Current Transformer Deisgn
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
 1st December 2019, 10:57 AM #21 MorbidFractal diyAudio Member   Join Date: Nov 2017 Yes. I got my sum wrong. The equation is right. I probably went number blind. It is kind of another example of where theory does not match practice or rather practicality. Generally cores have a Effective Core Area and Winding Area, Ae and Aw, which are roughly the same but not necessarily. ETD more or less. RM more core less winding. There are many sums that you might use to get a first guess only to find out that some other constraint spoils the result. If Ae = Aw then you would have to fit 2 x 50 primary turns on the core, plus the others. If you assign half to the primaries, not an unreasonable guess, then 100 turns in 2mm^2 gives you 0.02mm^2 per turn, good for 80mA at 4A/mm^2 or a wire diameter of 0.08mm which would be impractical. In the case of a push-pull power transformer supplied by a 12V battery your sums might suggest that you only need 1/One turn primaries but then you find out that the magnetising current equals the reflected load current which is not a very good idea so you start adjusting other parameters/constraints to arrive at a more meaningful solution. There is no one sum fits all and you end up having to iterate.
JLeon
diyAudio Member

Join Date: Nov 2019
Quote:
 Originally Posted by MorbidFractal Yes. I got my sum wrong. The equation is right. I probably went number blind. It is kind of another example of where theory does not match practice or rather practicality. Generally cores have a Effective Core Area and Winding Area, Ae and Aw, which are roughly the same but not necessarily. ETD more or less. RM more core less winding. There are many sums that you might use to get a first guess only to find out that some other constraint spoils the result. If Ae = Aw then you would have to fit 2 x 50 primary turns on the core, plus the others. If you assign half to the primaries, not an unreasonable guess, then 100 turns in 2mm^2 gives you 0.02mm^2 per turn, good for 80mA at 4A/mm^2 or a wire diameter of 0.08mm which would be impractical. In the case of a push-pull power transformer supplied by a 12V battery your sums might suggest that you only need 1/One turn primaries but then you find out that the magnetising current equals the reflected load current which is not a very good idea so you start adjusting other parameters/constraints to arrive at a more meaningful solution. There is no one sum fits all and you end up having to iterate.
Thank you, man. As a newbie, I also rely on self-study. I made a mistake, that is, I did not separate theory from actual engineering. If you didn't guide me so patiently, I might still be in this confused state. My English is very poor, I don't know how to express my gratitude.Anyway,thanks. HaHa

 1st December 2019, 03:48 PM #23 MorbidFractal diyAudio Member   Join Date: Nov 2017 No worries. You would be right to assume that I am making educated guesses. Unfortunately I've seen lots of sums that have not made much sense to me and have had to go back to basics to derive my own equally worthless ones. Then I haven't bothered extending things as much as I might or should. It's all bits and pieces. It all starts with L = UoUeAeN^2/Le and B = UoUeIN/Le L inductance Henries B flux density Tesla Uo permeability of free space 4PiE-7 Dimensionless Ue relative permeability Dimensionless N Number of turns. Ae Effective core area M^2 Le Effective core length M I current in the winding There is another common term called the specific inductance Al Al = UoUeAe/Le That's normally given as nano-henries per root turn but you have to be consistent with the overall dimensions. Ae might be M^2 but will be given as mm^2 so you have to adjust by 10E-6. Substitute for Al in the equation for inductance. L =AlN^2 Substitute for Al in the equation for flux density. BAe = AlNI I had to multiply by Ae on the left side for the Ae multiplying the right. Multiply both sides by N BAeN = AlN^2I AlN^2 is L BAeN = LI Rearrange for N N = LI/BAe If you have a saturation flux density, Bsat, and peak inductor current, Ipk, then given a core area and target inductance you can calculate the required number of turns to avoid saturating the core. Here's another one. Faraday's Law... E = -LdI/dT Shake it around a bit. Let's say you apply a voltage across an inductor. dI/dT = V/L The minus sign disappeared because you are driving the EMF rather than the inductor producing a back EMF. Assume the inductor is the primary of a transformer, Lmag the magnetising inductance, and V is the input supply, Vin, which you supply for a period of time, Ton. Also assume that the current starts at zero. At the end of Ton the current in the magnetising inductance is... Ipk = VinTon/Lmag We already have... N = LI/BAe Substitute and you get the minimum number of primary turns to avoid saturating the core... Npmin = VinTon/BsatAe It's all congenital, existing from birth or the base equations, or perhaps incestuous, interbreeding of the base equations. This is kind of square wave SMPS specific and uses SI units. A term like VinTon is integral volt seconds. In mains power electronics using sine waves you will often see the term 4.44 crop up which has something to do with the integral of a sine wave voltage. Same sort of thing. Last edited by MorbidFractal; 1st December 2019 at 03:50 PM.

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Room Acoustics & Mods     Music     diyAudio.com Articles     Car Audio     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Holton Precision Audio         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post carlosgn Power Supplies 5 9th January 2012 05:43 AM s_c_leach Power Supplies 9 26th April 2011 02:52 PM JDeV Parts 7 19th December 2009 09:49 AM xenu Digital Line Level 0 4th April 2009 08:18 AM

 New To Site? Need Help?

All times are GMT. The time now is 09:49 AM.