Hi all!
I have a part that I got somewhere a while ago, and I am not exactly sure what it is. I think it is an inductor, but there is a wire that goes from one side, all the way through the ferrite core in the center, and connects on the opposite side.
Is this in fact, an inductor?
And what would this wire change, when compared to an inductor without one?
Thanks in advance!
Hi
Yes it is an inducer inductor .
Inductor, not inducer. The joys of autocorrect!
Ok. Thanks for the confirmation. Any idea what the wire through the center does?
Hi
It is very common to use 1 or 1/2 Watt resistors of very high resistance of 10 MOhms or more to wind inductors, and to have a very good "mechanical resistance" and avoid variation in the distance between the coils.
This core can be just a resistor and not a ferrite core.
Given the differences in wire size, somewhat improbable. 
More likely to decrease the "Q" of the choke.
Interesting - its a coil wound on top of a resistor perhaps - the resistor defines the Q of the inductor. The tinned leads imply this is a manufactured item, not homemade.
There are some inductors and chokes with the leads coming out of the core (but not electrically connected to it) for mechanical strength, but they don't look quite like this.
A resistor/inductor combination can be used to prevent a resonant behaviour - for instance analog audio amplifiers typically have an output inductor that's in parallel with a 10 ohm resistor or so - this can be made by winding wire over the resistor.
One reason to have a core that's not magnetically active (ie a resistor) is to prevent the coil "singing" (ie vibrating due to magnetic forces) should the electrical signal match the mechanical resonances of an unsupported coil. This coil could simply be airwound, the wire is thick enough, but if you want to prevent mechanical resonance some sort of former is useful.
Thanks @MarkT
Do you think this inductor would be good for a subwoofer's LC filter?
I suspect that is where it is originally from.
When I do the math for the filter, act like this inductor doesn't have the wire through the center? The calculations are the same as one without?
It doesn't have a wire through the centre - its either open-circuit through the centre, or a resistor.
Without knowing / measuring the inductance there's no useful calculations to be done - if the nature of the core isn't known you can't calculate the inductance.
Oh, ok, got it. How do you measure the inductance? Would I need to measure the inductance and find the nature of the core? Or is just the inductance ok.
With an inductance meter. There is normally one on a good digital voltmeter.
But it will give you the inductance at a specific frequency.
The other way is to inject a signal into it of different frequencies and plot a curve of frequency against response.
The nature of the core determines the shape of the resonance curve you get.
With an oscilloscope? I still don't have one, as they are extremely pricey .
Could I use an online inductance calculator?
No you use a signal generator to generate the frequency and an AC millivoltmeter to measure the response. At these low frequencies a normal DVM would do.
You would have to know the core dielectric constant for any meaningful calculation.
With 15 air-wound turns, you must be joking!
We are talking Megahertz, not Hertz for this component!
Are you confusing this with the Zobel network of the driving amplifier?
Yeah, I was just wondering 
. I didn't think it was, because I have seen several LC filters with the inductors having ~100 wraps, not 15.
And much larger. 
I started a new job once and I was in a meeting and trying to get up-to-speed on the project... They were talking about a "simulator" and I very-seriously asked, "What's this stimulator?" I don't think I mis-heard it, I think I just mis-pronounced it but everybody got a chuckle out of it, including me!
