Inductor in very big values (500mH, NOT for crossover)

[gain-wire]

I didn't bother to do a search honestly, because I figured no one would have the answers to both of my questions.
First, I am wondering why it is that it's so difficult to find inductors or chokes over a couple mH anywhere. It seems as though no one makes these. I need something in the area of 200mH to 1H for an LC-based audio filter.

Second, have any of you compared the quality of the budget-friendly LCR meters available on ebay? I want to know why they are so cheap while classic LCR bridges from HP, Fluke and other notable companies remain over 200$.

thank you for your help,

gain-wire

[sawreyrw]

I suggest you use an active filter and eliminate the need for the large inductor.

[bear]

The way to get inductors of this size is to use some sort of core, laminated core, like a transformer. You size the core and type and gapped or not depending upon the application. They are sold. The Japanese use them all the time. UTC made them for audio, others did and may still.

The primary and secondary of an ordinary audio transformer can be used as well - depending again on the DC or lack thereof...

The cheap imported "digital meters" basically are oscillators that then coordinate the resulting frequency with an inductance value. The more expensive meters or bridges can deal with other parameters (such as "Q") as
well as measuring at different frequencies and power levels...

I'd look for a nice bridge.

_-_-bear

[akis]

Hi

I also want a 500mH coil for an audio circuit. I tried winding my own on a old AM/FM radio ferrite rod which is 12 cm length and 1cm diameter. After I wound almost the 11cm I measured 6.87mH... Almost 80 times less than what I need.

I looked in Farnell and they have a ready made 500mH - not sure if it will work
BOURNS JW MILLER|70F501AF-RC|INDUCTOR, CHOKE | Farnell United Kingdom - but I will get it anyway.

Ideally I would like some sort of heavy-duty ferrite cores where I could wind my own coils to reach 500mH without needing millions of turns. Do you know if any retailers have them?

[woody]

About the cheap LCR meters on ebay. The cheap one I bought sure is handy but
the inductance readings are about 10 to 20% off.

[infinia]

I also want a 500mH coil for an audio circuit. I tried winding my own on a old AM/FM radio ferrite rod which is 12 cm length and 1cm diameter. After I wound almost the 11cm I measured 6.87mH... Almost 80 times less than what I need.

a ferrite bar has a very large gap in the magnetic path, so the Al value is low.
get a core catalog 1st and then you will find non-gapped toroids or pot cores or other magnetic stuctures and materials that will give reasonable turns. You must check for the desired Q and also make sure it will meet any linearity targets (ie saturation) over the DC and AC signals present, steady state or under transients from your application.

[DF96]

Typical ferrite rod inductances will be a few hundred uH for MW and a few mH for LW, depending on how many turns are used. For 500mH you need a ferrite pot core.

[akis]

I just discovered farnell have the RM10 ferrite pot and bobbins and have ordered a couple to play with.

[abraxalito]

For an audio circuit, you might be able to get away with a synthetic inductor, otherwise known as a gyrator. With RM10 you'll likely need around 180 turns to reach a value of 500mH as the AL value I found is 16uH/N^2.

[mikey_audiogeek]

Originally Posted by gain-wire

I didn't bother to do a search honestly, because I figured no one would have the answers to both of my questions.
First, I am wondering why it is that it's so difficult to find inductors or chokes over a couple mH anywhere. It seems as though no one makes these. I need something in the area of 200mH to 1H for an LC-based audio filter.

Second, have any of you compared the quality of the budget-friendly LCR meters available on ebay? I want to know why they are so cheap while classic LCR bridges from HP, Fluke and other notable companies remain over 200$.

thank you for your help,

gain-wire

Audio Transformers By Cinemag Inc.