------Question for 2324-H-RC Please Put your question below------
Is it okay to expose the inductor to about 3kV if it’s only for microseconds?
The datasheet doesn’t mention a current rating.
Hello @allbrand,
Textbook: At T = 0, all voltage will be applied across the inductor. The current will increase according to tau = L/R.
In practice: The 2324-H-RC is a small part. There a high chance the 3KV will arc before the L/R hammer shorts out the 3 kV.
Please tell us more about your application. Specifically, what is the purpose of the inductor for your project. Is this an RF, filtering, pulse, or other type of application?
Sincerely,
Aaron
Thanks for the response! I need to characterize the breakdown of experimental gallium nitride and silicon carbide diodes under high reverse bias. I’m designing a PCB for an unclamped inductive switching test. The test diode is in parallel with a high voltage commercial MOSFET, with it’s anode attached to ground and the cathode connected to the same node as the MOSFET drain. This pair is in series with an inductor. To achieve the voltage needed, we charge up an inductor with a moderate DC voltage (ex: 30V), the current goes through the series MOSFET. Once the inductor has charged, we suddenly turn off the MOSFET (which takes less than one microsecond). The overvoltage driven by the inductor should trigger breakdown in the test diode.
Inductors aren’t usually sold with voltage ratings, and I understand that I can’t rely on the rating of the film insulated wire because that film is often damaged in inductor winding process.
Do you have advise on how to find inductors that wouldn’t arc, if this one is likely too? Could I just coat any inductor in epoxy, since that has a higher dielectric strength?
The peak voltage (neglecting series resistance) goes as V ~ I √L, where I is the peak current, L is the inductance. I intend to use larger inductors in addition to this one, it’s just that the test has been performed with 1 mH inductance for other diodes that had avalanche breakdown at <1kV.
Breakdown potentials in commercial inductors are often not well-characterized, due (I suspect) to it being bothersome to test and not particularly relevant to most applications.
As a rule, if performance in some dimension is not part of a component’s specification, it’s up to the user to determine suitability for purpose on a part-by-part basis, since if performance is not specified, consistency of such isn’t specified either.
That said, take some time to think about the matter from first principles; the voltage across an inductor is distributed across each winding, so the potential between one and the next is a fraction of the whole (depending on the number of turns) if we consider the potential for breakdown between portions of the winding itself. For an inductor design of the type pictured, the highest stresses are likely to occur where non-adjacent windings are physically proximate, such as where the start and end of winding meet, or where one end is crossed mid-span in the interest of making an inductor that’s convenient to mount horizontally.
The same kind of considerations can apply if one considers a possible fault from a winding to the core to a different winding. The core material itself can present a certain amount of resistivity, and if epoxy-coated before being wound, that coating is likely to provide some insulation value as well. How much exactly? Hard to tell for certain.
There’s also a potential for environmental contamination; at high potentials the presence of conductive schmoo on the surface of an insulator can provide an opportunity for an arc to initiate across the insulation surface.
A varnish-type material has traditionally been used for such purposes, and can serve a dual function of mechanically securing windings against mechanical vibration. Though epoxies vary, they tend to be rather viscous and to the degree that this results in entrained air bubbles or limited penetration into small areas, it can limit the improvement/reliability of the process for electrical insulation purposes.
Bottom line, it’s probably going to be up to you to test/validate whatever solution you settle on. One could certainly try the inductor mentioned; It might work, might not, or might work for a while; insulation breakdown phenomena can be cumulative. If a person wanted to be aggressive about the issue, a possible solution may be to build one’s own inductor by finding a core with a beefy Al value and winding it with a wire material rated for the potential in question. (L=Al*N2)
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A low-viscosity material like varnish is a great idea!
Moving the mid-span wire back to reduce voltage stress shouldn’t be hard. Implementing the inductor with several inductors in series will also reduce the maximum possible voltage between non-adjacent windings in close proximity. I hadn’t considered a fault including the core, but I think varnish will mitigate that risk. Since the breakdown potential will be uncertain even between nominally similar parts, I’ll get extra inductors.
Even if I use a wire with insulating film rated for kilovolts, the winding process will most likely stress the insulation and make tiny cracks. That will reduce the voltage rating by an unknown amount. I’d rather rely on additional coating applied after winding the inductor, instead of trusting the rating for film insulation on wire that hasn’t been forcefully wound.
Cleaning the conductive dust and oils off the insulator surface before applying varnish is great advice, thank you.
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