0 ohm Resistor wattage

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I have a 0 ohm resistor in series with the +5V power supply (as a
provision to disconnect, if not needed). The power drawn by the
connected circuit is 1A through this 0 ohm resistor. What should be
the wattage of this resistor? Since there is no voltage drop across
this resistor, can it be 0.1W or 5V * 1A = 5W? I am new to this stuff
and hoping to get help from this great forum.

-Mark

Re: 0 ohm Resistor wattage
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There is no such thing as a zero ohm resistor. Even a small piece of
wire has some resistance.

--
I'm never going to grow up.

Re: 0 ohm Resistor wattage

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Sure there is such a thing as a zero ohm resistor.....

To the OP, look up the data sheet for the part you are using, see what the
maximum current is.



Re: 0 ohm Resistor wattage
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The zero ohm resistors i've seen have just been resistor size
encapsulation around straight through lead wire. Usually used for pcb
links. Don't know about smd parts, but you could verify capability using
a bench supply in current mode, in the absence of other data...

Regards,

Chris



Re: 0 ohm Resistor wattage
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Thanks for the responses. As Chris said the 0 ohm resistor is for pcb
link and it is an SMD resistor of 0603 size. Assuming it is of 0.1
ohms and 0.1Watt for this discussion, it will allow more than 1A
(5/0.1) current that is required by the circuit after this 0 ohm
resistor but is the wattage OK?

-Mark


Re: 0 ohm Resistor wattage

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Ohms law ?.

Best thing to do would be to measure the actual value with 4 wire,
Kelvin clip ohm meter. 0.1 ohms sounds high for a real world
part of that value. More like 0.01 ohms or less...

Regards,

Chris

Re: 0 ohm Resistor wattage
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I think you missed my point, that everything has resistance. In this
case the jumper wire (which is what a 'zero ohm' resistor is) would have
resistance, and given enough current it would overheat.

--
I'm never going to grow up.

Re: 0 ohm Resistor wattage

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I didn't miss you point, in the context used, "zero" means zero nominal
resistance.



Re: 0 ohm Resistor wattage

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Bingo! Correct answer. There are zero ohm SMD resistors made so that pick
and place machines can install them. Google found this:

http://www.koaspeer.com/products/resistors/surface-mount-resistors/rk73z /

What you are looking for is the max current rating, not necessarily the
wattage (since dissipation will not be well defined for zero ohms).

--
Paul Hovnanian   snipped-for-privacy@hovnanian.com
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Re: 0 ohm Resistor wattage
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What you are looking for is the same size as that non-zero Ohm resistor you
might put into the same place instead of zero Ohm. I wouldn't bet my tooth
for it but, IMHO, current rating of e.g. 0603 zero Ohm resistor way exceeds
that of PCB traces you can put it across...

---
******************************************************************
*  KSI@home    KOI8 Net  < >  The impossible we do immediately.  *
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Re: 0 ohm Resistor wattage

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   The resistance of the solder joints may be higher than the SMD zero
ohm resistor.

--
You can't fix stupid. You can't even put a Band-Aidô on it, because it's
Teflon coated.

Re: 0 ohm Resistor wattage

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A more interesting question is what is the tolerance? Farnell do a nice
range of 1% ones. There are some 5% ones too but it is a false economy
IMO.

To the OP: Look at the datasheet for the current rating but it is a
pretty poor "zero ohm" resistor that can't take 1A.


--

John Devereux

Re: 0 ohm Resistor wattage
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The 5% units are invaluable--you can cherry pick the -5% units,
gleaning parts critical for use in FTL transmitters, flux capacitors,
perpetual motion machines, etc.

--
Cheers,
James Arthur

Re: 0 ohm Resistor wattage
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I like that idea. -5% of 0 ohm could be very handy to have :-)



Re: 0 ohm Resistor wattage

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A 0r resistor will probably have milliohms of actual resistance; the
datasheet should say so. 1 amp shouldn't cause significant voltage
drop, or heating, in any reasonable part, like an 0603 for example.

John


Re: 0 ohm Resistor wattage

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The designation 'zero ohm' is hyperbole.  It's a piece of wire, and it
has resistance.  If it's any good at all, it also has a current rating in
its data sheet, and maybe even some comments on whether that current
rating can be matched by the solder joint holding it onto the board.

I would assume that if the thing were no narrower than the traces that
can safely carry 1A on the board then you're OK -- but I'd still dig out
the data sheet in a spare moment, to be sure.

--
http://www.wescottdesign.com

Re: 0 ohm Resistor wattage
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Yes, even copper traces have current limits.

For 20m ohm jumper:

0201 1A
0402 1.5A
0603 2A
0805 2.5A
1206 3.5A
1210 5A
1218 7A

Re: 0 ohm Resistor wattage
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Why not look at the data sheet?

For example a Panasonic 0603 "zero" ohm resistor (they refer to it as
a "jumper" in the data sheet) is rated for 1A.

kevin

Re: 0 ohm Resistor wattage
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   Wire, etc has resistance - INCLUDING connectors and vias!
   Maybe in the region of 0.1 ohm.
   At a measly one amp, it is the current handling capability of the
wire, etc that you must be concerned with.

Re: 0 ohm Resistor wattage

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Vishay data here:

http://www.vishay.com/docs/31017/rcwp99.pdf



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