Inductors for passive EQs...

[ding]

I got the material 77 Amidon pot core and that is working but I have a situation with my meter and need some suggestions. My meter has 20mH, 200mH and 1H positions. My problem is that when I use it in 200mH mode it reads pretty accurate but as soon as I switch it to 1H mode it starts to go all wonky and I can't get an accurate measurement for the 269mH tap. Let me explain, I read the 169mH tap correctly in 200mH mode but as soon as I switch to H mode it gives me a measurement of 0.21H instead of 0.17H. So I am not sure how to measure correctly the 269mH tap since I am getting 0.31H but I feel the turns are correct. Here is a question...What would the taps measure if I connect com to 169mH and the red lead to "269mH?" I know it will not equal out to 100mH because "the relationship between turns and inductance is not linear." Also should I just trust that the inductance from 0.21H to 0.31H is 100mH and deduce that the 0.31H measurement is really 269mH?  Does all of this really matter?  :-\

Thanks,
Alain

 

[AErige]

Hi Alain,

Let's say your inductance has 2 taps after the start :
measurement between start and first tap gives you L1
measurement between first tap and second tap gives you L2
measurement between start and second tap gives you LΣ

you know N1²xAl=L1,N2²xAl=L2,NΣ²xAl=LΣ with NΣ=N1+N2

that gives you LΣ= L1 + L2 + 2 sqrt(L1xL2)

You can keep going by replacing L1 or L2 if you have more taps and want/can only measure small mH values.
But keep in mind that your Δerror is now 4 times the one you could have with only one measurement (gets worse with more taps measurements). I guess you would have to look at your measurement device specifications to see if its worth the extra measurement job.

For big inductance values, its better to put things into perspective and think in % of error and not value . For example, 100mH deviation could seem to be a lot but lets say you measure 4.1H instead of 4H for an inductor its only 2.5% of error. Even the core tolerance for Al can produce more (2% to 20%) or a low winding level which could cause an AL drop of up to 10% (wise to fill the winding window up even if it means bigger wire to do so $$$).

If you are rigorous, you can have tight tolerance (Inductors I build end up usually within 0.5-1% and when I use big Al value it's more around 1-2% by selecting cores).

To determine which L-mode of your L-meter is more precise, try to put one of the tap of your inductor in a resonant filter  you already have (high Q better) with a cap you measured , read F for the peak you got  and calculate L= 1/(4xPi²xF²xC) and compare L value of the tap with what you got with each mode of the L-meter (lets not forget that since inductance measurement can be frequency related, F should be in the ballpark of the frequency used by your l-meter though).

If you already measured your average Al in low L mode  and know that it measured quite right then I would trust the number of turn for the high values.

 

[ereder4]

Better stick this here rather than start a new topic. Is is a bad idea to bolt a gapped pot-core together with a metal fastener? I'm concerned that the ferrite might expand faster than the bolt and crack. Plastic fasteners are included, but I've found them to be basically worthless.

I've had some inductors sitting with metal bolts for over a year, no issues yet, but I'm worried if they're cooking in a rack full of hot tube equipment.

I have also run a small bead of superglue along the seam of the two halves, this seems to help stability quite a bit.

 

[snaper]

Hi Guys,

Was just surfing on the TME website, and fount these inductors...
Are these OK for (for example) a GPultec?

http://www.tme.eu/hu/details/5900-104-rc/axialis-tht-induktivitasok/bourns/#
http://www.tme.eu/hu/details/coil0810-22/vertikalis-szerelesu-tht-induktivitasok/ferrocore/#
http://www.tme.eu/hu/details/rl622-104k-rc/vertikalis-szerelesu-tht-induktivitasok/bourns/#
http://www.tme.eu/hu/details/rl622-473k-rc/vertikalis-szerelesu-tht-induktivitasok/bourns/#

 

[gyraf]

Some of them will probably work - the important parameters are inductance and resistance.

Keep resistance as low as possible for highest maximum-Q (if you need that, I don't)

Jakob E.

 

[snaper]

Some of them will probably work - the important parameters are inductance and resistance.

Keep resistance as low as possible for highest maximum-Q (if you need that, I don't)

Jakob E.

Thanks, god to know.
Just  bought a set from PCBGrinder