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high current inductors from copper tubing?
high current inductors from copper tubing?
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Old 17th October 2009, 08:21 PM   #1
star882 is offline star882  United States
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Default high current inductors from copper tubing?

For high current power supply circuits like a fast charger for an EV, could inductors be made by coiling copper tubing? It is cheap, commonly available, and low resistance. They can be cooled by pumping a nonconductive fluid like mineral oil or even air through them and their cross section makes more efficient use of material after accounting for skin effect. They can be painted if insulation is required.

Would the amount of tubing needed to get useful inductances be impractical? What would be the current rating of different sizes of tubing?

For example, a homemade EV charger contains two 150uH, 50A inductors. They cost about $27 each. How many feet of tubing at what minimum size would be needed to make equivalent inductors and how much cheaper would they be? Assume overall size is of little concern, like if the charger is designed to be installed in a garage.
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Old 17th October 2009, 09:16 PM   #2
Andrew Eckhardt is offline Andrew Eckhardt  United States
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Fluid cooled and tubular coils don't make much sense unless you are dealing with extremely high power (more than a 200A residential service provides) or RF... or maybe you'd be looking for very high power density, but you said you don't care about that. The whole idea of green transportation means that high efficiency figures heavily into the deal across the board, meaning that you'd seek to minimize loss before giving up and simply increasing dissipation capability. $27 bucks for single quantity parts to build a DIY electric car charger seems well in-range, not knowing anything else about your project.

Last edited by Andrew Eckhardt; 17th October 2009 at 09:19 PM.
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Old 17th October 2009, 09:35 PM   #3
star882 is offline star882  United States
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20' of 1/4" tubing only costs $12 at Lowe's. I think it would handle 50A just fine with just passive cooling, but how much of that tubing would be needed to make a 150uH inductor?
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Old 17th October 2009, 09:41 PM   #4
Andrew Eckhardt is offline Andrew Eckhardt  United States
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Far less than 20ft. (I take that back) Assuming you're winding an air core solenoid, the formulas are available via google. The length required will depend on the geometry of your choosing.

Last edited by Andrew Eckhardt; 17th October 2009 at 09:43 PM.
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Old 17th October 2009, 09:48 PM   #5
Conrad Hoffman is offline Conrad Hoffman  United States
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Tubing makes sense for RF, but my guess is your frequency isn't high enough for it to be a good choice. You might be better off with plain wire or maybe heavy litz wire optimized for the frequency in use, plus an *air gapped* core to keep the efficiency super high.
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Old 17th October 2009, 09:59 PM   #6
PB2 is online now PB2  United States
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Hi Star,

Are the ones that your looking at air core?
I think your talking about a lot of turns for 150 uH air core.

Is the schematic for this design online? I'm curious to take a look at it.

Last edited by PB2; 17th October 2009 at 10:01 PM.
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Old 17th October 2009, 10:10 PM   #7
rdf is offline rdf  Canada
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Quote:
Originally Posted by star882 View Post
For high current power supply circuits like a fast charger for an EV, could inductors be made by coiling copper tubing?
Standard practice in AM tower matching and phasing networks.
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Old 17th October 2009, 10:16 PM   #8
star882 is offline star882  United States
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It's not my design but you can find it at DIY Open Source EV Charger - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com .

I'm thinking air core as nothing special would be needed, but other materials can be used if they are easily available to the average DIYer.

And what would the current rating be for 1/4" tubing under passive cooling?
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Old 17th October 2009, 10:18 PM   #9
PB2 is online now PB2  United States
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This .pdf doc from the ARRL might help, but notice that the air core coils are around 10 to 20 uH:
www.arrl.org/tis/info/pdf/9708033.pdf
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Old 17th October 2009, 10:20 PM   #10
infinia is offline infinia  United States
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I would look at copper braid and powered iron cores (distributed gapped iron) depending on core choice and frequency, the cores losses could rival the Cu loss.
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