Which is the Value of This Resistor - Page 1
Forum section: electronics / beginners

author: tpd
author_rank: Contributor
timestamp: April 13, 2024, 05:42:51 pm
content: Hi,I have tried to calculate resistance of the blue resistor using 2 online calculators, but I think that I made a mistake.I have tried to mesaure the value using Ohmmeter in both directions, and I got app. 1 Ohm.The resistor is a part of the small chinese switcher 5 V / 6A.Can someone say its resistance, I prefere not to desolder the resistor to make measurements (according to calculators its resistance is more than 1 MOhm)?Thanks

author: Andy Watson
author_rank: Super Contributor
timestamp: April 13, 2024, 05:54:20 pm
content: 0.471% tolerance

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 13, 2024, 05:59:41 pm
content: Cheating using your measurement and the picture together I would suggest that it should be 0.56 ohms, nominally one percent.Reading the bands left to right black green blue silver black translates to 056 times 0.01 with the right hand band indicating tolerance.There is often a bit of confusion in reading these things due to the variety of conventions used (3, 4, 5 and sometimes even 6 bands) and the often difficult to discern colors even for those with good color vision (mine is good, but not the very best). Silver and grey are some of the more difficult to discern, but grey and white and yellow and gold are also common challenges. I always double check my interpretations with a meter.Getting an accurate reading on such a small resistor is a bit of a challenge. At very least, if your meter supports it, connect the leads and set the zero offset. A four wire Kelvin connection is better and the quality of the probes is also important because the contact resistance of garden variety probes can often be a significant fraction of an ohm. The good news is that the low value makes it less likely that other components in the circuit will materially affect the reading. There is little or no benefit to unsoldering it for the measurement.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 13, 2024, 06:01:19 pm
content: Quote from: Andy Watson on April 13, 2024, 05:54:20 pmIllustrates my point about colors. That green certainly shows tinges of yellow and the blue does edge toward violet. And for whatever reason, the 47 combination seems more popular than the 56. In my wanderings around various types of electronics I have probably seen five times as many 0.47, 4.7, 4.7K, 47K etc. than the similar series around 56.

author: IanB
author_rank: Super Contributor
timestamp: April 13, 2024, 06:13:18 pm
content: I'm going to say yellow-violet-silver. The yellow looks greenish because it is painted on top of a blue background, and the violet is bright. I think blue would be much darker.

author: tpd
author_rank: Contributor
timestamp: April 13, 2024, 06:19:36 pm
content: Quote from: CatalinaWOW on April 13, 2024, 05:59:41 pmI tought the same, but since it exploaded in the old switcher, the only way to be sure is to desolder it in the new one, then measure.Anyways, casual ohmmeter can't make such a measurement, miliohmmeter is necessary I suppose.

author: wasedadoc
author_rank: Super Contributor
timestamp: April 13, 2024, 06:44:18 pm
content: The colours of the 470k resistor at the bottom of the picture sway me towards 0.56 Ohm.

author: Rick Law
author_rank: Super Contributor
timestamp: April 14, 2024, 11:11:48 pm
content: The second Green-ish/Yellow-ish looking band is the question here. The Blue and Silver bands are clear and rather distinguishable from the other colors. Accepting that 3rd band as BLUE, that would make that last digit a 7. Green-Blue would make that 57 which would be a very rare value. Yellow-Blue would make that 47 which is far more common as resister value.So I think .47 is probably the answer.Why bother with color code anymore. Not only is the paint used causing variation. Room lighting also affects reading significantly. "Warm" (2000K to 3000K) lighting vs "DayLight" (5000K) vs "White" Light (>6000K) bulbs give me rather different colors,.I think, it is time to make that a numeric print.Today's manufacturing method can certainly print 047 small enough to fit on a 1/8 watt or 1/16 watt though hole resister.Then again, if some manufacturers are sanding off IC labels, why would they object to unreadable color codes...EDIT: Quick finger caused error. Some text from the very last paste was missing. Fixed.

author: wasedadoc
author_rank: Super Contributor
timestamp: April 14, 2024, 11:19:51 pm
content: Quote from: Rick Law on April 14, 2024, 11:11:48 pmOh dear! Blue is 6, not 7.And you don't know how to spell 'resistor'.

author: Rick Law
author_rank: Super Contributor
timestamp: April 14, 2024, 11:52:39 pm
content: Quote from: wasedadoc on April 14, 2024, 11:19:51 pmI erred.I was counting 0, so I got blue as the 7th number... Yup, you are right.I have to eat my word -- I am already overweight. Last thing I needed is to eat more.

author: tpd
author_rank: Contributor
timestamp: April 15, 2024, 09:55:05 am
content: Since the subject become a hit I have decided to disassamble it and make a measurement, the resistor is app. 0,5 Ohm, which is not obvious looking at chinese marking.D6 is MBRF10100CT, in second switcher that I bought it is labeled.Pay attention to soldering, these long, overlapping legs could make short circuit easily (I think it is necessary to check this before connecting it to mains).I don't know do Chinese test them before selling, but the first switcher, which I'm trying to fix, just exploded after powering it.I read about similar switchers on internet, people claim that they are not reliable, and very noisy.If you need a quality switcher, buy Meanwell or something similar.

author: donlisms
author_rank: Frequent Contributor
timestamp: April 15, 2024, 07:54:54 pm
content: Something you could try, if perhaps you want to be more sure of the resistance measurement, is clip the test leads both to the same side of the resistor to get a "zero" reading, then subtract that from the resistor measurement.This probably points more toward 0.47 as you have concluded; a little bit lower than the reading.That's just a thought.

author: Jwillis
author_rank: Super Contributor
timestamp: April 15, 2024, 08:43:20 pm
content: With very low resistor values measured with any DMM, you should always first check the resistance of the probes first before measuring the component. This should be done even with the best DMM's. Short the probes together and read the probe resistance. Subtract that reading from the measured resistor value.Best measurements for resistors below 1 ohm should be done with a 4 probe resistance meter for the most accurate measurement.

author: BTO
author_rank: Frequent Contributor
timestamp: April 16, 2024, 10:04:30 am
content: Quote from: tpd on April 13, 2024, 05:42:51 pmPiece of cake...go to a resistor calculatorhttps://www.digikey.com.au/en/resources/conversion-calculators/conversion-calculator-resistor-color-code1. Select a 5 Band Resistor2. Your first problem will be, which side is which,Well, Band cannot have a black, so the black side is band 1YOUR ANSWER IS 0.47 Ohms , 1% ToleranceDepending on how you interpreted the last band, Red or Brown if you picked Red it's 2% ToleranceEither way you should be getting a reading close to 0.47 Ohms, Not 1 Ohmif the yellow is a green it's 0.57 Ohms. What we can agree on is that the forum has agreed it is either 0.47 or 0.57 Ohm.it's not 1 OhmAlso.. YOU SHOULD DESOLDER IT TO GET THE CORRECT READING, At least 1 leg of itSee the Attachment

author: Vovk_Z
author_rank: Super Contributor
timestamp: April 16, 2024, 03:15:45 pm
content: If it's a usual power supply then used resistors are from E24 standard resistor values. So, 0,47 R makes sense, but not 0.57 R. Because there isn't such standard value in any E96, E192 series.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 17, 2024, 02:07:54 am
content: Quote from: Vovk_Z on April 16, 2024, 03:15:45 pmActually I believe that 0.47 and 0.56 are the choices, since those are valid values. Both the green (yellow?) and the blue (violet?) band are ambiguous in this picture. Depending on your display you may choose different options there. Only a good ohmmeter can resolve this. I suspect the supply will work adequately with either, but demand my right to be possibly wrong on this.