Here is the Computation of EI core Transformer Philippines Base

[tranqspogi]

The Power transformer

my Example is

the Primary is 220 volts (Philippines Base) but you can Deduce it by Dividing by 2.
the Secondary is 12-0-12volts or 0-12volts

we are going to compute specifies 12 volts output with 750ma current (my Example) converting milliamperes to ampere will give us. .75a , multiplying voltage by current gives us wattage or power.

12x.75 = 9 watts


after having solved for the wattage of the transformer, which is 9 watts, look at Tables 1, where 9 watts is listed, follow the table horizontally and pick up the date for the center leg, thickness and turns per volt.


Center leg - 3/4
thickness - 3/4
turns per volt - 10

see at Table 1 and Table 2

the nest step is to compute for the number of turns for the the primary and secondary coils respectively. the number of turns per volts in the primary is equal to the number of turns per volts in the secondary.


Primary coil - 220 volt (PHILIPPINES Base)
Secondary coil - 12 volts
Number of turns (primary) = 220x10 = 2200 turns
Number of turns (secondary) = 12x10 = 120 turns

having computed for the number of turns in the primary and secondary coils. determine the sizes of wire for these coils in the next step . before computing for the guage or size of wire (AWG) must find out the current capacities of wires and their corresponding sizes. this data is provided in table 2 .

the power formula is used again in solving for the currents of wires in the primary and secondary. dividing the watts over voltage gives us the current of the wire:


note:

I = Current, W = Wattage, E = Voltage


I = w/e


I secondary = 9watts/12volts = .75 a
I primary = 9watts/220volts = .04a


after having solved for the currents of wires pick up the corresponding sizes of wires from table 2. choose the closest current listed in the table.


Size of wires (Primary) - #35
Size of wires (Secondary) - #23


in case of a multi-voltage secondary, the higher voltage should be taken for computation. if the transformer has multiple secondary coils, the wattage of each coil is computed and then summed up. in other words, the wattage of the primary is equal to the total wattage of all secondary coils.

if the secondary coil is only center-taped, half of the wattage and current is taken to compute for the wattage of that coil.

the primary is 220-0 volts, the secondary is 12-0-12 volts

 

[ataul]

What is center leg and thickness? and what is the unit for what? (Inch or mm)??
I think center leg is, center of E part(core) witch is in the middle and winding(primary and secendery coil) around this and thickness is total core stacking.
this table is very useful if i understand.

 

[FRANK BRAUN]

Transformer cores are measured in inches. You're right the pages are old but still useful.

 

[banjak]

what do you mean by philippines base is that related to the core size?
What is center leg and thickness and what is the unit, they are used for what?
and what is the corresponding core size fore the calculated transformer above
thanks for your help.

 

[Techpolice]

is there no other formula?coz i have that kind of table here but only for 1000 watts trafo.i want to make 3000 watts of trafo.

 

[AndrewT]

The table on the left is using an EI core flux of approx 0.5T to 0.7T
This is a good value to use for an unknown material.

Once the transformer is built, you can test the Primary only (no secondary wound yet) to determine the actual primary no load current and from there determine the maximum usable Flux for the material you have.

 

[AndrewT]

The table on the right seems to be using ~3A/sqmm for the copper windings.
Modern transformers seem to use a higher current rating to save money on the copper in return for lower performance.

 

[kikodemy]

I remember Mr Marconi Pagarigan as the author of that book where the pics of the table both for wire gauge and relationship of power rating to the size of center leg were taken. I used that also before and It worked just fine only for 60 Hz silicon-iron core power transformer..

 

[TonyTecson]

what do you mean by philippines base is that related to the core size?
What is center leg and thickness and what is the unit, they are used for what?
and what is the corresponding core size fore the calculated transformer above
thanks for your help.

based on the fact that OP is based in the Philippines....
but traffo making is universal...i mean the principles are the same anywhere...

nowadays, i design my traffos based on 240volts line, where i am in metro manila
line voltages ranges from 230 to 240 depending on the time of day or night...

RDH3 and RDH4 are downloadable for free, chapter 5 deals with transformer designs...http://www.tubebooks.org/Books/RDH3.pdf http://www.tubebooks.org/Books/RDH4.pdf and http://www.ax84.com/static/rdh4/chapte05.pdf

 

[TonyTecson]

Transformer cores are measured in inches. You're right the pages are old but still useful.

there are also metric dimensions...

 

[srian]

How to determine the maximum usable Flux

The table on the right seems to be using ~3A/sqmm for the copper windings.
Modern transformers seem to use a higher current rating to save money on the copper in return for lower performance.

The table on the left is using an EI core flux of approx 0.5T to 0.7T
This is a good value to use for an unknown material.

Once the transformer is built, you can test the Primary only (no secondary wound yet) to determine the actual primary no load current and from there determine the maximum usable Flux for the material you have.

AndrewT, Please let me know how to determine the maximum usable Flux for the material you have Once the Primary only is built by measuring the
actual primary no load current.

 

[TonyTecson]

^your best bet is to get the data from the core manufacturer directly....

current densities are under the control of the designer and based on factors such as regulation and cost..

 

[TonyTecson]

is there no other formula?coz i have that kind of table here but only for 1000 watts trafo.i want to make 3000 watts of trafo.

a 3000 watt traffo will have a 2.25 inch center leg stacked to 4.5 inches...
finished traffo will weigh in at around 45 pounds estimated...

 

[AndrewT]

AndrewT, Please let me know how to determine the maximum usable Flux for the material you have Once the Primary only is built by measuring the
actual primary no load current.

plot the Primary Current vs Primary Voltage curve.
You will see the shape of the S curve.

It gives you the primary voltage for the highest impedance.
It gives the primary loss (magnetising current) when on no load.
It gives the heat generated in the primary+core at any primary voltage.
It gives an indication of the highest primary voltage that the core flux can manage.

A low flux material will start to saturate at a lower primary voltage than a high flux material. The curve shows this.

 

[AndrewT]

is there no other formula?coz i have that kind of table here but only for 1000 watts trafo.i want to make 3000 watts of trafo.

a 3000 watt traffo will have a 2.25 inch center leg stacked to 4.5 inches...
finished traffo will weigh in at around 45 pounds estimated...

The old fashioned formula/guide for core size is given by

VA ~ 31 * (core area)² * max usable flux.

using AJT's number of 2¼ by 4½ gives core area = 10.125
max power = 31*10.125² = 31 * 102.52 = 3178VA if max flux = 1T
for 0.7T that core reduces to ~2225VA
for 1.1T that core increases to ~3500VA

 

[TonyTecson]

the traffo designer has complete control of the parameters
in coming up with a design, it is all about choices...
no one formula can satisfy every requirements...

in my experience, even with the core capacity determined by formulas,
it is seldom realised in practice in terms of copper windings, and more oftern
that not, capacity based on copper current densities are ussually
smaller than what you get computing the core capacity...
and this is because of the limitations of the winding window in the EI cores...

using lower flux densities gives you a cooler running trafffo,
in my builds i seldom run at 1T, 0.6 to 0.9T is the ussual for me...

in my builds i prioritize heat as prime factor....

 

[AndrewT]

the traffo designer has complete control of the parameters
in coming up with a design, it is all about choices...
no one formula can satisfy every requirements...

in my experience, even with the core capacity determined by formulas,
it is seldom realised in practice in terms of copper windings, and more oftern
that not, capacity based on copper current densities are ussually
smaller than what you get computing the core capacity...
and this is because of the limitations of the winding window in the EI cores...

if one stacks the laminations so that the centre leg is roughly square then one usually finds there is adequate window area for the required copper @ ~3A/sqmm. But if one adopts a very long stack as in the AJT example where the 4½" stack is double the core leg width of 2¼", then one finds that the core has increased VA rating of 4 times, but there is no more window area for the 4 times copper required. The design can never achieve low regulation because the is insufficient room for the copper.

using lower flux densities gives you a cooler running trafffo,
in my builds i seldom run at 1T, 0.6 to 0.9T is the ussual for me...

in my builds i prioritize heat as prime factor....

The allowable flux depends on the core lamination material. One can ask the manufacturer for their specification, or one can test the primary current against the ampere turns wound onto the core.

 

[TonyTecson]

or you can derate the capacity, no one can prevent you from saying
that your traffo is a 1kva traffo when it can do more...

 

[JMFahey]

if one stacks the laminations so that the centre leg is roughly square then one usually finds there is adequate window area for the required copper @ ~3A/sqmm. But if one adopts a very long stack as in the AJT example where the 4½" stack is double the core leg width of 2¼", then one finds that the core has increased VA rating of 4 times, but there is no more window area for the 4 times copper required. The design can never achieve low regulation because the is insufficient room for the copper.The allowable flux depends on the core lamination material. One can ask the manufacturer for their specification, or one can test the primary current against the ampere turns wound onto the core.

Fully agree.

I wind my own transformers by the thousands since forever (think 40 years or so) and found it the cheapest way to do things is to use the best iron commercially available 😱 .

I use EI locally cut on demand, from VERY good Russian made sheets, imported originally for high performance electrical motors.

Routinely use them at 15000 Gauss (1.5T for the youngsters in the audience 😀 )
There I minimize iron weight (so I minimize iron cost).

I also design around square stacks.
There I minimize on copper cost.

To be more precise, I fill windows to the brim with copper (I routinely have to hammer or press windings to fit the E sheets) but the prize is I can make light compact amps and have excellent voltage regulation.

Colleagues and competitors make fun at my "matchbox" transformers ... until they measure them that is 😛

I also use Motor rated wire (Class F or H) , guaranteed 155/180C under high vibration or stress.

A b*tch to stripe for soldering, suppliers always offer me "Transformer rated" "self stripping" enamelled wire, what is universally used today, officially rated 130C ... looks good, huh?

Problem is that on overheating enamel *evaporates* leaving behind shiny copper, turning primary into a solid bar of copper, resiatance measured in the thousandths of ohms and, of course, no inductance, while motor rated type smells and browns but holds the insulation.

I have repaired amps where I found a nail, a 20A fuse pulled from a car or a roll of aluminim cigarette paper was found inside the fuse holder , brown toasted paper tape wrapping, molten and twisted plastic bobbins ... and the transformer kept working.

Only problem from the 1.5T designed transformers is that inductance decreases to half what's expected, and turn on rush current is 2X as much as before, I have had to rise line fuse ratings by 50% because of that.

Maybe I should add a slow start circuit.

 

[TonyTecson]

let the end product do the talking.....
proudly philippine made.....nylon shoulder bushings on screws, teflon insulated pigtails...
Z11 cores, done by Alphatronics, no affiliation with them, but i buy traffo supplies from them...

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