Wire wound Power Resister reactance to AF

C

Chris W

Guest
I am planing on making a dummy load for an audio amplifier to do some
testing and was wondering if this resister would have a significant
amount of reactance with frequencies in the range of 20 to 20,000hz?
The spec sheet doesn't give any details on that.



http://www.newark.com/vishay-dale/rh0508r000fe02/power-resistor/dp/41K9178

I will be using 8 of them in various configurations of series and
parallel to get 2 4 8 and 16 ohm loads. They do offer a version that is
supposed to have very low reactance but it is hard to find and is about
triple the cost.


--
Chris W
KE5GIX

"Protect your digital freedom and privacy, eliminate DRM,
learn more at http://www.defectivebydesign.org/what_is_drm"

Ham Radio Repeater Database.
http://hrrdb.com
 
If it's a dummy load to stand in for speakers,
why worry about inductive reactance when
speakers have it also?
Click to expand...
Good point.


Why are you trying to substitute a purely
resistive load when the rated "ohms" of a
speaker specifically is inductive reactance.

What brain fart made you think that
8 ohms inductive reactance is the same
as 8 ohms of pure resistance in the first place?
Click to expand...
I don't think that. But since the impedance curve for every speaker is
different, I don't know what else to do and have seen other similar designs.



--
Chris W
KE5GIX

"Protect your digital freedom and privacy, eliminate DRM,
learn more at http://www.defectivebydesign.org/what_is_drm"

Ham Radio Repeater Database.
http://hrrdb.com
 
On May 12, 1:57 pm, Chris W <1qaz...@cox.net> wrote:
I am planing on making a dummy load for an audio amplifier to do some
testing and was wondering if this resister would have a significant
amount of reactance with frequencies in the range of 20 to 20,000hz?
The spec sheet doesn't give any details on that.
Click to expand...
http://www.newark.com/vishay-dale/rh0508r000fe02/power-resistor/dp/41K9178

I will be using 8 of them in various configurations of series and
parallel to get 2 4 8 and 16 ohm loads.  They do offer a version that is
supposed to have very low reactance but it is hard to find and is about
triple the cost.

--
Chris W
KE5GIX
Click to expand...
If it's a dummy load to stand in for speakers,
why worry about inductive reactance when
speakers have it also?

Why are you trying to substitute a purely
resistive load when the rated "ohms" of a
speaker specifically is inductive reactance.

What brain fart made you think that
8 ohms inductive reactance is the same
as 8 ohms of pure resistance in the first place?

And you're a licensed Ham?


I found the DRM information interesting though.

Protect your digital freedom and privacy, eliminate DRM, learn more at

http://www.defectivebydesign.org/what_is_drm
 
On Tue, 12 May 2009 13:22:51 -0700 (PDT), Greegor <Greegor47@gmail.com>
wrote:

On May 12, 1:57 pm, Chris W <1qaz...@cox.net> wrote:
I am planing on making a dummy load for an audio amplifier to do some
testing and was wondering if this resister would have a significant
amount of reactance with frequencies in the range of 20 to 20,000hz?
The spec sheet doesn't give any details on that.

http://www.newark.com/vishay-dale/rh0508r000fe02/power-resistor/dp/41K9178

I will be using 8 of them in various configurations of series and
parallel to get 2 4 8 and 16 ohm loads.  They do offer a version that is
supposed to have very low reactance but it is hard to find and is about
triple the cost.

--
Chris W
KE5GIX

Why are you trying to substitute a purely
resistive load when the rated "ohms" of a
speaker specifically is inductive reactance.
Click to expand...
---
No, it isn't.

The rated 'ohms' of a speaker is its impedance, of which its inductive
reactance (and capacitive reactance) are a part.
---

What brain fart made you think that
8 ohms inductive reactance is the same
as 8 ohms of pure resistance in the first place?

And you're a licensed Ham?
Click to expand...
---
What's the attitude for?

JF
 
On Tue, 12 May 2009 17:24:02 -0500, John Fields
<jfields@austininstruments.com> wrote:

What's the attitude for?
Click to expand...
Massive Ego, compensating for a tiny weenie?
--
 
"Chris W"
I am planing on making a dummy load for an audio amplifier to do some
testing and was wondering if this resister would have a significant amount
of reactance with frequencies in the range of 20 to 20,000hz? The spec
sheet doesn't give any details on that.

http://www.newark.com/vishay-dale/rh0508r000fe02/power-resistor/dp/41K9178
Click to expand...

** Such resistors have very little inductive reactance, when used in values
more than a few ohms.

You can expect their values to remains constant ( +/- 0.1%) over the audio
range and way beyond too.



..... Phil
 
"Greegor"

If it's a dummy load to stand in for speakers,
why worry about inductive reactance when
speakers have it also?


** Yep - practically all loudspeakers have a rising impedance curve at
high frequencies.

With bass drivers the rise begins above 500Hz and with tweeters it begins
above 3 to 5 kHz.


Why are you trying to substitute a purely
resistive load when the rated "ohms" of a
speaker specifically is inductive reactance.

** There you are quite wrong.

The rated impedance for all bass drivers and most other drivers too is at
taken at a frequency where the load impedance IS resistive.

For nearly any bass driver, this frequency is around 250 Hz and the
impedance value is 10 to 25% greater than the DC resistance.


What brain fart made you think that
8 ohms inductive reactance is the same
as 8 ohms of pure resistance in the first place?

** The OP never made any such silly assumption.

And you're a licensed Ham?


** Are you ?


...... Phil
 
On 2009-05-12, Chris W <1qazse4@cox.net> wrote:
I am planing on making a dummy load for an audio amplifier to do some
testing and was wondering if this resister would have a significant
amount of reactance with frequencies in the range of 20 to 20,000hz?
The spec sheet doesn't give any details on that.
Click to expand...
It will have less inductance than a loudspeaker.
 
"Jasen Betts"
Chris W

I am planing on making a dummy load for an audio amplifier to do some
testing and was wondering if this resister would have a significant
amount of reactance with frequencies in the range of 20 to 20,000hz?
The spec sheet doesn't give any details on that.

It will have less inductance than a loudspeaker.
Click to expand...

** Says Jasen B, just like a sick little puppy with three legs

- hobbling along behind the rest of the pack.

Till a truck runs him over .....

Splaattt........



..... Phil
 
"Chris W" <1qazse4@cox.net> wrote in message
news:nEjOl.24228$CN5.3550@newsfe23.iad...
I am planing on making a dummy load for an audio amplifier to do some
testing and was wondering if this resister would have a significant amount
of reactance with frequencies in the range of 20 to 20,000hz? The spec
sheet doesn't give any details on that.



http://www.newark.com/vishay-dale/rh0508r000fe02/power-resistor/dp/41K9178

I will be using 8 of them in various configurations of series and parallel
to get 2 4 8 and 16 ohm loads. They do offer a version that is supposed
to have very low reactance but it is hard to find and is about triple the
cost.


--
Chris W
KE5GIX
Click to expand...
A friend was using some 22ohm versions of those resistors for the same
job. An impedance sweep ...
http://i44.tinypic.com/iggllx.jpg
No problem.
My note say 9.8uH in series with 22ohms. Can't imagine the 8ohms part being
much different. Incidentally, those gimormous 300Watt versions, have only
1uH series inductance!.
 
"john jardine"

http://www.newark.com/vishay-dale/rh0508r000fe02/power-resistor/dp/41K9178

A friend was using some 22ohm versions of those resistors for the same
job. An impedance sweep ...
http://i44.tinypic.com/iggllx.jpg
No problem.
My note say 9.8uH in series with 22ohms.
Click to expand...
** Obviously wrong number for L.


Can't imagine the 8ohms part being much different. Incidentally, those
gimormous
300Watt versions, have only 1uH series inductance!.
Click to expand...

** Proves that a smaller version must have less than 1uH of inductance.


...... Phil
 
On Thu, 14 May 2009 11:56:45 +1000, "Phil Allison" <philallison@tpg.com.au>
wrote:

"john jardine"


http://www.newark.com/vishay-dale/rh0508r000fe02/power-resistor/dp/41K9178

A friend was using some 22ohm versions of those resistors for the same
job. An impedance sweep ...
http://i44.tinypic.com/iggllx.jpg
No problem.
My note say 9.8uH in series with 22ohms.

** Obviously wrong number for L.
Click to expand...
A 50 watt 8 ohm in this style from my stock measures 130 nH @ 10kHz

Can't imagine the 8ohms part being much different. Incidentally, those
gimormous
300Watt versions, have only 1uH series inductance!.


** Proves that a smaller version must have less than 1uH of inductance.
Click to expand...
A 250 watt 4 ohm unit I have measures 850 nH @ 10kHz

..... Phil
Click to expand...
 
"The Phantom"
"Phil Allison"
"john jardine"


http://www.newark.com/vishay-dale/rh0508r000fe02/power-resistor/dp/41K9178

A friend was using some 22ohm versions of those resistors for the same
job. An impedance sweep ...
http://i44.tinypic.com/iggllx.jpg
No problem.
My note say 9.8uH in series with 22ohms.

** Obviously wrong number for L.

A 50 watt 8 ohm in this style from my stock measures 130 nH @ 10kHz
Click to expand...

** OK - what does a 63mm length of wire (ie the distance between the
terminals of that resistor ) measure on your rig ??



...... Phil
 
On Thu, 14 May 2009 13:26:18 +1000, "Phil Allison" <philallison@tpg.com.au>
wrote:

"The Phantom"
"Phil Allison"

"john jardine"


http://www.newark.com/vishay-dale/rh0508r000fe02/power-resistor/dp/41K9178

A friend was using some 22ohm versions of those resistors for the same
job. An impedance sweep ...
http://i44.tinypic.com/iggllx.jpg
No problem.
My note say 9.8uH in series with 22ohms.

** Obviously wrong number for L.

A 50 watt 8 ohm in this style from my stock measures 130 nH @ 10kHz


** OK - what does a 63mm length of wire (ie the distance between the
terminals of that resistor ) measure on your rig ??
Click to expand...
The meter was zeroed with a heavy copper shorting plate, then:

A 63 mm piece of 16 gauge copper wire, pressed down as close to the fixture (to
minimize loop area) as I can get it, measures 21 nH @ 10 kHz.

A 63 mm piece of 30 gauge copper wire, pressed down as close to the fixture as I
can get it, measures 37 nH @ 10 kHz.

When I measured the resistor, I could only get the body of the resistor snug up
against the fixture, not the actual current path, so there was more loop area
than with the wire.

Of course, the OP, using these resistors for his load, would have much more loop
area unless he exercised extreme care. The inductance of the resistor isn't
going to be the main determinant of the inductance of his setup.

..... Phil
Click to expand...
 
"The Phantom" <phantom@aol.com> wrote in message
news:ijqn051jjsq0852gid2r25m8iorgeteakv@4ax.com...
On Thu, 14 May 2009 13:26:18 +1000, "Phil Allison"
philallison@tpg.com.au
wrote:


"The Phantom"
"Phil Allison"

"john jardine"


http://www.newark.com/vishay-dale/rh0508r000fe02/power-resistor/dp/41K9178

A friend was using some 22ohm versions of those resistors for the
same
job. An impedance sweep ...
http://i44.tinypic.com/iggllx.jpg
No problem.
My note say 9.8uH in series with 22ohms.

** Obviously wrong number for L.

A 50 watt 8 ohm in this style from my stock measures 130 nH @ 10kHz


** OK - what does a 63mm length of wire (ie the distance between the
terminals of that resistor ) measure on your rig ??

The meter was zeroed with a heavy copper shorting plate, then:

A 63 mm piece of 16 gauge copper wire, pressed down as close to the
fixture (to
minimize loop area) as I can get it, measures 21 nH @ 10 kHz.

A 63 mm piece of 30 gauge copper wire, pressed down as close to the
fixture as I
can get it, measures 37 nH @ 10 kHz.

When I measured the resistor, I could only get the body of the resistor
snug up
against the fixture, not the actual current path, so there was more loop
area
than with the wire.

Of course, the OP, using these resistors for his load, would have much
more loop
area unless he exercised extreme care. The inductance of the resistor
isn't
going to be the main determinant of the inductance of his setup.




..... Phil
Click to expand...
Interesting!.
Just measured a (to hand) 20ohm. Shows 5uH. Then measured a Welwyn 0.1ohm
and it showed 60nH. Both seem reasonable numbers as I'd assumed all these
types of resistor were wirewounds (observed via the flotsam of experimental
disasters). From the figures you quote, it looks like the construction
varies from maker to maker.
In pursuit of geek science and with a milling machine to hand, I opened up
the Welwyn 20ohm.
A la ...
http://i43.tinypic.com/2d8fi2o.jpg
 
On Thu, 14 May 2009 16:02:12 +0100, "john jardine" <zen177928@zen.co.uk> wrote:

"The Phantom" <phantom@aol.com> wrote in message
news:ijqn051jjsq0852gid2r25m8iorgeteakv@4ax.com...
On Thu, 14 May 2009 13:26:18 +1000, "Phil Allison"
philallison@tpg.com.au
wrote:


"The Phantom"
"Phil Allison"

"john jardine"


http://www.newark.com/vishay-dale/rh0508r000fe02/power-resistor/dp/41K9178

A friend was using some 22ohm versions of those resistors for the
same
job. An impedance sweep ...
http://i44.tinypic.com/iggllx.jpg
No problem.
My note say 9.8uH in series with 22ohms.

** Obviously wrong number for L.

A 50 watt 8 ohm in this style from my stock measures 130 nH @ 10kHz


** OK - what does a 63mm length of wire (ie the distance between the
terminals of that resistor ) measure on your rig ??

The meter was zeroed with a heavy copper shorting plate, then:

A 63 mm piece of 16 gauge copper wire, pressed down as close to the
fixture (to
minimize loop area) as I can get it, measures 21 nH @ 10 kHz.

A 63 mm piece of 30 gauge copper wire, pressed down as close to the
fixture as I
can get it, measures 37 nH @ 10 kHz.

When I measured the resistor, I could only get the body of the resistor
snug up
against the fixture, not the actual current path, so there was more loop
area
than with the wire.

Of course, the OP, using these resistors for his load, would have much
more loop
area unless he exercised extreme care. The inductance of the resistor
isn't
going to be the main determinant of the inductance of his setup.




..... Phil


Interesting!.
Just measured a (to hand) 20ohm. Shows 5uH. Then measured a Welwyn 0.1ohm
and it showed 60nH. Both seem reasonable numbers as I'd assumed all these
types of resistor were wirewounds (observed via the flotsam of experimental
disasters). From the figures you quote, it looks like the construction
varies from maker to maker.
In pursuit of geek science and with a milling machine to hand, I opened up
the Welwyn 20ohm.
A la ...
http://i43.tinypic.com/2d8fi2o.jpg
Click to expand...
You'll notice that on the web page the OP linked:

http://www.newark.com/vishay-dale/rh0508r000fe02/power-resistor/dp/41K9178

under description, it says "Resistor Element Material: Ceramic". I assume that
would account for the low inductance.
 
"john jardine"
Just measured a (to hand) 20ohm. Shows 5uH. Then measured a Welwyn 0.1ohm
and it showed 60nH. Both seem reasonable numbers as I'd assumed all these
types of resistor were wirewounds (observed via the flotsam of
experimental disasters). From the figures you quote, it looks like the
construction varies from maker to maker.
In pursuit of geek science and with a milling machine to hand, I opened up
the Welwyn 20ohm.

http://i43.tinypic.com/2d8fi2o.jpg
Click to expand...

** That pic shows a coil of presumably nichrome wire with about 66 turns on
a 7.5mm diameter and about 50 mm long.

Using this on-line calculator:

http://my.athenet.net/~multiplx/cgi-bin/airind.cgi

L = 4.6uH

A resistor of only 0.1 ohms is likely made with flat strip conductor and far
fewer turns than the example in the pic.

8 turns gives about 60 nH.



........ Phil
 
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