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 co= il. Have you verify your coil design using the Faraday law? Vasile On Tue, Feb 26, 2013 at 11:34 AM, Manu Abraham wro= te: > 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 w= ell. > 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 requ= ired > power, while it is drawing more than the required current. Is the transfo= rmer > 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 --=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 .