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How to wind transformer???

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S.hassan

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i want to build a transformer 220vac to 12v dc 2amp. please help me how
many turns in primary and secondary core Area. Swg wire size for primary
and Secondary . Please tell me a simple formula's for that
Thank's
 
i want to build a transformer 220vac to 12v dc 2amp. please help me how
many turns in primary and secondary core Area. Swg wire size for primary
and Secondary . Please tell me a simple formula's for that
Thank's

Not an easy request. I suspect only a few people if any here have actually constructed a transformer from scratch. One also needs to know the type and size of the core material. I have seen projects where you take an existing transformer of the proper power rating/primary voltage and just remove the outside secondary winding, counting the turns used. That gives one the volts per turn value, and replace with a new secondary winding using the turns per volt value obtained.

Good luck
Lefty
 
Don't bother.

You need to have enough primary turns and iron in the core to give you the back-emf equal to the supply voltage. You also need that core to be laminated, and made out of iron that has suitable magnetic properties. The whole lot needs to be held together well or it will buzz.

Something like MULTICOMP | MCFG030/12 | Transformers & Accessories | Power Products | Farnell UK isn't very expensive and has it all done for you.

If you want a DC output you will need a rectifier and smoothing capacitor. You may need a regulator as well, depending on what you are powering.

As LeftyRetro says, modifications to existing transformers are often a lot easier than starting from scratch. It is also easier on larger transformers as there is more room and you need less turns for any particular voltage.
 
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I suggest to ask this question in a ham forum. Many of them still make their transmitter HV-transformers themselves and should be able to give you some basics.
 
NOT WORTH IT!

I had a professor give us this as a "learning project", one that really didn't have that much practical value, just theoretical, to prove a point.

Here is what I got out of it...

-VERY expensive. Laminated magnet wire (the red colored stuff) was about $24 bucks a roll. You will need about two rolls for a 120VAC to 12V step-down.

-Takes forever to roll manually. Your talking about thousands of turns; with a 1/2 inch core, it took me over 2500 on the primary to get the winding resistance up enough to keep from keep very high current flows.
And if you get bored sitting there rolling, and start watching t.v. and accidentally let it slip, around the 1500th roll or so, it ALL comes apart like a damn slinky.:eek: Then you get to start all over...........

-Hums like crazy, even when not under load.

All that, and a lot of time and calculations, for 12VAC output.:rolleyes:

IMHO...
It would be MUCH easier, and cheaper to just buy a transformer, especially one that of that common a ratio, and current rating, that you have listed.

But if you have/want to?

Please tell me a simple formula's for that

Need to know first:
-Core diameter
-Permeability

Here is a good source: Source
 
I've wound a new secondary on a 100VA transformer to get 230V on the secondary, it was around 1200 turns and took ages.

It's much easier to just buy one.
 
Hi there,


There are formulas to simplify the construction of a transformer somewhat,
as long as you know your core material characteristics.
For the kind of transformer you are talking about, it sounds like a power
transformer that will be plugged into the line. For this we can use this
well known formula to get the flux density:

B=V*10^8/(K1*4.44*N*A*f)

where

B is the flux density in gausses
V is the rms ac voltage
N is the number of turns
A is the core cross sectional area in square cm
f is the frequency in Hertz
K1 is the stacking factor (taken as 0.9 for 1x1 interleaved)

From this you can calculate the number of turns required for the primary,
knowing the Bmax for your core material type and the other things.
A square cross section is an efficient design, so make your core
cross section square by stacking as many laminations as required.
It's also a good idea to leave some margin on B, such as 90 percent.
For a really good design, go with 75 percent. Thus, for a core material
that can go up to 20000 gauss design for 15000 instead. That leaves
room for high line too.

Next you have to figure out the wire gauge for both the primary and
secondary. You can do this by looking at some wire tables and
using a guide of 500 circular mils per amp, or look up some data on
some magnetics manufacturers sites for more direct tables for this.

Once you have the primary, you can calculate the secondary turns
according to the turns ratio required, and then the gauge of the
secondary.

Once you have all this, you can then calculate the area that both primary
and secondary (plus some mylar tape between windings) will take up
in the core window area, and decide if your core is large enough. If not,
you'll have to go to a bigger core. If there is too much room left over,
you might go to a smaller core.

There is also an isolation safey issue. You have to make sure that the
windings of the secondary can never come into contact with the windings
of the primary, even in the event of a melt down. One way of doing
this is to wind the primary on 1/2 of the length of the center post of the
core, and the secondary on the other 1/2, with insulation between.

After this you would want to varnish it by dipping it into an enclosed
pool of varnish and then pumping all the air out. This gets the varnish
into all the cracks. The varnish helps to reduce noise as well as
protects the construction, and also helps with heat conduction.


After you do all this you can plug it in and try it out, or you could
purchase one that already has the output you need and use that :)
 
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