Which types of resistors are more stable in front of temperature variations

[VanitarNordic]

Hi,

I have a project which current flow could cause the resistor to warm up. All resistors are unstable in front of temperature changes and their values might increase or decrease, but some types are more stable and can tolerate more or show less temperature resistance variation.

if I am right the parameter named "temperature coefficient", but I don't know low values are better or high values. Besides some designers told me to use 1% 2-3W metal film resistors. They are best. is this true?   

[DaJMasta]

The higher the tempco, the more they will change with a given change in temperature, so you're looking for low tempco parts.

Some of the best are the metal foil resistors, and some of the cheapest thick film/carbon resistors are some of the worst, but there are a bunch of fairly inexpensive intermediate types which could fit the bill depending on what you need.  In your case though, the tempcos are in ppm, not as high as percents, probably, and the fluctuation may not be all that far when heating up 50C or something from high currents... so maybe it doesn't matter too much for your application, and maybe, if it does, you can just get a few resistors to put in parallel - lowering the current through each and reducing the temperature of each, reducing the change in resistance.

The 1% you mention is probably the initial tolerance, not the temperature coefficient.

[VanitarNordic]

The higher the tempco, the more they will change with a given change in temperature, so you're looking for low tempco parts.

Some of the best are the metal foil resistors, and some of the cheapest thick film/carbon resistors are some of the worst, but there are a bunch of fairly inexpensive intermediate types which could fit the bill depending on what you need.  In your case though, the tempcos are in ppm, not as high as percents, probably, and the fluctuation may not be all that far when heating up 50C or something from high currents... so maybe it doesn't matter too much for your application, and maybe, if it does, you can just get a few resistors to put in parallel - lowering the current through each and reducing the temperature of each, reducing the change in resistance.

The 1% you mention is probably the initial tolerance, not the temperature coefficient.

Thank you for your reply
1% was suggested because these two resistors should have identical valuse either, as close as possible. In accompany with temperature stability.

[Neilm]

1% was suggested because these two resistors should have identical valuse either, as close as possible. In accompany with temperature stability.

1% is not very tight for precision resistors. 0.1% resistors are quite common with reasonable tempcos.

[BrianHG]

You do realize you can go to Digikey, search resistors, select for example chip resistors with package and may be a few other options like here:
https://www.digikey.com/products/en/resistors/chip-resistor-surface-mount/52?k=resistor&k=&pkeyword=resistor&pv7=197&pv7=2&pv7=1&FV=1f140000%2Cffe00034%2C403d0f%2C403d1f%2C400004%2C400005&quantity=0&ColumnSort=0&page=1&stock=1&nstock=1&pageSize=25

Then, scroll the the right on your web browser and see at the top selection columns after features "Temperature Coefficient" & select the accuracy you want.  The values work in "±%change PPM" /vs/ "temp change in °C".

At "±10ppm/°C", you are already at around 61 cents for 1 resistor, 47 cents each for 10.
At "±5ppm/°C", you are already at around 2.15$ for 1 resistor, 1.90$ each for 10.
At "±2ppm/°C", you are already at around 10.64$ for 1 resistor, 9.80$ each for 10.

A normal 1% resistor usually has a ±100ppm/°C tempco, but they cost 10 cents each, or, 1.5 cents each for 10.
While, a better 1% resistor with a ±50ppm/°C tempco,will cost 10 cents each, or, 7.6 cents each for 10.

Your best bang for the buck are the resistors with a ±10ppm/°C tempco.

[VanitarNordic]

You do realize you can go to Digikey, search resistors, select for example chip resistors with package and may be a few other options like here:
https://www.digikey.com/products/en/resistors/chip-resistor-surface-mount/52?k=resistor&k=&pkeyword=resistor&pv7=197&pv7=2&pv7=1&FV=1f140000%2Cffe00034%2C403d0f%2C403d1f%2C400004%2C400005&quantity=0&ColumnSort=0&page=1&stock=1&nstock=1&pageSize=25

Then, scroll the the right on your web browser and see at the top selection columns after features "Temperature Coefficient" & select the accuracy you want.  The values work in "±%change PPM" /vs/ "temp change in °C".

At "±10ppm/°C", you are already at around 61 cents for 1 resistor, 47 cents each for 10.
At "±5ppm/°C", you are already at around 2.15$ for 1 resistor, 1.90$ each for 10.
At "±2ppm/°C", you are already at around 10.64$ for 1 resistor, 9.80$ each for 10.

A normal 1% resistor usually has a ±100ppm/°C tempco, but they cost 10 cents each, or, 1.5 cents each for 10.
While, a better 1% resistor with a ±50ppm/°C tempco,will cost 10 cents each, or, 7.6 cents each for 10.

Your best bang for the buck are the resistors with a ±10ppm/°C tempco.

Unfortunately because of sanctions I can not buy components from US based component stores. Maybe some european stores could deliver components which I am not quite sure if it worthes to buy just few resistors and pay hight postal fees.

[VanitarNordic]

1% was suggested because these two resistors should have identical valuse either, as close as possible. In accompany with temperature stability.

1% is not very tight for precision resistors. 0.1% resistors are quite common with reasonable tempcos.

How is the availability of 0.1% resistors in 2w or 3w range?

[BrianHG]

Through hole
https://uk.rs-online.com/web/c/passive-components/fixed-resistors/through-hole-fixed-resistors/?searchTerm=resistors&applied-dimensions=4294867345,4294860902,4294851853,4294860900,4294805764,4293564420,4294873066,4293286515,4294881347,4294881294,4294876472&rpp=100

Just modify my selection filters, at this power level, most are between 15 and 25ppm/K
I included 1watt. just use 2 in series or parallel for 2watt.

SMD
https://uk.rs-online.com/web/c/passive-components/fixed-resistors/surface-mount-fixed-resistors/?applied-dimensions=4294860902,4294851853,4294869461,4294805764,4294873066,4294881347,4294867345&rpp=100

[BrianHG]

https://uk.rs-online.com/web/c/passive-components/fixed-resistors/through-hole-fixed-resistors/?searchTerm=resistors&applied-dimensions=4294873066,4294869461,4294851853,4294860902&rpp=100

5w and 3w are the most popular in +/-20ppm/degC

[Jwillis]

Iran should have access to Amazon and Ebay .I believe China and some European countries ship to Iran. I think Canada will ship to Iran as well ,electronic components are not on any restriction list I've seen.

[VanitarNordic]

Iran should have access to Amazon and Ebay .I believe China and some European countries ship to Iran. I think Canada will ship to Iran as well ,electronic components are not on any restriction list I've seen.

No, I don't have access to eBay or Amazon. According to the US Department of Treasury, no US-based company can have financial transaction or technology delivery with Iran, except with permission. Therefore some of the high-tech companies even are blocked for the Iranian IP address!

This does not apply to non-US companies, therefore Yes, I can buy from Canadian or whatever other stores, if they could deliver and shipment costs are not high.

I can buy components from online and local stores either, but mostly, their purchase sources are from China. The Chinese provided components vary too much in terms of quality from source to source and you can not trust that much on their offered parts. Therefore if the project is in the way that quality matters and we need some genuine/original components, that would be a problem.

[cellularmitosis]

Hello,

Here are my notes on resistors.

https://docs.google.com/spreadsheets/d/1ehaeZ3XRQLUmOXZ1fhGlg-V5EXQ1VFFxHjfW145CqyA

[VanitarNordic]

Hello,

Here are my notes on resistors.

https://docs.google.com/spreadsheets/d/1ehaeZ3XRQLUmOXZ1fhGlg-V5EXQ1VFFxHjfW145CqyA

Thank you, but the resistors would be in the range of 2W because high current will pass through them, that's the reason why temperature coefficient is important here. These two resistors must be identical and temperature stable. Therefore at least 1%-2W resistors. The value is specifically 390 Ohm.

[BravoV]

Whats your budget ?

[RobK_NL]

It would be very helpful if you could tell us a bit more about what you are trying to achieve.

You talk about "high current" through a 390Ohm resistor. At 2W, that's only about 70mA max.

Also, will the two resistors always have the same current going through them? What is your error budget?

[Conrad Hoffman]

A wire-wound should be quite good. Use a higher wattage so the temperature rise will be lower and thus the change in resistance will be lower. Maybe use a metal body and put it on a heat sink.

[VanitarNordic]

It would be very helpful if you could tell us a bit more about what you are trying to achieve.

You talk about "high current" through a 390Ohm resistor. At 2W, that's only about 70mA max.

Also, will the two resistors always have the same current going through them? What is your error budget?

High current has mentioned in relative to other parts of the circuit. actually, the current does not flow continuously through the resistor but it would be in form of short pulses.

Actually I purchased two 1%-2W resistors from local stores and I'll test them to see what happens, but generally, I can put maximum 2USD aside for each resistor, but it depends. I must see what it is.