resistor help again

Discussion in 'General Electronics Chat' started by tpozak, Jul 26, 2008.

  1. tpozak

    Thread Starter New Member

    Jul 26, 2008
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    Please let me ask one more thing I should have been clearer on in my previous post. If I have a 10w and 15w resistor wired in parallel or series, what is the 'total' wattage they can handle. Thanks again for your help.
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
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    What are their values? And what voltage are you putting across them? If they are both the same value, then they can safely dissipate 25Watts total in parallel. If they are not the same value, then details become very important.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    What is the value of the resistors in Ohms?

    If you wire them in parallel, they will divide the power according to their resistance, not their power rating.

    Same thing if you wire them in series.
     
  4. tpozak

    Thread Starter New Member

    Jul 26, 2008
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    I was afraid it wasn't going to be simple as I had hoped. An actual example would be 15w/4.3ohm and 12w/10ohm, wired in parallel. I could just use a 3ohm resistor, but need more wattage than a single resistor can handle (at least what I've seen available). Thanks, Todd
     
  5. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Those two wired in series can be placed across 17.65 W source (maximum), limited by the current through the 10 ohm 12 W resistor. In parallel, the source can be 21.45 W (maximum), limited by the voltage on the 4.3 ohm 15W resistor.

    Individually, they can handle their rated value.
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    I just happen to have a 3 Ohm, 50 Watt, 1% resistor sitting next to my keyboard. I pulled it out of... um... something or other a while back. I'll probably never use it. You want it? I can mail it to you.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Have a look at this page:
    http://www.bcae1.com/lpad.htm
    It explains L-pads pretty well.
    Remember, you want the amplifier to see the impedance it needs.
    Connecting a pair of L-pads in parallel or series will complicate things a great deal.

    Use the page to figure out the resistance values and wattages you really need. Then we can go from there.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    I have a 1 Ohm 50W 1% resistor and a 4 Ohm 50W 1% resistor with banana plugs on each end that are invaluable for measuring current. I got tired of blowing fuses in my DMM's when set to mA range. :rolleyes: Much safer to measure voltage drop across a known resistance.

    Having some high-Watt low-Ohm resistors around can be quite handy for measuring things.
     
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