# Homebrew Transformer

J

#### Jamie

Jan 1, 1970
0
Hello! I'd like to try building a step-down power transformer from
scratch. Can anyone recommend any how-to sites? Googling didn't turn up
anything useful, maybe I was using a bad search string.

If you don't know of any sites, is it easy to build a step down
transformer? I'm uncertain about what would be a decent easy-to-find
material for the core. I'd like to try building one that steps down 120
volts to 15 volts.

From what I've read, the primary winding should have 6-8 turns per
volt, so I would want 960 turns on my primary, and 64 turns on my
secondary winding.

Thanks,

- Jamie

The Moon is Waning Gibbous (98% of Full)

M

#### Michael Black

Jan 1, 1970
0
Jamie said:
Hello! I'd like to try building a step-down power transformer from
scratch. Can anyone recommend any how-to sites? Googling didn't turn up
anything useful, maybe I was using a bad search string.

If you don't know of any sites, is it easy to build a step down
transformer? I'm uncertain about what would be a decent easy-to-find
material for the core. I'd like to try building one that steps down 120
volts to 15 volts.

From what I've read, the primary winding should have 6-8 turns per
volt, so I would want 960 turns on my primary, and 64 turns on my
secondary winding.

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

D

#### Don Taylor

Jan 1, 1970
0
Jamie said:
Hello! I'd like to try building a step-down power transformer from
scratch. Can anyone recommend any how-to sites? Googling didn't turn up
anything useful, maybe I was using a bad search string.
If you don't know of any sites, is it easy to build a step down
transformer? I'm uncertain about what would be a decent easy-to-find
material for the core. I'd like to try building one that steps down 120
volts to 15 volts.

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.
From what I've read, the primary winding should have 6-8 turns per
volt, so I would want 960 turns on my primary, and 64 turns on my
secondary winding.

I vaguely remember guidelines like that.

P

#### Phil Allison

Jan 1, 1970
0
"Don Taylor"

* WARNING !!

This is a completely insane idea.

FORGET IT !!

........ Phil

P

#### Pooh Bear

Jan 1, 1970
0
Jamie said:
Hello! I'd like to try building a step-down power transformer from
scratch. Can anyone recommend any how-to sites? Googling didn't turn up
anything useful, maybe I was using a bad search string.

If you don't know of any sites, is it easy to build a step down
transformer? I'm uncertain about what would be a decent easy-to-find
material for the core. I'd like to try building one that steps down 120
volts to 15 volts.

From what I've read, the primary winding should have 6-8 turns per
volt, so I would want 960 turns on my primary, and 64 turns on my
secondary winding.

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

P

#### Pooh Bear

Jan 1, 1970
0
Don said:
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.

You're an idiot who's seriously dangerous.

Graham

C

#### [email protected]

Jan 1, 1970
0
Don said:
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.

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.

B

#### Bob Eld

Jan 1, 1970
0
Jamie said:
Hello! I'd like to try building a step-down power transformer from
scratch. Can anyone recommend any how-to sites? Googling didn't turn up
anything useful, maybe I was using a bad search string.

If you don't know of any sites, is it easy to build a step down
transformer? I'm uncertain about what would be a decent easy-to-find
material for the core. I'd like to try building one that steps down 120
volts to 15 volts.

From what I've read, the primary winding should have 6-8 turns per
volt, so I would want 960 turns on my primary, and 64 turns on my
secondary winding.

Thanks,

- Jamie

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

P

#### Phil Allison

Jan 1, 1970
0
"Bob Eld"
There is NO SUCH RULE that a primary should have 6-8 turns per volt.

** 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

........ Phil

D

#### Don Taylor

Jan 1, 1970
0
Phil Allison said:
"Don Taylor"
* WARNING !!
This is a completely insane idea.
FORGET IT !!
....... 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.

B

#### Bob Eld

Jan 1, 1970
0
Phil Allison said:
"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

....... Phil

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
Bob

P

#### Phil Allison

Jan 1, 1970
0
"Don Taylor"
"Phil Allison"

Why?

** 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

P

#### Phil Allison

Jan 1, 1970
0
"Bob Eld"
"Phil Allison"

I guess if you want to be sloppy about it and not calculate anything then
you can use one of these rules.

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

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

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.

** 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.

If you want to know what your transformer or any circuit for that
matter is predicted to do you calculate the values,

** Crapology.

their needs.

you don't pull them out of your ass (arse).

** **** off - YOU ARROGANT FOOL.

......... Phil

D

#### Don Taylor

Jan 1, 1970
0
Phil Allison said:
"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

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.

P

#### Phil Allison

Jan 1, 1970
0
"Don Taylor"

** BEWARE OF THIS DAMN IDIOT !!!

OR HE WILL KILL SOME INNOCENT PERSON

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

........ Phil

B

#### Bobo The Chimp

Jan 1, 1970
0
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

M

#### Michael A. Terrell

Jan 1, 1970
0
Bobo said:
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

P

#### Phil Allison

Jan 1, 1970
0
"Don Taylor"

** BEWARE OF THIS DAMN IDIOT !!!

OR HE WILL KILL SOME INNOCENT PERSON

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

........ Phil

M

#### [email protected]

Jan 1, 1970
0

Type these 2 words into Google:-

Transformer kit

(1)
RS components in the UK sell transformer kits

http://rswww.com

They show a 100 VA E + I kit for £31.95 UK

(2)
Maplin (UK) sell an E + I kit for £16.66 UK price, delivery extra, no
mention of frequency.

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
supplied in the kit. Dimensions: Width 89mm x Depth 68mm x Height 75mm.
Weight: 1400g.

(3)
A US firm called Toroid Corporation of Maryland sell kits 80VA = $30, 1400VA$106. "Made for 60 Hz" it says.

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 =
(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.

P

#### [email protected]

Jan 1, 1970
0
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.

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.

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