5 mohm resistor...

J

John Larkin

Guest
https://www.dropbox.com/sh/ha6eyf28soy5p2g/AADnz3bK-yJAoDIIJs9g1LYDa?dl=0

This one is solid metal (manganin?) machined down to trim resistance.

I guess we\'ll fake a Kelvin connection and hope for the best.

--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon
 
L

Lasse Langwadt Christensen

Guest
fredag den 13. maj 2022 kl. 01.50.45 UTC+2 skrev John Larkin:
https://www.dropbox.com/sh/ha6eyf28soy5p2g/AADnz3bK-yJAoDIIJs9g1LYDa?dl=0

This one is solid metal (manganin?) machined down to trim resistance.

I guess we\'ll fake a Kelvin connection and hope for the best.

https://www.analog.com/en/analog-dialogue/articles/optimize-high-current-sensing-accuracy.html
 
P

Piotr Wyderski

Guest
John Larkin wrote:

https://www.dropbox.com/sh/ha6eyf28soy5p2g/AADnz3bK-yJAoDIIJs9g1LYDa?dl=0

This one is solid metal (manganin?) machined down to trim resistance.

I guess we\'ll fake a Kelvin connection and hope for the best.

Why bother if there are ready-made four-terminal devices available at
Mouser? I am happily using its 500uOhm version.

Best regards, Piotr
 
S

server

Guest
On Thu, 12 May 2022 17:36:02 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

fredag den 13. maj 2022 kl. 01.50.45 UTC+2 skrev John Larkin:
https://www.dropbox.com/sh/ha6eyf28soy5p2g/AADnz3bK-yJAoDIIJs9g1LYDa?dl=0

This one is solid metal (manganin?) machined down to trim resistance.

I guess we\'ll fake a Kelvin connection and hope for the best.

https://www.analog.com/en/analog-dialogue/articles/optimize-high-current-sensing-accuracy.html

We do want giant pads in big solid copper pours, without thermals, to
heat sink these resistors.

And we can adjust our scalings for any measured systematic error.

5% accuracy would be OK in this application. We could calibrate each
resistor if we wanted to, but it\'s not worth the hassle in this case.

The resistors each drive an INA281, on the +48 bus. We measure the ca
20 amp current from the power supply, and the current into each of the
8 plugin boards.

https://www.dropbox.com/s/gr57bhafemypi63/P940_box_9.jpg?raw=1




--

Anybody can count to one.

- Robert Widlar
 
S

server

Guest
On Fri, 13 May 2022 10:19:48 +0200, Piotr Wyderski
<bombald@protonmail.com> wrote:

John Larkin wrote:

https://www.dropbox.com/sh/ha6eyf28soy5p2g/AADnz3bK-yJAoDIIJs9g1LYDa?dl=0

This one is solid metal (manganin?) machined down to trim resistance.

I guess we\'ll fake a Kelvin connection and hope for the best.

Why bother if there are ready-made four-terminal devices available at
Mouser? I am happily using its 500uOhm version.

Best regards, Piotr

We have that part in stock. At about 10 amps per resistor, we need a
part with big pads, for good electrical and thermal behavior.

Pseudo-Kelvin contacts to 2-terminal resistors, or arrays of parallel
resistors, seem to work very well.

https://www.dropbox.com/s/83f2bewe6igvor5/P902B6.jpg?raw=1



--

Anybody can count to one.

- Robert Widlar
 
J

John Larkin

Guest
On Fri, 13 May 2022 09:30:46 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Fri, 13 May 2022 10:19:48 +0200, Piotr Wyderski
bombald@protonmail.com> wrote:

John Larkin wrote:

https://www.dropbox.com/sh/ha6eyf28soy5p2g/AADnz3bK-yJAoDIIJs9g1LYDa?dl=0

This one is solid metal (manganin?) machined down to trim resistance.

I guess we\'ll fake a Kelvin connection and hope for the best.

Why bother if there are ready-made four-terminal devices available at
Mouser? I am happily using its 500uOhm version.

Best regards, Piotr


We have that part in stock. At about 10 amps per resistor, we need a
part with big pads, for good electrical and thermal behavior.

Pseudo-Kelvin contacts to 2-terminal resistors, or arrays of parallel
resistors, seem to work very well.

https://www.dropbox.com/s/83f2bewe6igvor5/P902B6.jpg?raw=1

This ain\'t bad:

https://www.dropbox.com/s/c9qprnlur96usox/5.41_mohm.jpg?raw=1

https://www.dropbox.com/s/juqef50e5chvptx/5.07_mohm.jpg?raw=1

It should be even better on a proper PCB with pseudo-Kelvin
between-the-pads connections.


--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon
 
L

Lasse Langwadt Christensen

Guest
lørdag den 14. maj 2022 kl. 01.44.41 UTC+2 skrev John Larkin:
On Fri, 13 May 2022 09:30:46 -0700, jla...@highlandsniptechnology.com
wrote:
On Fri, 13 May 2022 10:19:48 +0200, Piotr Wyderski
bom...@protonmail.com> wrote:

John Larkin wrote:

https://www.dropbox.com/sh/ha6eyf28soy5p2g/AADnz3bK-yJAoDIIJs9g1LYDa?dl=0

This one is solid metal (manganin?) machined down to trim resistance.

I guess we\'ll fake a Kelvin connection and hope for the best.

Why bother if there are ready-made four-terminal devices available at
Mouser? I am happily using its 500uOhm version.

Best regards, Piotr


We have that part in stock. At about 10 amps per resistor, we need a
part with big pads, for good electrical and thermal behavior.

Pseudo-Kelvin contacts to 2-terminal resistors, or arrays of parallel
resistors, seem to work very well.

https://www.dropbox.com/s/83f2bewe6igvor5/P902B6.jpg?raw=1
This ain\'t bad:

https://www.dropbox.com/s/c9qprnlur96usox/5.41_mohm.jpg?raw=1

https://www.dropbox.com/s/juqef50e5chvptx/5.07_mohm.jpg?raw=1

how did you measure it?
 
S

server

Guest
On Sat, 14 May 2022 02:07:21 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

lørdag den 14. maj 2022 kl. 01.44.41 UTC+2 skrev John Larkin:
On Fri, 13 May 2022 09:30:46 -0700, jla...@highlandsniptechnology.com
wrote:
On Fri, 13 May 2022 10:19:48 +0200, Piotr Wyderski
bom...@protonmail.com> wrote:

John Larkin wrote:

https://www.dropbox.com/sh/ha6eyf28soy5p2g/AADnz3bK-yJAoDIIJs9g1LYDa?dl=0

This one is solid metal (manganin?) machined down to trim resistance.

I guess we\'ll fake a Kelvin connection and hope for the best.

Why bother if there are ready-made four-terminal devices available at
Mouser? I am happily using its 500uOhm version.

Best regards, Piotr


We have that part in stock. At about 10 amps per resistor, we need a
part with big pads, for good electrical and thermal behavior.

Pseudo-Kelvin contacts to 2-terminal resistors, or arrays of parallel
resistors, seem to work very well.

https://www.dropbox.com/s/83f2bewe6igvor5/P902B6.jpg?raw=1
This ain\'t bad:

https://www.dropbox.com/s/c9qprnlur96usox/5.41_mohm.jpg?raw=1

https://www.dropbox.com/s/juqef50e5chvptx/5.07_mohm.jpg?raw=1


how did you measure it?

Lascar power supply, short-circuit current 1.27 amps, and my Fluke
benchtop DVM probing the two red dots.

It\'s a 1% resistor, and a pseudo-Kelvin connection should get me close
to the resistor tolerance.

I wonder how they connect to them while they are trimming/machining
the 5m value.



--

Anybody can count to one.

- Robert Widlar
 
L

Lasse Langwadt Christensen

Guest
lørdag den 14. maj 2022 kl. 16.37.13 UTC+2 skrev jla...@highlandsniptechnology.com:
On Sat, 14 May 2022 02:07:21 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

lørdag den 14. maj 2022 kl. 01.44.41 UTC+2 skrev John Larkin:
On Fri, 13 May 2022 09:30:46 -0700, jla...@highlandsniptechnology.com
wrote:
On Fri, 13 May 2022 10:19:48 +0200, Piotr Wyderski
bom...@protonmail.com> wrote:

John Larkin wrote:

https://www.dropbox.com/sh/ha6eyf28soy5p2g/AADnz3bK-yJAoDIIJs9g1LYDa?dl=0

This one is solid metal (manganin?) machined down to trim resistance.

I guess we\'ll fake a Kelvin connection and hope for the best.

Why bother if there are ready-made four-terminal devices available at
Mouser? I am happily using its 500uOhm version.

Best regards, Piotr


We have that part in stock. At about 10 amps per resistor, we need a
part with big pads, for good electrical and thermal behavior.

Pseudo-Kelvin contacts to 2-terminal resistors, or arrays of parallel
resistors, seem to work very well.

https://www.dropbox.com/s/83f2bewe6igvor5/P902B6.jpg?raw=1
This ain\'t bad:

https://www.dropbox.com/s/c9qprnlur96usox/5.41_mohm.jpg?raw=1

https://www.dropbox.com/s/juqef50e5chvptx/5.07_mohm.jpg?raw=1


how did you measure it?
Lascar power supply, short-circuit current 1.27 amps, and my Fluke
benchtop DVM probing the two red dots.

on the second one you could directly get a measurement of the difference
by comparing the voltage on the red dots and on the two \"main\" connections
 
S

server

Guest
On Sat, 14 May 2022 12:26:56 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

lørdag den 14. maj 2022 kl. 16.37.13 UTC+2 skrev jla...@highlandsniptechnology.com:
On Sat, 14 May 2022 02:07:21 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

lørdag den 14. maj 2022 kl. 01.44.41 UTC+2 skrev John Larkin:
On Fri, 13 May 2022 09:30:46 -0700, jla...@highlandsniptechnology.com
wrote:
On Fri, 13 May 2022 10:19:48 +0200, Piotr Wyderski
bom...@protonmail.com> wrote:

John Larkin wrote:

https://www.dropbox.com/sh/ha6eyf28soy5p2g/AADnz3bK-yJAoDIIJs9g1LYDa?dl=0

This one is solid metal (manganin?) machined down to trim resistance.

I guess we\'ll fake a Kelvin connection and hope for the best.

Why bother if there are ready-made four-terminal devices available at
Mouser? I am happily using its 500uOhm version.

Best regards, Piotr


We have that part in stock. At about 10 amps per resistor, we need a
part with big pads, for good electrical and thermal behavior.

Pseudo-Kelvin contacts to 2-terminal resistors, or arrays of parallel
resistors, seem to work very well.

https://www.dropbox.com/s/83f2bewe6igvor5/P902B6.jpg?raw=1
This ain\'t bad:

https://www.dropbox.com/s/c9qprnlur96usox/5.41_mohm.jpg?raw=1

https://www.dropbox.com/s/juqef50e5chvptx/5.07_mohm.jpg?raw=1


how did you measure it?
Lascar power supply, short-circuit current 1.27 amps, and my Fluke
benchtop DVM probing the two red dots.

on the second one you could directly get a measurement of the difference
by comparing the voltage on the red dots and on the two \"main\" connections

You mean to measure where the end wires are soldered?

The \"1 oz\" copper is about 580 uohms per square, so that would add 2
mohms or so.

I could dremel/xacto a bit better and get more Kelvin-ish.



--

Anybody can count to one.

- Robert Widlar
 

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