Resistor material

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Man-wai Chang

Film resistors are 5 times more expensive than carbon resisters. Why?

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Man-wai Chang said:
Film resistors are 5 times more expensive than carbon resisters. Why?
Click to expand...

It depends on where you buy them.

For example, as a hobbyist years ago, I was buying resistors for $0.05
each, while my local RadioShack store sold two for $1.00. The quantity
you buy, affects the price.

Buying resistors at retail (from a corner store), may not reflect the
price paid at a large electronics manufacturing facility.

For me at the current time, the "mixed bag" is
the cheapest means to get a desired resistor. By buying this
locally, I avoid shipping charges if buying them on the Internet.
I end up with plenty of leftovers, but I then sort those into my
storage bins, which already have tons of resistors in them.

http://www.thesource.ca/estore/prod...log=Online&category=Resistors&product=2719018

*******

A big variable in the price of electronics, is the price of copper,
used in copper wire. The leads of the resistor may have some copper
present.

Recently, I repaired a plumbing leak. The pipe involved was 3" diameter
copper. A local plumbing supply, only sells 12 foot lengths of such
pipe. They wanted $350.00 for a 12 foot length. In other words, close
to $30 per foot of pipe. Copper is almost like gold now. I eventually
found a source of a small piece of copper pipe, and the retailer had
mistakenly priced it at $20 per foot, so I got (relatively) lucky.

It also means, if you have scraps of copper left over, to save them
and drive over to the metal recycler, first getting a quote from
them per pound, to see what you can get for it.

Copper is so expensive, at a small manufacturing facility in one
Canadian province, thieves went through the facility and ripped
all the wiring out of it. Just for the copper. The facility was
so badly damaged, the owner is abandoning the refurbishment
project that was under way, and moving elsewhere.

The time to buy all your copper, was Jan. 2009 :-) Copper
is now no longer affordable.

http://www.kitconet.com/charts/metals/base/spot-copper-5y-Large.gif

Paul
 
A big variable in the price of electronics, is the price
of copper, used in copper wire. The leads of the resistor
may have some copper present.
Click to expand...

Not many factories are left in Hong Kong. So what used to be cheap
components now become hobby items, driving up the price.
Copper is so expensive, at a small manufacturing facility in one
Canadian province, thieves went through the facility and ripped
all the wiring out of it. Just for the copper. The facility was
so badly damaged, the owner is abandoning the refurbishment
project that was under way, and moving elsewhere.
Click to expand...

Is copper getting expensive because it's used to make bullets? Well...

Lastly, why film resistors are more expensive than carbon resistors? Is
it just the shop?

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Man-wai Chang said:
Not many factories are left in Hong Kong. So what used to be cheap
components now become hobby items, driving up the price.


Is copper getting expensive because it's used to make bullets? Well...

Lastly, why film resistors are more expensive than carbon resistors? Is
it just the shop?
Click to expand...

Here is a metal film resistor for approx $0.01 each.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=RNF18FTD10K0TR-ND

A carbon film resistor sells for $0.006 each, or about 60% of the price of
the metal film. Perhaps the metal film is a precious metal ?

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=CF18JT10K0TR-ND

I doubt your retailer is charging a penny for each one :-) As you can see,
the markup is pretty decent. Especially when you buy two resistors for $1.00
at a RadioShack or equivalent. That is a 50x markup.

http://en.wikipedia.org/wiki/Resistor#Metal_film

"Metal film resistors are usually coated with nickel chromium (NiCr), but might
be coated with any of the cermet materials listed above for thin film resistors.
Unlike thin film resistors, the material may be applied using different techniques
than sputtering (though that is one such technique). Also, unlike thin-film
resistors, the resistance value is determined by cutting a helix through the
coating rather than by etching. (This is similar to the way carbon resistors
are made.) The result is a reasonable tolerance (0.5, 1, or 2%) and a temperature
coefficient that is generally between 50 and 100 ppm/K.[8] Metal film resistors
possess good noise characteristics and low non-linearity due to a low voltage
coefficient. Also beneficial are the components efficient tolerance, temperature
coefficient and stability."

If I check the prices as a function of resistance value, it doesn't seem to
vary that much, implying the material cost is pretty low. If the metal used
in the metal film was expensive, you'd expect the cost of the various
resistor values to be different.

Paul
 
Man-wai Chang said:
Film resistors are 5 times more expensive than carbon resisters. Why?
Click to expand...

http://en.wikipedia.org/wiki/Resistor#Foil_resistor

Carbon is cheaper than metal which requires more processing. When the
raw materials cost more so does the finished product. Far better
accuracy and stability also costs more money.

Intro to High Precision Resistor Industry
http://www.texascomponents.com/pdf/Intro_High_Precision.pdf
The common carbon resistor isn't even listed in Table 1 since this
article is about precision. Carbon resistors are 5% tolerance (well, 1%
to 10%): 20 to 200 times the minimal tolerance listed for the precision
types here.

Foil in Action
http://www.texascomponents.com/pdf/foil_in_action.pdf
 
Film resistors are 5 times more expensive than carbon resisters. Why?
Click to expand...

Thank you all. Time to play with potential divider to charge my iPod
from AC.

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Not many factories are left in Hong Kong. So what used to be cheap
components now become hobby items, driving up the price.


Is copper getting expensive because it's used to make bullets? Well...
Click to expand...

Partially, copper is used as a jacket material on the bullet
(projectile) as well as part of the brass alloy used for the cartridge
case (shell).
Lastly, why film resistors are more expensive than carbon resistors? Is
it just the shop?
Click to expand...

Depends on what the quality level of "film resistor" you be talkin bout.
The good ones are a ceramic (insulator) base covered with a resistive
but conductive film. The film is cut-away (trimmed) by a laser beam,
water jet, or similar until the desired resistance is achieved, then the
outer coating/shell and markings are applied.

Carbon resistors are just short pieces of extruded carbon-based
conductive but resistive compound encased in a shell.

That's just the raw manufacturing part.

Probably the big difference is in testing and sorting for value (actual
ohms), plus the inevitable tolerance regarding temps and such.

Typically, film resistors are used when tight values and toleranced are
needed. (they are usually called precision resistors).

Carbon resistors are usually used where +/- 20% works fine. The reality
is that much electronic circuitry is even looser than that.

The big difference is when there are "flame-resistance" issues. Film
resistors usually "pop" with little heat or flames, whereas plain old
carbon resistors often can put out veritable fireballs and smoking pyres
when they blow.





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