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Toroidal inductor wire size

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polashd

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For my banch power supply (variable, IC Lm2576, input 40vdc, output 2v to 37v, Frequency is 52kHz. Current out 20mA to 3A (3.65A max)) I wound an inductor of 330uf. The core is iron powder toroidal T94-26 (OD-23.9mm, ID-14.2mm, H-7.92). I wound 74 turns of 2 strands of wire (Dia- 0.457mm).
I need to know the right wire size (diameter & no. of strands) for the inductor.
 
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If I understand you correctly, you are using strands of wire from hookup wire to make your inductor? If this is so, then you should start over with the correct wire type which is usually called magnet wire, or enameled copper wire. Second, to achieve the inductance you want of 330uH, the T94 material probably is not a good choice based on the inductance index (AL). AL= uH/100 turns.
Using the AL, the number of turns can be computed by the following formula: N = 100 × sqrt ( LμH / AL ), and the inductance can be calculated LμH = AL × N2 / 10000
In using the info from the following link: https://cromwell-intl.com/radio/copper-wire/
It appears to get the inductance you want at that low frequency, you should be using a different powder mix material like the T200 or better yet use the ferrite material FT-xxxx.

The TI datasheet list recommended inductors to use, why not just use one of the suggested parts, or is this a hard to get item for you. Please provide your location info so we can suggest suppliers for your area.
 
For my banch power supply (variable, IC Lm2576, input 40vdc, output 2v to 37v, Frequency is 52kHz. Current out 20mA to 3A (3.65A max)) I wound an inductor of 330uf. The core is iron powder toroidal T94-26 (OD-23.9mm, ID-14.2mm, H-7.92). I wound 74 turns of 2 strands of wire (Dia- 0.457mm).
I need to know the right wire size (diameter & no. of strands) for the inductor.


You need a table similar to this...
https://www.powerstream.com/Wire_Size.htm

The things to consider,
- is there enough space to get all wraps in one layer?
- If multilayer is needed, how is the inductance changed?
- What is the skin depth at 52kHz (will some thickness of the wire not conduct anyhow because of the skin effect)
- What is the ampacity of various wire sizes?
- will the wire act as a heat sink (for cores with lots of Eddie currents).

Assuming an efficient core material, it looks like 23 gauge wire should fit in your inner circumference (barely). Frequency is ok for 100% skin depth and ampacity is ok 3 to 4 amps.

Good luck.
 
If I understand you correctly, you are using strands of wire from hookup wire to make your inductor? If this is so, then you should start over with the correct wire type which is usually called magnet wire, or enameled copper wire. Second, to achieve the inductance you want of 330uH, the T94 material probably is not a good choice based on the inductance index (AL). AL= uH/100 turns.
Using the AL, the number of turns can be computed by the following formula: N = 100 × sqrt ( LμH / AL ), and the inductance can be calculated LμH = AL × N2 / 10000
In using the info from the following link: https://cromwell-intl.com/radio/copper-wire/
It appears to get the inductance you want at that low frequency, you should be using a different powder mix material like the T200 or better yet use the ferrite material FT-xxxx.

The TI datasheet list recommended inductors to use, why not just use one of the suggested parts, or is this a hard to get item for you. Please provide your location info so we can suggest suppliers for your area.

I am guessing that the ferrite core of listed size will not get to 3 amps at only 50kHz - saturation must be considered.
 
If I understand you correctly, you are using strands of wire from hookup wire to make your inductor? If this is so, then you should start over with the correct wire type which is usually called magnet wire, or enameled copper wire. Second, to achieve the inductance you want of 330uH, the T94 material probably is not a good choice
-I've using magnet wire.
-The inductor has been made and used in the circuit. The psu outputs even over 4A (my need is upto 3A) .
The inductor gets little hot(not as hot that I can't touch) at around 3A.
I asked the question to get suggestion for better efficiency (I'm not an expert).
 
If the efficiency is low, and the inductor is heating, you are likely saturating the core, even @ 3A, which goes right back to the wrong size core, or the wrong core material..
 
It outputs even more then 4A. But gets little hot. I need better efficiency.

Most iron powder cores can handle 120C. Check the datasheet. It seems really hot but, the new automotive (engine compartment) cores are rated at 175 to 200C.
 
It outputs even more then 4A. But gets little hot. I need better efficiency.

All iron powder cores are quite lossy,
The Micrometals material -26 has good Al and low cost. But you can select a better material like -52, at slightly higher cost.

Or, if you really want to drop your core losses, use a Kool-mu core from MicroMetals.
 
I need to know whether 2 strands of 0.457mm wire is enough for 52kHz frequency and 3A RMS current or I have to re-wind with more strands of narrower wire?
Can anyone please suggest.
 
I need to know whether 2 strands of 0.457mm wire is enough for 52kHz frequency and 3A RMS current or I have to re-wind with more strands of narrower wire?
Can anyone please suggest.

Yes, that should be fine. Using thicker wire doesn't help at those frequencies because of the skin effect. Using two wires as you suggest is better to get 100% skin depth. Also, you can read this table to see you are using approximately 25 gauge wire. Just make sure it is enamel coated or insulated some how. I am not sure it will fit as many turns as you need, you may not have enough room in that little core. Finally, make sure you cut two pieces, lay them next to each other and wind identically. DO NOT fold the wire and then wind. That would mean the current returning after the fold is flowing in opposite direction as the current flowing to the fold - and canceling out all magnetic effects needed for inductance.

https://www.powerstream.com/Wire_Size.htm
 
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