Author Topic: Source for resistor kits  (Read 27929 times)

0 Members and 1 Guest are viewing this topic.

Offline (In)Sanity

  • Regular Contributor
  • *
  • Posts: 229
  • Country: us
Source for resistor kits
« on: January 17, 2013, 12:58:30 am »
Does anyone happen to know a good source for relatively inexpensive,  but relatively good metal film resistor kits ?   I'm tired of the stuff coming out of China,  it's either fake (Carbon film) or just really poor quality.   There must be someone that's selling resistor kits that cover the full range for reasonable prices and still have decent quality?

I had finally tapped in to a batch of resistors I got from sure electronics years ago only to find they were all fake.  Not only were they fake they had a 540 ppm temperature coefficient on the 100k resistors I tested.  They are of course also negative coefficient just like a carbon film.   

If needed I'll just start ordering resistors from the major distributors one value at a time.   I'm just not finding they have the types of kits I really want in metal film.  Too granular. 

Thanks,

Jeff
« Last Edit: January 17, 2013, 01:59:55 am by (In)Sanity »
 

Offline robrenz

  • Super Contributor
  • ***
  • Posts: 3035
  • Country: us
  • Real Machinist, Wannabe EE
Re: Source for resistor kits
« Reply #1 on: January 17, 2013, 01:47:13 am »
Jameco has some nice reasonable quality resistor kits HERE.

Offline AlphZeta

  • Regular Contributor
  • *
  • Posts: 244
  • Country: us
    • Kerry D. Wong
Re: Source for resistor kits
« Reply #2 on: January 17, 2013, 01:55:19 am »
Dipmicro has some metal film ones (kits) as well (http://dipmicro.com/store/SET-RF405). I ordered from them a few times and their service is pretty good and shipping is fast and relatively inexpensive.
 

Offline Nirios

  • Regular Contributor
  • *
  • Posts: 62
  • Country: us
Re: Source for resistor kits
« Reply #3 on: January 17, 2013, 02:07:11 am »
Amazon has a decent kit.  1/4 watt 1% metal film in individually labeled bags.  No issues with the one I ordered, I would get them again if I needed more.

http://www.amazon.com/Joe-Knows-Electronics-Value-Resistor/dp/B003UC4FSS/ref=sr_1_2?ie=UTF8&qid=1358388036&sr=8-2
 

Offline (In)Sanity

  • Regular Contributor
  • *
  • Posts: 229
  • Country: us
Re: Source for resistor kits
« Reply #4 on: January 17, 2013, 03:15:57 am »
Amazon has a decent kit.  1/4 watt 1% metal film in individually labeled bags.  No issues with the one I ordered, I would get them again if I needed more.

http://www.amazon.com/Joe-Knows-Electronics-Value-Resistor/dp/B003UC4FSS/ref=sr_1_2?ie=UTF8&qid=1358388036&sr=8-2

I was looking at those a little while ago.   I assume when heated the resistance increases ?   It's a quick way to find out if they are most likely real and a sure way to know if they are fake.   The ones I had naturally decreased in resistance when heated.   I tossed them back in their bag and they can sit until I use some of them for stuff like pull-up resistors or such. 

I'm not sure why anyone would include zero ohms and actually include it as a count.  That's a bit questionable practice.

I'm looking at the other links as well. 

Thanks,

Jeff
 

Offline Nirios

  • Regular Contributor
  • *
  • Posts: 62
  • Country: us
Re: Source for resistor kits
« Reply #5 on: January 17, 2013, 06:38:28 pm »
I was looking at those a little while ago.   I assume when heated the resistance increases ?   It's a quick way to find out if they are most likely real and a sure way to know if they are fake.   The ones I had naturally decreased in resistance when heated.   I tossed them back in their bag and they can sit until I use some of them for stuff like pull-up resistors or such. 

I'm not sure why anyone would include zero ohms and actually include it as a count.  That's a bit questionable practice.

I actually never tested them.  I do have a meter and a hot air reflow gun.  What test would you like to see?  I'm now curious to see how they perform.
 

Offline ftransform

  • Frequent Contributor
  • **
  • Posts: 729
  • Country: 00
Re: Source for resistor kits
« Reply #6 on: January 17, 2013, 06:51:24 pm »
I have a batch of metal film resistors that have varying temperature coefficents.

I have ordered carbon film and metal film resistors (both from our chinese friends).

I selected two same value resistors and scraped the epoxy off and I could see a difference between the two resistors, the the spiral on the carbon film one was less reflective then the metal film one.
When I performed heating tests on two of my metal film resistors I found that
47 ohm resistor -> decreases
15k resistor -> increases.

Comparing the two devices visually (I do not have a microscope), I'd say the colour and shine of the bands is similar.

I do not think temperature testing is a good way to distinguish between carbon and metal film. Remember tempco is specified as +- for these devices.
« Last Edit: January 17, 2013, 06:53:17 pm by ftransform »
 

Offline (In)Sanity

  • Regular Contributor
  • *
  • Posts: 229
  • Country: us
Re: Source for resistor kits
« Reply #7 on: January 17, 2013, 07:04:43 pm »
Interesting,   more clarification on this issue would be great from someone with the knowledge to do so.   I think carbon is always negative..but I could be wrong. 

Jeff
 

Offline ftransform

  • Frequent Contributor
  • **
  • Posts: 729
  • Country: 00
Re: Source for resistor kits
« Reply #8 on: January 17, 2013, 07:13:06 pm »
Here is a photograph I took (excuse the lack of lighting) between a supposed carbon film and supposed metal film resistor.

http://image.bayimg.com/71b0b4fe2f0a029ec69bd522d3cbffe2204c2113.jpg
The resistor on top is a 47ohm 5% tolerance carbon film resistor, measuring about 50 ohms and the other one is a 1% metal film measuring about 47 ohms.

It is difficult to catch the difference on camera but the difference in reflectivity is easily visible through a magnifying glass and bright light. I am not a resistor expert so take this with a grain of salt.

Perhaps a  reaction with mineral acid can confirm the band material.

« Last Edit: January 17, 2013, 07:16:44 pm by ftransform »
 

Offline (In)Sanity

  • Regular Contributor
  • *
  • Posts: 229
  • Country: us
Re: Source for resistor kits
« Reply #9 on: January 17, 2013, 07:17:30 pm »
Pretty much the same findings I've found with regard to the color of the film.   

Also I just found this,  not sure how accurate it is.

http://hyperphysics.phy-astr.gsu.edu/hbase/tables/rstiv.html

The interesting part is it lists carbon as negative.

Thanks,

Jeff
 

Offline ftransform

  • Frequent Contributor
  • **
  • Posts: 729
  • Country: 00
Re: Source for resistor kits
« Reply #10 on: January 17, 2013, 07:20:18 pm »
Yea, both resistors in that picture drop when they are heated with a lighter.
 

Offline (In)Sanity

  • Regular Contributor
  • *
  • Posts: 229
  • Country: us
Re: Source for resistor kits
« Reply #11 on: January 17, 2013, 07:29:06 pm »
It would be interesting to know if you have any in that batch that increase ?   Without torching your resistor collection of course.   Just a little bit of heat will tell you.   

I've not found any in my collection of fake metal film that go up instead of down when heated.

Jeff
 

Offline ftransform

  • Frequent Contributor
  • **
  • Posts: 729
  • Country: 00
Re: Source for resistor kits
« Reply #12 on: January 17, 2013, 07:55:21 pm »
It would be interesting to know if you have any in that batch that increase ?   Without torching your resistor collection of course.   Just a little bit of heat will tell you.   

I've not found any in my collection of fake metal film that go up instead of down when heated.

Jeff

I might some time later in the day when I feel a burst of energy. That really is alot of work so I'm hoping someone else on the forum will have some insight that will prevent me from having to do it. I would need to test 1, 10 , 100, 1000, 10000, 100000, 1M

How did you know that your metal films are fake?
I'm gonna go out on a hunch here and say that the low values will have a negative tc and the higher values will have a positive tc.


http://www.electro-tech-online.com/general-electronics-chat/39279-metal-film-temperature-coefficient.html

« Last Edit: January 17, 2013, 07:59:07 pm by ftransform »
 

Offline (In)Sanity

  • Regular Contributor
  • *
  • Posts: 229
  • Country: us
Re: Source for resistor kits
« Reply #13 on: January 17, 2013, 08:08:01 pm »
Based on the info in that forum I would say,  if you have one that goes up when heated your entire batch is good.   It's what I've also seen.   If you can't find a single one that goes up then their is a good chance they are really remarked carbons.   

Jeff
 

Offline kcs

  • Regular Contributor
  • *
  • Posts: 160
Re: Source for resistor kits
« Reply #14 on: January 17, 2013, 08:55:02 pm »
Interesting topic. I was about to order this kit.
 

Offline ftransform

  • Frequent Contributor
  • **
  • Posts: 729
  • Country: 00
Re: Source for resistor kits
« Reply #15 on: January 17, 2013, 09:03:32 pm »
Based on the info in that forum I would say,  if you have one that goes up when heated your entire batch is good.   It's what I've also seen.   If you can't find a single one that goes up then their is a good chance they are really remarked carbons.   

Jeff

so they can somehow shine up carbon ?
Why not just scratch it off and look?
 

Offline (In)Sanity

  • Regular Contributor
  • *
  • Posts: 229
  • Country: us
Re: Source for resistor kits
« Reply #16 on: January 17, 2013, 11:46:53 pm »
Based on the info in that forum I would say,  if you have one that goes up when heated your entire batch is good.   It's what I've also seen.   If you can't find a single one that goes up then their is a good chance they are really remarked carbons.   

Jeff

so they can somehow shine up carbon ?
Why not just scratch it off and look?

From what I've seen so far the metal film and carbon film do look a bit different once you scrape off the enamel.   I doubt they would bother to disguise it beyond just being blue and the extra band.   The only reason I can see against the scratch method is if you want to figure out a larger grouping of them,   or perhaps loose resistors or maybe even those you pulled from another device.   

For me it's not really the cost of the resistors, it's just getting what you paid for.   How do I know that if I pay $50 for a kit that I'm getting quality vs the $20 kit.   I need to improve my small environmental chamber to better plot the temperature coefficient of various parts.   Having a 6 1/2 digit mete certainly has come in handy.    I can tell if a resistor goes positive or negative often just be waving my hand at it.    Touch it and it's really obvious.   I think I forgot that many people don't have those extra digits.

Jeff
 

Offline ftransform

  • Frequent Contributor
  • **
  • Posts: 729
  • Country: 00
Re: Source for resistor kits
« Reply #17 on: January 18, 2013, 01:05:28 am »
Based on the info in that forum I would say,  if you have one that goes up when heated your entire batch is good.   It's what I've also seen.   If you can't find a single one that goes up then their is a good chance they are really remarked carbons.   

Jeff

so they can somehow shine up carbon ?
Why not just scratch it off and look?

From what I've seen so far the metal film and carbon film do look a bit different once you scrape off the enamel.   I doubt they would bother to disguise it beyond just being blue and the extra band.   The only reason I can see against the scratch method is if you want to figure out a larger grouping of them,   or perhaps loose resistors or maybe even those you pulled from another device.   

For me it's not really the cost of the resistors, it's just getting what you paid for.   How do I know that if I pay $50 for a kit that I'm getting quality vs the $20 kit.   I need to improve my small environmental chamber to better plot the temperature coefficient of various parts.   Having a 6 1/2 digit mete certainly has come in handy.    I can tell if a resistor goes positive or negative often just be waving my hand at it.    Touch it and it's really obvious.   I think I forgot that many people don't have those extra digits.

Jeff

I really don't think they will mix in fake resistors. They are in a tape and making a special machine to "cut" the tapes would be expensive and their not done by hand because those leads are thin and you would see the imperfections from human hands + the cost of labor would not be worth it as resistors are cheap.  I also noticed that the epoxy on the carbon ones is slightly different then the epoxy on the metal film ones.

I would not trust high precision low tempco resistors from ebay but I think for general purpose it is fine. IMO that kind of kit will be good enough for development purposes, once you get the prototype going then order better more expensive parts from digikey. Resistors are cheap enough that you should never need to recycle them..

Having cheap parts on hand is really useful too, because then you can build your circuit with two different kinds of parts and see how well it performs. Maybe you will discover that your circuit performs adequately using the cheapest of parts, and you can get a better feel of what to expect if you want to mass produce your product cheaply. Exactly why I bought carbon film resistors in addition to metal film resistors.

The thought of having an assortment is super awesome resistors is nice but thats rich people shit.
« Last Edit: January 18, 2013, 01:14:41 am by ftransform »
 

Offline (In)Sanity

  • Regular Contributor
  • *
  • Posts: 229
  • Country: us
Re: Source for resistor kits
« Reply #18 on: January 18, 2013, 02:08:23 am »
Sadly what I found was the Radio Shack 500 resistor assortment I have out performs the fake metal films from China.   Using a make shift environmental chamber based on a peltier cooler/heater I started graphing the temperature coefficient of various resistors I had.   I had some metal films that were around 40-50 ppm/C and shockingly some Chinese surface mount resistors that were < 10 ppm/C with repeated tests.    The Radio Shack assortment came in around 340-350ppm/C and the fake Chinese metal films came in about 540 ppm/C.    So all that being said for basic day to day development I'm better off going down to RS and buying their kit.   For actual production I'm far better off using SMD components,  which is what I normally do anyway.    The tolerance on all of them was within spec.

I don't have a good enough assortment of quality resistors lying around for doing any type of precision work.   It's the temperature coefficient that kills me.   I have some resistor on the way from Amazon that I'll report back on.   

It would be nice to have a verified list of suppliers to purchase from.

Jeff
 

Offline Psi

  • Super Contributor
  • ***
  • Posts: 7939
  • Country: nz
Re: Source for resistor kits
« Reply #19 on: January 18, 2013, 03:49:30 am »
Anyone tried ordering 100 of every value from digikey?
« Last Edit: January 18, 2013, 03:57:43 am by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline (In)Sanity

  • Regular Contributor
  • *
  • Posts: 229
  • Country: us
Re: Source for resistor kits
« Reply #20 on: January 18, 2013, 04:08:45 am »
Anyone tried ordering 100 of every value from digikey?

I thought about doing just that.   Perhaps even just the E48 range,  although the E96 range would be nice. 

385 values to cover the E48 range.   So figure $2-$4 per 100 for decent resistors.   That's $770 -  $1540 for 38,500 resistors.  That's a lot of resistors and a lot of money.   Perhaps ten each would be a bit more realistic.    Actually thinking about this it's no wonder the Chinese makes fake ones.  They can sell hundreds of their fake kits for one of the real kits sold.

Jeff
 

Offline ftransform

  • Frequent Contributor
  • **
  • Posts: 729
  • Country: 00
Re: Source for resistor kits
« Reply #21 on: January 18, 2013, 05:58:31 pm »
I still don't understand what you mean by fake. Do you mean poor performance or disguised carbon film resistors?

As a relative test I compared two 11k resistors:
1) Chinese metal film
2) Digikey http://www.digikey.com/product-detail/en/MFR-25FBF-11K0/11.0KXBK-ND/13227

Their initial values after stabilization in a 2 ohm measurement on a 6.5 digit meter were within 2 ohms of each other.
Anyway, I nulled out the meter and performed a finger pinch heating test, being careful not to touch the leads. I held them for a while (it took lets say 20+ seconds to stabilize).
The digikey one, listed at +- 100ppm, stabilized at ~ +1.6 ohms.
The ebay one, listed as 100ppm (i think?), stabilized at ~ -3 ohms.

I don't know how hot my hand makes em but they are similar size and I was holding it similarly. When I released my fingers the resistors went back to null (as good as they will get in a slightly drafty room) and the results were fairly repeatable (lets say to 0.2 ohms).

So it seems that worst case, assuming the digikey resistor is in spec, the chinese one has -200ppm temperature coefficent.
I'd imagine that the digikey resistor is slightly better then its spec, (as dave jones demonstrated that the tolerance of resistors listed as 1% was more like 0.5 percent) then I don't think the chinese ones are too bad.

Perhaps I will try pressing them against a light bulb in a styrofoam box or something. Getting a stable thermal environment seems like a complete motherfucker.
« Last Edit: January 18, 2013, 06:41:46 pm by ftransform »
 

Offline bjorg

  • Newbie
  • Posts: 3
 

Offline (In)Sanity

  • Regular Contributor
  • *
  • Posts: 229
  • Country: us
Re: Source for resistor kits
« Reply #23 on: January 18, 2013, 08:41:02 pm »
What I have are remarked carbon films with a temperature coefficient of around 540 ppm/C for a 100k resistor.  They have steel leads and are generally low quality.   I have some Radio Shack carbon films that measured around 350 ppm/C for the same value resistor.   So not only are my Chinese resistors "Fake" metal film aka disguised,  remarked,  etc.   They are also very low quality for even a carbon film. 

Jeff
 

Offline ftransform

  • Frequent Contributor
  • **
  • Posts: 729
  • Country: 00
Re: Source for resistor kits
« Reply #24 on: January 18, 2013, 08:57:58 pm »
What I have are remarked carbon films with a temperature coefficient of around 540 ppm/C for a 100k resistor.  They have steel leads and are generally low quality.   I have some Radio Shack carbon films that measured around 350 ppm/C for the same value resistor.   So not only are my Chinese resistors "Fake" metal film aka disguised,  remarked,  etc.   They are also very low quality for even a carbon film. 

Jeff

Damn, well if you can use those in your design reliably then you will be a chinamaster.  :-+
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf