how can i compute the size of the wire in a step-up transformer?

Question

given the following data f=60hz, Vinput=110volts, Voutput=220volts,P=1kw.

Answer 1

#14 might be a bit large for this, especially for the secondary, you'll need a larger core than the minimum size necessary to accomodate it. Current in the primary would be max of about 9 amps, half that in the secondary, so maybe #16 or 17 for the primary, #19 or 20 for the secondary.

The proper way to do this is rather involved and is usually an iterative process where you start with a guess for a particular core, then:

determine it's total core losses for the design in watts,

shortcut by assuming the same resistive losses for the wires (i.e, double the value, this is a common simplification based on the theory that the core losses and the winding losses should be about equal),

determine if this total wattage is a safe value for the environment, (if about right, stick w/this core for now, if not, go to next larger/smaller core and start over)

pick a wire size for each winding, calculate losses for #turns (which must fit the core window, calculate that also), length, etc......


See what I mean? Transformer design is practically a specialty if you need the "ideal" solution, i.e. the most cost-effective for a particular app. If just something "good enough" it can be a bit simpler, tho with a larger core and more copper than the minimum necessary.

Anyway, try #16 for primary, #19 for secondary first, ideal may actually be a bit smaller.

Answer 2

The main reason for multi stranded conductors is for installing into systems that may suffer from vibration probably because they are in equipment that is mobile, such as in aircraft, boats or vehicles to name just a few examples. The benefit of the multi strand is that unlike the single strand it performs better under continuous vibration. Whereas the single strand wire possibly can weaken and fracture under those conditions. Wire and cables are all rated and have a maximum current rating that must not be exceeded. Wire is rated according to current rating (Amps) that can safely pass along it, the higher the current the thicker the wire. It is critical to get this RIGHT. Lets just talk briefly about what can go wrong in principal - if you attach an appliance to an under rated cable (to thin that is - or too long!) the voltage will drop and then the cable will heat up and eventually may catch FIRE. OHMS LAW SAYS - When the voltage goes down the current goes up. Think of your wiring like a piece of plumbing, if you tried to force water under pressure through a pipe and then tried to greatly increase the flow and pressure, the pipe would eventually burst, and the only solution to this problem is to get a bigger bore pipe and the problem is solved.

Answer 3

Calculate the current in the primary and secondary and choose the appropriate wire size from the tables. For your power of 1 kw, size 14 is probably safe for both the secondary and primary.