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resistor question?

Discussion in 'General Electronics Discussion' started by subplay, Jul 2, 2013.

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  1. subplay

    subplay

    17
    0
    Jun 2, 2013
    Hi I have a schematic im rebuilding. on the diagram, the resisitors feeding the leds are 330 ohm. But in there there is one resistore the says 3.3m

    What is this one can you please help, and would anyone be able to give me a link to where to buy in the uk..

    Thanks again all
     
  2. subplay

    subplay

    17
    0
    Jun 2, 2013
    Whats a 3.3m resistor?

    Hi all im making a circuit of a schematic, I need 10 330ohm resistors, but 1 x 3.3m

    Can anyone clarify what that is? and is there a link where I could pick up one from...

    or is the 3.3m another way of saying 330 ohms?

    Thanks
     
  3. davenn

    davenn Moderator

    13,833
    1,950
    Sep 5, 2009
    hi
    is it really shown as 3.3m or is it really shown as 3.3M or 3M3 ?

    3.3M or 3M3 = 3.3 MegaOhms ( they don't make 3.3 milliOhm resistors as far as I'm aware)

    Upper and lower case lettering is extremely important to get correct in electronics and physics in general

    and Mr Ohm would prefer you capitalise his surname ;)

    lower case m = milli (1/1000th) upper case M = million

    Dave
     
    Last edited: Jul 3, 2013
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
    2,837
    Jan 21, 2010
    That is either 3.3M (3,300,000 Ohms) or 3.3m (0.0033 Ohms).

    Can you check whether it's "m" or "M", and even better, show us the schematic.

    A 3.3m resistor would typically be in series with a high current load (say between 30 and 200A) or as a shunt for a current meter (effectively the same).

    A 3.3M resistor is a very high value and would be (perhaps) in a timing circuit, or other places with very low currents.
     
    Last edited: Jul 3, 2013
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
    2,837
    Jan 21, 2010
    Subplay, can you see why we get annoyed by people starting multiple threads for exactly the same topic?
     
  6. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    There are several places to get components in the UK. I get my bits from R.F Potts of Derby. Most big towns have a Maplins. RS components, Farnell, Cricklewood, Bowood are alternatives to get them by post.
     
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Ohm should not be spelled with an initial capital unless you are specifically talking about Mr. Georg Simon Ohm, or his Law. It's correct to say that a resistor value is 10 ohms (without the capital O).

    When a unit is written as a single letter, the capital is used; for example, 10 µF (microfarads). There are exceptions: seconds should always use the lower-case letter: ps, ns, µs, ms, s, to distinguish them from siemens, the unit of conductance, which uses the upper-case letter. Times written with units of "µS" and "mS" are often seen, but are wrong.

    The SI units for resistance should be written milliohm, ohm, kilohm (not kiloohm or kilo-ohm) and megohm (not megaohm or mega-ohm).

    Other units that are named after people follow the same pattern:

    picofarad, nanofarad, microfarad, millifarad, farad (named after Michael Faraday);

    microvolt, millivolt, volt, kilovolt, megavolt (named after Alessandro Volta);

    nanoamp, microamp, milliamp, amp (named after Ampere);

    nanohenry, microhenry, millihenry, henry (named after Joseph Henry) (There doesn't seem to be a consensus on whether the plurals should be written microhenrys, etc, or microhenries, etc.)
     
  8. davenn

    davenn Moderator

    13,833
    1,950
    Sep 5, 2009
    I could agree except where there is a prefix else its a capital

    Henry etc

    SI units

    Base units: *Ampere ·*Candela ·*Kelvin ·*Kilogram ·*Metre ·*Mole ·*Second

    Derived units: *Becquerel ·*Coulomb ·*Degree Celsius ·*Farad ·*Gray ·*Henry ·*Hertz ·*Joule ·*Katal ·*Lumen ·*Lux ·*Newton ·*Ohm ·*Pascal ·*Radian ·*Siemens ·*Sievert ·*Steradian ·*Tesla ·*Volt ·*Watt ·*Weber

    Dave
     
  9. Miguel Lopez

    Miguel Lopez

    252
    63
    Jan 25, 2012
    Units are only represented with capital letters symbols when they are derived from a person's name.

    second, meter, mol, candela, radian....etc should always be represented as symbols using non-capital letters.

    The only exception that I now remember is litre, which can be represented with a capital "L" to diferentiate it from the symbol for length "l" or from the number "1"
     
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Thanks Miguel for the clarification.
     
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