Resistor on a 48V charger?

Discussion in 'Power Electronics' started by kje, Jul 2, 2016.

  1. kje

    Thread Starter New Member

    May 6, 2012
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    What kind of resistor do I need here? I know the capacitor on C6, but what number is on the resistor? R18? And ohm?
    20160702_181152.jpg
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What happened to the original?
    Just guess work at this point without an identical board.!!
    Max.
     
  3. kje

    Thread Starter New Member

    May 6, 2012
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    It's impossible to read anything from the original resistor as it blow up...
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    So you imagined that we could reach back in time AND read the mind of the original designer.
     
    MaxHeadRoom likes this.
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Looks like its a smpsu, using a lm3???
     
  6. Papabravo

    Expert

    Feb 24, 2006
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    Boy that was helpful!!
     
  7. crutschow

    Expert

    Mar 14, 2008
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    If you don't have any info on the circuit, then anything we say is pure guesswork.
     
  8. kje

    Thread Starter New Member

    May 6, 2012
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    Ok. What should I do now? Can I test with a random resistor?
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Do some reverse engineering of the circuit and it may be possible to suggest a value.
    Max.
     
  10. Papabravo

    Expert

    Feb 24, 2006
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    What @MaxHeadRoom means is that if you examine the board carefully you may be able to create a schematic. From that schematic, the design can be compared to similar designs, and the value of R18 can be determined with some level of precision. Are you up to the task? It won't be easy.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    By the wire gauge and outline size and the proximity to the missing electrolytic, I would guess it is in the circuit in or around the power input /DC supply/bridge rectifier part of the charger.
    Max.
     
  12. kje

    Thread Starter New Member

    May 6, 2012
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    Is it dangerous to try with a random resistor value?
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It is much better to use an educated guess based on the reverse engineered part of the circuit, rather than 'Random selection'!
    Max.
     
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