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Inductor color code

  1. Dec 10, 2014 #1
    hi, i just bought an inductor that was labeled 68mH, but the colors are violet gray brown silver. doesn't this make it 680uH (0.68mH)?
  2. jcsd
  3. Dec 10, 2014 #2


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    violet is 7 not 6 ;)

    so 780 uH unfortunately some companies use m for micro instead of for milli
    only measuring it with an inductance meter would confirm the value

    so I have to ask ... are you sure you read all the colours correctly ? :)
    Last edited: Dec 10, 2014
  4. Dec 10, 2014 #3
    hmm, that's even more confusing actually, i connected two of those in series to wall power 123.5V and i read 0.1A, really confused
  5. Dec 10, 2014 #4


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    ??? what did you do ???

    please tell me you are joking and didn't really do something so silly ?
  6. Dec 10, 2014 #5
    i know i know..... but i had no inductance meter and i needed to test the inductance values for another circuit.
    i was safe about it (i think) :P
  7. Dec 10, 2014 #6
    oh, and to

    it's actually gray, violet, gray, brown, gray
  8. Dec 10, 2014 #7
    i'm not actually an EE major so if i'm doing something wrong, it's because i actually don't know any better so please, some feedback would be nice; lol maybe even life saving :)
    i didn't just stick an inductor in the wall socket fyi. i calculated the theoretical current and put a fuse in place based on the number (which was in series with an ampmeter), and yes i had a switch in place with the power off while connecting everything. the curious thing is that the inductors turned out to be less than what i thought on the order of mH) the meter only read 0.1A, with very little heat dissipation so it couldn't have bee resistance that was responsible for the low current measured. i'd like some feedback on this please.
  9. Dec 10, 2014 #8


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    Staff: Mentor

    @iScience -- in the future, use a 12VAC wall wart power source instead of the AC Mains please. No reason to be shocking yourself or others, or starting a fire...
  10. Dec 10, 2014 #9

    jim hardy

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    780 X 2pi X 60 = 294053
    so your inductor should have been either 294 ohms or 0.294 ohms, depending on whether it's milli or micro henries.

    Did you read its DC resistance beforehand? Did your test change it? What is it now?

    How big is that thing? To support line voltage i'd imagine it looks rather like a transformer.
    Can you post a link to the catalog page where you bought it?

    Agreed, that test was risky. Glad you didn't make a big flash. Did fuse blow?
  11. Dec 10, 2014 #10
    will do! thanks for the advice

    yup, around 100ohms DC.

    the purpose of that test was to measure the current to see if it correlates with my theoretical value (3.2A (the 'violet' turned out to be blue, sorry, and this theoretical is not accounting the DC resistance)), it very much did not. i felt the inductors after disconnecting the circuit, they were rather hot which would actually make sense if they were made of thin wires, conductance would be limited and the resistance would get even higher due to the heat.

    length: less than half the size of a quarter.
    width: about twice the width of a quarter.

    nope, 3.5A fuse in place, .1A measured current.

    the store i bought it from looks like they haven't yet gotten their site fully up and running, but it was one of these kinds of inductors, except gray, violet, gray brown gray.

  12. Dec 10, 2014 #11

    jim hardy

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    Well okay then..

    I'm surprised it didn't go up in smoke

    294 ohms of inductance and 100 ohms of resistance add to 310 ohms

    and 120volts /310ohms = 0.386 amps expected

    i dont know why you measured only 0.1 amp
    Analog or digital meter? Set for AC amps? Test lead plugged into current measuring jack? Meter internally fused at 0.2 amp, like mine?

    Glad you're having fun - this is the age of technology and we should enjoy it to the max.

    Thanks for the updates !

    old jim
  13. Dec 11, 2014 #12

    yup, except, i had the meter on the I_max=20A setting, does this offer more resistance?

    digital. is there something that varies between the two?

    always! and thanks a bunch for your feedback
  14. Dec 11, 2014 #13


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    just for your learning ... note the 2 different colour code systems there
    a 4 band and a 5 band


    note the top 2 should be turned 180 deg so colour code is read BL RD BK Silver the silver being the tolerance band

    the bottom one 5 band is read a little differently
    the first band silver is a military identifier, then you have BL GY RD for the value, then Gold for the standard tolerance

  15. Dec 12, 2014 #14

    jim hardy

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    No, it offers less. There is an internal resistor and the meter measures the millivolts produced across it, calculates amps by Ohm's law and displays results. They size the resistor for each scale so that it's an easy conversion - like 200 millivolts for 2 or 20 or whatever amps, just move the decimal is all the calculation necessary....

    Now - there should be a ten or twenty amp fuse inside the meter.
    It is not at all uncommon to blow that fuse while working around a car battery - one forgets to move the test lead out of the current jack, selects volts scale and connects probes across battery - pffft but a good fuse will blow silently..

    Well, digital meters are always plus or minus one count in the least significant digit.
    Not knowing whether your meter is three of four or five digit,
    reading of 00.1 amps means between 00.0 and 00.2
    reading of 00.10 means between 00.09 and 00.11
    and so on.
    So when you said ".1 amp" , that'd fit a 3 digit meter set to ten or twenty amp scale with a blown internal fuse .
    That's why i like an analog meter - you can see the needle move which confirms fuse is conducting.

    IF you find the internal fuse open, spend the extra bucks to get an exact replacement. Those are a fast acting current limiting fuse, usually 600 volt.
    It's an important safety matter.

    old jim

    ps bravo to you for that fused test setup...

    One of the handiest pieces of test equipment i ever bought was a Variac adjustable transformer.
    They're pricey new but do show up on Ebay ......
    With one of those and a doorbell transformer (or wall wart) you have a finely adjustable low volts AC source. With a car batttery charger you have a fine adjustable DC source but you have to add filter caps.... and be sure it's a heavy transformer based charger not the electronic doodads they're selling nowadays. Junked furnaces have a nice little 240::24 volt transformer.....
    Last edited: Dec 12, 2014
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