Did I Fry It?

Discussion in 'General Electronics Chat' started by pntrbl, May 10, 2008.

  1. pntrbl

    Thread Starter Active Member

    Apr 21, 2008
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    0
    I'm working on a circuit to monitor battery voltage. In order to test the circuit it seemed wise to add a pot to vary the battery level and this in fact did work for a minute or so. But then it all went dead ....

    What happened was the wiper on the pot opened up. At 1st I thought it was just because it was a cheap Chinese pot from the Shack, but now I think yours truly did it in himself because I didn't check the power req. :eek:

    It "was" a 15 turn PCB mount that's rated .75 watts. My DMM says my circuit is 143 ohms from supply to gnd. 12v/143 and I get 84 mA. 12v times 84 mils gets me just at a watt.

    Was it me? LOL! Well, at $2 it was a cheap lesson.

    SP
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If you didn't get smoke and flames, you've been cheated. Demand a replacement ;)

    Add a 220 Ohm 1 Watt resistor between the pot and the DUT (device under test.) 58mA max then.

    You're still pushing your luck with a 0.75w pot.
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    All part of the fun, everyone has fried something at one time or another, and if they say they've only done it once their probably lying. I think I'll start a thread about it.
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The entire resistance of the pot is rated at 0.75W. If the pot is set to half resistance then its max rating is half of 0.75W which is 0.375W. If the pot is set to a low resistance then its power rating is very low.
     
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