that video contains all information you will ever need....
if that video can not help you, nothing will...
i get asked a lot of times about formulas.....
but in the end, how you do it is what really matters...
Dear AndrewT respect to all your help during this thread.
Still I Can't understand How to determine Maximum VA capacity of My toroidal core. I know How to calculate turn per volt. If my core is 100VA i have to determined my secondary total output not over than 100VA. Don't matter how I wind Thin wire or Thick Wire. But How to calculate Maximum VA Capacity of toroidal Core.Is any formula Like EI lamination have core area= E canter leg width*stack height than squaring the result gives you maximum VA capacity of Ei core.
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Your core is good for a bit more than 200 VA. But for audio use it is important not to run the core in saturation. When you do it puts odd order harmonics on the AC power mains. So use the core around 120-150 VA.
That is why you should wind the primary first and test the current draw.
Be sure to apply a layer of insulation to the core before you begin winding it.
Then after testing the primary another layer of insulation befor the secondary.
You can also add a shield if aluminum foil but be sure it is completely insulated so it doesn't act as a shorted turn.
That is why you should wind the primary first and test the current draw.
Be sure to apply a layer of insulation to the core before you begin winding it.
Then after testing the primary another layer of insulation befor the secondary.
You can also add a shield if aluminum foil but be sure it is completely insulated so it doesn't act as a shorted turn.
Thanks Simon7000
How do you calculate core Maximum VA rating.please give details because as per my understanding core VA=OD-ID*Ht/2. in my situation
10cm-6cm*5cm=20/2=10cm2. than squired of 10cm=100VA. Now how do you calculate almost double VA than me?
I don't know where that formula comes from. It is way oversimplified. VA depends on far more factors including temperature rise, type of core material and even in some cases the maximum and minimum load.
The rules of thumb used to be based on weight alone but they didn't work either.
The computer programs that do it are not freeware. But after you design a bunch if transformers it is "Feel" that develops. Then you test before building a second unit or going into production.
The book that best describes transformer design is a book called:
Transformer and Inductor Design Handbook by Colonel McLyman.
He worked for the JPL in the 80s and invented his own formulas for designing transformers and inductors and a lot of the manufacturers have adopted his system.
Most of the book is for designing ferrite and powder core transformers since nobody uses silicon anymore.
There is literally only one chapter for designing silicon power transformers and there is no example given for toroidal cores however.
You don't start with the core and work out how much power it is good for .. you start from voltages, currents, power and operating flux density, frequency, efficiency, regulation, window utilisation factor and temperature rise goal .. to name but a few lol.
He has tables in the book for the different types of material which he calculated over many years apparently experimenting. The manufactures have now adopted his system and they have similar tables for their materials.
Each transformer needs about 15/20 calculations/formulas to arrive at the correct core for the job and even then it is evidently only a guide.
I think your best bet would be to simply weigh the core and look up the electronic retailers' websites like RS Components in the UK and check out the various data sheets for different cores and compare weights to power outputs and it will be accurate enough for your needs.
You will still be left with problems such as calculating the number of turns to step down/up voltages etc.
Transformer and Inductor Design Handbook by Colonel McLyman.
He worked for the JPL in the 80s and invented his own formulas for designing transformers and inductors and a lot of the manufacturers have adopted his system.
Most of the book is for designing ferrite and powder core transformers since nobody uses silicon anymore.
There is literally only one chapter for designing silicon power transformers and there is no example given for toroidal cores however.
You don't start with the core and work out how much power it is good for .. you start from voltages, currents, power and operating flux density, frequency, efficiency, regulation, window utilisation factor and temperature rise goal .. to name but a few lol.
He has tables in the book for the different types of material which he calculated over many years apparently experimenting. The manufactures have now adopted his system and they have similar tables for their materials.
Each transformer needs about 15/20 calculations/formulas to arrive at the correct core for the job and even then it is evidently only a guide.
I think your best bet would be to simply weigh the core and look up the electronic retailers' websites like RS Components in the UK and check out the various data sheets for different cores and compare weights to power outputs and it will be accurate enough for your needs.
You will still be left with problems such as calculating the number of turns to step down/up voltages etc.
BTW as you are in India there has to be many very cheap books there on everything electronic. I have picked up at least three fantastic books on various subjects from India.
Power Electronics Laboratory by O.P Arora by Narosa Press ... UNBELIEVABLY good book 400/500 rupees.
Also Electrical Machine Design Handbook by Palani by New Age International Publishers which is unfortunately about motors etc but there has to be a very cheap book available on transformers as well from one of those publishers,
Power Electronics Laboratory by O.P Arora by Narosa Press ... UNBELIEVABLY good book 400/500 rupees.
Also Electrical Machine Design Handbook by Palani by New Age International Publishers which is unfortunately about motors etc but there has to be a very cheap book available on transformers as well from one of those publishers,
according to McLyman these are the parameters you need from the manufacturer of your material:
W_tcu grams [copper weight, grams]
W_tfe grams [iron weight, grams]
MLT cms [mean length turn]
MPL cms [magnetic path length]
W_a [window area in cm^2]
A_c cm^2 [effective cross section of the core in cm^2]
A_p cm^4 [area product, cm^4]
K_g cm^5 [core geometry coefficient, cm^5]
A_t cm^2 [surface area of the transformer, cm^2]
[btw those powers are correct]
if you can supply these data and then say what voltages, currents and frequency you require it would then be possible to calculate the appropriate power and appropriate primary and secondary wire sizes.
We can also assume:
Frequency, 50/60Hz
Efficiency, 95%
Regulation, 5 %
Operating flux density, 1.6 tesla
Window utilization, 0.4
Temperature rise goal, 30°C
W_tcu grams [copper weight, grams]
W_tfe grams [iron weight, grams]
MLT cms [mean length turn]
MPL cms [magnetic path length]
W_a [window area in cm^2]
A_c cm^2 [effective cross section of the core in cm^2]
A_p cm^4 [area product, cm^4]
K_g cm^5 [core geometry coefficient, cm^5]
A_t cm^2 [surface area of the transformer, cm^2]
[btw those powers are correct]
if you can supply these data and then say what voltages, currents and frequency you require it would then be possible to calculate the appropriate power and appropriate primary and secondary wire sizes.
We can also assume:
Frequency, 50/60Hz
Efficiency, 95%
Regulation, 5 %
Operating flux density, 1.6 tesla
Window utilization, 0.4
Temperature rise goal, 30°C
why worry about whether your core is 200 va or such?
you build that so that 200 watts of power output is possible,
but in my experience, your traffo can be 200watts, yet when listening to
music, that traffo will supply perhaps 20 to 50 watts or power.....
right, and that core will never stop delivering when asked 201 watts....
this is a concept that newbies find hard to grasp...
i use imperial units of densities, 0.33 pounds per cu. in copper density, and 0.27 pounds per cu inch core...
for copper ampacities, i use anywhere between 300 to 700 circular mils per ampere.....
these are what i use in my design calculations, figures in paper are adjusted as i go...
you build that so that 200 watts of power output is possible,
but in my experience, your traffo can be 200watts, yet when listening to
music, that traffo will supply perhaps 20 to 50 watts or power.....
right, and that core will never stop delivering when asked 201 watts....
this is a concept that newbies find hard to grasp...
i use imperial units of densities, 0.33 pounds per cu. in copper density, and 0.27 pounds per cu inch core...
for copper ampacities, i use anywhere between 300 to 700 circular mils per ampere.....
these are what i use in my design calculations, figures in paper are adjusted as i go...
You can use that test table to extract some guidance for your primary winding.
Take the middle set of values for 1.5T
Vac = 6.66 and Turns = 20
T/V = 3 and V/T = 0.333
You then need 240/6.66 * 20 = 720 Turns for a 240Vac feed driven to 1.5T
going across to 1.8T
You would need 240/7.992 * 20 = 601 Turns for a 240Vac feed driven to 1.8T
You can see from the currents that the 1.85T is too far into saturation.
But using that for 253Vac feed you would need 253/8.214 * 20 > 616 Turns to avoid that level of near saturaton for a maximum of 253Vac.
That would indicate you should probably use between 620Turns and 720Turns for your primary.
What is your worst case highest supply voltage?
That would probably require three layers of Primary winding where it passes through the middle of the core.
Do we need to insulate the three layers from each other?
Or can we rely on the inherent insulation of the 2layer enamel coating to give sufficient insulation on widely different voltages between the overlapping turns?
Some enameled wire is made with a 3layer coating for extra insulation, but I think it is not easily available.
Take the middle set of values for 1.5T
Vac = 6.66 and Turns = 20
T/V = 3 and V/T = 0.333
You then need 240/6.66 * 20 = 720 Turns for a 240Vac feed driven to 1.5T
going across to 1.8T
You would need 240/7.992 * 20 = 601 Turns for a 240Vac feed driven to 1.8T
You can see from the currents that the 1.85T is too far into saturation.
But using that for 253Vac feed you would need 253/8.214 * 20 > 616 Turns to avoid that level of near saturaton for a maximum of 253Vac.
That would indicate you should probably use between 620Turns and 720Turns for your primary.
What is your worst case highest supply voltage?
That would probably require three layers of Primary winding where it passes through the middle of the core.
Do we need to insulate the three layers from each other?
Or can we rely on the inherent insulation of the 2layer enamel coating to give sufficient insulation on widely different voltages between the overlapping turns?
Some enameled wire is made with a 3layer coating for extra insulation, but I think it is not easily available.
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Thanks AndrewT
If I use 1.5T then need 240/6.66 * 20 = 720 Turns for a 240Vac .But if I use 23 SWG(dim-0.61mm,current-0.76mA) magnet wire for primary than primary VA is 240*0.75=182VA is it ok to use that .or I have to use lower SWG to get about 100 to 130VA for Primary.How to primary magnet wire gauge chose without knowing Core maximum VA reating?
You don't know the final VA.
You would need to build the transformer and do what the manufacturer does. Test the idle current and idle temperature and see if they meet your specification.
Set to maximum resistive load current.
Check the temperature and regulation. See if those meet your specification.
If any fall outside, then adjust and retest.
You would need to build the transformer and do what the manufacturer does. Test the idle current and idle temperature and see if they meet your specification.
Set to maximum resistive load current.
Check the temperature and regulation. See if those meet your specification.
If any fall outside, then adjust and retest.
assume that you have a primary va of 200, at line of 240 volts, that is 200/240 A
or 0.83A.....
now if you read my post #29, you will find that i use anywhere from
300 to 700 circular mils per ampere, say you want 700 cm per ampere current density,
so you want a magnet wire with a circular mill area of 0.83 x 700 or 583.
now that is a #22 or #23, i would choose #22....
so there you have it, happy building......
Means I have to wind all calculated primary turn or just few turn with Difrrent gauge of magnet wire
You would have to wind on the Primary and the Secondaries and all the insulation to be able to test the temperatures of the core, the hottest part of the Primary and the hottest part of the Secondary. You can also check the regulation.
You would only need the Primary to check the idle current.
You cannot do any other testing with only the Primary in place.
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Why can't I calculate Maximum VA of core in Toroidal transformer like in EI lamination core I can calculate Final VA by just doing E center leg width*stack height and square the result I get maximum VA of EI lamination core.I wind EI transformer of 14.72cm2 Core area its maximum VA is 216VA and i get secondary out 45/3.7=166VA almost 75% of maximum capacity.
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