My back-of-the-envelope calculation says that the ( 342 strands of 0.05mm ) has a cross section area roughly equivalent to AWG 25 - which is only good for 2 to 3 amps in open air; less if it's bundled up or buried in a transformer winding.
Dale
Dale
using 3.1A per sqmm of cross section, indicates that ~3.87sqmm of cross section is required at low frequency.
At VHF and above a bit more will be required to take skin effect into account.
At VHF and above a bit more will be required to take skin effect into account.
I have ordered some litz wire 32 * 0.112mm so this should give a few amps.
I will wind it bifilar in pairs to get more current.
I will wind it bifilar in pairs to get more current.
32 * 0.112mm is 0.315 sqmm.
two bundles gives 0.63 sqmm.
That has an LF current capacity of ~2A.
If you double that for low duty cycle, you still get only 4Apk, not 12A.
two bundles gives 0.63 sqmm.
That has an LF current capacity of ~2A.
If you double that for low duty cycle, you still get only 4Apk, not 12A.
nigel, since smps traffo's have such short lengths of wires, the practice for mains traffos wrt to wire size is quite different....
AJT,
are you suggesting that 12A through 0.63sqmm is an appropriate current target?
i.e. 19A/sqmm
are you suggesting that 12A through 0.63sqmm is an appropriate current target?
i.e. 19A/sqmm
no i am not suggesting anything, i am just relating my observations dismantling smps traffos.....i have hundreds of those....
The litz wire arrived but it looks way too thin.
Its pretty expensive too. £30 for 100g.
So I have gone back to 22swg enamelled copper wire times 4 to get the current.
Its pretty expensive too. £30 for 100g.
So I have gone back to 22swg enamelled copper wire times 4 to get the current.
"In Litz wire, with multiple levels of twisting very fine insulated wires, the amount of copper may be less than 30% of the total cross-section"
(from: Magnetics Design for Switching Power Supplies - Lloyd H. Dixon)
"None of the wire manufacturers gives very useful information on current density versus current capacity versus temperature rise versus wire size"
(from: Demystifying Switching Power Supplies - R. Mack)
Table 8-1 shows a sample of current capacity versus wire size versus current density. The temperature rise in Table 8-1 is for single layer coils. Temperature rise will be greater for multiple layer coils.
and yes, current densities in ATX psu is much higher than that, as AJT mentions; however there is also this fan; if this fan fails, life of this psu will be rather short ...
(from: Magnetics Design for Switching Power Supplies - Lloyd H. Dixon)
"None of the wire manufacturers gives very useful information on current density versus current capacity versus temperature rise versus wire size"
(from: Demystifying Switching Power Supplies - R. Mack)
Table 8-1 shows a sample of current capacity versus wire size versus current density. The temperature rise in Table 8-1 is for single layer coils. Temperature rise will be greater for multiple layer coils.
and yes, current densities in ATX psu is much higher than that, as AJT mentions; however there is also this fan; if this fan fails, life of this psu will be rather short ...
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