2
\$\begingroup\$

Here we identify the color code determining the values of non-inductive wire wound resistors, specifically Yageo's NKN series (but applicable to other manufacturers of this class), which are a unique and separate case recognizable by a final black stripe, NOT TO BE CONFUSED WITH CASES OF normal 3 or 4 BAND RESISTORS WITH AN ADDED TEMPERATURE COEFFICIENT BAND, which are then often wrongly interpreted/read as 4 or 5 band resistors respectively, as is the case in the answer of which my question was wrongly deemed a duplicate of! The non-inductive resistors treated in this question use a unique color coding scheme which differs greatly from the standard code, and as this issue has never been raised on Stack Exchange or the internet at large, it is valuable to present an explanation of its recognition and interpretation, as it is otherwise almost impossible to find information about them.

I was just disassembling an Asus 19V 4.74A laptop SMPS power brick, and came across these two resistors. I am at a loss as to their values, as neither seem to follow the standard color code we all know and love... Both test 0.0 or 0.1 on my multimeter, and both look brand spanking new, no burn marks, and the power supply works a treat. My guess is that these are some kind of fancy current sensing resistors, with super low resistances (the standard color code doesn't allow for anything lower than 0.01 Ohm). Any of you kind folks seen something like this before, and could maybe explain the code for this type of niche resistor? enter image description here enter image description here enter image description here To my mind one is brown, black, silver, gold, black and the other gray green silver gold black.

May the wiseth shareth their wisdom with us mortals!

\$\endgroup\$
2
  • 2
    \$\begingroup\$ In this specific case, I'd put my money on non-inductive over temperature coefficient, based on the images. I think I can see the windings, along with the fact that the final band is black. Interesting Article \$\endgroup\$ Aug 24, 2021 at 21:18
  • 1
    \$\begingroup\$ Nope @TomCarpenter looks like this is something called a 'non-inductive wire wound resistor' specifically indicated by a final black last band, the resistor analyzed in your link is of standard type, just with a temperature rating band last (green in that case). \$\endgroup\$
    – parkside
    Aug 24, 2021 at 22:31

2 Answers 2

4
\$\begingroup\$

These are likely (we can't know for sure without knowing the manufacturer) non-inductive wire-wound power resistors. This is sometimes characterized by that final black band.

They, unlike normal wire-wound resistors, avoid inductance by having half the windings wrap the opposite direction. You can kind of see that under the ceramic.

You are quite right in that they are probably for current sensing.

https://forum.digikey.com/t/when-your-5-band-resistor-is-not-a-5-band-resistor/1501

\$\endgroup\$
15
  • 2
    \$\begingroup\$ @Aaron We can't know for sure based on what is posted. If you read my comment under Tom's you see that I would bet on non-inductance over tempco because I can see the windings under the ceramic, and this is common in low-value current sense resistors. The fact that it is black also makes it more likely to be non-inductive. Also, some of the pictured ones look just like Yageo resistors, and this is how they mark them. The image in my answer, while from Digikey, is originally from a Yageo datasheet. \$\endgroup\$ Aug 24, 2021 at 21:28
  • 1
    \$\begingroup\$ Another thing that makes me lean that way: sub 1 Ω wire-wound resistors with a tempco of 250ppm? You would have to try hard to make one that bad (I've never seen one over 200ppm, and they easily achieve 50ppm). \$\endgroup\$ Aug 24, 2021 at 21:34
  • 1
    \$\begingroup\$ @parkside I'm not sure and would not like to make a misleading guess...I will say, most multimeters have a hard time giving accurate reading under 1 Ω, so take those reading with a grain of salt (unless you are using a special low-impedance reading meter) \$\endgroup\$ Aug 25, 2021 at 14:05
  • 1
    \$\begingroup\$ @evildemonic I figured something like that, but I tried putting both resistors in series and measuring them, 0.1+0.85 should have given me 0.9-1.0 on the multimeter (UT191T) but even so it read 0.1/0.2. The multimeter should be OK at measuring that kind of resistance form my experience no? \$\endgroup\$
    – parkside
    Aug 25, 2021 at 14:10
  • 1
    \$\begingroup\$ @evildemonic the picture is just a placeholder, showing a 'normal' br-bl-sl-gl-bl 1-0-0.01-5%-NKN, so 0.1 Ohm. BUT, the data sheet say the offer the NKN series in an E24 series, from 0.03 Ohm and up, meaning they would have to be able to represent 0.03 0.033 0.036 0.039 0.043 0.047 0.051 0.056 0.062 0.068 0.075 0.081 0.091. This lead me to find their newest datasheet hidden on their site: BINGO check page 13: yageo.com/upload/media/product/products/datasheet/lr/… they show multipliers gray and white, 0.001 and 0.0001 respectively! \$\endgroup\$
    – parkside
    Aug 26, 2021 at 14:11
3
\$\begingroup\$

So after much searching and some great advice from @evildemonic I managed to find a datasheet with an updated/more detailed table of the resistor color code markings. Our guess is that these are Yageo NKN series wire-wound non-inductive resistors (available E24 0.03-220 Ohm, 1-7W), 1W type. Now that datasheet says these should have a green colored body, and these are grey, but some show the Yageo ones in grey too, so whatever, even if they are clones, they follow this numbering scheme. The defining characteristic is a final black band, indicating non-inductive (and not a temperature coefficient marking, as these are 300ppm/K, a class that doesn't exist in the traditional marking scheme, black would otherwise be 100/200/250 ppm/K depending on who you ask). I figure some other companies might also use this scheme for 'ultra' low value resistors (anything lower than 0.01 Ohm or requiring a further decimal in the tens of miliohms). One other thing I've seen is also pink as the 0.001 multiplier, in some other companies datasheet, just to give you an idea if you're picking your brain deciphering some odd looking resistor.

Here is the color code: enter image description here

Full datasheet: https://www.yageo.com/upload/media/product/products/datasheet/lr/YAGEO%20NKN_datasheet_2021v0.pdf

So the answer is:

  • brown black silver gold black 1 | 0 | x0.01 | 5% | non-inductive => 0.1 Ohm enter image description here
  • grey green grey gold black 8 | 5 | x0.001 | 5% | non-inductive => 0.085 Ohm enter image description here
\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.