Inductance of 820 ohm 10w wirewound

"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:96e2baFsu4U1@mid.individual.net...
"Phil Allison"


I'll even give you the formula:

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




.... Phil



Thanks very much.
Click to expand...
 
StrandElectric wrote:
"Trevor Wilson" <trevor@rageaudio.com.au> wrote in message
news:96fdmmFailU3@mid.individual.net...
Phil Allison wrote:
"Trevor Wilson"
StrandElectric wrote:

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,

** 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.


**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.


--
Trevor Wilson
www.rageaudio.com.au
Hi Trevor, I presume you mean setting up a tuned circuit with known
capacitance and seeing what frequency it resonates at?
Click to expand...
**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
 
"Trevor Wilson"
Phil Allison wrote:

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

Usually, much lower value resistors.
Click to expand...
** 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.

The principle is the same however.
Click to expand...
** No it isn't.


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

Read my other posts in this thread.


..... Phil
 
"Trevor Wilson"

All you need to do is:

Measure the resistance.
Measure the total reactance at (say) 100kHz).
Click to expand...
** That second job is not possible.

The Z value will be exactly the same as the resistance.

Try 100MHz instead and then see how a few pF of strays ruins the outcome.



..... Phil
 
"StrandElectric"

Oh dear, back to type. That was a very mild comment from me hardly
requiring such an extreme put down!
Click to expand...
** Listen fuckhead.

**YOU** will not say what you are up to and the same time you BLAME me for
not knowing.

How fucking CRAZY is that ?????

Bet anything what you are doing with that 820 ohm resistor is 100% nuts.
---------------------------------------------------------------------------------

No, there's much I don't know but I know that, and don't mind asking for
opinions,
Click to expand...
** Then like most fuckwits on usenet - you PICK the one YOU like the best
and ignore the correct one or ones.

That is both extradinarily stupid and very bad mannered.




..... Phil
 
"Trevor Wilson" <trevor@rageaudio.com.au> wrote in message
news:96fm90F1k3U3@mid.individual.net...
StrandElectric wrote:
"Trevor Wilson" <trevor@rageaudio.com.au> wrote in message
news:96fdmmFailU3@mid.individual.net...
Phil Allison wrote:
"Trevor Wilson"
StrandElectric wrote:

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,

** 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.


**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.


--
Trevor Wilson
www.rageaudio.com.au
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.
Click to expand...
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.

--
Trevor Wilson
www.rageaudio.com.au
Click to expand...
 
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.
 
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