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Re: Out-of-tolerance zero ohm resistors

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  In Israel, the income tax is 105%.

Re: Out-of-tolerance zero ohm resistors
On 2015-06-01 17:53, John Larkin wrote:
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If you mean to say that its noise level would be 4kT|R|, then, no.
Of course, it does add noise, but it may be more or less, depending.

Jeroen Belleman

Re: Out-of-tolerance zero ohm resistors
On 2015-05-31 5:20 PM, George Herold wrote:
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It can make all the Johnson noise it wants to, I'd have a perfect  
business model for those and would soon retire on my own island,  
including landing strip and private jet :-)

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Out-of-tolerance zero ohm resistors
10A?  Zero-ohms aren't usually rated for that current.  RTDS.

The Keystone or Harwin parts are solid metal (in the clanky punch-pressed  
sense, not just like metal foil) and good for infinitely more current  
than... your puny PCB traces can do. :)

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
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Re: Out-of-tolerance zero ohm resistors
On Friday, May 29, 2015 at 12:40:47 PM UTC-4, Tim Williams wrote:
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I did, they are, but thanks...

Cheers,
James Arthur

Re: Out-of-tolerance zero ohm resistors
Tim Williams wrote...
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 Where do you get zero-ohm Harwin resistors?


--  
 Thanks,
    - Win

Re: Out-of-tolerance zero ohm resistors
On Sunday, May 31, 2015 at 6:36:30 AM UTC-4, Winfield Hill wrote:
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In Harwaii?  :-)

DigiKey has them.  They're called SMD 'shunts' or 'jumpers,'
http://www.digikey.com/product-search/en?pv2928%&FV=fff40016%2Cfff800a8%2Cfffc03b8%2C2dc15a6&mnonly=0&newproducts=0&ColumnSort=0&page=1&chp=0&quantity=0&ptm=0&fid=0&pageSize25%

Here's one:
 http://www.digikey.com/product-detail/en/S1911-46R/952-1740-2-ND/3131053

Cheers,
James Arthur


Re: Out-of-tolerance zero ohm resistors
snipped-for-privacy@yahoo.com wrote:
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   Well, i have a serious problem stemming from those parts that are  
LESS that the nominal resistance rating....


Re: Out-of-tolerance zero ohm resistors
On Sat, 30 May 2015 00:29:56 -0700, Robert Baer

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  Would not "negative resistance" have some potential positive
applications?

  Just what is "nominal" for a "zero ohm resistor"?

  Should you be nominated for being "problematic"?  :-)

  Just an observation.

Re: Out-of-tolerance zero ohm resistors
DecadentLinuxUserNumeroUno wrote:
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   May i have 20% tolerance rating?

Re: Out-of-tolerance zero ohm resistors
On 2015-05-29 8:13 AM, snipped-for-privacy@yahoo.com wrote:
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20A over 1206 (or 1210) sounds rather excessive. Normally they are  
spec'd lower such as 2A or 5A overload, like here:

https://www.maritex.com.pl/media/uploads/PRODUKTY_PDF/pas/RMC2512-F.pdf

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Out-of-tolerance zero ohm resistors
On 5/29/2015 10:13 AM, snipped-for-privacy@yahoo.com wrote:
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A 1210-size 2oz copper trace will have a temperature rise of 45C with  
10A through it.

Re: Out-of-tolerance zero ohm resistors
us:

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  Shit, man!  Just put a poly fuse in there!  ;-)

Re: Out-of-tolerance zero ohm resistors
On Saturday, May 30, 2015 at 4:06:41 PM UTC-4, John S wrote:
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Are you perhaps calculating for a continuous, round, equivalent cross-section
in air, where the adjacent sections are dissipating similar power, and with
much less surface area than the wide, flat trace?

I calculate a 2oz. trace has a resistance of 273 microhms per square.

A 2.5 x 3.2 section 2oz. trace--comprising 1.28 squares--would have a
resistance of 349 microhms, drop 36mV, and dissipate 36mW @ 10.2A.
That's not awful.

(Not quite as good as the Keystone zero-ohm part, granted.)

The siemens-deficient substitute part, however, dropped 125mV @ 10.2A,
dissipating 1.28W.  Even so, that part's temp. rise was only 15C
referenced to the heat sink 1.5cm away on the other side of the board, and
only ~7C (IIRC) over the surface the offender was mounted on, all measurements
in dead air & insulated with bubble-wrap. (The heat sink is 1/4 inch aluminum
plate, in thermal contact with a 50x60mm heat-generating patch of the board.)

Accordingly, I'd expect temp rise of the 1210 2oz trace to be (very roughly)
(36mW/1.28W) * 15C, or about .4C.

Cheers,
James Arthur

Re: Out-of-tolerance zero ohm resistors
On 5/31/2015 8:41 AM, snipped-for-privacy@yahoo.com wrote:
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I did not manually calculate. I used PCB Toolkit V6.8 available from  
<www.saturnpcb.com> .

Re: Out-of-tolerance zero ohm resistors
On Sun, 31 May 2015 06:41:54 -0700 (PDT), snipped-for-privacy@yahoo.com
wrote:

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My ancient "Reference Data for Radio Engineers" has a nomograph (!)
that suggests more like 20C rise (100 mil wide trace, 2 oz, 10 amps).
That was probably for an oldie 0.062 double-sided board. A multilayer,
with internal planes, will cool traces a lot better. In most cases,
the voltage drop is a bigger concern than trace heating.



--  

John Larkin         Highland Technology, Inc
picosecond timing   laser drivers and controllers

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Re: Out-of-tolerance zero ohm resistors
On Sunday, May 31, 2015 at 12:53:33 PM UTC-4, John Larkin wrote:
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I'd believe that for a long trace on a single or double-layer board.

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The immediate situation is just a .12" length along a much fatter trace
though, plus aggressive solid pours in four internal layers, ground on the
bottom, then a massive heat sink not far away.

Which brings up a good point--instead of 0.10" (1210), we'd fill the gap
with something wider, closer to 0.20".

Cheers,
James

Re: Out-of-tolerance zero ohm resistors
On Sun, 31 May 2015 10:06:49 -0700 (PDT), snipped-for-privacy@yahoo.com Gave
us:

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  Also placing additional PTHs nearby such elements soaks/conducts heat
better too.

Re: Out-of-tolerance zero ohm resistors
On Sunday, May 31, 2015 at 1:51:33 PM UTC-4, DecadentLinuxUserNumeroUno wrote:
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A 1210 (3.2x2.5mm) patch of 0,2mm FR-4 (one six-layer board ply) has a
thermal resistance of ~120C/W to the copper pour underneath.

So, 36mW (or 20mW) wouldn't be any sort of big deal all by itself.

A stalagmite / stalactite array might make a useful heat exchanger
somewhere.  But I found it easier to nail top and bottom together,
then heatsink the bottom.  

Cheers,
James Arthur

Re: Out-of-tolerance zero ohm resistors
On Sun, 31 May 2015 09:53:25 -0700, John Larkin

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  Also use 4oz.

  Most "modern" "digital" PCBs are gold.  Probably neither 2oz or 4oz
numbers are accurate.

  PS boards likely are still old style HASL copper with a tight mask.

  Remember the "rivulet days".?

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