Inductance of 820 ohm 10w wirewound

Probably quite manufacturer dependent???

Yes , depends on turns and type/length of wire included

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"StrandElectric"

** The inductance is so small it is totally irrelevant compared to the 820 ohms of resistance.

.... Phil

Phil. That depends entirely on the frequency in use, in this case up to 30 Megs!

I still neeed that measurement.

**That's because there is no one, correct answer. Some wirewound resistors are bifilar wound, which exhibits far lower inductance figures than regular wound resistors. You need specify which resistor you are using. Better still, you should contact the manufacturer, as he/she will be able to provide all the data you require. Even betterer, would be for you to measure the inductive reactance of the resistor, as this data is likely to be far more useful to you.

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Trevor Wilson
www.rageaudio.com.au

"StrandElectric"

** The change in impedance is not going to be more than 2 ohms - and might be up or down. ** Try using this.

You should get about 0.3 uH

At 30 MHz, this has a Z of 56 ohms

The new impedance of your 820 ohm resistor is then 822 ohms - in theory.

You are wasting your time.

..... Phil

** Invariably labelled "non inductive" and cost way more.

** 10W, WW = standard rectangular cement coated resistor. ** If you speak Chinese.

** OK - you go get a 10W, 820 or 1000ohm cement resistor and YOU measure its inductance.

Go on - try !!

.... Phil

*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

That's a bit hasty Phil, as you don't know what I'm trying to do and what degree of accuracy I'm aiming at..

Agreed Trevor, but my crude instrument is very poor at measuring L. I was hoping that someone who uses Jaycar 10% R would also have a decent measuring instrument.

Agreed Phil!

"StrandElectric"

** No it is not.

** Not knowing what you are doing IS your problem !!

You know nothing twit.

.... Phil

"StrandElectric"

** Calculate the impedance of 20pF of stray capacitance at 30MHz.

I'll even give you the formula:

Xc = sq. rt ( 2 . pi . F .C )

Imbecile.

.... Phil

"Phil Allison"

I'll even give you the formula:

Xc = 1 / ( 2 . pi . F .C )

.... Phil

**I did not suggest that you try to measure inductance. I said you should measure INDUCTIVE REACTANCE. BIG difference.

All you need to do is:

Measure the resistance. Measure the total reactance at (say) 100kHz). Subtract the resistance and you are left with inductive reactance. With the inductive reactance figure, you will be able to calculate the inductance.

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Trevor Wilson
www.rageaudio.com.au

**I said: INDUCTIVE REACTANCE.

**I've done so on many occasions. Though, I hasten to add, not 820 Ohm resistors. Usually, much lower value resistors. The principle is the same however. I don't see the point in trying to measure inductance directly. As you have already stated, the resistance value will completely swap the inductive reactance value. With rudimentary test equipment, it is simple enough to measure the total reactance and perform the appropriate maths to calculate inductance.

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Trevor Wilson
www.rageaudio.com.au

Oh dear, back to type. That was a very mild comment from me hardly requiring such an extreme put down! The last few posts from you have been really helpful. Now you have degenerated into the same person I remember from long ago. No, there's much I don't know but I know that, and don't mind asking for opinions, including yours, one of which hopefully won't be how to speak/type in a civilised manner to your correspondents, beacuse you have a bit to learn about that.

Hi Trevor, I presume you mean setting up a tuned circuit with known capacitance and seeing what frequency it resonates at?

Thanks, apart from the completely unneceassry last word. I am loath to killfile you because you often post good sense. Could you try not to be so childish and nasty with it?