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Old 22nd November 2009, 12:27 PM   #1
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Join Date: Oct 2008
Post Litz Wire Selection

Hi All.


I need some help selecting the proper LITZ wire, before I buy it. for my SMPS.

Details.

CORE: ETD59

FREQUENCY: 125KHZ

OUTPUTS:
SEC-1 85VAC 10A
SEC-2 85VAC 10A

SEC-3 20VAC 1A
SEC-4 20VAC 1A

SEC-5 16VAC 1A

INPUT VOLTAGE:220v~ (360vdc)


I saw one wire at e-bay litz wire 10/44, idont understant what is the 10/44.

Anyway any help with selecting the proper wire is more than appreciated.

Thanks...
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Old 25th November 2009, 05:31 PM   #2
Gopher is offline Gopher  United Kingdom
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I think the first number (10) is the American Wire Gauge and the second number is the number of insulated strands.
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Old 25th November 2009, 09:28 PM   #3
TechGuy is offline TechGuy  United States
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Location: Connecticut
I found this chart useful for wire gauge vs frequency:
American Wire Gauge table and AWG Electrical Current Load Limits with skin depth frequencies

Here is a Skin effect Calculator:
TRANSFORMERS

At 125 Khz you need a wire diameter less than 26 gauge to cover 100% of a solid conductor. Of course heavier gauge wire will work, but you will have derate the current capacity.

10/44 means 10 parallel wires at 44 gauge. Which is probably too small for your output (16V @1A) since 40 gauge wire can only transport about 90 ma (44 is even lower).

Another option is to wind your transformer using a several parallel enamel magnetic wires. A parallel set of two 28 gauge enamel magnetic wire should provide sufficient current capacity for your 20V and 16V outputs. For the 85V@10A, you need about 8 strands of 28 gauge wire. Generally I find I can only wind up to five parallel strains before its difficult to keep them flat and even (important when you transformer has multiple layers. You will probably need to wind two sets of 4 strand per layer to get all 8.

You may be able to use4 strands of 24 gauge, but I can't find the equation or a skin effect calc you will provide the max. recommend current capacity for a given wire gauge and frequency. A 24 gauge copper wire can transport about 3.5 amps @ 68 Khz. My guess is that switching at 125 Khz would reduce the current capacity by about 20%. 4 * 2.8A = 11.2 Amps.

FWIW: I would ditch the 16 V winding and use a simple switching regulator to provide the 16V output. This would make regulation easier. Its difficult to have good regulation with multiple outputs. I would even suggest two outputs 1 at 85V and the other at 24V and use two adjustable simple switchers to output 16V and 20V for tighter voltage regulation. This would greatly simply your transformer design.

FYR: http://www.national.com/ds/LM/LM2576.pdf 3A-Step-down regulator.
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Old 28th November 2009, 09:22 PM   #4
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Default Tech guy

Please note that the 10/44 LITZ wire is 30AWG outer diameter!!


Do you think if i get 20/44 will do the JOB??????


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Old 2nd December 2009, 10:15 PM   #5
TechGuy is offline TechGuy  United States
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Quote:
Originally Posted by microsim444 View Post
Please note that the 10/44 LITZ wire is 30AWG outer diameter!!

Do you think if i get 20/44 will do the JOB??????

Definately not for the 10A. if it was 20/40 (40 gauge) it would carry only 90ma*20 or 1.8 Amps. I don't know what the current capacity of 44 gauge wire but I bet is considerable less than 90 ma. The outer thickness is meaning less All that matters is how much copper is available to transport current. Litz 44 is used for very high frequency ( > 1 Mhz) switching. You don't need it, since your only switching at 125 Khz.

Why don't you read my entire earlier post and use my recommendation.
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Old 2nd December 2009, 10:19 PM   #6
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Default Design

I have already submitted my schematic and transformer specs, to the manufacturer, and its almost finished, so I am no longer worried about it any more, I am in the PCB design process, looking for a company who could do it.

its designed to deliver +-100VDC 10AM, 10AMP at full load!!

Its costly since its the first!
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