Post by thread:[EE] Carbon film vs Metal film resistors

I have grown so accustomed to using metal film resistors for 'everyday' applications that carbon film doesn't usually feature in my thinking. A Taiwanese manufacturer has asked whether they can substitute carbon film for metal film in a design. They claim that cf costs are far lower. Volumes are only moderate (1,000 - 10,000 products per year at most). Most resistors are operated at far below their power and voltage ratings. My initial reaction is that whereas most resistors could technically be changed to CF, the cost savings would be minimal compared to other costs and that sacrificing the reliability of metal film would not be worthwhile. I'm also dubious about the merits of allowing CF as they would almost certainly be Chinese* sourced with unknown (indeed non-existent) provenance and aimed at bottom of the market, quality-irrelevant applications. (I've little doubt that there is a reason that they are cheap). Thoughts? - or recent experiences with modern CF resistors. Am I too prejudiced against a new 'mature' technology? Russell McMahon * I've no doubt that when it makes sense to do so China can produce products of superb quality. But I also have little doubt that the burgeoning market / what the market will bear / caveat emptor / take no thought for the morrow ... / aspects of the present market explosion mean that quality will often be, at best, only as good as it has to be.

I'm skeptical that the carbon film scheme will reliably dissipate the heat without changing value considerably. The Chinese have an enormous problem here in the colonies- many companies have pulled back their plastics molds (if the chinese will give them back) due to unethical business practices on several levels. Before I would change, I would run a bunch of tests. --Bob Russell McMahon wrote: {Quote hidden}>I have grown so accustomed to using metal film resistors for >'everyday' applications that carbon film doesn't usually feature in my >thinking. > >A Taiwanese manufacturer has asked whether they can substitute carbon >film for metal film in a design. They claim that cf costs are far >lower. Volumes are only moderate (1,000 - 10,000 products per year at >most). Most resistors are operated at far below their power and >voltage ratings. > >My initial reaction is that whereas most resistors could technically >be changed to CF, the cost savings would be minimal compared to other >costs and that sacrificing the reliability of metal film would not be >worthwhile. I'm also dubious about the merits of allowing CF as they >would almost certainly be Chinese* sourced with unknown (indeed >non-existent) provenance and aimed at bottom of the market, >quality-irrelevant applications. (I've little doubt that there is a >reason that they are cheap). > >Thoughts? - or recent experiences with modern CF resistors. >Am I too prejudiced against a new 'mature' technology? > > > > Russell McMahon > >* I've no doubt that when it makes sense to do so China can produce >products of superb quality. But I also have little doubt that the >burgeoning market / what the market will bear / caveat emptor / take >no thought for the morrow ... / aspects of the present market >explosion mean that quality will often be, at best, only as good as it >has to be. > > > -- Note: To protect our network, attachments must be sent to spam_OUTattachTakeThisOuTengineer.cotse.net . 1-520-850-1673 USA/Canada http://beam.to/azengineer

At 01:01 AM 2/10/2006 +1300, you wrote: >I have grown so accustomed to using metal film resistors for >'everyday' applications that carbon film doesn't usually feature in my >thinking. I suppose you're talking about leaded resistors. >A Taiwanese manufacturer has asked whether they can substitute carbon >film for metal film in a design. They claim that cf costs are far >lower. Volumes are only moderate (1,000 - 10,000 products per year at >most). Most resistors are operated at far below their power and >voltage ratings. >My initial reaction is that whereas most resistors could technically >be changed to CF, the cost savings would be minimal compared to other >costs High purchasing costs of unpopular resistors in such tiny quantities may be influencing their request. With the carbon film, they may have them around or they can buy reel quantities for a few dollars and not worry about it. >and that sacrificing the reliability of metal film would not be >worthwhile. I'm also dubious about the merits of allowing CF as they >would almost certainly be Chinese* Taiwan has a number of quality resistor manufacturers, many (all, probably) of which now have their factories on the mainland. The brand is more important than where the factory is plunked down- because the QC will depend on management and how much they value their name. What you probably don't want is a 'lowest bidder' type of generic part, which is more of a crap-shoot. >sourced with unknown (indeed >non-existent) provenance and aimed at bottom of the market, >quality-irrelevant applications. (I've little doubt that there is a >reason that they are cheap). > >Thoughts? - or recent experiences with modern CF resistors. >Am I too prejudiced against a new 'mature' technology? Depends on the circuit. And if you trust the manufacturer to use name- brand parts. In China you also have the problem of counterfeit parts. BTW, I've seen MANY MORE reliability problems with metal film, especially Taiwanese metal film. CF outright failures and serious drift issues are very rare, IME. They make so many billions of them... There's another option- you can supply the resistors. I've done that for really cheap parts where I'm worried about quality issues. They probably roll their eyes at the dumb big-nose (ben dan da bi tzi) who pays 10 times as much for about the same thing, but so what? Of course leaded parts are an order of magnitude more expensive to ship than SMT. >Best regards, Spehro Pefhany --"it's the network..." "The Journey is the reward" .....speffKILLspam@spam@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com ->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff

All, Another point of interest is in noise contribution. Carbon film resistors inherently have a higher noise figure than metal film. So if noise is an issue, don't use carbon film resistors. I believe generally speaking, carbon film resistors have a noise value that is typically twice that of metal film. And in most cases, it is three to four times as high. Just food for thought. Regards, Jim {Quote hidden}> I have grown so accustomed to using metal film resistors for > 'everyday' applications that carbon film doesn't usually feature in my > thinking. > > A Taiwanese manufacturer has asked whether they can substitute carbon > film for metal film in a design. They claim that cf costs are far > lower. Volumes are only moderate (1,000 - 10,000 products per year at > most). Most resistors are operated at far below their power and > voltage ratings. > > My initial reaction is that whereas most resistors could technically > be changed to CF, the cost savings would be minimal compared to other > costs and that sacrificing the reliability of metal film would not be > worthwhile. I'm also dubious about the merits of allowing CF as they > would almost certainly be Chinese* sourced with unknown (indeed > non-existent) provenance and aimed at bottom of the market, > quality-irrelevant applications. (I've little doubt that there is a > reason that they are cheap). > > Thoughts? - or recent experiences with modern CF resistors. > Am I too prejudiced against a new 'mature' technology? > > > > Russell McMahon > > * I've no doubt that when it makes sense to do so China can produce > products of superb quality. But I also have little doubt that the > burgeoning market / what the market will bear / caveat emptor / take > no thought for the morrow ... / aspects of the present market > explosion mean that quality will often be, at best, only as good as it > has to be. > > --

>and that sacrificing the reliability of metal film would >not be worthwhile. I'm also dubious about the merits of >allowing CF as they would almost certainly be Chinese If you are going to introduce significant cost differences by using metal film, then you may find counterfeit items appearing using CF ones instead in a rip off product. My response to your requirement for using MF is do you really need the tolerance accuracy? MF is normally supplied to 2% or tighter, CF is typically 5%, but not having dealt with Chinese production, I don't know if these are the tolerances they would supply.

If I recall....carbon film is a better choice in high voltage applications, less chance of arcing? That thought was from a design I worked on some 10 years ago, where the application was high voltage RF, and the guy doing the design specifically put in carbon "Paul James E." <jamespKILLspamintertex.net> wrote: All, Another point of interest is in noise contribution. Carbon film resistors inherently have a higher noise figure than metal film. So if noise is an issue, don't use carbon film resistors. I believe generally speaking, carbon film resistors have a noise value that is typically twice that of metal film. And in most cases, it is three to four times as high. Just food for thought. Regards, Jim {Quote hidden}> I have grown so accustomed to using metal film resistors for > 'everyday' applications that carbon film doesn't usually feature in my > thinking. > > A Taiwanese manufacturer has asked whether they can substitute carbon > film for metal film in a design. They claim that cf costs are far > lower. Volumes are only moderate (1,000 - 10,000 products per year at > most). Most resistors are operated at far below their power and > voltage ratings. > > My initial reaction is that whereas most resistors could technically > be changed to CF, the cost savings would be minimal compared to other > costs and that sacrificing the reliability of metal film would not be > worthwhile. I'm also dubious about the merits of allowing CF as they > would almost certainly be Chinese* sourced with unknown (indeed > non-existent) provenance and aimed at bottom of the market, > quality-irrelevant applications. (I've little doubt that there is a > reason that they are cheap). > > Thoughts? - or recent experiences with modern CF resistors. > Am I too prejudiced against a new 'mature' technology? > > > > Russell McMahon > > * I've no doubt that when it makes sense to do so China can produce > products of superb quality. But I also have little doubt that the > burgeoning market / what the market will bear / caveat emptor / take > no thought for the morrow ... / aspects of the present market > explosion mean that quality will often be, at best, only as good as it > has to be. > > --

>-----Original Message----- >From: .....piclist-bouncesKILLspam.....mit.edu [EraseMEpiclist-bouncesspam_OUTTakeThisOuTmit.edu] >Sent: 09 February 2006 15:40 >To: Microcontroller discussion list - Public. >Subject: Re: [EE] Carbon film vs Metal film resistors > > >If I recall....carbon film is a better choice in high voltage >applications, less chance of arcing? That thought was from a >design I worked on some 10 years ago, where the application >was high voltage RF, and the guy doing the design specifically >put in carbon Carbon film is a better choice for RF because they have lower inductance than metal film. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. =======================================================================

On Thu, 9 Feb 2006 15:57:20 -0000, you wrote: >>If I recall....carbon film is a better choice in high >>voltage applications, less chance of arcing? That >>thought was from a design I worked on some 10 years ago, >>where the application was high voltage RF, and the >>guy doing the design specifically put in carbon > >Had that in Cockroft-Walton (sp?) multipliers for instruments in space. >carbon resistors specified for arc-over reasons. Probably solid-carbon though - film resistors are not good at HV, due to poor surge capability, and spiral-cut ones can arc between turns. My marx generator (http://www.electricstuff.co.uk/marxthree.html) used to eat 10KV-rated film resistors due to surge currents - after replacing with solid-carbon ones it's been fine.

>>Had that in Cockroft-Walton (sp?) multipliers for instruments in space. >>carbon resistors specified for arc-over reasons. > >Probably solid-carbon though - film resistors are not good >at HV, due to poor surge capability, and spiral-cut ones >can arc between turns. My marx generator >(http://www.electricstuff.co.uk/marxthree.html) used to eat >10KV-rated film resistors due to surge currents - after >replacing with solid-carbon ones it's been fine. Yeah, I think they were. They were the ones that relate to the story a while back about resistor values of carbon resistors, and I told a tale about checking their resistance as they were warmed up to expel moisture.

I have carbon film resistors in stock if you need some. Rich ----- Original Message ----- From: "Russell McMahon" <apptechspam_OUTparadise.net.nz> To: "PIC List" <@spam@PICLISTKILLspamMIT.EDU> Sent: Thursday, February 09, 2006 7:01 AM Subject: [EE] Carbon film vs Metal film resistors {Quote hidden}>I have grown so accustomed to using metal film resistors for > 'everyday' applications that carbon film doesn't usually feature in my > thinking. > > A Taiwanese manufacturer has asked whether they can substitute carbon > film for metal film in a design. They claim that cf costs are far > lower. Volumes are only moderate (1,000 - 10,000 products per year at > most). Most resistors are operated at far below their power and > voltage ratings. > > My initial reaction is that whereas most resistors could technically > be changed to CF, the cost savings would be minimal compared to other > costs and that sacrificing the reliability of metal film would not be > worthwhile. I'm also dubious about the merits of allowing CF as they > would almost certainly be Chinese* sourced with unknown (indeed > non-existent) provenance and aimed at bottom of the market, > quality-irrelevant applications. (I've little doubt that there is a > reason that they are cheap). > > Thoughts? - or recent experiences with modern CF resistors. > Am I too prejudiced against a new 'mature' technology? > > > > Russell McMahon > > * I've no doubt that when it makes sense to do so China can produce > products of superb quality. But I also have little doubt that the > burgeoning market / what the market will bear / caveat emptor / take > no thought for the morrow ... / aspects of the present market > explosion mean that quality will often be, at best, only as good as it > has to be. > > --

Is that carbon film or carbon composition? ----- Original Message ----- From: "Alan B. Pearce" <spamBeGoneA.B.PearcespamBeGonerl.ac.uk> To: "Microcontroller discussion list - Public." <TakeThisOuTpiclistEraseMEspam_OUTmit.edu> Sent: Thursday, February 09, 2006 10:57 AM Subject: Re: [EE] Carbon film vs Metal film resistors > >If I recall....carbon film is a better choice in high >>voltage applications, less chance of arcing? That >>thought was from a design I worked on some 10 years ago, >>where the application was high voltage RF, and the >>guy doing the design specifically put in carbon > > Had that in Cockroft-Walton (sp?) multipliers for instruments in space. > carbon resistors specified for arc-over reasons. > > --

> The real world uses carbon film except where conditions dictate > otherwise. > > If you don't trust the supplier, what does it matter if they provide > crappy metal film or crappy carbon film? They are a bad supplier, > find > someone else. Besides, you can always specify accepted manufacturers > and > part numbers. A significant issue is that I have essentially no control of what happens after the project assumes a life of its own. I can set gross parameters which may well be adhered to (such as CF or MF resistors) but if I get down to part numbers and suppliers there is no certainty that that will not be changed without me knowing. And I have no good information on the quality of the available Asian manufacturers. MF, being a dearer and more 'complex' product, arguably set a higher entry level to manufacturers offering them. One could also argue that the potentially higher profit levels may attract inferior producers :-). All in all, it seems more likely that I will get a dependable result with MF if the cost difference as a % of total component cost is not severe. Here I tend to just say "SFR16" and all is well :-). (That sort of spec transcends manufacturing location. I note that the first box of them that I grabbed says "Made in Brazil". I have no idea how good the typical quality of Brazilian electronics components is but I have some confidence in the people who decided to get them made there). RM

Russell McMahon wrote: > (That sort of spec transcends manufacturing location. I note that the > first box of them that I grabbed says "Made in Brazil". I have no idea > how good the typical quality of Brazilian electronics components is but > I have some confidence in the people who decided to get them made > there). I don't think there is such a thing as "typical quality" of produced anything for a country. There maybe could be an average and a standard deviation (if there were a satisfactory scalar measure for quality), but even if there were, in almost all cases the variety of different qualities produced in any country makes a "typical" quality practically inexistent. Gerhard

On Mon, 13 Feb 2006, Gerhard Fiedler wrote: > Russell McMahon wrote: > >> (That sort of spec transcends manufacturing location. I note that the >> first box of them that I grabbed says "Made in Brazil". I have no idea >> how good the typical quality of Brazilian electronics components is but >> I have some confidence in the people who decided to get them made >> there). > > I don't think there is such a thing as "typical quality" of produced > anything for a country. There maybe could be an average and a standard > deviation (if there were a satisfactory scalar measure for quality), but > even if there were, in almost all cases the variety of different qualities > produced in any country makes a "typical" quality practically inexistent. I think that there is. The average level of services, manpower training and pay, causes average businesses to produce an average quality class of products. Peter