a transformer"

Sounds like he wants to build a transformer. People have done stranger things.

Way back in high school we cut up a pile of coat hangers to get the iron. We taped them into a thick bundle, put a few thousand turns of wire around them and made ourselves an induction coil.

You would put a heavy copper ring over the end of it, plug the coil into the wall for a second, and shoot the ring to make dents in the ceiling tile.

The only insane thing was I decided to hold the ring in place and told them to plug it in. A little surprisingly, I was able to hold the ring in place. More surprisingly, it suddenly became REALLY hot and I was left with two burns on the ends of my thumb and finger, before I yelled and let go of it to fly towards the ceiling. I didn't try that again. But I did learn about induction heating that way.

the

under

I guess if you want to be sloppy about it and not calculate anything then you can use one of these rules. Five turns per volt on a 1sq inch core at

90% stacking would give a flux density of 15.5kGauss at 50 Hz. That's ok for many applications but a bit high for low noise applications such as audio preamps. If you want to know what your transformer or any circuit for that matter is predicted to do you calculate the values, you don't pull them out of your ass (arse). Bob

"Don Taylor"

** Because it is VERY STUPID and VERY DANGEROUS !!!

The OP wants a transformer to use on the AC Supply.

THAT means DANGEROUSLY high energy and FATAL electrocution risks are involved.

YOU have no comprehension of these matters, at all.

F U C K O F F - B L O O D Y I D I O T !!!

....... Phil

"Bob Eld"

** The rules are based on careful calculations & actual commercial practice.

The "sloppy" one is you - Mr arrogant asshole.

** Massive red herring - Mr arrogant asshole.

It is BLINDINGLY obvious that by using MORE than 5 turns per volt per sq inch one can reduce I mag to any desired level below that of a typical mains transformer.

** Crapology.

Most folk buy ready make transformers and use them as is or adapt them to their needs.

** Fuck off - YOU ARROGANT FOOL.

........ Phil

Well then I guess I have to apologize. You see I was born, raised and trained in a different century, I guess back before all this stuff became so VERY DANGEROUS!!!

I do wonder now and then how some of those around me stayed alive long enough to procreate with all the terrors in the world.

I would say to you what I once said to a manager, but I'll let it go.

But I would caution you, do you realize how deadly soldering irons and automobiles are? I'd recommend you staying at least 1000 meters away from any of those.

Maybe they should just pack Phalluson in bubble-wrap and stick him back inside his Mom's womb.

Cheers! Bobo

Why? So he can be aborted a second time?

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

"Don Taylor"

** BEWARE OF THIS DAMN IDIOT !!!

OR HE WILL KILL SOME INNOCENT PERSON

MAYBE YOU ................

....... Phil

Kits are readily available.

Type these 2 words into Google:-

Transformer kit

(1) RS components in the UK sell transformer kits

They show a 100 VA E + I kit for =A331.95 UK

(2) Maplin (UK) sell an E + I kit for =A316.66 UK price, delivery extra, no mention of frequency.

[quote] A transformer kit having a ready wound 120-240V mains primary winding, E and I laminations, end frames and clamping bolts. Secondary windings can be wound using enamelled copper wire for a total power output not exceeding 100VA. To find the number of secondary turns required, multiply output voltage required by 4.16 turns per volt, +1% for each multiple of 10VA loading. Wire for winding the secondaries is not supplied in the kit. Dimensions: Width 89mm x Depth 68mm x Height 75mm. Weight: 1400g. [/quote]

(3) A US firm called Toroid Corporation of Maryland sell kits 80VA =3D $30,

1400VA $106. "Made for 60 Hz" it says. [quote] The many advantages of custom designed toroidal transformers are now available to you in small quantities with little investment required.

When our standard transformers are not suitable or when exact output data cannot easily be established, you now have a less expensive alternative to a full custom design. Toroid Corporation offers kits with factory made primaries, available in five power ratings and come with complete instructions. All kits are made for 60 Hz operation.

(1) Calculate Volts x Amps (RMS) for each winding. The SUM of these VA-ratings must be smaller than the rated VA for the kit to be chosen. (2) Rated DC power replaces the VA rating if the transformer is used to supply rectifiers with capacitor filters as loads. Calculate PDC =3D (DCVolts + 2) x DCAmps for each bridge rectifier supplied by the transformer. The SUM of the PDCs for all rectifiers must be smaller than the Rated DC Power for the transformer. If any rectifier uses two diodes and a center tapped secondary instead of a regular bridge conversion, its PDC is: 1.4 x (DCVolt + 1) x DCAmps.

The kit does not include magnet wire for the secondary windings. (Available from motor repair shops)

Options The price for the kit (please see chart) does not include engineering assistance to calculate wire size and length. Should you like us to do this work for you, we would be happy to help you for a fixed fee of $175.00 per design. Required magnet wire would then be shipped with the transformer kit from the factory at no extra charge. [/quote]

I tried this formula with some approximations:

Np = Vrms * sqr2 * 10^8 / (2*Pi*f*Ae*Bm)

Vrms = 230 sqr2 = 1.41 ..? f = 50 Ae = 1 cm^2 Bm = 10000 Gauss (Get a feeling this value is wrong)

Np = 230 * 1.41 * 10^8 / (2* 3.14* 50* 1* 10000) = 10328 turns

Correct?

44 turns/volts seems a lot..

For mains transformers I prefer to buy. But for signal or small dc/dc it might be useful.

Done wrong, it can be.

He didn't say, but quite likely.

Done wrong, it can be. Done with care, at most he'll get to know what overheated magnet wire smells like.

I think he has.

To the OP: The idea of winding a toroid out of steel wire isn't half bad. Just see to it that the bundle is at 2 cm across and as tight as possible. I don't think there's a real need for fusing the ends together. I'd suggest some 1000 to 1200 turns of fine gauge wire for the primary. Connect it in series with a fuse of at most one ampere. If you want/need to touch any part of it, first check it out with one of those neon light pen thingies. Wear rubber soles and touch it with your right hand only.

- YD.

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