Author Topic: Inductive Current Limiting Educational Demonstrations  (Read 149 times)

Offline ChrisBoden

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Inductive Current Limiting Educational Demonstrations
« on: September 07, 2021, 06:31:07 PM »
Greetings everyone,

I’m working on a serious bit of power supply mojo and am hoping some of the more learned members of the community may be able to offer some insight, and perhaps help smooth some of the potholes in my education.

The goal is to make a current limiting inductor with the following specifications.

Weight - <500lbs
Size - <2’ cube
Rating - 50A Continuous for 1 hour with passive cooling.
Selectable current limiting in 10 steps from 5 to 50A, 5A increments.
0-240VAC Operating voltage

As I see it, there are at least 3 ways to do this.

A - Custom wound multi-tap inductor with a single winding on a large EI core. Paired with a rather chonky 1P-10T switch and we’re off to the races.

B- Continuously variable inductor, likely extricated from a stick welder of some manner. This gives a higher degree of variability for some applications.

C - An array of individual inductors with a switching network (perhaps contactors?). I imagine this would be a collection of ~127mH inductors. This idea would take up the most physical space, but it could be pretty awesome as a demonstration piece (note, all of these would be for educational use).

D - Fancy Solid State Silicon Mojo, Software, and Two Months of swearing at an Arduino.

In the end, I intend to build each one of these (and more if you have interesting ideas?). But to start off, I’d like to build “A”.

I don’t have a need to hand-build this inductor from scratch, and would be perfectly fine having it done by a shop. But before I can start calling around, I first wanted to make certain of my math and try to spot any problems I may be missing. Hence, coming here for peer review before taking the plunge and getting the inductor made.

Am I correct in that all I need is a simple, single coil inductor of say 6AWG wire (50A) with 10 taps spaced at values of 127mH (to give 5A steps in current limiting)?

The nagging thought festering in the back of my mind is that this may function not unlike an autotransformer to an extent. I mean, if I’m running this in a way where I’m loading only a section of the inductor, does it not drive the free end of the coil up to a potentially (heh) very high voltage? Is this something to worry about, or am I just being dumb?
I welcome all thoughts, opinions, and wild conjecture.

Thank you everyone! :)

Kindest regards,

cb

Offline davekni

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Re: Inductive Current Limiting Educational Demonstrations
« Reply #1 on: September 08, 2021, 04:17:18 AM »
Quote
The nagging thought festering in the back of my mind is that this may function not unlike an autotransformer to an extent. I mean, if I’m running this in a way where I’m loading only a section of the inductor, does it not drive the free end of the coil up to a potentially (heh) very high voltage? Is this something to worry about, or am I just being dumb?
Yes, it will be an autotransformer.  Not necessarily a disaster.  Have you estimated the number of turns needed, or at least the turns ratios for each tap?  Do all the turns need to be 6AWG? (Or a bit larger since turns are compact, not spread out as in building wiring.)  With more complex switching, you could use sections in parallel for 50A and in series for lower currents.

Quote
0-240VAC Operating voltage
Current will be proportional to voltage.  Is 25A max fine for 120V?
David Knierim

Offline DashApple

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Re: Inductive Current Limiting Educational Demonstrations
« Reply #2 on: September 13, 2021, 09:45:03 PM »
I had a ballast made that is rated 50A at 230V continuous , Uses a 230mm EI section core but in my case I pack the I section to control the current , Having taps is ideal but makes for a more bulky winding

Target range was 15 - 150mH , Wire is rectangle copper with a total winding resistance just under 0.3 Ohms since I wanted minimal voltage drop over the windings
« Last Edit: September 13, 2021, 09:51:07 PM by DashApple »

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Re: Inductive Current Limiting Educational Demonstrations
« Reply #2 on: September 13, 2021, 09:45:03 PM »

 


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