Resistor color code, silver third ring. - Page 1
Forum section: electronics / beginners

author: davidut5
author_rank: Contributor
timestamp: March 08, 2024, 04:55:09 pm
content: So, i have two resistors, one is burnt, the other one is ok and is just to compare.What colors do you see, and what values? Then i will tell you what measured value has the good one.The burnt one i see RED-BLACK-SILVER-GOLD-GREEN this is incorrect as most calculators cannot input silver as third ring.The good one i see VIOLET-GREEN-SILVER-GOLD-RED this is also incorrect as above.Majority on fb said third ring is grey not silver, but the measured good resistor contradicts them.What is your opinion?The resistor is in the source of a mosfet in a pc atx psu, the mosfet also shorted.Thank you.

author: ejeffrey
author_rank: Super Contributor
timestamp: March 08, 2024, 05:12:14 pm
content: Who says you can't have silver as the third band? That is a 5% 0.1 ohm resistor.

author: johansen
author_rank: Super Contributor
timestamp: March 08, 2024, 05:13:18 pm
content: its a current sense resistor, so something in the .01 ohm range is going to be expected.i tend to think the silver is grey, and the multiplier is 0.1but it could be the silver is the multiplier and they are on the order of 0.010 ohms and 0.075 ohmshttps://eepower.com/resistor-guide/resistor-standards-and-codes/resistor-color-code/#

author: Ian.M
author_rank: Super Contributor
timestamp: March 08, 2024, 05:34:53 pm
content: First:2 (red) 0 (black) /100 (silver) = 0.2 ohms, 5% (gold) then there's that pesky green band. On six band resistors a green last band would indicate a 20 ppm/K temperature coefficient, but on a two digit & multiplier resistor its more likely to be a manufacturer specific code indicating the resistor type.The second is a bit ambiguous, but as there is no '21' in the E24 series, I'd go for:7 (violet) 5 (green) /100 (silver) = 0.75 ohms, 1% (brown), and red is the manufacturer code band.

author: davidut5
author_rank: Contributor
timestamp: March 08, 2024, 05:40:24 pm
content: Ian, that makes the most sense. So in fact they are 4 band after all. The good one measures 0.66R on my multi-tester, so silver definitely makes sense.

author: AndyBeez
author_rank: Frequent Contributor
timestamp: March 08, 2024, 05:41:20 pm
content: Tricky. [Gold dress? Blue dress?] I say silver band.And I agree with@Ian.M's values. The third band can only be silver on a three band (excluding tolerance) plan as four bands, only allows grey.Incidentally, if these were five band inductors, the first band would always be silver!

author: tooki
author_rank: Super Contributor
timestamp: March 08, 2024, 05:43:44 pm
content: Quote from: Ian.M on March 08, 2024, 05:34:53 pmIndeed. I was wondering how the prior replies arrived at 0.1 and 0.01 ohms, since that didn’t make sense no matter which end one started with.

author: Ian.M
author_rank: Super Contributor
timestamp: March 08, 2024, 05:44:51 pm
content: Quote from: davidut5 on March 08, 2024, 05:40:24 pmYes, those '328' component testers tend to be inaccurate for low ohm resistors. Do a four wire measurement using a CC/CV bench supply (or other current source) to put 100 mA through it and you should measure 75 mV.@tooki,

author: davidut5
author_rank: Contributor
timestamp: March 08, 2024, 06:51:54 pm
content: Did 1000mA, and measured 760mV, close enough. Used my mastech multi-meter and a dc-dc cc/cv step down converter. No precision tools here.

author: Ian.M
author_rank: Super Contributor
timestamp: March 08, 2024, 07:02:58 pm
content: 1A is getting high enough to run into heating problems in higher value low ohm resistors. If you want to make up a permanent low ohm test jig, I'd recommend a 100mA current source and a x10 OPAMP circuit to amplify the sensed voltage for direct readout of 0-2 ohms on a DMM's 2V range. Put a diode in series with the negative side of the supply to get the OPAMP neg. supply 0.7V below ground so you don't need a very good RRIO OPAMP.