What approaches to replacing / repairing an inductor

[mikeydee77]

I have a Behringer power amp board with a burnt and smelly inductor... Since it is stereo you can also see an undamaged one on the picture below.

The inductor burnt out becuase a cap was short, so although the amp works OK, I doubt it will ever be reliable as it looks like there will be shorted turns. Since I am a bit bored, I thought I would replace the inductor which according the schem is 21uH but I have no idea what power rating.

My options seem to be:
Use a 22uH inductor - possibly removing a couple of turns, if critical - but since I don't know the power rating do I just go the closest size is there a better way to estimate the power rating?
Could I rewind the inductor, what kind of wire would I be looking to buy? How could I test its inductance

L1 21uH
Wire outer diameter is 1.36mm / 0.053"
~44 turns on a 36mm OD core.

[Jon Snell]

I would count the turns as I remove the wire, cut a new length of Enameled Copper Wire of the same guage and wind a new coil.
Take photos as you unwind as that will remind you where the coil sat on the ferrite.

[nickb]

Rewind it is the easiest and best option. You have the wire diameter, probably 1.25mm copper after allowing for the insulation, and the number of turns. Use polyester insulated grade 2 wire as it has a higher temperature rating.

50g 1.25mm Polyester Enamelled Copper Wire https://www.wires.co.uk/acatalog/TX_0750-2000.html

[mikeydee77]

I am inspired... Will give it a go and we shall see how it goes.

Cheers, Mike

[glebert]

Here is a calculator you can use to get a bit more into the specifics. https://coil32.net/online-calculator...alculator.html

[Helmholtz]

Calculator is useless if the permeability of the ferrite or the AL value of the core are not known.
Using the old core and duplicating the turns number will give correct inductance.

[glebert]

Calculator is useless if the permeability of the ferrite or the AL value of the core are not known.
Using the old core and duplicating the turns number will give correct inductance.

Yeah, that's why I said he would have to reverse calculate based on the dimensions and number of turns of the original inductor. It is only "useless" if someone isn't interested in using it.

[Helmholtz]

Yeah, that's why I said he would have to reverse calculate based on the dimensions and number of turns of the original inductor. It is only "useless" if someone isn't interested in using it.

Sorry, I don't understand.
What's wrong with using the original core and turns number?

As he knows the inductance and turns number, there's no need for reverse calculation. If required, the AL value of the core can be easily found from L/turns number squared.

[glebert]

Sorry, I don't understand.
What's wrong with using the original core and turns number?

As he knows the inductance and turns number, there's no need for reverse calculation. If required, the AL value of the core can be easily found from L/turns number squared.

Hell, I don't know, maybe he would like to use a different wire size, or a different core, or just know how an inductor worked.

[g1]

Not too many places there can be shorted turns on that one. I would say you can pry apart the shorts and add insulation without even needing to change the wire.
Sorry if that is offensive to anyone, but really, there is no overlap of windings there at all.
Maybe it's quicker to rewind if you already have the same wire handy.

[Helmholtz]

Hell, I don't know, maybe he would like to use a different wire size, or a different core, or just know how an inductor worked.

Wire size is determined by the current in the application and shouldn't be decreased. Wire size has no significant influence on inductivity.

[Leo_Gnardo]

Calculator is useless if the permeability of the ferrite or the AL value of the core are not known.
Using the old core and duplicating the turns number will give correct inductance.

Is it possible the original ferrite core's permeability was affected by heat from the roasted copper coil? Other than that, I say, yes rewind on the same core.

[nosaj]

Is it possible the original ferrite core's permeability was affected by heat from the roasted copper coil? Other than that, I say, yes rewind on the same core.

Yes it is possible cores get burned all the time on baluns for antennas.
nosaj

[Delta362]

I'd rewind it. I had one fail (bifilar windings of 362uH each) in a Fender Passport Deluxe PD250 that I ended up rewinding because it was discontinued and I was unable to find a suitable replacement. Mine took two opposite windings of 9ft long each of 19 AWG Copper Magnet Wire MW0156. It took me about an hour to do. Yours looks like it would be relatively easy to rewind. As mentioned above, just count the turns and take your time.

[Helmholtz]

Is it possible the original ferrite core's permeability was affected by heat from the roasted copper coil? Other than that, I say, yes rewind on the same core.

It would have to be cracked. That's very unlikely as ferrites are sintered at extremely high temperatures.
A replacement core should have same size and AL value.