Out-of-tolerance zero ohm resistors

An assembly house apparently substituted some 1210 zero-ohm resistors with another mfr's part. They're passing >10A, so part characteristics matter.

The substitute parts measure 12.5 milliohms, dissipating an extra 1.3W in an enclosed unit that doesn't appreciate that.

The Vishay parts spec'd list 4 milliohms max, but actually measure 2.5 milliohms. Much better.

Just for fun I measured the drop across the solder fillets too--only 1mV out of 126mV total. Insignificant.

I figure they're both out of tolerance though, one by infinity percent, and the other by 5*infinity percent.

Someone put those in for

Reply to
dagmargoodboat
Loading thread data ...

On a sunny day (Fri, 29 May 2015 08:13:23 -0700 (PDT)) it happened snipped-for-privacy@yahoo.com wrote in :

Try to but some with negative R.

Reply to
Jan Panteltje

They would have to be shipped with "keepers", like some supermagnets or big energy storage caps. UPS probably wouldn't allow them.

--
John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 
 Click to see the full signature
Reply to
John Larkin

Marketing slogan: "Resistance is futile."

Cheers, James Arthur

Reply to
dagmargoodboat

Reply to
rickman
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 
 Click to see the full signature
Reply to
Tim Williams

You have nothing to lose but your ohms.

--
John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
 Click to see the full signature
Reply to
John Larkin

I did, they are, but thanks...

Cheers, James Arthur

Reply to
dagmargoodboat

On Fri, 29 May 2015 09:21:22 -0700 (PDT), snipped-for-privacy@yahoo.com Gave us:

You have to say that like Yoda in this instance....

"Futile, resistance is..."

Reply to
DecadentLinuxUserNumeroUno

On Fri, 29 May 2015 09:50:50 -0700, John Larkin Gave us:

"All electrons will be assimilated..."

Reply to
DecadentLinuxUserNumeroUno

Well, i have a serious problem stemming from those parts that are LESS that the nominal resistance rating....

Reply to
Robert Baer

On Sat, 30 May 2015 00:29:56 -0700, Robert Baer Gave us:

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.

Reply to
DecadentLinuxUserNumeroUno

20A over 1206 (or 1210) sounds rather excessive. Normally they are spec'd lower such as 2A or 5A overload, like here:

formatting link

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

I want the ones that are -1%.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

A 1210-size 2oz copper trace will have a temperature rise of 45C with

10A through it.
Reply to
John S

On Sat, 30 May 2015 15:07:17 -0500, John S Gave us:

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

Reply to
DecadentLinuxUserNumeroUno

Where do you get zero-ohm Harwin resistors?

--
 Thanks, 
    - Win
Reply to
Winfield Hill

Sound like the substitute parts are skimping on the Siemens, using only

80 instead of 400. It's certainly sharp practise, that way they can make five times as many parts from one bag of Siemens, plus the counting is quicker.

Cheers

--
Syd
Reply to
Syd Rumpo

Yeah, they took lhe line of least resistance. No, wait....

Cheers

Phil Hobbs

Reply to
Phil Hobbs

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

Reply to
dagmargoodboat

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.