Ferrite Inductor Tolerance
in [Design]
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From: Joerg on 13 Jun 2010 11:02 Ian Bell wrote: > On 12/06/10 23:00, Joerg wrote: >> Ian Bell wrote: >>> On 12/06/10 16:07, John Larkin wrote: >>>> On Sat, 12 Jun 2010 10:22:59 +0100, Ian Bell<ruffrecords(a)yahoo.com> >>>> wrote: >>>> >>>>> 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 >>>> >>>> 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%. >>> >> >> 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 >> > > 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. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Ian Bell on 13 Jun 2010 13:32 On 13/06/10 15:28, Tim Williams wrote: > "Ian Bell"<ruffrecords(a)yahoo.com> wrote in message > news:hv2ok0$3q3$1(a)localhost.localdomain... >> 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 > 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
From: Ian Bell on 13 Jun 2010 13:40 On 13/06/10 16:02, Joerg wrote: > Ian Bell wrote: >> On 12/06/10 23:00, Joerg wrote: >>> Ian Bell wrote: >>>> On 12/06/10 16:07, John Larkin wrote: >>>>> On Sat, 12 Jun 2010 10:22:59 +0100, Ian Bell<ruffrecords(a)yahoo.com> >>>>> wrote: >>>>> >>>>>> 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 >>>>> >>>>> 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%. >>>> >>> >>> 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 >>> >> >> 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. > 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
From: John Larkin on 13 Jun 2010 14:10 On Sun, 13 Jun 2010 18:40:25 +0100, Ian Bell <ruffrecords(a)yahoo.com> wrote: >On 13/06/10 16:02, Joerg wrote: >> Ian Bell wrote: >>> On 12/06/10 23:00, Joerg wrote: >>>> Ian Bell wrote: >>>>> On 12/06/10 16:07, John Larkin wrote: >>>>>> On Sat, 12 Jun 2010 10:22:59 +0100, Ian Bell<ruffrecords(a)yahoo.com> >>>>>> wrote: >>>>>> >>>>>>> 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 >>>>>> >>>>>> 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%. >>>>> >>>> >>>> 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 >>>> >>> >>> 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. >> > >Thanks for the input but I think you have misunderstood me. I already >have a source of suitable inductors. Then why don't you ask them? Of course, one problem with inductors is that L tends to vary with frequency, so what they measure and what you measure may not be the same. John
From: John Larkin on 13 Jun 2010 14:24
On Sun, 13 Jun 2010 09:28:21 -0500, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"Ian Bell" <ruffrecords(a)yahoo.com> wrote in message >news:hv2ok0$3q3$1(a)localhost.localdomain... >> 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... I've done audio-range, fractional-H filter inductors as BIG pot cores, with decent Qs. Never again. I don't think I'd do a signal-processing LC filter below maybe 1 MHz nowadays. John |