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A hard to resist problem

Discussion in 'General Electronics Discussion' started by Draugr Rekkr, Dec 22, 2015.

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  1. Draugr Rekkr

    Draugr Rekkr

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    Dec 22, 2015
    [​IMG]

    I got some 1/2 watt resistors from a shop called Jaycar here in New Zealand and then I wanted to get a lot more and since I'm a cheap student I didn't want to spent a whole lot of money at Jaycar, I jumped on eBay to get more 1/2 watts for cheaper as I'm sure plenty of people do but when I received them today I found that they were 2x bigger then the ones from Jaycar so I checked the packaging on both the Jaycar resistors and the eBay ones and tho only difference that I could find was that the Jaycar ones were labelled 0.5w and the eBay ones were 1/2w... Correct me if I'm wrong but 0.5 and 1/2 is the same thing right? So why are the eBay resistors bigger? I'll post an image of them side by side too show you what I mean.
     
    Last edited by a moderator: Dec 23, 2015
  2. Gryd3

    Gryd3

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    Jun 25, 2014
    That image does not work...
    In any case, there are different types of resistors which would affect size.
    Wirewound resistors for example. We can tell you which is which when we see...
     
  3. Draugr Rekkr

    Draugr Rekkr

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    Dec 22, 2015
    Fixed I think... Can you see it now?
     
  4. davenn

    davenn Moderator

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    Sep 5, 2009
    Hi There
    welcome to EP :)

    yup :)

    I would have expected the smaller ones to be 1/4 watt, they look to be the same standard ones I use

    Knowing how bad Jaycar are at electronics, I wouldn't be surprised if they were mislabelled
    mine come from a good source in the original packets of 1000, I will check the label and see if
    it states the wattage

    The eBay ones you have are obviously a different brand, so maybe they are 1W instead of 1/2 watt
    but let me see what my ones are first before jumping to that conclusion

    Dave
     
  5. dorke

    dorke

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    Jun 20, 2015
    Agree,the smaller ones look like 1/4W.
    You can actually check the wattage by a simple worm up test:
    Use a PS to create 1/4W on the resistors.
    a 1/2w one will not get warm while a 1/4w will.
     
    hevans1944 likes this.
  6. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    You can also measure the lead diameter. Smaller wattage resistors usually have smaller lead diameters than larger wattage resistors. And the method of @dorke works too. I use 1/4 watt almost exclusively for solderless breadboarding because 1/2 watt (and higher) resisitor leads either have to be shoved into the holes with some effort, possibly damaging the springy contacts inside, or a smaller diameter 22 to 24 AWG wire has to be soldered to the leads.
    OTOH, 1/8 watt and smaller have leads that are too small in diameter. They tend to fall out or make poor contact, especially if the hole has been used for a 1/2 watt resistor previously.
     
  7. Draugr Rekkr

    Draugr Rekkr

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    Dec 22, 2015
    Okay cool thanks! I want to start making guitar peddles of all different sizes so smaller the better!
     
  8. davenn

    davenn Moderator

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    Sep 5, 2009
    OK ... mine that look the same style, colour, size as those on the right in your pic, are definitely 1/4W NOT 1/2W
    Which would make those larger ones your pic most likely 1/2 W

    Dave
     
  9. Martaine2005

    Martaine2005

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    May 12, 2015
    Just a question..
    Those on the right, have very thick leads in comparison to the left resistors.
    My 1/4 watt resistors have really small leads.
    May be they are 1/2 watt on the right and 1 watt on the left?

    [​IMG]
    Martin
     
  10. Draugr Rekkr

    Draugr Rekkr

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    Dec 22, 2015
    When I get home I'll put some of my 1/4 wat next to them with a ruler. The 1/4 watt ones I have are smaller still then the smaller ones in this photo
     
    davenn likes this.
  11. davenn

    davenn Moderator

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    Sep 5, 2009
    cool, that will give an indication
    my 1/4 W metal film ones are 6mm long and 2mm wide ( diameter)
     
  12. Martaine2005

    Martaine2005

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    May 12, 2015
    I meant to edit my picture actually and forgot.
    I did take a photo with a ruler.. They are 6mm x 2mm like Daves..

    DSC01078.JPG
     
  13. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    It's difficult to tell really. A lot of the resistors that look like the old 1/4 W are now actually rated for 1/2 W for the same size. You can even get 0.6 W in the same 1/4 W size (6.2 x 2.3).
    Thanks
    Adam
     
  14. Draugr Rekkr

    Draugr Rekkr

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    Dec 22, 2015
    I'm home and I've taken a photo of the 1/4 watt, "Supposed" 1/2 watt and the bigger 1/2 watt and I've taken a photo next to a ruler and it seems that the 1/4 and the small 1/4 are the same size but I did find the pack that the small 1/2 watt were in and it said it was "mini" could that be the reason it's so small?
    Resistor.png
     
  15. Gryd3

    Gryd3

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    Jun 25, 2014
    Well.. here's the tricky part.
    Smaller parts have less surface area to dissipate heat, and will get hotter than their larger counterparts.
    You cannot make a more 'efficient' resistor smaller and cooler because the Wattage rating is the rating of how much power it can 'waste'. To run smaller, you would end up running hotter or requiring a heat-sink. To run cooler, you would need to run bigger or with a heat-sink.
    It does not add up for me, and I am inclined to say that the 'mini' will get very toasty or even burn up well before the regular ones.
     
  16. cjdelphi

    cjdelphi

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    Oct 26, 2011
    Why all the confusion people?!

    The ones from ebay are 1/2watt
    The ones from jaycar a 1/4watt

    The size = wattage it can dissipate

    You could sit a block of ice on top of a 1/4resistor and turn it into a 10w resistor (until the ice melted)

    Ps a 220k 1/2w resistor is simply a waste of board space, any resistor in the half or more watt range over 100k has to be for high voltage applications, stick with 1/4watt resistors unless it's rating is lower than 1k ohm from source between 6-12v

    You only need extra wattage if you're powering something in series with the resistor, otherwise 9/10 times the current will be tiny requiring less than 1/4w
     
    Gryd3 likes this.
  17. cjdelphi

    cjdelphi

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    Oct 26, 2011
    Oh and yes, jaycar sold you 1/4w not 1/2w what did you pay? I hope you never paid for 1/2watt resistors!
     
  18. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    The power rating on ANY device depends on how much temperature rise it can withstand before catastrophic failure occurs. As @cjdelphi noted, a block of ice with the resistor embedded in the ice will turn a 1/4 watt resistor into a 10 watt resistor at least until the ice melts. Even so, the heat generated must reach the surrounding environment and there is always thermal resistance in the way. So, given two resistors of the same physical dimensions, one rated 1/4 watt and the other 1/2 watt (and labeled "mini") there are several options. The most obvious one is the label "mini" is meaningless as far as power dissipation is concerned. It could just means smaller than regular size. Then, along with the small size, come limitations on power dissipation that are probably comparable or identical to the resistor identified as 1/4 watt. In other words, both resistors, despite the labeling and hype, are both 1/4 watt resistors.

    There is a second possibility. The 1/2 watt resistor in a 1/4 watt-sized package may be of high-temperature construction, designed to run hotter without failing, changing resistance, or other undesirable characteristics. A lot depends on material selection. But one thing is certain: the "mini" resistor will run a LOT hotter with 1/2 watt dissipation than the 1/4 watt resistor with 1/4 watt dissipation. This is simple thermodynamics. There is the same surface area from which to dissipate heat (usually by air convection) but twice the power to dissipate. Ergo, hotter resistor with 1/2 watt dissipation, no matter what it says on the package.

    If I were you, I would do what @dorke suggested: hook both resistors up to a power supply and apply the same quarter-watt of power to both. I am guessing, based on their sizes being virtually identical, that both will get equally warm. Repeat this test using the physically larger 1/2 watt resistor and you should feel a noticeable difference in temperature because the "real" 1/2 watt resistor has a larger surface area from which to dissipate the quarter watt of power.

    If all the resistors are the same value, just connect them in series and apply enough voltage so you are supplying at least 1/4 watt of power to each one (set total power, equal to DC supply voltage times current, to 0.75 watts). Use your "temperature calibrated" thumb and forefinger to measure the temperature rise. Note you should try this only with small-valued resistors so the applied voltage is "safe" to work with. If you have a 5 V DC supply, the resistance should be about 33 ohms each for three in series.
     
    dorke likes this.
  19. shrtrnd

    shrtrnd

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    Jan 15, 2010
    I tend to agree with the idea that the resistors in question are 1/4W
    I would like to share some other trivia concerning this:
    I was receiving a specific size surface mount resistor, when suddenly I started receiving a smaller device with the same part number.
    I contacted the manufacturer, and they confirmed that (I think this was in the late 1990's) that the new equivalent device was the same power rating, but that they had switched to
    a new component composition, and the newer smaller surface mount resistor was indeed rated at the same wattage.
    It'd take me a while to go search my papers to find the manufacturer and year of conversion if anybody really needs to know the specifics, I just wanted to say that
    there has been an effort to change resistor composition over the years to manufacturer smaller components with the same wattage rating.
    I don't think that's the case in this instance though, just trivia concerning the topic under discussion.
     
    hevans1944 and Gryd3 like this.
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