Maker Pro
Maker Pro

Building a transformer

R

Rich Grise

Jan 1, 1970
0
I would recommend reading up from every source. I have built torroids
using the winding which was orginally a variac. These were 110 volt
units. You automatically have a primary so all you need to do is wind
the secondaries on top. I have also done the other type of transformer,
schelacing.the iron plates. I would also recomend what others have, buy
surplus on the market. Combine transformers if you can't find them.

I used to work for a battery charger manufacturer who made their own
transformers. They had a machine to stack the lams, alternating, of course,
and a big machine to spin the bobbin while the guy hand-wound the windings
on it. Then, when it was all stacked, they'd whack it to make sure all of
the lams were as tight as they could get them, bolt it up, hypot it, and
then bake them and dip them in hot varnish.

BTW, I don't think there are many USENETizens who would consider
themselves part of any "collective" - that's the Borg. =:-O

Good Luck!
Rich
 
A

ArameFarpado

Jan 1, 1970
0
ArameFarpado said:
this will be a 600Watt transformer

you will need iron of 150mm EEE and III (a standard dimension)
a form of 50x54mm

primary:
use 1.35mm diameter wire
roll 377 spirals

secondary:
use wire of 1.77mm diameter (if this does not exist, get the after next in
diameter)
weld first out line (60v)
roll 104 spirals
weld second out line (0v)
roll 104 spirals
weld third out line (60v)


put the irons one by one always alternate positions
tight as much as you can the irons
dive it into hot varnish and let it dry

this is just the transformer, i guess you will also want to pass AC to DC
and maybe a voltage regulator controlled by a variable resistor, but that
is another story ;)


regards
ArameFarpado

Forgot one detail:

first rool the primary coil
them put a plastic or corse paper strip to isolate the 2 coils
then rool the secundary coil
 
G

Genome

Jan 1, 1970
0
Jim Thompson said:
I was just trying to distinguish the number from those that the "music
power" types like to bandy around.

For instance peak instantaneous power would be 800W ;-)

...Jim Thompson
--

You haven'''t got a basic fucking clue have you. Here we are going for
rentry and some idiot wants to wake up Jim for the recip for fried eggs. The
air sytem might be loaded but we're 15 minutes to slash and two minits from
scoff with ALL the trimmings and someone wants to check the database.

Absolutlyee blodddy amaxzing.

DNA
 
F

Father Haskell

Jan 1, 1970
0
Tim said:
Jim said:
message
On Tue, 8 Aug 2006 13:44:27 -0700, "RST Engineering \(jw\)"


What primitive semiconductors did you use in the output stage, or was it a
toob device? Did we have 2N3055s in '75? I don't memember.

Jim


[snip]

I'm trying to remember what semiconductors I used. But, IIRC,
2N3055's *were* available around that time.

...Jim Thompson


Was it Ge or Si ?


It was Silicon. I didn't use any Germanium power devices since I
boosted my car radio back when I was a junior in high school.

...Jim Thompson

Correction: it _is_ silicon.
http://www.onsemi.com/pub/Collateral/2N3055-D.PDF.

Digi-Key has them for $2.10 a pop, in the TO-3 case, no less.

2N3055s are as common as 2N2222s. Salvage them from junked
supplies or amps, and the cost is nothing.
 
R

Rich Grise

Jan 1, 1970
0
That depends on how the leakage inductance is produced, and whether you
can remove it, which you must in order to use it as a conventional
transformer

Taking out the old secondary is almost trivial, with a hacksaw and a
chisel. ;-)

But apparenlty, you need to add windings to the primary to bring the
magnetizing current down, or somethiing like that. I have an old MOT
that I've been experimenting with, and the idling current is just way
too much for any self-respecting 60 Hz trannie, albeit they do have
to account for the shunts, which current-limit the output.

On and off, I've been poking around with this thing, but now I'm at
a crossroads with it - do I cut it open, take the bobbin out, and
enhance the primary that way, or do I thread more #18 Formvar wire
through it until I build up another layer of windings? So far,
threading the new wire through has turned out to be much more of
a PITA than I had expected, so it's kind of on the back burner for
the moment.

Good Luck!
Rich
 
P

Paul E. Schoen

Jan 1, 1970
0
Mark Fortune said:
I would need the option of both +v and -v in respect to ground, but only
sometimes at the same time (ie when testing audio circuits, but not when
doing logic circuits) if I switched one of the secondary windings off...
would I still be saving half the power?


Wastage is becoming more apparent as I read more and more posts... and am
considering rethinking to a more energy efficient design now.

I was (originally) thinking big heatsink with some thermal controlled
fans screwed on.


switching psus I know nothing about, but think I will research this. Any
good places to start (apart from the obvious google)?

This might be a good candidate for a triac phase fired circuit such as:

http://www.st.com/stonline/products/literature/an/3566.pdf

These can be noisy, but they are very efficient, and low in cost.

If you want to make your own transformer, www.toroid.com has transformer
kits. I think a 1.4 kVA core (available in 120 or 120/240) is about $100. I
have used that same core (actually 4 of them) to build a transformer rated
at 5.6 volts at 1000 amps continuous. I used bus bar for the secondary. You
can do the same thing with an old Variac. However, it is a tedious process
to wind a high voltage winding. The 1.4 kVA core has 0.7 volts per turn, so
you'd need nearly 90 turns for each of your 60 volt outputs.

Most importantly, consider exactly what you need the supply for, and build,
buy, or modify according to the exact specifications you actually require.
You must look at efficiency, weight, size, line and load regulation, max
and min voltage adjustment, ripple, noise, overshoot or droop on load
change, response time, cost, and time to design, build, and troubleshoot.

You can get so much high quality equipment on eBay and at electronic flea
markets, that building your own is usually only for very special
requirements or as a learning experience.

For logic circuits, I would recommend a separate 5 VDC (or 3.3, etc.)
designed for that purpose, with a good crowbar overvoltage protection
circuit. A wide range adjustable bench supply can too easily generate a
spike that will wipe out (or incrementally damage) all the logic circuits.
It might be a good idea to put a crowbar on the logic board.

Good luck,

Paul
 
B

Bob Eld

Jan 1, 1970
0
Jim Thompson said:
I was just trying to distinguish the number from those that the "music
power" types like to bandy around.

For instance peak instantaneous power would be 800W ;-)

...Jim Thompson

Yea I know. That's very common in the audio industry but we Engineers should
know better and use the proper terms. America is stupid enough without us
adding to it, don't ya think?
 
J

Jim Thompson

Jan 1, 1970
0
What primitive semiconductors did you use in the output stage, or was it a
toob device? Did we have 2N3055s in '75? I don't memember.

Jim
[snip]

I'm trying to remember what semiconductors I used. But, IIRC,
2N3055's *were* available around that time.

...Jim Thompson

It's in my GE handbook from 1973. ISTR some magazine article from 1971
using it, but I'm not going up in the attic dusting off that pile of
old mags.

- YD.

I've run out of library shelf space, so I've been donating out of date
books (like "Mother of All Windows" for Win95) to charity book sales
;-)

...Jim Thompson
 
Y

YD

Jan 1, 1970
0
What primitive semiconductors did you use in the output stage, or was it a
toob device? Did we have 2N3055s in '75? I don't memember.

Jim
[snip]

I'm trying to remember what semiconductors I used. But, IIRC,
2N3055's *were* available around that time.

...Jim Thompson

It's in my GE handbook from 1973. ISTR some magazine article from 1971
using it, but I'm not going up in the attic dusting off that pile of
old mags.

- YD.
 
J

James Sweet

Jan 1, 1970
0
Mark said:
Greetings to the collective.

For my next project I want to build a bench power supply and do away
with this old switch mode AT computer PSU that i'm currently using.

The design I have in mind will be pretty beefy, giving a wide range of
fixed and variable output voltages (i'm thinking from -50v up to +50)
and deliver up to 5amps of current. if my estimates are right i'll need
a 600va+ (100v * 5a + overhead) transformer to do the job well. Now i've
had a look at some transformers in this range, and they're a little out
of my price range. so now i'm considering building my own.

The specifications I need are as follows:

primary: 0-230v @ 50Hz
Secondary: 60v-0-60v
secondary output current max: 5A

I have an intermediate understanding of transformers, but have never
actually built one, hence I am seeking advice from those with experience
in this field.
So where do I start? what type of core is best for this application? - I
have a friend who's blasting off that toroids are best, but i'd like a
second opinion, and what kind of wire to use for the primary and
secondaries? what are good safety practices regarding insulation? Is
this even a feasable project to undertake (moreso on the money side than
timewise). Any other advice also greatly appreciated.

regards,
Mark


Look for a surplus transformer, you won't save any money trying to build
one yourself.

That's a BIG supply to be using a linear regulator for, I suggest
looking at some of the switcher IC's available now days, National
Semiconductor makes a series called Simple Switchers which are FAR
easier to work with than designing a switcher from scratch and they have
HV versions which are good to 80V or so.
 
J

James Sweet

Jan 1, 1970
0
Jim said:
What primitive semiconductors did you use in the output stage, or was it a
toob device? Did we have 2N3055s in '75? I don't memember.

Jim

[snip]

I'm trying to remember what semiconductors I used. But, IIRC,
2N3055's *were* available around that time.

...Jim Thompson


Wasn't that around the time the Dynaco ST-400 came out? I rebuilt one of
those once, seems like it used a bunch of big Motorola power
transistors, I forget the numbers but they weren't 3055's. Seems like
there were 4 of each polarity per channel, or maybe it was 2, I do
remember the heatsinks were HUGE.
 
J

John Woodgate

Jan 1, 1970
0
dated Wed said:
Wasn't that around the time the Dynaco ST-400 came out? I rebuilt one
of those once, seems like it used a bunch of big Motorola power
transistors, I forget the numbers but they weren't 3055's. Seems like
there were 4 of each polarity per channel, or maybe it was 2, I do
remember the heatsinks were HUGE.

Many manufacturers used 'custom' devices which were allegedly tested to
custom specifications by the device manufacturer. The Vcc max might be
higher than for the normal device, and/or beta range might be less.
 
J

John Woodgate

Jan 1, 1970
0
dated Wed said:
Does nobody knows howto calculate transformers anymore?

this will be a 600Watt transformer

Does nobody know how to calculate rectifier circuits any more?

This will need to be a 900 W transformer.
 
P

Phil Allison

Jan 1, 1970
0
"James Sweet"
Wasn't that around the time the Dynaco ST-400 came out?


** 1973, according to this schematic:

http://www.audio-circuit.dk/Schematics/Dynaco_ST400.pdf


I rebuilt one of those once, seems like it used a bunch of big Motorola
power transistors, I forget the numbers but they weren't 3055's.


** Nope - more like the 100 volt, 200 watt, 30 amp MJ802 / 4502 devices.

Seems like there were 4 of each polarity per channel, or maybe it was 2, I
do remember the heatsinks were HUGE.


** The power devices were operated in *series* instead of parallel mode as
used in other high power amps. Made the Vcc and SOA requirements of the
output devices sooooo much easier.

2N3055s and the similar BDY20 appeared in the late 1960s, as did the RCA
38494 and 40411 used in the famous Quad 303 hi-fi amplifier.




........ Phil
 
J

John Woodgate

Jan 1, 1970
0
dated Wed said:
RCA 38494 and 40411 used in the famous Quad 303 hi-fi amplifier.

38494 is a custom part number, but 40411 looks like a standard part.
What substitute devices are used for repairs?

My 303 suffered its second elco failure recently, and an elco in the 33
preamp came out in sympathy. Coincidence. Of course, I put new elcos in
both channels.
 
E

Eeyore

Jan 1, 1970
0
John said:
38494 is a custom part number, but 40411 looks like a standard part.
What substitute devices are used for repairs?

I've replaced 40411s with 2N3773.

Graham
 
T

Tim Shoppa

Jan 1, 1970
0
Lostgallifreyan said:
By a lot of cheap toroidals on eBay, 5A at some low voltage that doesn't
sell well.

I have to agree with the sentiment 100%. Surplus transformers are
always going to be cheaper than custom-built :). Most oddball
transformers on E-bay sell for pennies on the dollar (actually most
don't sell at all!)

And construction and mounting-wise, a lot of small transformers are way
easier to deal with than one mammoth one. Above a very small number of
VA you start building the case and mounting reinforcements around the
transformer anyway :).

Tim.
 
A

Adrian Tuddenham

Jan 1, 1970
0
I think what you're saying is "try learning on some smaller transformers
first" I might just do that, cos it'd be a PITA if I screw up on a big
one and have to unwind it all again :]

Very small transformers have large numbers of turns and the wire is
thinner. Somewhere around 50 to 100 VA is a good size to learn on.

If you can get a split bobbin, you will avoid a lot of safety issues.


For winding heavy wire, I find it best (in the absence of a large enough
winding machine) to tie one end of the wire to the front gatepost, then
lay it down the side of the house and down the back garden path. I walk
up the garden, reeling-in the wire onto the bobbin and counting the
turns as I go. The tension is easy to control by just keeping a steady
pull against the wire.

Carry tools, string, insulation material and adhesive tape in your
pockets; you won't be able to put the core down to go and fetch them
because the windings will spring undone.
 
I

isw

Jan 1, 1970
0
Mark Fortune said:
Greetings to the collective.

For my next project I want to build a bench power supply and do away
with this old switch mode AT computer PSU that i'm currently using.

The design I have in mind will be pretty beefy, giving a wide range of
fixed and variable output voltages (i'm thinking from -50v up to +50)
and deliver up to 5amps of current. if my estimates are right i'll need
a 600va+ (100v * 5a + overhead) transformer to do the job well. Now i've
had a look at some transformers in this range, and they're a little out
of my price range. so now i'm considering building my own.

The specifications I need are as follows:

primary: 0-230v @ 50Hz
Secondary: 60v-0-60v
secondary output current max: 5A

I have an intermediate understanding of transformers, but have never
actually built one, hence I am seeking advice from those with experience
in this field.
So where do I start? what type of core is best for this application? - I
have a friend who's blasting off that toroids are best, but i'd like a
second opinion, and what kind of wire to use for the primary and
secondaries? what are good safety practices regarding insulation? Is
this even a feasable project to undertake (moreso on the money side than
timewise). Any other advice also greatly appreciated.

Look for a blown-out 200-400 watt audio amplifier (or receiver) at a
garage sale. The transformer you'll find in it will be pretty close to
what you want. The amp will also include a lot of other very useful
items such as big heat sinks, and so on.

Isaac
 
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