Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Resistor with allowed voltage 800V but only 25W power rating. How is this possible?

  1. Jun 1, 2012 #1
    I recently bought this resistor:

    http://www.radioshack.com/product/index.jsp?productId=12573233

    I want to hook it up to about 50V DC, but I want to know if this would be harmful to the resistor. According to the description it can handle up to 800V, but its power rating is only 25W. This doesn't make sense to me, because according to that power rating even a 9V battery would break it.

    Anyone know how to reconcile the two? Would 50V be okay?
     
  2. jcsd
  3. Jun 1, 2012 #2

    AlephZero

    User Avatar
    Science Advisor
    Homework Helper

    Re: Resistor with allowed voltage 800V but only 25W power rating. How is this possib

    These resistors come in a wide range of values. The "800V" rating would only make practical sense for the high values resistors and for short duration voltage pulses, so the average power stayed within the 25W power rating.

    Alternatively the 800V might be the breakdown voltage between the actual resistor and the outside of the casing. (In other words it would be OK if one end of the resistor was at 800V above ground potential and the other end was 799V above ground).

    http://www.nteinc.com/resistor_web/pdf/twentyfive.pdf

    At 50V DC the power dissipation would be 50^2 / 0.47 = 5.3 kW, so a 25W resistor isn't going to last very long. It mgiht explode rather than just catching fire, operated so far outside its power rating.
     
  4. Jun 1, 2012 #3
    Re: Resistor with allowed voltage 800V but only 25W power rating. How is this possib

    Ah, I understand perfectly. Thanks Aleph!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Resistor with allowed voltage 800V but only 25W power rating. How is this possible?
Loading...