Zero ohm resistors, why??

[Sal Brisindi]

Here is a auction on ebay I am curious about.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4664&item=3822300078

Why would there be a zero ohm resistor? Can't you use a piece of wire
instead?

Thanks,
Sal Brisindi
http://www.numitron.com

 

[Spehro Pefhany]

On Wed, 23 Jun 2004 01:27:38 GMT, the renowned Sal Brisindi
<salb203@optonline.net> wrote:

Here is a auction on ebay I am curious about.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4664&item=3822300078

Why would there be a zero ohm resistor? Can't you use a piece of wire
instead?

They can be inserted by the same machines that insert resistors- note
the tape. They are also easy to insert by hand if you buy the bulk
kind, if you keep to the usual spacing. I designed the things into
dozens of products..

Of course the "1/4W" is an indirect reference to the body size.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[Dave Platt]

In article <40D8DC89.77C732D0@optonline.net>,
Sal Brisindi <salb203@optonline.net> wrote:

Here is a auction on ebay I am curious about.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4664&item=3822300078

Why would there be a zero ohm resistor? Can't you use a piece of wire
instead?

Zero-ohm resistors are made in the same physical sizes as
small-wattage non-zero-ohm resistors. They can be handled by
automatic pick&place equipment, independent of the fact that they've
got zero ohms inside. The bulk of the "resistor" body gives the
automated equipment something to grab onto (usually using a vaccum
hold, I believe).

Wire jumpers would either require manual placement, or a different
sort of automated-placement tool.

I'd guess that the slight additional cost involved in purchasing "zero
ohm resistor" parts, is usually more than compensated for by the fact
that they don't have to be treated specially during automated assembly.

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[buckworth@hennypenny.net]

Sal Brisindi wrote:

Here is a auction on ebay I am curious about.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4664&item=3822300078

Why would there be a zero ohm resistor? Can't you use a piece of wire
instead?

Thanks,
Sal Brisindi
http://www.numitron.com

Some other reasons:

1) so you can measure current easily during development
2) to allow the board to have optional current paths, in case there are
other devices that must change and cause the wiring to change
3) to allow you to connect two nodes together (Pwr Gnd and Analog Gnd)
in a CAD system, and still allow full checking

 

[Don Klipstein]

In article <40D8DC89.77C732D0@optonline.net>, Sal Brisindi wrote:

Here is a auction on ebay I am curious about.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4664&item=3822300078

Why would there be a zero ohm resistor? Can't you use a piece of wire
instead?

I heard that "Mil spec" circuit boards have to lack wires jumping from
one point to another on the board. My guess is that wires could get
snagged while removing boards to service them or otherwise while servicing
them.
But there are no rules banning use of components on a circuit board.
And if they say a zero ohm resistor is a wire, then they open the wormcan
of saying a 1 ohm resistor is a wire if you use it where a zero ohm one
would achieve essentialy the same results, and that a 100 or a 143 ohm
resistor in series with a high impedance signal path at least in many
cases is a wire, and how do they go about regulating usage of 100 and
143 ohm resistors?

At this point, I would guess that wires (or preferably cables) can only
connect to a "mil spec" board via connectors...

- Don Klipstein Jr. (don@misty.com)

 

[Don Klipstein]

In article <k4ohd0hba31t9tp8dt7qaj255krj531pef@4ax.com>, Spehro Pefhany wrote:

On Wed, 23 Jun 2004 01:27:38 GMT, the renowned Sal Brisindi
salb203@optonline.net> wrote:

Here is a auction on ebay I am curious about.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4664&item=3822300078

Why would there be a zero ohm resistor? Can't you use a piece of wire
instead?

They can be inserted by the same machines that insert resistors- note
the tape. They are also easy to insert by hand if you buy the bulk
kind, if you keep to the usual spacing. I designed the things into
dozens of products..

Of course the "1/4W" is an indirect reference to the body size.

If the amount of current that results in dissipating 1/4 watt into the
"resistor" does not significantly heat the copper foils that it is
soldered to, then it appears to me that this is a safe current.

Than again, in typical usage this is .7 inch of wire, and it appears to
me that the leads of a 1/4 watt resistor are 24 AWG (or .5 mm dia.) tinned
copper, resistance at 100 degrees C is approx. 1.8, maybe 1.9 milliohms...
Current that results in 1/4 watt dissipation here is around 11-11.8 amps
- keep in mind guidelines for what the foil traces can hangle - I suspect
that will be the limiting factor.

Also - power ratings of mil-spec resistors are often half that of
commercial grade resistors of the same size. This limits a "1/4 watt"
"zero" to somewhere around 8 amps (or the amount of current that the
circuit board traces can handle, whichever is less).

**********************

Power rating of a resistor may depend on heatsinking effects of either
the leads or *near-resistor-body* circuit board traces that are oversized
for the amount of current actually being conducted. This may mean that a
1/4 watt zero ohm resistor may only safely pass 8-11 amps when its ends
are in close contact with conductors that don't have much of a temperature
rise at this amount of current.

Keep in mind that my "measurement" of the wire size of a "1/w4
watt" resistor might be "off by a size", and that I am not especially
certain that 1/4 watt zeros aren't made with AWG 26 (.4 mm dia.) wire. A
..7 inch length of that dissipates 1/4 watt at 100 degrees C at somewhere
around 9-9.5 amps, and 1/8 watt at 100 degrees C at somewhere around
6.25-6.7 amps.

Also, unless you have circumstances unusually favorable to 24 gauge
wire (such as heatsinking of a very short piece by something much
thicker), the safe current carrying capacity will be closer to whatever
the "norm" is for 24 gauge wire. I do not know this figure for sure, but
I believe it is somewhere around 2 amps.
(Transformer windings with AWG 24 may be safe only at much lower
currents like around .5 amp due to a large assembly of adjacent turns all
producing heat, heat from other windings, and heat from the core.)

- Don Klipstein (Jr.) (don@misty.com)

 

[Mike Harrison]

On Wed, 23 Jun 2004 01:35:13 GMT, Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> wrote:

On Wed, 23 Jun 2004 01:27:38 GMT, the renowned Sal Brisindi
salb203@optonline.net> wrote:

Here is a auction on ebay I am curious about.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4664&item=3822300078

Why would there be a zero ohm resistor? Can't you use a piece of wire
instead?

They can be inserted by the same machines that insert resistors- note
the tape. They are also easy to insert by hand if you buy the bulk
kind, if you keep to the usual spacing. I designed the things into
dozens of products..

Of course the "1/4W" is an indirect reference to the body size.
I also doubt they are carbon film....

A few years ago, a listing in the Farnell catalogue for these read :

Resistance : 0 ohms
Tolerance : 5%

 

[Spehro Pefhany]

On Wed, 23 Jun 2004 11:07:11 +0100, the renowned Mike Harrison
<mike@whitewing.co.uk> wrote:

On Wed, 23 Jun 2004 01:35:13 GMT, Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> wrote:

On Wed, 23 Jun 2004 01:27:38 GMT, the renowned Sal Brisindi
salb203@optonline.net> wrote:

Here is a auction on ebay I am curious about.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4664&item=3822300078

Why would there be a zero ohm resistor? Can't you use a piece of wire
instead?

They can be inserted by the same machines that insert resistors- note
the tape. They are also easy to insert by hand if you buy the bulk
kind, if you keep to the usual spacing. I designed the things into
dozens of products..

Of course the "1/4W" is an indirect reference to the body size.
I also doubt they are carbon film....

Some kind of nickel alloy, IIRC, from the manufacturer's data. But so
are low values of "carbon film" resistors!

A few years ago, a listing in the Farnell catalogue for these read :

Resistance : 0 ohms
Tolerance : 5%

I design instruments and controls a lot- if only I could get a
precision 1% version...

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[Spehro Pefhany]

On Wed, 23 Jun 2004 02:57:50 +0000 (UTC), the renowned
don@manx.misty.com (Don Klipstein) wrote:

In article <k4ohd0hba31t9tp8dt7qaj255krj531pef@4ax.com>, Spehro Pefhany wrote:
On Wed, 23 Jun 2004 01:27:38 GMT, the renowned Sal Brisindi
salb203@optonline.net> wrote:

Here is a auction on ebay I am curious about.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4664&item=3822300078

Why would there be a zero ohm resistor? Can't you use a piece of wire
instead?

They can be inserted by the same machines that insert resistors- note
the tape. They are also easy to insert by hand if you buy the bulk
kind, if you keep to the usual spacing. I designed the things into
dozens of products..

Of course the "1/4W" is an indirect reference to the body size.

If the amount of current that results in dissipating 1/4 watt into the
"resistor" does not significantly heat the copper foils that it is
soldered to, then it appears to me that this is a safe current.

W is a dissipation, not a current. Zero ohm resistors have a rating in
current. You have to read the actual manufacturer's data sheet to find
this, not some catalog hacked together by a distributor.

The body has a thin layer of metal alloy over a ceramic core- it's NOT
a wire staight through. The whole thing is made by resistor
manufacturing equipment.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[Sal Brisindi]

Thank you all for your input. Now I know why there is a zero ohm resistor.

Regards,
Sal Brisindi
http://www.numitron.com

"buckworth@hennypenny.net" wrote:

Sal Brisindi wrote:
Here is a auction on ebay I am curious about.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4664&item=3822300078

Why would there be a zero ohm resistor? Can't you use a piece of wire
instead?

Thanks,
Sal Brisindi
http://www.numitron.com


Some other reasons:

1) so you can measure current easily during development
2) to allow the board to have optional current paths, in case there are
other devices that must change and cause the wiring to change
3) to allow you to connect two nodes together (Pwr Gnd and Analog Gnd)
in a CAD system, and still allow full checking

 

[Ken Finney]

"Don Klipstein" <don@manx.misty.com> wrote in message
news:slrncdhp4m.kid.don@manx.misty.com...

In article <40D8DC89.77C732D0@optonline.net>, Sal Brisindi wrote:
Here is a auction on ebay I am curious about.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4664&item=3822300078

Why would there be a zero ohm resistor? Can't you use a piece of wire
instead?

I heard that "Mil spec" circuit boards have to lack wires jumping from
one point to another on the board. My guess is that wires could get
snagged while removing boards to service them or otherwise while servicing
them.
But there are no rules banning use of components on a circuit board.
And if they say a zero ohm resistor is a wire, then they open the wormcan
of saying a 1 ohm resistor is a wire if you use it where a zero ohm one
would achieve essentialy the same results, and that a 100 or a 143 ohm
resistor in series with a high impedance signal path at least in many
cases is a wire, and how do they go about regulating usage of 100 and
143 ohm resistors?

At this point, I would guess that wires (or preferably cables) can only
connect to a "mil spec" board via connectors...

Milspec boards are allowed to have jumper wires. There is typically
a limit based on the surface area of the board, but you almost never
approach it, because after only a couple, it is cheaper to re-layout
the board to incorporate the jumpers and/or use zero ohm chips.

 

[Boris Mohar]

On Wed, 23 Jun 2004 11:14:23 GMT, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

A few years ago, a listing in the Farnell catalogue for these read :

Resistance : 0 ohms
Tolerance : 5%

I design instruments and controls a lot- if only I could get a
precision 1% version...

Best regards,
Spehro Pefhany

You would still have to throw half of them out because they would have
negative resistance.

--

Boris Mohar

 

[cpemma]

Boris Mohar wrote:

On Wed, 23 Jun 2004 11:14:23 GMT, Spehro Pefhany
speffSNIP@interlogDOTyou.knowwhat> wrote:

A few years ago, a listing in the Farnell catalogue for these read :

Resistance : 0 ohms
Tolerance : 5%

I design instruments and controls a lot- if only I could get a
precision 1% version...

Best regards,
Spehro Pefhany

You would still have to throw half of them out because they would
have negative resistance.

I'd keep those for the perpetual motion machine.

 

[John Miller]

Boris Mohar wrote:

You would still have to throw half of them out because they would have
negative resistance.

No, no, no.

Those, you connect in series and use as a perpetual source of energy.

--
John Miller
Email address: domain, n4vu.com; username, jsm

"Die? I should say not, dear fellow. No Barrymore would allow such a
conventional thing to happen to him."
-John Barrymore's dying words

 

[Greysky]

"John Miller" <me@privacy.net> wrote in message
news:cbce5c$r1h$2@n4vu.com...

Boris Mohar wrote:
You would still have to throw half of them out because they would have
negative resistance.

No, no, no.

Those, you connect in series and use as a perpetual source of energy.

Now you've gone and done it. The Govt. was hoping that the secret to
infinite energy would never leak out, because it turns out to be so bloody
easy! Everyone who has participated in this particular discussion will
disappear over time. The secret must never be allowed to be divulged....
;-(