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Ferrite Inductor Tolerance

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Ian Bell

Jan 1, 1970
0
When winding modest inductors of a few hundred milliHenries on a ferrite
core, given Al and a number of turns, what is the typical tolerance on
the actual value of inductance when these are made in quantity?

Cheers

Ian
 
A

amdx

Jan 1, 1970
0
Ian Bell said:
When winding modest inductors of a few hundred milliHenries on a ferrite
core, given Al and a number of turns, what is the typical tolerance on the
actual value of inductance when these are made in quantity?

Cheers

Ian

I don't know, but given the brand, size, form and material, the
manufacturers site
would probably have that info. I have Ferroxcube and Amidon catalogs if
you are using those let me know.
Mike
 
I

Ian Bell

Jan 1, 1970
0
I don't know, but given the brand, size, form and material, the
manufacturers site
would probably have that info. I have Ferroxcube and Amidon catalogs if
you are using those let me know.
Mike


The ones I am thinking of are the VTB series by Carnhill.

Cheers

Ian
 
J

Joerg

Jan 1, 1970
0
Ian said:
When winding modest inductors of a few hundred milliHenries on a ferrite
core, given Al and a number of turns, what is the typical tolerance on
the actual value of inductance when these are made in quantity?

That depends on how much you are willing to pay and whether it is a
higher power core. 5% to 20% are common tolerance values, sometimes with
inductors from China I spec 30% when it has to be really low cost.
 
I

Ian Bell

Jan 1, 1970
0
An ungapped ferrite core could be all over the place. 25% wouldn't
surprise me. They will vary with temperature, too. You can buy gapped
pot cores in tolerances around 2-5%, I think. Or use a pot core with a
slug adjuster if you need 1% or better. See the datasheets.

Powder-type cores can be bought with better tolerances.

The people who wind inductors commercially get the exact number of
turns every time.

John


It seems to me there are quite a few factors that could affect the
actual inductance achieved and perhaps the least of them is the accuracy
in counting the number of turns. I would expect there to be some
tolerance in the Al value of the ferrite, that its exact dimensions
would have an effect along with how neatly or otherwise the turns are
wound. I have absolutely no idea if these are the major factors nor of
the likely size of the actual major factors affecting the actual
inductance. I am just trying to get a feel for the likely tolerance of
ready made inductors.

The reason I ask is am am designing some passive audio filters and I
know exactly what tolerance of resistance and capacitance I can obtain
but not a clue about inductance. It is no good me using 1% capacitors
and resistors if inductors normally fail to achieve 5%.

Cheers

Ian
 
J

Joerg

Jan 1, 1970
0
Ian said:
It seems to me there are quite a few factors that could affect the
actual inductance achieved and perhaps the least of them is the accuracy
in counting the number of turns. I would expect there to be some
tolerance in the Al value of the ferrite, that its exact dimensions
would have an effect along with how neatly or otherwise the turns are
wound. I have absolutely no idea if these are the major factors nor of
the likely size of the actual major factors affecting the actual
inductance. I am just trying to get a feel for the likely tolerance of
ready made inductors.

The reason I ask is am am designing some passive audio filters and I
know exactly what tolerance of resistance and capacitance I can obtain
but not a clue about inductance. It is no good me using 1% capacitors
and resistors if inductors normally fail to achieve 5%.

You can get 5% catalog inductors from Delevan, Miller, TDK and several
others. If it needs to be more precise then you'd be off to boutique
lines, meaning $$$.

Example:

http://www.delevan.com/seriesPDFs/1782.pdf

But sit down before looking at prices for the F grade (1%), they can run
well north of $10 a piece in small qties and several months leadtime.
Hardly anyone does this stuff for audio anymore since DSPs became cheap.
Last time I designed an analog wideband audio phase shifter was ...
<scratching head> ... oh, about 20 years ago :)

If it absolutely has to be analog there's opamp gyrators, maybe that
could work? Sure would be cheaper.
 
N

Nico Coesel

Jan 1, 1970
0
Ian Bell said:
wound. I have absolutely no idea if these are the major factors nor of
the likely size of the actual major factors affecting the actual
inductance. I am just trying to get a feel for the likely tolerance of
ready made inductors.

The reason I ask is am am designing some passive audio filters and I
know exactly what tolerance of resistance and capacitance I can obtain
but not a clue about inductance. It is no good me using 1% capacitors
and resistors if inductors normally fail to achieve 5%.

I'd expect more like tens of percents. Keep in mind that the
inductance also varies with current. Thats why you always see air core
inductors in loudspeaker filters. If you need accurate inductors you
better to use a gyrator circuit.

http://sound.westhost.com/dwopa.htm#inductor
 
A

Archimedes' Lever

Jan 1, 1970
0
You can get 5% catalog inductors from Delevan, Miller, TDK and several
others. If it needs to be more precise then you'd be off to boutique
lines, meaning $$$.


Nobody needs to be that precise. Nobody here anyway.
 
J

Joerg

Jan 1, 1970
0
Archimedes' Lever said:
Nobody needs to be that precise. Nobody here anyway.


Ahm, I have been. But that was in the RF world and done with active
laser trim. Sometimes down to 0.25%.
 
A

Archimedes' Lever

Jan 1, 1970
0
Ahm, I have been. But that was in the RF world and done with active
laser trim. Sometimes down to 0.25%.


Laser trim of an inductor? Small form factor maybe. Anything in the
power realm has no need of that level of precision and there are few
ferrite formulations that can hold any such tolerance, even merely
sitting on the shelf.
 
J

Joerg

Jan 1, 1970
0
Archimedes' Lever said:
Laser trim of an inductor? Small form factor maybe. Anything in the
power realm has no need of that level of precision and there are few
ferrite formulations that can hold any such tolerance, even merely
sitting on the shelf.


Well, Ian wrote that his app isn't power but precision audio. Different
thing.
 
J

Joerg

Jan 1, 1970
0
John said:
Active filters make more sense at audio frequencies. Inductors are big
and expensive and have rotten Qs down there, so you have to do a
predistorted filter design if you want any frequency response
accuracy. PITA.

I did get nice results with discarded 88mH toroid inductors from Missy
Bell though, built lots of filter with those back at college. Until one
sunny day I looked in the box ... all gone :-(

But you are right, if there is power available active is the way to go.
Or DSP :)
 
J

Joerg

Jan 1, 1970
0
John said:
We buy 2% inductors and 1% capacitors to make LC clock oscillators in
our digital delay generators.

Once you get above 100uH though prices can go through the roof.
 
B

BlindBaby

Jan 1, 1970
0
Once you get above 100uH though prices can go through the roof.

Just the same... once you get up there, tight tolerance is of little
importance. 5% is fine.

You want precision? You buy 500 cheap, 5% coils, and use in-house
matching and culling techniques to get the matched set that you desire at
a far far cheaper overall cost.
 
T

Tim Williams

Jan 1, 1970
0
Ian Bell said:
Those devices seem to be in the sub milliHenry range, the one I need are
in the humfreds of milliHenries.

Fractional henry? In 1% sizes? With Q more than 1? Ya, they call those
op-amps. You don't have any choice now...

Tim
 
J

Joerg

Jan 1, 1970
0
BlindBaby said:
Just the same... once you get up there, tight tolerance is of little
importance. 5% is fine.

How do you deduce that it's of little importance? Got a spy camera in
every enterprise, worldwide? :)

You want precision? You buy 500 cheap, 5% coils, and use in-house
matching and culling techniques to get the matched set that you desire at
a far far cheaper overall cost.


Environmentally and financially not very friendly unless you can sell
the excess for a reasonable price. Also, I found that when inductors
were at minus 15%-20% then, usually, the whole series was. In fact
sometimes over months. So no dice there, I would not sign the ECO for that.
 
J

Joerg

Jan 1, 1970
0
Ian said:
Those devices seem to be in the sub milliHenry range, the one I need are
in the humfreds of milliHenries.

Then you'll likely have to live with 5%, for example:

http://www.yuden.co.jp/us/product/pdf/elhl_e.pdf

There are other ideas but you'd have to let us know about the nature of
the product. Things such as yearly qty, why it must be passive, how many
inductors per unit, whether end-test trimming is ok, et cetera.
Otehrwise it'll all be speculation.
 
I

Ian Bell

Jan 1, 1970
0
Fractional henry? In 1% sizes? With Q more than 1? Ya, they call those
op-amps. You don't have any choice now...

Tim

Fractional Henry, yes. I never said I wanted 1%, I just wanted to know
what is the likely tolerance. Q or more than one is easy with inductors
even of several Henries.

Cheers

Ian
 
I

Ian Bell

Jan 1, 1970
0
Then you'll likely have to live with 5%, for example:

http://www.yuden.co.jp/us/product/pdf/elhl_e.pdf

There are other ideas but you'd have to let us know about the nature of
the product. Things such as yearly qty, why it must be passive, how many
inductors per unit, whether end-test trimming is ok, et cetera.
Otehrwise it'll all be speculation.

Thanks for the input but I think you have misunderstood me. I already
have a source of suitable inductors. What I am interested in is the
factors that govern the tolerance of a production inductor (as it comes
off the line and before any selection process) and what the resultant
overall tolerance is likely to be for inductors around 1H. I am not
asking for help designing a product or in selecting parts.

Cheers

Ian
 
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