Inductance of 820 ohm 10w wirewound

[StrandElectric]

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.

 

[atec77]

Probably quite manufacturer dependent???

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

 

[Phil Allison]

"StrandElectric"

Can anybody with a good inductance meter, please measure a 10 watt
wirewound resistor of 820ohms and tell me the inductance.

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



..... Phil

 

[StrandElectric]

"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.

 

[Trevor Wilson]

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.

**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.

 

[Phil Allison]

"StrandElectric"

"Phil Allison" "StrandElectric"

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

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

I still neeed that measurement.

** 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.

You are wasting your time.


...... Phil

 

[Phil Allison]

"Trevor Wilson"

**That's because there is no one, correct answer. Some wirewound resistors
are bifilar wound,

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

You need specify which resistor you are using.

** 10W, WW = standard rectangular cement coated resistor.

Better still, you should contact the manufacturer, as he/she will be able
to provide all the data you require.

** If you speak Chinese.

Even betterer, would be for you to measure the inductive reactance of the
resistor,

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

Go on - try !!


..... Phil

 

[StrandElectric]

"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.

You are wasting your time.


..... Phil

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..

 

[StrandElectric]

**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.

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.

 

[StrandElectric]

"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

Agreed Phil!

 

[Phil Allison]

"StrandElectric"

"Phil Allison"
That's a bit hasty Phil,

** No it is not.

as you don't know what I'm trying to do

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

You know nothing twit.



..... Phil

 

[Phil Allison]

"StrandElectric"

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.

** 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]

"Phil Allison"


I'll even give you the formula:

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




..... Phil

 

[Trevor Wilson]

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.

**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.

 

[Trevor Wilson]

"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.

**I said: INDUCTIVE REACTANCE.

Go on - try !!

**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.

 

[StrandElectric]

"StrandElectric"

** No it is not.



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

You know nothing twit.



.... Phil

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.

 

[StrandElectric]

**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.

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

 

[StrandElectric]

"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

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?

 

[StrandElectric]

"Phil Allison"


I'll even give you the formula:

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




.... Phil

Thanks very much.

 

[Trevor Wilson]

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

**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.