Making litz wire at home

Silvio

Member
Here you will find my experiences when making litz wire at home based on information that I gathered through the net. I also examined and experimented myself with several types and these are my findings.

Cannot upload zipped file of 1.16MB If anyone wish to see this file I can post it through his mail address
 
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MicrosiM

Administrator
Staff member
Hi Silvio

Problem solved, now you can upload files up to 3MB in size.

I still can increase that if you like!

Thanks
 

Silvio

Member
Thanks very much MicrosiM I will upload a few threads of general knowledge about smps in SMPS information. I guess this will be the right place to post them.
 

Silvio

Member
Here you will find my experiences when making Litz wire at home based on information that I gathered through the net. I also examined and experimented myself with several types and these are my findings.
 

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IVANELECTRIC

New member
Excellent article Silvio, I discovered this table a long time ago but I am not sure if I apply it correctly. In the case that I use my smps at 50kHz ...... I could use 23AWG wire, but if I only have 18AWG (it supports 17kHz) I must do 3x18AWG (3x17kHz) ????. Or in that 3x18AWG arrangement it will only handle more current but will still work at a maximum frequency of 17kHz? Thanks and regards!
 

Silvio

Member
18AWG is too thick to use in smps. The thickest wire to be used is 0.8mm as this goes down to 20Khz. Making a switching power supply working lower than this frequency is not practical as the core will not be utilized efficiently.
Due to skin effect at high frequency AC tend to travel around the circumference of the copper wire. Using thicker wire will be useless as the skin depth will be only to a certain amount according to the frequency used. The higher the frequency the thinner the wire should be. We then use multiple thin wires to overcome this problem, either side by side or twisted together.
 

IVANELECTRIC

New member
18AWG is too thick to use in smps. The thickest wire to be used is 0.8mm as this goes down to 20Khz. Making a switching power supply working lower than this frequency is not practical as the core will not be utilized efficiently.
Due to skin effect at high frequency AC tend to travel around the circumference of the copper wire. Using thicker wire will be useless as the skin depth will be only to a certain amount according to the frequency used. The higher the frequency the thinner the wire should be. We then use multiple thin wires to overcome this problem, either side by side or twisted together.
I mean that (to see if I explain myself better):
If I have 25AWG I can use that wire up to a maximum working frequency of 85kHz (preferably not to reach the maximum) ...... assuming that my smps works at 75kHz ........ I could use 25AWG, but if not had that wire? If I had 23AWG? (which supports 53kHz) what would I do? Is there any possible combination of wires that can be made? The only thing I know is that as I put more wires in parallel, the more current it will support. But how often would it be done?
Thanks again! Each answer that he gives me is enriching for me and surely for those who read this post.
 

Silvio

Member
As discussed already, if the copper wire is thicker then the skin depth for that particular frequency it will not be utilized fully and the center core will be invisible to the current. Using thicker wire than needed will occupy more space on the bobbin. 50 Khz is also a good switching frequency and anything between 20 and 80Khz is good. Ferrite cores tend to give higher power for a given core size as the frequency goes higher. Be careful but try not to exceed 100Khz as core losses tend to get higher. When at higher frequency the flux density needs to be lower due to losses encountered. I found that a frequency between 40 and 80Khz is the best range for Half and full bridge topologies.

Some rules of thumb for you regarding current density.
For an smps working at full current and at 100% duty cycle then the current density will be 3.2 amps per mm^2
For 80% duty then the current density will be 4A per mm^2
For audio purpose from 6 to 8A per mm^2 possibly with a cooling fan blowing at the transformer.

Example. If I am designing a transformer to work in an audio amplifier and my output current is to be 6A. The frequency of oscillation is 60Khz.
So for a frequency of 60Khz according to the table not more than 0.5mm copper wire is to be used.
So now we calculate the cross sectional area of a single wire Area of a circle = Pie x Radius squared so 3.142 x 0.25 x0.25 = 0.196 mm^2
This diameter will give us a current of 0.196 x 6A = 1.17A for each 0.5mm wire used
Now we divide 6A / 1.17 =5.12 wires so we cannot make a partial wire and we have to round off either for 5 or 6 wires. If there is enough space in the transformer bobbin then use 6 wires either side by side or twisted together depending on the fit. We try to cover the length of the bobbin as much as possible leaving enough margin space at the ends. You can also opt for 2 bundles of 3 wires twisted together which will also make 6 wires. You have to see what fits best according to the number of turns needed.
With six wires the current density lowers to about 5A per mm^2

I hope my explanation is clear enough
 
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