Reading ohms on a Multi-value Resistor

Discussion in 'General Electronics Chat' started by Doug Roper, Jun 2, 2015.

  1. Doug Roper

    Thread Starter New Member

    Jun 2, 2015
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    I'm by no means an electrician. I know the basics but I rebuild small engines and occasionally those engines come on a generator. I have a RadioShack 17 Analogue Multimeter. The settings are continuity, X10, X100 and X1K. On motors I usually set it on X10 to check the coils. I've rebuilt the motor on a Honda EW171 Generator/Welder. It is producing nothing even after flashing. So far I'm assuming the winding is shot.
    The Shop Manual for the Generator has testing for diagnostic purposes. Most of them are for continuity but there are some where I have to get or meet certain ohms. Right now I have on my desk a 4 color Multivalue Resistor (see attached). The colors are from left to right: Red, Blue, White/Red and Red/White. I set the Meter at X10 and get the following:
    Red to Blue (req 160 ohms) I'm getting 5 ohms
    Red to White/Red (req 167 ohms) I'm getting 10 ohms
    Red to Red/White (req 173 ohms) I'm getting 170 ohms
    Blue to White/Red (req 7 ohms) I'm getting 160 ohms
    Blue to Red/White (req 13 ohms) I'm getting 180 ohms
    Am I doing something wrong or is the resistor defective? DSCF9384[1].jpg
     
  2. PackratKing

    Well-Known Member

    Jul 13, 2008
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    Is the resistor isolated from the rest of the circuitry it is designed to function in... Your picture shows it as wired... roadmap it, remove the wires and measure again
     
  3. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    The above example confirms the fact that your readings are being 'interfered with' by circuitry connected to the resistor (i.e. based upon physical order Red-To-White must show less resistance [via the resistor alone] than Red-To-Blue)

    If you wish to test the resistor, please disconnect it from other components/circuitry

    Best regards
    HP
     
  4. Doug Roper

    Thread Starter New Member

    Jun 2, 2015
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    It's been removed at you saw in the attached picture and sitting on my desk. It's almost as if the readings are the opposite of what it should be. It can't be a misprint in the Shop Manual can it? I think I checked it about 5 times. Would a defective resistor like that would keep the generator from functioning?
     
  5. Doug Roper

    Thread Starter New Member

    Jun 2, 2015
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    The wires are solder on. According to the instructions designed for repair shops I test it against the terminals inside the connectors. guide.jpg
     
  6. ian field

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    Oct 27, 2012
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    On two of the sections, you can see the turns of resistance wire - being thick wire and not many turns, the resistance isn't going to be huge. the other section that looks smooth probably has a lot of turns of thin wire and higher resistance.

    Most types of resistor usually fail by going high in value or completely open circuit - that type would most likely look damaged if it was damaged.

    Very occasionally wire wound resistors go low in value, but they usually have to have been glowing red under a fault condition for that to happen.
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    You can tell by the winding pitch that the resistance between the taps will be as I show...

    res.gif
     
  8. Doug Roper

    Thread Starter New Member

    Jun 2, 2015
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    I don't think it is possible that I'm doing it wrong. There is no polarity in reading resistant on a resistor correct? Now as I mentioned, mind is a RadioShack (hear they are closing up) with 2 selections DCmA, 3 ACV, 5 DCV, 3 battery test then as I said before the selection option for ohms is 1. Continuity, 2. X10, 3. X100 and 4. X1K.
    The dial for ohms reads, of course from right to left, 0 then 4 short tic and a longer which I'm assuming is .5 the 4 short ticks then the long which is 1 and so forth. The highest is 500. Now say I set it on X10 and the needle falls on the 4th tick left of 0 that would mean 4 ohms. If the needle fell on 10 then that would be 100 ohms.
    If on the other hand I set it on X100 and the needle fell on the 4th tick then it would be 40 ohms. I'm not trying to be funny, just need to be sure I'm seeing this correctly or is there something else I need to do to get the correct reading.
     
  9. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Hard time visualizing the face of the Ohmmeter. Can you post a picture?

    Sounds like the X1 Ohms scale is 0 to 500Ω
    X10 is 0 to 5000Ω
    X100 is 0 to 50KΩ
     
  10. Doug Roper

    Thread Starter New Member

    Jun 2, 2015
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    I thought the little ticks are like .1, .2. .3 till it get to 1 the 1.1, 1.2, 1.3 and up.
     
  11. MikeML

    AAC Fanatic!

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    Ignore my previous post, and reread it again...
     
  12. Doug Roper

    Thread Starter New Member

    Jun 2, 2015
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    meter.jpg I smell something burning. Oh! It's my brain. I'm going to sit on this for tonight and then resume tomorrow if your don't mind...LOL. This 56 year old brain can only handle so much. Thank for committing your time. I'll get it....I know it!
    Let me throw one more picture at you. Hope you can see it. Set at X10, Red to Blue.
     
  13. ian field

    Distinguished Member

    Oct 27, 2012
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    You could apply a bit of Ohm's law if you have an adjustable PSU - just measure the current through the resistor while applying a known fixed voltage, you can calculate the Ohms from current and voltage. And its a linear scale - not all bunched up at one end.
     
  14. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    You read the Ohms scale from right to left.

    The Picture shows the needle at 0.5. (First big mark is 1). Since the scale is set to x10, the meter reads 5Ω. You would get a better reading by putting the meter in the x1 range; then the needle should be close to mid scale, making a more accurate reading...

    Hey, this advice comes from a 72yo brain, so there is some hope for you...
     
    Last edited: Jun 2, 2015
  15. Doug Roper

    Thread Starter New Member

    Jun 2, 2015
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    You lost me from "You could". I'm brain dead right now. I've been working on a John Deere 212 Lawn Tractor right now. I've got to order a new carb on ebay. The main nozzle was locked in and clogged up bad. These type nozzles have tiny pin size holes along the side to atomize the fuel. I buggered it up trying to get it out to clean. That's what people get for storing equipment with gas still in it.
     
  16. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Especially the crap gas that has Ethanol in it.

    I'll pass a trick. I steal a bit of 100LL AvGas out of the airplanes to use in my lawn mower, weed wacker, generator, roto-tiller etc. 100LL (blue Aviation Gasoline) leaves absolutely no residue when it evaporates, and it will not hurt rubber things, like o-rings and diaphragms. It is a bit pricey ($5+ per us gallon). I have about 120gals of it readily available in two airplanes...
     
  17. Doug Roper

    Thread Starter New Member

    Jun 2, 2015
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    The is no X1 unless the continuity selection is it.
     
  18. ian field

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    Oct 27, 2012
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    For a short while I worked on a farm, where I found a 46 gal drum of something that smelled vaguely similar to diesel.

    One of the workers informed me it was a mixture of diesel and weed killer.

    As the wages were pretty lousy, I used this stuff to supplement the petrol in my motorcycle tank.

    There was something of a performance increase - but it ate exhaust pipes one after the other!
     
  19. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That is a wire wound resistor and generally if they fail it is because of over current/overheat and can be seen visually, that one looks nice and clean and no sigh of overheat, not to say an open is impossible, just that there does not outwardly appear anything wrong with it.
    Max.
     
  20. Doug Roper

    Thread Starter New Member

    Jun 2, 2015
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    I see you love flying. I used to fly back and forth from Jacksonville, Fl to Ft. Lauderdale, FL when I was in graphics school in a 12 seat twin prop Beechcraft 99. Love it!
     
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