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# Transformer design

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• thanks , Regards

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• so far so good

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• @clime If you know the current that the wire has to carry and the current density that you will use, a useful formula is sqrt(amps/CD*820). This will give you the approxiate dia in mm. For example, a wire that has to carry ,8 amps at 2000 amps per square inch, the formula will give .572, nearest size is .56mm dia. Current density, for small transformers from say 20 VA upto 500 VA, you can use a CD of 2000 amps per square inch just to get a wire size to start off the design. Work out the losses adjusting the wire dia up or down untill you get the losses/window fill that is acceptable.

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• what is the formula in determining the primary circular mill or the size of magnet wire for primary and secondary?.tnx

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• i need formula for determin the valu of core size for constructing the transformer

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### Transformer design

1. 1. Sulaim b. Ab Qais 2012 DESIGN A TRANSFORMER This paper guides a simple and practical calculation in designing a transformer. The hands-on work can be understood from this video http://www.youtube.com/watch?v=s6NyTprQCBI MATERIALSMasking tape, wax paper, copper cable, magnet copper wire, sandpaper, silicon-iron sheet, formwork,soldering wire CALCULATION1. Determine the load power, P.Let say, P=300W2. Find the primary winding current. Malaysia using 230 VAC, +10%,-6%, thus the current would be; Ip = P/V Ip = 200W/230V = 0.87 A, thus the wire that we will using for primary winding is 0.26 mm2Let say the secondary winding voltage, Vs = 40 VAC Is = 200W/40V = 5 A, thus the wire that we will using for secondary windings is 1.31 mm23. Find the size of the cable for primary windings and secondary windings.By referring to the table below we can determine the size of primary and secondary coil (magnet wire). Table: cable size for safe current carrying capacity American Wire Gauge (AWG) Area size (mm2) Current (max) 30 0.05 0.22 29 0.06 0.29 28 0.08 0.3 27 0.1 0.4
2. 2. Sulaim b. Ab Qais 2012 26 0.14 0.5 25 0.16 0.6 24 0.25 0.8 23 0.26 1.0 22 0.34 1.2 21 0.38 1.6 20 0.5 2 19 0.65 2.6 18 0.75 3.2 17 1.04 4.1 16 1.31 5.2 15 1.65 6.6 14 2.5 8.3 13 2.6 5.1 12 4 5.13 11 4.15 6.16 10 6 2.21 9 6.62 5.26 8 8.36 33.3 7 10.6 44.24. Find the section kernel Section kernel = 𝑃 = 200 = 14.4 cm2Thus, the size of the centre core is 14.4 cm2. We can use any combination of length and width to get thearea. For example, 3.8 cm x 3.8 cm = 14.4 cm2 L= 3.8 cm W= 3.8 cm
3. 3. Sulaim b. Ab Qais 2012 Width,W Length,L5. Calculate the number of turn for primary windings. Turn per volt = 42/section kernel *42 is a constant = 3 turns/volt No of turn (primary) , Np = 3 x 230 = 690 turn6. Calculate the no. of turn for secondary windings (refer table above) No of turn (primary) , Ns = 3 x 40 = 120 turnSELECTED Q & A1. Why primary windings and secondary windings of the transformer didn’t short circuit?The windings will act as an inductor when AC current flow in it, blocking the high current. Thoughvoltage is applied, current flowing, impedance also exists. Thats why the transformer doesnt get shortcircuited. Insufficient number of coil due to miscalculation will result in short circuit.
4. 4. Sulaim b. Ab Qais 20122. Is a transformer is obeying ohms law or not?Ohms law is for determining the behavior of electricity through a load (a resistor). Transformer isnothing more than a pair of inductor. A transformer by itself is not a load. You apply Ohms lawseparately to the primary circuit and to the secondary circuit of a transformer. You do not use Ohms lawto learn how the primary induces current in the secondary. The current that we calculate is themaximum (short circuit) or ideal transformer current. If we put resistor at any side it still obeys ohm’slaw.3. Why we usually use magnetic copper wire for the windings?Magnetic copper have insulation. To build a transformer, solenoid or inductor each turning wire cannotshort with the other from the side.REFERENCE1. http://www.construyasuvideorockola.com/construc01.php2. http://answers.yahoo.com/question/index?qid=20090705145110AAjSE333. Suruhanjaya Tenaga Malaysia (ST).