Just making sure - Substituting 1/2 watt resistors in place of 1/4 watt resistors

Discussion in 'General Electronics Chat' started by Lumenosity, Oct 29, 2017.

  1. Lumenosity

    Thread Starter Member

    Mar 1, 2017
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    I read this before posting this.....
    http://www.electronics-tutorials.ws/resistor/res_7.html

    But it didn't answer my question in clear enough terms for me.....I'm not the brightest bulb

    Here's the question.....
    The 1/4 watt and 1/2 watt ratings are simply the maximum watts the resistor can dissipate.....is that correct?

    In other words, I "could" use a 10Watt resistor in replace of a 1/4 watt resistor, as long as they have the same R value, if for example I was stranded on a barren, rocky alien planet and my ascent spacecraft booster motors would not fire unless I replace one, 1/4 watt 300 ohm resistor, but all I have is a 10Watt, 300 ohm resistor.

    Am I doomed to die on this alien planet? Or will I be saved by the 10Watt resistor?
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    You can almost always use the larger wattage resistor. There are cases with high-speed circuits where you have to select a resistor with lower capacitance or inductance or even changes in resistance vs temp. But, in general, bigger is fine except it take more board space, and costs more.
     
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  3. dl324

    AAC Fanatic!

    Mar 30, 2015
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    Yes, but conservative designs usually derate dissipation for increased reliability.

    Assuming you weren't on the ragged edge of not being able to launch with the added weight...

    One of my instructors in college worked on a circuit that was in a satellite doing some research on the Sun. He used a 1W resistor instead of a 1/4W because that was all they had available...
     
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  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    And now that satellite is orbiting 0.0000001% slower than it was designed for.
     
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  5. crutschow

    Expert

    Mar 14, 2008
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    Larger wattage resistors (above a couple watts) may be wire-wound types and they will have significantly more inductance than lower wattage, film-type resistors.
    That could affect AC or digital signal circuit operation, so you must be aware of that.
     
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  6. spinnaker

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    Oct 29, 2009
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    And it took .0001 % more fuel to lift that resistor. What the heck, tax dollars grow on trees after all. ;)
     
  7. be80be

    AAC Fanatic!

    Jul 5, 2008
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    I remember when I was young had lots of 1/2 watt and 1 watt the 1/2 watt worked find but the 1 watt cause problems they where wire-wound types. Then I got into transistors and the shack started sealing 1/8 and 1/4 watt i poped some 1/8 watt. Boy I miss them days.
     
  8. Lumenosity

    Thread Starter Member

    Mar 1, 2017
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    "Shack ?
    What's that ????
     
  9. dl324

    AAC Fanatic!

    Mar 30, 2015
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    In the US, that's a reference to Radio Shack/Tandy Corp that used to be a source of electronic components. Most/all of the stores have since closed.
     
  10. bertus

    Administrator

    Apr 5, 2008
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  11. ian field

    AAC Fanatic!

    Oct 27, 2012
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    Some types of resistor construction, like wire wound are significantly inductive - and some types of circuit can't have that.

    There are a few rules to follow - but generally a bigger resistor is not a problem.
     
  12. Lyonspride

    Active Member

    Jan 6, 2014
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    I thought the thing to do was use the smallest components possible and to hell with the consequences, because that's someone else's job and unnecessarily making a PCB the size of a postage stamp is all that matters :p
     
  13. MrAl

    AAC Fanatic!

    Jun 17, 2014
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    Hi,

    One of the often overlooked qualities of a 1/2 watt resistor over a 1/4 watt resistor is durability. This i think boils down to more strength in the leads for 1/2 watt units. This is the same for using 1/4 watt over 1/8 watt.
    I worked in a place a long time ago where we got a lot of military jobs and we were never allowed to use 1/8 watt resistor units simply because of the durability issues based on vibration and general principle that stronger is better for high reliability.

    In my own personal at home stuff, i find that 1/2 watt resistors hold up better than 1/4 watt units over time especially if the circuit is not placed into a box of some type. The 1/2 watter can handle being rough handled better than the 1/4 watt because the leads are heavier and the body is stronger too.

    This does not even take the wattage requirement into account where both the 1/2 and 1/4 watts maybe dissipate 1/16 watt or something. The 1/2 watt is just a physically stronger component.

    Of course i am talking about the through hole components, but SMD parts are stronger too in larger packages. The difference may not be as big a deal there though because they lie so flat on the PC board. You'd have to smash one to break it i think.
     
  14. Tonyr1084

    Distinguished Member

    Sep 24, 2015
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    One interesting note on wire wound resistors: I've seen double wire wound resistors where half of the coil is (for the sake of conversation) left turn wound and the other half is right turn wound. Thus, the two opposing turns cancel out any inductance that a normal wire wound resistor would have.
     
  15. ian field

    AAC Fanatic!

    Oct 27, 2012
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    Size/price isn't straightforward - in general; smaller components consume less weight of raw materials and are cheaper, but miniaturisation tends to be priced at a premium. A massively over spec resistor might not burn out in a fault condition where a correctly rated part might.
     
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