EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: franklin19c on May 14, 2020, 04:49:32 pm
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I've been looking for hours trying to find a 9Ohm through hole resistor, and I can't find one. I may be missing something, but I don't even see them in the 100 piece sets on AliExpress or eBay. Any suggestions on where to look? There's a Microcenter near by, but I don't want to wait in line to get in the building with the restrictions going on right now.
I'm trying to fix an cheap miltimeter with a fried resistor, so it's not really worth the trouble, but I'm just trying to find an excuse to work on something. I'm decent a soldering, but I'm new to actually repairing a board. Any help is greatly appreciated. I feel like this is a dumb question, so feel free to point and laugh. I just want to figure out what I'm doing wrong.
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You can use E24 value 9,1 R, but it definitely won't be as accurate.
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There are nifty freeware calculators, which will assist you in generating any arbitrary value with a parallel or series combination of resistor values.
I am using ResCalc, but there are several others. And as long as you have your antivirus program up to date, they should be safe to use.
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Are you sure its 9? That's not a standard value in any series AFAIK. Even Digikey doesn't stock any.
They'll sell you some from Vishay if you wait 10 weeks and order at least 1000.
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9 ohms is typical for multimeters, but are normally only available as complete, matched sets with 9, 90, 900, 9k etc.
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Are you sure its 9? That's not a standard value in any series AFAIK.
Since it is in a meter, the 9 ohms (presumably 9.0 ohms) is necessary for the accuracy of some meter range. The meter manufacturer would have special ordered, or perhaps custom made their own. At 9 ohms, it could be a hand made wirewound resistor using small gauge wire.
Or use combinations of series or parallel resistors as suggested by schmitt trigger.
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I'm pretty sure it's a 9 Ohm, but I attached a couple pictures. The multiplier band looks to be silver, but that's where it was burnt most. The calculator that I was using shows 9 Ohm +/- .25%.
There's a lot of space, so I may be able to hook a small series of resistors in there to get to 9ohm.
I'm going to check out ResCalc now.
I didn't even know about the E24 resistors. That sounds like it may work, I have some more reading to do...
Thanks for the replies.
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Like I said, it's a typical "multimeter"-resistor.
As a quick fix, two 18-ohm resistors in parallel will do the trick.
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^^ As Benta said, two 18 Ohm resistors in parallel.
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I have to add - try to find 0.1% (18R 0.1%).
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Another option is buy a bunch of 9.1 ohm resistors and then go through and measure them until you find one that's as close as you can find to 9 ohms. You can buy 100 resistors for just a few dollars.
The pair of 18 ohm resistors in parallel is probably less work though.
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Alternatively, Dave used 2.2 + 6.8 to get 9 in the µCurrent.
Another option is buy a bunch of 9.1 ohm resistors and then go through and measure them until you find one that's as close as you can find to 9 ohms.
That's more than 1% off so you would need some rather shitty resistors, I wouldn't put such crap in a DMM out of concern about stability :P
There is also the question how to actually measure a 9Ω resistor with <1% precision, it's not exactly straightforward without somewhat specialized equipment.
By the way, the function of such resistor in typical 3.5 digit DMMs is the 20mA DC current range and IIRC other current ranges won't work too without it.
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How about 9.1 ohms and 820 ohms in parallel? Or 10 ohms and 91 is pretty close to 0.1%.
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9 OHM 0.6W 0.5% AXIAL
https://www.digikey.ca/product-detail/en/vishay-bc-components/MBB02070C9008DC100/MBB02070C9008DC100-ND/5060937 (https://www.digikey.ca/product-detail/en/vishay-bc-components/MBB02070C9008DC100/MBB02070C9008DC100-ND/5060937)
Unfortunatley you have to buy a 1000 of them. Which sucks
Might narrow down the product .
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Like I said, it's a typical "multimeter"-resistor.
As a quick fix, two 18-ohm resistors in parallel will do the trick.
Or 4.3 and 4.7 Ohm or 6.8 and 2.2 Ohm in series. As mentioned above there are plenty of online calculators. Those are just some values which popped into my head. No doubt there are plenty of other combinations of two E24 resistors to give 9 Ohms.
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I know you specifically asked for through hole ,but why couldn't you use a surface mount. The vias should guarantee connection to both sides of the board.
You could use something like https://www.digikey.ca/en/products/detail/vishay-foil-resistors-division-of-vishay-precision-group/Y17469R00000B0R/8624626 (https://www.digikey.ca/en/products/detail/vishay-foil-resistors-division-of-vishay-precision-group/Y17469R00000B0R/8624626)
The SMR3DZ has a length of about 7mm. It's not a conventional approach but it might work. They're pretty expensive still at $40
It's an option
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You could find a high precision 10.00 ohm (say, 0.1%) resistor and connect a reasonable 91 ohm (lower power and smaller) in parallel to obtain nominal 9.010 ohms. If the 91 is 5% low (86.45 ohms), you get 8.963. If 1% low (90.09), you get 9.001. Piggybacking a physically small resistor in parallel with a larger leaded part is usually simpler than series connection. What accuracy do you want?
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Mouser part numbers:
279-YR1B10RCC 10 ohm, 0.1% $0.51 qty 1
279-YR1B90R9CC 90.9 ohm, 0.1% $0.58 qty 1
Parallel combination is 9.009 ohms +/- 0.1% (maybe less % if one is + and the other is -). They are 1/4 watt resistors which is what the old one appears to be.
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You can use this online calculator to build nominal 9 Ohm out of whatever stock you have: http://kirr.homeunix.org/electronics/resistor-network-finder/ (http://kirr.homeunix.org/electronics/resistor-network-finder/) (For actual accurate 9 Ohm you may need to try and measure, and/or use 0.1% error resistors).
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In addition to rescalc, digikey also has a whole host of calculators.
https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-parallel-and-series-resistor (https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-parallel-and-series-resistor)
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Thanks again for all the replies and options.
Since this is just a cheap multimeter that I'm working on, two 18 ohm resistors (which seem to be more common) in parallel is what I'm going to try first.
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I know you specifically asked for through hole ,but why couldn't you use a surface mount. The vias should guarantee connection to both sides of the board.
You could use something like https://www.digikey.ca/en/products/detail/vishay-foil-resistors-division-of-vishay-precision-group/Y17469R00000B0R/8624626 (https://www.digikey.ca/en/products/detail/vishay-foil-resistors-division-of-vishay-precision-group/Y17469R00000B0R/8624626)
The SMR3DZ has a length of about 7mm. It's not a conventional approach but it might work. They're pretty expensive still at $40
It's an option
I bet he could buy at least two of those multimeters brand new for the same price as that $40 resistor
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I think I have a sack of 9 Ohm resistors. I will check next time I think of it.
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Thanks again for all the replies and options.
Since this is just a cheap multimeter that I'm working on, two 18 ohm resistors (which seem to be more common) in parallel is what I'm going to try first.
Just be aware that an 18 Ohm 5% resistor will be guaranteed to be at least 1% off, otherwise the manufacturer would sell it as a 1%'er. So look for one that's 1% low and one that's 1% high and put those in parallel. That should be very close.
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That's not guaranteed and certainly not for 5% because the only small 5% resistors today are carbon film and with most manufacturers 5% is already the highest grade they offer.
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Back in the days of carbon composition resistors, you could have used a 8.2 Ohm resistor, & a small three cornered file to tweak it "just right". ;D
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Instead of letting out the magic smoke, you would let in the healing moisture...
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I seem to remember a dab of your wife's nail varnish being an essential part of the procedure - resistor filing, like fly tying, being a purely male pursuit. :)
EDIT: Actually I think that was more on sold carbon resistors.
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IIRC, you could also grind edges of disc ceramic capacitors to reduce their capacitance. (Try that with a MLCC!)
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I was wrong. I have a sack of 1.9 Ohm resistors, not 9 Ohm.
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Is that a DT-830 DMM? :o
Do you have a more accurate DMM to help you select resistors? Two 18R would be the way to go, but if you are trying to be precise, you would want to measure the combo with a better DMM.
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Not sure if anyone has brought this up.. but here's a link, but they are not 1%, and they are wirewound, but you can get them in single quantities.
Mouser (https://au.mouser.com/Passive-Components/Resistors/Wirewound-Resistors/Wirewound-Resistors-Through-Hole/_/N-7fx9i?Keyword=9+Ohm&FS=True)
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Thanks again for all the replies and options.
Since this is just a cheap multimeter that I'm working on, two 18 ohm resistors (which seem to be more common) in parallel is what I'm going to try first.
Just be aware that an 18 Ohm 5% resistor will be guaranteed to be at least 1% off, otherwise the manufacturer would sell it as a 1%'er. So look for one that's 1% low and one that's 1% high and put those in parallel. That should be very close.
Perhaps 60 years ago but I no longer believe that's the case. 5% tolerance resistors tend to be made of cheaper materials such as carbon film which use a different process than 1% metal film resistors.
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FINAL UPDATE:
Multimeter is working perfectly. The 18 ohm resistors I bought were much bigger, but I was able to put 2 in parallel and make it work. It's not pretty, but it works.
Resistors measured 18.2 ohms, so the 2 in parallel were 9.1 ohm, but the measurements are very close to another multimeter that I compared the measurements to.
Thanks again to everyone. I learned a lot, and it was fun.
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If your two resistors measure to 9.1 ohms, that is a standard value for 5% tolerance resistors.
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Resistors measured 18.2 ohms, so the 2 in parallel were 9.1 ohm, but the measurements are very close to another multimeter that I compared the measurements to.
Did you take into account that 0.2Ω could easily be resistance of the test probes and cables alone? ;)
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If you don't have a four-terminal ohmmeter to remove the problem mentioned above, you can measure resistance with two DMMs: one in series to measure current and another across the resistor to measure voltage. Place the current at the ends of the wire, and the voltmeter across the resistor very close to the body for accurate results. You will be limited by the accuracy of the current measurement.
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If you decide to change out your two 18Ω resistors, Mouser has 9Ω 1% from Vishay/Dale
https://www.mouser.com/ProductDetail/Vishay-Dale/RS1%5C29R000FE70?qs=sGAEpiMZZMvNd0dY0KymzuzWSQ9ynPoRBnvoju4%252BWFM%3D (https://www.mouser.com/ProductDetail/Vishay-Dale/RS1%5C29R000FE70?qs=sGAEpiMZZMvNd0dY0KymzuzWSQ9ynPoRBnvoju4%252BWFM%3D)
They are 3/4W but still only 8mm long.
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If you decide to change out your two 18Ω resistors, Mouser has 9Ω 1% from Vishay/Dale
https://www.mouser.com/ProductDetail/Vishay-Dale/RS1%5C29R000FE70?qs=sGAEpiMZZMvNd0dY0KymzuzWSQ9ynPoRBnvoju4%252BWFM%3D (https://www.mouser.com/ProductDetail/Vishay-Dale/RS1%5C29R000FE70?qs=sGAEpiMZZMvNd0dY0KymzuzWSQ9ynPoRBnvoju4%252BWFM%3D)
They are 3/4W but still only 8mm long.
Sure, but why would you buy a $4 resistor to repair a $3 multimeter? ;)
Any series/parallel combination that gets close will be more than adequate in this application.
Personally, I would probably have pulled out a 9.1 and shunted a little 1/8W 1K across it since I have lots of those. Close enough. Probably way closer than the original resistor in an 830. :)
An 820 ohm would be even closer.
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:horse:
FINAL UPDATE:
Multimeter is working perfectly.