I have been researching how to build power transformers but I am stuck on finding the proper wire gauge for winding the primary. In order to find the correct wire size I have to know the current in the primary coil. I have two different formulas from different sources for this that say different things.
METHOD 1 The first is an article written back in 1947. Which says "the primary circuit VA is 1.4 times the total secondary VA.
METHOD 2 the other formula is from a transformer calculator which is Vp x Ip = Vs x Is. Then divide primary VA / Vp (115)
My example problem is this
- Vp (primary voltage) = 115
- Ip (primary current) = ???
- Vs (secondary voltage) = 19.2 volts
- Is (secondary current) = 1.5 amps
When using Method 1 we get Ip = 0.35 amps. This seems to makes sense because the primary should be more current than the secondary to make up for any losses.
When using Method 2 we get Ip = 0.25 amps. This has the primary and secondary VA being equal. Which contradicts the first method which says primary VA is 1.4 times the secondary VA.
So which one is correct?