# Re: Choke size?

```Original poster: BunnyKiller <bunnikillr@xxxxxxx>

Hey Steve...

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dont know the formula for the iron core choke ( but somebody here does :) ) but I do know a way to find the reactance resistance (L) ...
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you need a variac and an amp meter and volt meter... connect the variac to the choke as you would a load and turn the variac all the way down, turn on variac, attach voltmeter to variac outputs, btw have the amp meter in series with one of the outputs of the variac... slowly raise the voltage on the variac at about 5 - 10 volts per reading. Take a reading of voltage and amperage go to next 5 or 10 volt level read again....do this until you reach a point where the choke either starts to hum a bit or the amp reading spikes ( core saturation) use Ohms law to find "resitance" of voltage and current for each reading set. Next, use the formula to find inductance from the "resistances" you had collected. Average out all the inductance results and there ya go ...
```a close approximation of the inductance of the choke...

Scot D

Tesla list wrote:

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```Original poster: "Steve Studer" <reddykguy@xxxxxxxxxxx>

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Does anyone know of a formula for calculating the inductance of a choke with an iron core? I have 4 chokes the size of large mot's they have about 30 turns of .250" flat copper wire. I cannot seem to find any formulas except for air core formulas. I would like to use two of these for a DC resonant power supply. I just don't have any idea what the inductance might be.
```Thanks,
Steve

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