Hi Vasile, It took some time for me to find the issue. Faradays law has been verified = and it looks applicable. As it looks like, the issue seems to be Rac/Rdc related, where Rac is optimal but Rdc isn't. ie Rac/Rdc < 1. I have another question, but will address it in another thread/post. Best Regards, Manu On Sat, Mar 2, 2013 at 12:28 AM, Vasile Surducan wrote= : > Hi Manu, > > Your email is far too long and maybe a few people will read it to the end= .. > As far I've understood you have less wire as it should be on the primary = coil. > Have you verify your coil design using the Faraday law? > > Vasile > > On Tue, Feb 26, 2013 at 11:34 AM, Manu Abraham w= rote: >> Hi, >> >> I worked out a transformer based on these calculations: >> >> http://www.icecomponents.com/images/document/PDF/SMPS.pdf >> >> The transformer is driven by 8xIRF540's on each primary >> The IRF540's are driven using a IRF2110 MOSFET gate driver >> A dsPIC supplies 98kHz square wave at 22, 37, 42% duty cycles >> for transformer testing purposes. The duty cycles and frequency >> have been verified with a logic sniffer. >> >> (1) Core Selection >> EPCOS E55/28/21, material=3DN87 >> http://www.epcos.com/inf/80/db/fer_07/e_55_28_21.pdf >> Frequency=3D100kHz >> Core can handle upto 1000W at 100kHz >> Output power required =3D ~200-300W >> B=3D100mT >> Ae=3D354mm^2 >> >> (2) Transformer calculations >> >> Duty Cycle max (Dmax)=3D0.5 >> Minimum DC Voltage (Vdc min)=3D9V >> >> >> (3) Estimating E-T value >> E-T=3D1*10^6 * (Dmax)*(Vdc min)/f >> >> =3D 1*10^6 * (0.5)*(9)/100,000 >> =3D 450 >> >> (4) Primary Turns Count. >> Determining minimum primary turns >> Np=3DE-T*10^2/(B*Ae) >> >> =3D 450*100/(100*354) >> =3D 1.2711 turns ~2 turns >> >> (5) Turns Ratio >> For a push pull converter >> >> Ns/Np =3D Vs/(Vdc min * Dmax) >> >> Ns =3D Vs * Np/(Vdc min * Dmax) >> >> =3D 250 * 1.2711/(9 * 0.5) >> =3D 70.62 ~71 >> >> >> Ns/Np =3D 71/1.2711 =3D 55.857 >> Ns =3D 55.87 * Np >> Np =3D 55.87 * 2 =3D 112 turns ~ 120 turns >> >> (6) Wire Size >> Assume 400 circular mils per 1 ampere >> Total circular mils=3D400*I >> for AWG30=3D79.2 circular mils >> for 250W, 250W/250V=3D1A >> >> For secondary at 1A, >> 400/79.2=3D5.05=3D6strands of AWG30 >> >> For the primary; with 250W output >> Core loss=3D3.8W ~4W >> with efffeciency of 87% >> >> Primary Power =3D 254*100/87 =3D 291.95=3D292W >> >> Since 2 primary coils, each primary powers 292 / 2 =3D 146 >> Current through each primary =3D 146/12 =3D 12.1A ~12A >> for 12A at primary, for 12A, 12 * 6 strands of AWG30 >> >> At hand, I am having some litz wire of 45SWG, 90 strands in all. >> So, for the Primary, I used 6 strands of the litz with 2 turns and >> for the secondary 120 turns with 2 strands of the said litz wire. >> >> The results what I get is as follows.. >> >> With Ferrite Core (E55/28/21) >> >> Test: (1) >> >> No Load, Inverter OFF, Battery Voltage: 14.5V >> Frequency=3D98kHz >> With 22% Duty Cycle, Resistive Lamp Load (230V): >> >> Load (Watts) Current Battery Voltage >> @230V DC (A) DC (V) >> -------------------------------------------- >> No Load 8.6A 13.7V >> 40W 8.4A 13.6V >> 60W 8.7A 13.6V >> 100W 9.6A 13.6V >> >> Test: (2) >> >> Frequency=3D98kHz >> With 37% Duty Cycle, Resistive Lamp Load: >> >> Load (Watts) Current Battery Voltage >> @230V DC (A) DC (V) >> -------------------------------------------- >> No Load XXX XXX >> 40W 14.6A 13.6V >> 60W 17.0A 13.6V >> 100W 18.5A 13.4V >> >> >> At hand, I have a Yellow Powdered Toroid Ring with the following >> dimensions. I don't have much details about this toroid, except >> that the shop from where I bought, the shop keeper told me that >> it was a powdered iron core from China, which could handle about >> 200kHz. >> >> I did a quick transformer with 2 turns of the same litz (6 strands) >> for the primary and 4 turns of litz (4 strands) for the secondary. >> The transformer thus has a ratio of 1:2, which should justify a 1:1 >> voltage transfer for a square wave 25% duty cycle. >> >> Test : (3) >> >> With powdered Iron Core (Yellow Toroid) >> OD=3D58mm ID=3D35mm >> >> No Load, Inverter OFF, Battery Voltage: 13V >> Frequency=3D98kHz >> With 42% Duty cycle, Resistive Lamp Load (12V): >> >> Load (Watts) Current Battery Voltage >> @12V DC (A) DC (V) >> -------------------------------------------- >> No Load 5.0A 12.5V >> 35W 7.5A 12.0V >> 70W 8.5A 11.9V >> >> >> The results are quite different from what I was expecting.. >> (a) Even at no-load the converter seems to be drawing too much current. >> (b) The converter fails to deliver the proper output load >> (i) As in test 3, with 35W the lamp appears to be in it's proper >> brightness >> with 70W, the lamp lost a lot of the brightness. >> >> These 2 issues are visible in Tests 1 and 2 as well as can be seen. >> Any idea, what could be wrong with my transformer calculations/design ? >> with the 40W (230V) lamp, though not at full brightness, it glows quite = well. >> At 60W the brightness is even lesser, at 100W the filament is a bit more= than >> yellow. It looks to me that the transformer is unable to deliver the req= uired >> power, while it is drawing more than the required current. Is the transf= ormer >> getting into saturation ? >> >> If so, what's wrong in my calculations/design ? >> >> What can I do to fix my calculations and hence my design ? >> >> Any help ? >> >> >> >> Thanks, >> >> Manu >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .