current capacity of wire in smps transformer

[eem2am]

Hello,

The following datasheet for enamelled copper wire (ECW) states that ECW of diameter 0.56mm (SWG24) has a current carrying capacity of 0.381A.

Enammelled copper wire datasheet:
http://www.farnell.com/datasheets/24248.pdf


However, the following web page states that wire of diameter 0.574mm (AWG23) has a transmission current carrying capacity of 0.729A.

American Wire Gauge table and AWG Electrical Current Load Limits with skin depth frequencies

So, whn I am winding my SMPS transformer primary winding, in which the RMS current is 0.58A, will I be OK with ECW of diameter 0.574mm?

…according to the second reference, I will be ok, according to the first, I will not be OK………..who should I believe?

 

[Militoy]

The guidelines for current density limits in magnet wire are just that – guidelines. They’re offered as a starting point to work with, and as a way to compare different wire sizes. In an SMPS transformer, winding turn numbers are typically small, and winding lengths and thermal path distances are short. As opposed to a fixed limit of current for a given copper wire size, a designer will usually design for a maximum desired resistive loss in each winding – considering skin effect and proximity losses. Allowing for operating frequency - it would not be unusual to use 23 gauge magnet wire at over 2 Amps current.

 

[trobbins]

eem, have you determined skin depth for the fundamental frequency? Remember that if you are using square waveforms, then the harmonics will have smaller skin depths.

Have you determined a layer/interleaving build and determined proximity effect influences.

You may want to convert to A/mm2 or /mil2, as many people design to certain acceptable levels of current density for a given skin depth percentages - which usually involves going to bi-tri..filar or a power litz.

Ciao, Tim