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Buying resistors; better just to get 1 Watts?

Discussion in 'General Electronics Discussion' started by NuLED, Jun 26, 2013.

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  1. NuLED

    NuLED

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    Jan 7, 2012
    Hi guys - I just want to get a pack of resistors; they come in 1/4, 1/2, and 1 watts.

    Should I just get the 1 watt or 1/2 watt ones? Is the power rating a measure of durability and it will be OK to have a higher power rating for low current circuits? Or do I need to get the wattage as close as possible to the circuitry?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,264
    2,717
    Jan 21, 2010
    It depends what you're using them for.

    For general electronics work, you might be able to get away with 1/4W for everything.

    These days 1/2W are about the size that 1/4W used to be.

    If you need the dissipation, then you need to get a resistor that will handle the appropriate amount of power. Typpically you want something that can handle 50% to 100% more power (at least) than you are dissipating. This will prevent things getting too hot. But using a 50W resistor in place of a 1/8W resistor will generally do no more harm than take up more space and cost a lot more.

    Another thing is the voltage rating for capacitors. This is rarely anissue, but where it is an issue you need to be aware that higher powered resistors often have a higher voltage rating and that placing resistors in series allows you to add up their voltage ratings (as long as the resistance values are equal). Voltage ratings are often in the region of 200V, so for electronics powered by batteries you will typically never have to worry about it.

    If size is not a concern 1/2W metal film resistors would be fine for most low power stuff. If you ever need a slightly larger dissipation you can place resistors in series or parallel.
     
  3. NuLED

    NuLED

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    Jan 7, 2012
    Thanks Steve. Looks like probably I will be OK buying a pack of half watts.

    I'm just using them for these beginning electronics books I am reading, doing their circuitry. Voltage is 12V or less (probably eventually will be 5V once I get into the programmable stuff with microcontrollers, etc.).
     
  4. KJ6EAD

    KJ6EAD

    1,114
    157
    Aug 13, 2011
    Another consideration is that ¼W resistors are the largest that can be placed side by side on a standard 0.1" (2.54mm) spaced breadboard or prototyping PCB without interference.
     

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    Last edited: Jun 26, 2013
  5. NuLED

    NuLED

    294
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    Jan 7, 2012
    Ok thanks, that makes sense. Didn't know it.

    I think for my current purposes it is OK, as I don't think any circuits I create in the coming one or two months will be too crowded.

    I'll probably get a box of those Joe Knows Electronics packs, which are well labelled. I discovered that an Elenco pack I had was missing some items that I need. Also capacitors.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,264
    2,717
    Jan 21, 2010
    I have some 0.6W metal film resistors that are the same size as that...

    Here they are... 2.3mm diameter.
     
  7. CluQu

    CluQu

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    May 22, 2013
    My uncle gave me some old resistors. Holy crap they are huge. My son has these toys called "Mighty Beanz". They looks like a gel cap of Tylenol. In any case they are about that big. I think they are 1/2 Watt idk. To told to even really tell.:cool:
     
  8. CluQu

    CluQu

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    May 22, 2013
    I have the Elenco Cap/Res/Diode kits. Very nifty and worth the price.
     
  9. NuLED

    NuLED

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    Jan 7, 2012
    Yes I got the elenco packs but they were missing some types. Anyway I went ahead and ordered the Joe packs as well, so I think I will be good for a while.
     
  10. aharrison

    aharrison

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    Nov 14, 2010
    For general-purpose "whiteboard" breadboards, I use the "Xicon" carbon film 1/4 axial resistors from Mouser Electronics- about $$4 for 200 of the same value. I've used tens of thousands of them with never a single defect.
    Data sheet: http://www.mouser.com/ds/2/351/XC-600035-197929.pdf
    Keep in mind that these aren't precision types, and that their temperature coefficients aren't sutable for instances where more-stable types, such as metal-film units, are better choices.
     
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