# Inductance of 820 ohm 10w wirewound

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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.

Re: Inductance of 820 ohm 10w wirewound

Probably quite manufacturer dependent???

Re: Inductance of 820 ohm 10w wirewound

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

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Re: Inductance of 820 ohm 10w wirewound

"StrandElectric"

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

....  Phil

Re: Inductance of 820 ohm 10w wirewound

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

I still neeed that measurement.

Re: Inductance of 820 ohm 10w wirewound

"StrandElectric"

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

** Try using this.

http://www.daycounter.com/Calculators/Air-Core-Inductor-Calculator.phtml

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.

.....  Phil

Re: Inductance of 820 ohm 10w wirewound

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..

Re: Inductance of 820 ohm 10w wirewound

"StrandElectric"

** No it is not.

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

You know nothing twit.

....  Phil

Re: Inductance of 820 ohm 10w wirewound

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

Re: Inductance of 820 ohm 10w wirewound

**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.

--
Trevor Wilson
www.rageaudio.com.au

Re: Inductance of 820 ohm 10w wirewound

"Trevor Wilson"

**  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

Re: Inductance of 820 ohm 10w wirewound

Agreed Phil!

Re: Inductance of 820 ohm 10w wirewound

**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.

--
Trevor Wilson
www.rageaudio.com.au

Re: Inductance of 820 ohm 10w wirewound

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

Re: Inductance of 820 ohm 10w wirewound

**No. You are simply measuring the inductive reactance. All you require is a
signal source, a high freqency millivoltmeter, a known non-inductive
resistor (or resistors) and a pocket calculator.

You are over-thinking the whole thing. As Phil has already stated, trying to
measure inductance, with a resistor of such a value is fraught with
difficulty.

--
Trevor Wilson
www.rageaudio.com.au

Re: Inductance of 820 ohm 10w wirewound

Yes, understood. Certainly this ancient brain now gets it that R swamps the
L and the C.  Unfortunately (because I had much to learn from him) Phil's
nasty childish ways and foul language have now caused me to block him, so I
won't see any of his wisdom.

Re: Inductance of 820 ohm 10w wirewound
I took a hammer to a 820 Ohm 7 Watt wire wound resistor
http://www.flickr.com/photos/nowyouseeitall/5865323071/in/photostream

This damaged the wire in the process, but it allowed me
to measure the diameter to be about 0.04mm.

The end caps are like shorted turns which will
reduce the inductance, which is probably of the
order of 1 microHenry, and completely swamped
by the resistance.

HTH, G.

Re: Inductance of 820 ohm 10w wirewound

"Trevor Wilson"

**  Weeeeellllll  -  that is what I am asking you to try  !!!

** That is the whole point.

The nature of the "coil" is much the same over a wide range of resistance
values.

As is the turn to turn capacitance.

**  No it isn't.

** You have not tried to do it and are still making silly assumptions.

....  Phil

Re: Inductance of 820 ohm 10w wirewound

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.

Re: Inductance of 820 ohm 10w wirewound

"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