dear JMFahey
Thanks for your reply.Before this core, I already build 360VA Toroidal transformer, on 9.5 sq cm core and that's working fine.Core size for that trans' was OD-100mm,ID-60mm,Height-50mm.
My formula for toroidal transformer is as follows
Power handling capacityToroid
VA=5.0*J*Bm*f*Ac min*ID²*10^7
where:
VA =Power handling capacity (VA),
J =Current density (A/ mm2),
Bm =Maximum induction ( Tesla),
f =Frequency ( Hz),
ID =Inside diameter (mm),
Ac min =Effective cross-sectional area (mm2).
I´ve seen that formula somewhere else, the least I can say is that I find it weird, it´s mixing 2 different sets of parameters as if improving just one it will compensate deficiencies in the other; it does not work that way.
You have two main VA limiting mechanisms, you need to address both.
1) magnetic core saturation, which is what I calculated.
Iron is iron, whether it´s toroid or EI shaped, it can only pass so much power without saturation.
Conventional safe design considers 10000 Gauss which I used, IF iron is *measured* and stands 15000 with no problem, so be it, but unless demonstrated otherwise, 10000 it is and that´s what I used, end result somewhat above 150 VA.
*Good* iron could give you safe 225VA but I don´t know what you have.
2) too high resistive loss in copper.
Being a toroid usually you´ll have a more "generous" window, so you can fit more wire there.
Fine, you will reduce resistive loss, improve regulation, but won´t significantly improve total power which can be pulled from that core section.
As said before, with care you might pull 50% more and with less drop but not 4X the basic rating, looks too optimistic.
You have two main VA limiting mechanisms, you need to address both.
1) magnetic core saturation, which is what I calculated.
Iron is iron, whether it´s toroid or EI shaped, it can only pass so much power without saturation.
Conventional safe design considers 10000 Gauss which I used, IF iron is *measured* and stands 15000 with no problem, so be it, but unless demonstrated otherwise, 10000 it is and that´s what I used, end result somewhat above 150 VA.
*Good* iron could give you safe 225VA but I don´t know what you have.
2) too high resistive loss in copper.
Being a toroid usually you´ll have a more "generous" window, so you can fit more wire there.
Fine, you will reduce resistive loss, improve regulation, but won´t significantly improve total power which can be pulled from that core section.
As said before, with care you might pull 50% more and with less drop but not 4X the basic rating, looks too optimistic.
The core it's self doesn't have to handle anything, the core does not "give" any power, it's the copper wire that has to handle the needed power, the core is just an intermediary, it doesn't care how much power you ask it to transfer as long as you make sure it's far enough from saturation, and saturation does not come from excessive power, or from too much current drawn from the windings, saturation comes from to much induction, meaning it comes from a too small turns per volt ratio. The issue with any core is the number of turns needed to handle the voltage ( which depends on the core size ) and the wire gauge needed to handle the current. All of that has to fit inside the window, that is the limiting factor. With a big enough window, you can fit more copper, thus you can get more power despite the core's cross section, but at some point, the wire length becomes too large, meaning the DC resistance becomes too large, thus the copper losses become too large, that's what gives the need for a compromise, and the empiric formula P=S^2 is exactly that, a compromise, not a fixed limit.
In this case you would need at least 3,6 turns per volt ( i would recommend 4 ), are you sure you can fit all of that wire inside the window? Calculations can be made to be sure, but i rather doubt it can be done...
In this case you would need at least 3,6 turns per volt ( i would recommend 4 ), are you sure you can fit all of that wire inside the window? Calculations can be made to be sure, but i rather doubt it can be done...
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dear MarianB
I already build 360VA Toroidal transformer, on 9.5 sq cm core and that's working fine.using the same equation. I get 35-0-35Vac/5A on that transformer windows are of that core is 2826 mm2.Total window are for primary & secondary winding I used is 1500mm2 little over 50%
Core size for that trans' was OD-100mm,ID-60mm,Height-50mm.
Now, in this case, required turn per volt is 2.60. I have windows are 4415 mm2, May require Windows area for total winding for700VA, is a little bit more than 3500 mm2.so why can't I
wind 700VA transformer on this core.Core quality is M4(0.27mm strip width), CRGO.
I already build 360VA Toroidal transformer, on 9.5 sq cm core and that's working fine.using the same equation. I get 35-0-35Vac/5A on that transformer windows are of that core is 2826 mm2.Total window are for primary & secondary winding I used is 1500mm2 little over 50%
Core size for that trans' was OD-100mm,ID-60mm,Height-50mm.
Now, in this case, required turn per volt is 2.60. I have windows are 4415 mm2, May require Windows area for total winding for700VA, is a little bit more than 3500 mm2.so why can't I
wind 700VA transformer on this core.Core quality is M4(0.27mm strip width), CRGO.
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The core is M4, CRGO.
Test certificate for 9.5 sq cm core which I build 360VA transformer.From core manufacturer link below
https://drive.google.com/file/d/0B5ROBprWe44vYnBURUt0MVNxTkdSRXFqUjhuWHpBUFg5X1Nv/view?usp=sharing.
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That only shows it has been tested in some conditions, but it does not show any curves, any graphs, nothing about how far the core is from saturation, how much losses there is, etc, temperature of the core...
If you can present a document that shows all of that, only then can you be sure that 1,4T is safe, but even if it is, i would hate to think about the core temperature, especially at max power when the copper losses heats up the copper wire, and that can only add to the thermal stress.
If you can present a document that shows all of that, only then can you be sure that 1,4T is safe, but even if it is, i would hate to think about the core temperature, especially at max power when the copper losses heats up the copper wire, and that can only add to the thermal stress.
Measure your primary+core and plot the graph Iprimary vs Vprimary
A core with too little iron soon shows up as excessive Iprimary before one reaches the maximum mains voltage.
The only solutions are to add more iron, or add more turns, or bin the core and start again.
A core with too little iron soon shows up as excessive Iprimary before one reaches the maximum mains voltage.
The only solutions are to add more iron, or add more turns, or bin the core and start again.
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Dear marainB
Please understand I already build 360VA transformer on that core. And that transformer I used to drive 80W Amplifier, which rectifier required 35-0-35Vac/5A.I run that amplifier contently 5 to 7 hour daily.during amp operating transformer is a little worm.
Doesn't really matter how much power you draw from it, from the core losses point of view, more important is the length of time it has to work with that turn per voltage ratio.
I still think is a bit too economic at that flux but if you say it does not heats up too much then so be it, maybe it's a better quality core... This way it could probably provide enough window area for the needed windings, so you could probably get what you need from it, but still i would test it as thoroughly as i can with a resistive load, a scope and a couple of multimeters, just to be sure it will perform ok in time.
I still think is a bit too economic at that flux but if you say it does not heats up too much then so be it, maybe it's a better quality core... This way it could probably provide enough window area for the needed windings, so you could probably get what you need from it, but still i would test it as thoroughly as i can with a resistive load, a scope and a couple of multimeters, just to be sure it will perform ok in time.
I'll bet San did not test the VA output nor did he check the temperature of the windings and core towards the end of the VA test.
dear AndrewT
Yes, I Just check op voltage of transformer after the build.It gives what I wanted 35-0-35Vac, And then I feed directly 80W amp through rectifier it working fine for me that's it.
New core to build transformar
Hello Tony sir
I have toroidal core of following size, it's more than 1kva.
so I can wind two 35Vac and two 55Vac on it.
can it is enough for Apex Mono B500 and stereo Ax-14 amp. Because I think total Power requirements is near about 800 Va.
Or I have another 800 VA toroidal core.
please help.
Best regards
Hello Tony sir
I have toroidal core of following size, it's more than 1kva.
so I can wind two 35Vac and two 55Vac on it.
can it is enough for Apex Mono B500 and stereo Ax-14 amp. Because I think total Power requirements is near about 800 Va.
Or I have another 800 VA toroidal core.
please help.
Best regards
Attachments
anyway, if i were you sanbadgujar, i would have ketp a note of the original turns per volt or primary data....
Not really sure of how did you got that power rating, but anyway, you would need about 3,6 turns per volt for 50hz ( 3 turns per volt for 60 hz ), or maybe a bit less for a higher flux density. You have 6358 mm^2 available winding window area, thus you can calculate the number of turns for each winding and the wire thickness...
I believe all needed info is in the topic here.
Sorry i didn't know
RIP our dear friend.
I learn many think from you sir. You will be missed.
Hello tony sir and marianB sir
hear is my calculation for toroidal core.
I make about 5 to 6 toroidal transformar base on this calculation,
please see attachment.
Attachments
you can use it for 800va
at primary side with 2/5 turns per volt and 230v/50hz core works at 1/5 tesla.
you should use at least 1.2mm diameter wire for primary and for less copper losses and continuously load condition 1/5mm would be better choice
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