Re: Inductance of 820 ohm 10w wirewound: OOPS

Jun 22, 2011 1 Replies



>> Can anybody with a good inductance meter, please measure a 10 watt
>> wirewound resistor of 820oms and tell me the inductance. I am getting
>> wildly different figures from various sources.
>>
>> Thanks all.
> *if* it's a straight coil of wire with an air core, then Wheelers formula
> gives a reasonable result for inductance.
>
> L (uH) = (r*r + n*n) / (9r + 10l)
>
> Dimensions all in inches.
> r = coil radius
> n = no of turns
> l = coil cylinder length
>
>

Sorry, correct equation:



L (uH) = (r*r*n*n) / (9r + 10l)

"Bruce Varley"

** That formula is not gonna be accurate since it assumes the turns are close packed - which they cannot be in a WW resistor.

So the number you get will be high by a factor of maybe 2 or 3.

.... Phil

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