Toroidal core calculation

AndrewT · 2016-07-29 6:00 pm

That looks good.

Now measure idle current as you increase primary voltage.
Plot the results and you should get an "S" curve.
If the current starts to get too big at your highest primary voltage then you need to consider whether to add on a few more turns or just accept it will run a bit hotter when mains voltage is at it's highest.
Alternatively if at highest primary voltage the current remains lowish, you have the option to remove a few turns.

TonyTecson · 2016-07-29 11:49 pm

if you do not own a variac, you can simply use the series lamp tester, if the lamps lights very dim, then you have a viable toroid...

if you have an adjacent winding short, then that lamp will light full bright...

these are the two things to watch out for, first is that you have sufficient turns,
and second that you do not have adjacent winding shorts...

sanbadgujar · 2016-07-30 11:39 am

AJT said:
if you do not own a variac, you can simply use the series lamp tester, if the lamps lights very dim, then you have a viable toroid...

if you have an adjacent winding short, then that lamp will light full bright...

these are the two things to watch out for, first is that you have sufficient turns,
and second that you do not have adjacent winding shorts...

Thanks tony

I tried wind 10 turn for secondary just for test I get 2.7 Volt.Means 3.7
turn/volt .why I get less voltage per turn. It is 3.03 turn/volt when I test core with some winding before final primary winding.

sanbadgujar · 2016-07-30 11:51 am

AndrewT said:
That looks good.

Now measure idle current as you increase primary voltage.
Plot the results and you should get an "S" curve.
If the current starts to get too big at your highest primary voltage then you need to consider whether to add on a few more turns or just accept it will run a bit hotter when mains voltage is at it's highest.
Alternatively if at highest primary voltage the current remains lowish, you have the option to remove a few turns.

Thanks Andrew T

please give simple method to test I have vary basic equipment like digital multi meter, some mains transformer, some power resister I dint have veritable power supply.I get 2.7 volt in secondary with 10 turn of magnet wire. why Its less voltage when I test before primary winding it is 3.2 volt on 10 turn

AndrewT · 2016-07-30 2:40 pm

I use a Variac to feed the primary with voltage from 0Vac to 254Vac and measure the voltage drop across a 10r in the primary feed.
Carefull, that resistor is at mains voltage !

sanbadgujar · 2016-08-03 11:55 am

Hello tony & andrewT
I am winding center tap for this trafo of 35 0 35 using duel winding method(2 wire at same time ) ,if i want lower voltage from same winding can it possible ?
e.g for 25 0 25

AndrewT · 2016-08-03 12:04 pm

Have you tested the Primary winding yet?

You don't need a secondary winding to check the primary turns.

AndrewT · 2016-08-03 12:08 pm

sanbadgujar said:
Hello tony & andrewT
I am winding center tap for this trafo of 35 0 35 using duel winding method(2 wire at same time ) ,if i want lower voltage from same winding can it possible ?
e.g for 25 0 25

You can wind on a 35-25-0-25-35 five tap winding,
The centre tap is common to all.
You can use the 35-0-35 to create a dual polarity supply of ~±50Vdc
You can use the 25-0-25 to create a dual polarity supply of ~±36Vdc
You can wire up both (2 bridge rectifiers and 4 smoothing capacitors) and have 4 voltages available. But all 4 are referenced to the same centre tap and thus to the same Zero Volts.
Take care with multiple taps that you don't exceed the current capacity of any one part of a winding.

sanbadgujar · 2016-08-03 12:34 pm

AndrewT said:
You can wind on a 35-25-0-25-35 five tap winding,
The centre tap is common to all.
You can use the 35-0-35 to create a dual polarity supply of ~±50Vdc
You can use the 25-0-25 to create a dual polarity supply of ~±36Vdc
You can wire up both (2 bridge rectifiers and 4 smoothing capacitors) and have 4 voltages available. But all 4 are referenced to the same centre tap and thus to the same Zero Volts.
Take care with multiple taps that you don't exceed the current capacity of any one part of a winding.

Thanks andrewT
I am using one tap at single time.

sanbadgujar · 2016-08-08 11:53 am

AndrewT said:
You can wind on a 35-25-0-25-35 five tap winding,
The centre tap is common to all.
You can use the 35-0-35 to create a dual polarity supply of ~±50Vdc
You can use the 25-0-25 to create a dual polarity supply of ~±36Vdc
You can wire up both (2 bridge rectifiers and 4 smoothing capacitors) and have 4 voltages available. But all 4 are referenced to the same centre tap and thus to the same Zero Volts.
Take care with multiple taps that you don't exceed the current capacity of any one part of a winding.

Hello Andrew t
I am completed all secondary winding
As follows 35 25 0 25 35 but when I measure 35 volt winding respective 0 it showing both 35 volt is OK but when I measure 25 volt winding respective to 0 volt one 25 volt tap shows 10 volt why this happing it shows 25 0 10

AndrewT · 2016-08-08 1:26 pm

you counted wrong?

sanbadgujar · 2016-08-09 11:17 am

AndrewT said:
you counted wrong?

Hello andrewT

Can you help to looking photo of completed transformer.

AndrewT · 2016-08-09 12:41 pm

Measure each of the tap to tap resistances.
You might be able to see the shorter windings and work out from that where you went wrong.

sanbadgujar · 2016-08-09 1:00 pm

AndrewT said:
Measure each of the tap to tap resistances.
You might be able to see the shorter windings and work out from that where you went wrong.

I think you don't understand what i trying to say.
When i connect both 35 volt winding in series I get 35-0-35 volt but can't get 25-0-25 volt.To get 25-0-25 volt I have to connect both 25 volt winding in series.so thear is no short.

Ketje · 2016-08-09 2:02 pm

It looks like you have made the tap on the same place for the two windings

To get 35-0-35 and 25-0-25 you have to do it like this,
Mona

simon7000 · 2016-08-09 2:49 pm

Ketje said:
It looks like you have made the tap on the same place for the two windings
To get 35-0-35 and 25-0-25 you have to do it like this,
Mona

I think you got it exactly right! Fortunately he can cut his tap and rewire one so that he effectively changes the start winding to the end one.

TonyTecson · 2016-08-10 10:53 am

what is the problem here? i see none...
it is just a matter of connecting them right..

sanbadgujar · 2016-08-10 11:08 am

Thank for all diyers

Hi all

Yes I have to connect one tap winding in series to get dual supply from that tap.Means If i want 35-0-35 volt I have to connect both 35 volt winding in series. And if I want 25-0-25 volt connect both 25 volt winding series. Problem is I had to use only one dual supply at a time.That's Ok for me I am going to use one tap at a single time. Thanks for all diyers who help me design toroidal transformer.

sanbadgujar · 2017-06-13 12:33 pm

New toroidal transformer to make

Hello

I have new core to build toroidal transformer, core size as follows
OD-125mm,ID-75mm,Height-50mm
My customer need 50-0-50AC/7A=700VA, Main's voltage 230VAC/50Hz

I think the Toroidal core is more than 700VA. So both winding is as follows

cross section area of core=1200 mm2, window area=4415mm2
Primary turn - 580 with 1.42mm diameter magnet wire.
secondary turn - 252 with 2.34mm diameter magnet wire.
Help me with any suggestion.

JMFahey · 2017-06-13 3:17 pm

No way that core will handle 700VA, sorry.
You have a 2.5cm*5cm section core, so 12.5 sq cm.
Best case, it will handle 150VA .

Primary turns for 230V mains= 828.
Wire diameter: 0.50mm will be fine.

Secondary turns: whatever you need to get proper voltage.

Toroidal core calculation

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