Can an Inductors value decrease over time or for other reasons? - Page 1
Forum section: electronics / beginners

author: Andy-In_over_my_head
author_rank: Regular Contributor
timestamp: February 05, 2017, 10:01:32 pm
content: I don't think I need to write much more... the Subject is the majority of the question...Thanks!Oh, and by "over time" I mean like years.... not mS and such..

author: retrolefty
author_rank: Super Contributor
timestamp: February 05, 2017, 10:07:21 pm
content: Quote from: Andy-In_over_my_head on February 05, 2017, 10:01:32 pmDecrease in time only if you remove turns on the inductor.

author: Andy-In_over_my_head
author_rank: Regular Contributor
timestamp: February 05, 2017, 10:16:57 pm
content: Decrease in time only if you remove turns on the inductor.Thanks, I love a good (or bad) joke sometimes.... haha.Some metals decay over time. I'm far from educated on that subject.I feel I entered into Pandoras box when I tried to figured this out on my own.

author: Benta
author_rank: Super Contributor
timestamp: February 05, 2017, 10:19:01 pm
content: The answer is yes, but it is extremely rare.One mechanism is remanence (residual magnetization), where an inductor not designed for DC current is subjected to such.This will shift its B-H curve, apparently reducing the inductance.Degaussing can cure this, but the (circuit) root cause should be analyzed.There are other possibilies, eg, core corrosion, but that would be immediately recognizable.BTW, I suppose you mean milliseconds, abbreviated "ms", and not millisiemens, "mS"

author: Andy-In_over_my_head
author_rank: Regular Contributor
timestamp: February 05, 2017, 10:19:43 pm
content: Please let me clarify one thing.... Or 2 things....WITHOUT REMOVING TURNS OR OVERHEATING AND MELTING THE COAT OVER THE COPPER...

author: Andy-In_over_my_head
author_rank: Regular Contributor
timestamp: February 05, 2017, 10:23:16 pm
content: Quote from: Benta on February 05, 2017, 10:19:01 pmIs there a way to tell if the inductor has been designed for AC?I have the luck of a bald man whos been given hair clippers for his birthday....

author: retrolefty
author_rank: Super Contributor
timestamp: February 05, 2017, 10:26:01 pm
content: Quote from: Andy-In_over_my_head on February 05, 2017, 10:23:16 pmAn inductor only works with AC. At DC an inductor is just a resistor of some nominal resistance.

author: Vtile
author_rank: Super Contributor
timestamp: February 05, 2017, 10:30:09 pm
content: Quote from: retrolefty on February 05, 2017, 10:26:01 pmDC inductor can be also solenoid or some other type of electromagnet or a coil in meter movement.

author: Benta
author_rank: Super Contributor
timestamp: February 05, 2017, 10:30:24 pm
content: QuoteNot really.Inductors designed for DC will usually have an air gap in the core, but it's mostly hidden under the windings. Only a destructive inspection will give the answer... and there are also DC specified coils without gap.Frankly, only a datasheet of the inductor will help here.Welcome to the Wonderful World of Magnetics.

author: Benta
author_rank: Super Contributor
timestamp: February 05, 2017, 10:34:43 pm
content: QuoteThat was not the question. Stop muddying the waters, please.QuoteThat was ALSO not the question.

author: Vtile
author_rank: Super Contributor
timestamp: February 05, 2017, 10:39:24 pm
content: Quote from: Benta on February 05, 2017, 10:34:43 pmYou are correct.I must add that I didn't calculate the chokes as a "DC inductor". Rise or fall of the edge =/= DC in my brains.

author: james_s
author_rank: Super Contributor
timestamp: February 05, 2017, 10:51:57 pm
content: I've had parts of the core crumble and fall out, that will cause the value to decrease. It's not very common though unless equipment has been abused.

author: Benta
author_rank: Super Contributor
timestamp: February 05, 2017, 10:53:44 pm
content: One other source of reduced inductance over time is operation at elevated temperature.Some ferrites and iron cores don't like this.Again, it's practically impossible to analyze by just inspecting the part.

author: wraper
author_rank: Unknown
timestamp: February 05, 2017, 11:01:25 pm
content: Quote from: retrolefty on February 05, 2017, 10:26:01 pmInductor "works at DC", say in power rail to block AC ripple. but if High DC current flows, core becomes saturated and inductance drops drastically. So yes, indeed, inductor can be made for DC by avoiding core saturation at high DC current.

author: Benta
author_rank: Super Contributor
timestamp: February 05, 2017, 11:06:39 pm
content: Also didn't read the question. Sigh...

author: CatalinaWOW
author_rank: Super Contributor
timestamp: February 05, 2017, 11:24:03 pm
content: Quote from: retrolefty on February 05, 2017, 10:07:21 pmTrue, but not as silly as it sounds. Insulation failure can lead to shorted turns which removes them.As a direct answer to the OPs question, no, not without something failing (technically that is true for resistors and capacitors also), but there are a couple of failure mechanisms that can occur. Inductors that have no ferromagnetic core components have fewer failure mechanisms. Coils which are low density (translates to thick insulation) have fewer failures. Coils which mechanically restrain the coils from movement have fewer failure mechanisms.

author: Andy-In_over_my_head
author_rank: Regular Contributor
timestamp: February 06, 2017, 04:36:52 am
content: An inductor only works with AC. At DC an inductor is just a resistor of some nominal resistance.Though not my question... I'm glad you said this cause I honestly didn't think of this until you wrote it....Even though I'm only 4 months into this all with an infinite amount to learn (infinite because I'm not sure how much there is to learn yet)I am still very aware of a whole lot more then... at least anyone in my family knows....I don't know... I guess it just makes sense after I melt a couple breadboards....But all the inductors I've played with all have to have alternating current (mosfet or 555 or whatever) to increase the voltage.... so I guess that makes sense...Again, I'm sure there are countless obstacles I haven't encountered... but it's the small statements the bridge gaps for me...So thanks...

author: BravoV
author_rank: Super Contributor
timestamp: February 06, 2017, 04:57:46 am
content: Yes, if the core is deteriorating physically or chemically, like rusting & chipping at this welding transformer.

author: james_s
author_rank: Super Contributor
timestamp: February 06, 2017, 07:15:18 am
content: Holy crap, did he dredge that thing out of the ocean!?

author: Cupcakus
author_rank: Contributor
timestamp: February 06, 2017, 07:22:54 am
content: Looks like it still works, I think that picture alone answers the original question.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 06, 2017, 01:29:10 pm
content: In fact, unequivocally yes!But not usually to a significant degree.In the absence of any quirky weasel conditions, like corrosion or residual magnetization or fault conditions.Ferromagnetic materials age over time. The permeability drops approximately as log(time) since the material was last cooled below the Curie temperature.This effect is more familiar in ferroelectricmaterials: type 2 dielectrics (ceramic capacitors with X7R, Y5P, Z5U, etc. codes). There, aging is very pronounced because the "core" is "ungapped", i.e., the electric field is applied to the dielectric and nothing else. This is why the energy storage capability is one of the worst, among all capacitor types. They are optimized for low impedance under 0V bias conditions, and that's it. (Precisely the same as ferrite beads, which are optimized for high impedance under 0A bias conditions!)Inductors don't normally suffer from aging, because the core is almost always gapped, which reduces losses and improves stability (making the change in permeability less significant). Under carefully controlled conditions (stable temperature and humidity), you might be able to measure this change on a real part. It will be small, less than 1%.Tim