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Battery Charger 12x24 volt

Discussion in 'Troubleshooting and Repair' started by dull spark, Aug 8, 2011.

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  1. dull spark

    dull spark

    33
    0
    Aug 8, 2011
    charger almost new, switched on, then loud bang, inspection found 35v 1000uf cap had exploded, closer inspection found 6 rectifier diodes mounted to a 6 inch square alloy plate, two of these had failed diode test, these diodes are a button type like a watch battery,they are held against the alloy plate with little brass spring strips, the diode contact against the alloy plate is poor,insulation has melted between the spring clips and the button diodes,I have tried to purchase new diodes of this type, but no luck, help ,
     
  2. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Picture(s)...
     
  3. Reaper_666

    Reaper_666

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    Aug 12, 2011
    could use some pictures otherwise we can't help
     
  4. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    RE charger 12/24 volts

    Calculate the power ratings of the charger, build a full wave bridge rectifier and replace filter capacitor, for a not sure try a 35 amp full wave square package rectifier, Lucas terminals.

    Probably the filter capacitor was reverse polarity, or crap diodes, repair replace switch on test go, should be that easy. Dave. :)
     
  5. dull spark

    dull spark

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    Aug 8, 2011
    pictures of charger soon,
    thank you.
     
  6. dull spark

    dull spark

    33
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    Aug 8, 2011
    will send photo detail of wireing, diodes,transformer,&PC board,
    thank you.
     
  7. dull spark

    dull spark

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    Aug 8, 2011
    12/24 volt chargers

    Photos as requested, thank you.
     

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  8. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Thanks for the pic's.
    Never saw anything made like that before, and it doesn't seem like a sound design to mount those diodes like that. And why 6?
    It's hard to imagine what the wiring diagram looks like, but I'd try to replace 4 of those diodes with a 35-50A square bridge rectifier.
    The remaining 2 diodes might supply the electronics, and here it might suffice to use one half of a 10A bridge rectifier.
    The negative side of the 1000uF 35V capacitor is connected to a +12V terminal. That might not be correct.
     
  9. dull spark

    dull spark

    33
    0
    Aug 8, 2011
    12/24 volt battery charger

    Dear Resqueline,
    thanks for taking the time to look at this horrible setup,I bought this charger 2yrs ago, it is out of warranty now, it did charge 3 batteries, it has a boost start feature for flat batteries on any 12/24 volt vehicle,but this was never used. when i last used it i noticed that the transformer had developed a high pitch hum,then 30 secs later, bang capacitor up in smoke, I traced back to the centrer tap transformer, no wireing faults, but tested 6 button diodes and found two of them faulty and the insulating melted, i tried to buy same in the UK.but no luck, I got 10 from the US on ebay 4 day delivery, I used 2 new and 4 old to see what might happen i made a new cooling alloy plate and fixed the diodes firmly to the alloy plate,replaced an old cap from a, TV switched charger on ,90 seconds Bang cap gone, It then struck me that a forum member suggested cap may be in wrong polarity, so i had one cap left 25v 1000uf the original was 35v 1000uf, stand clear, yes we have lift off, just charged a big tractor battery from flat, transformer quite and cool, diode alloy plate very warm, battery fully charged,green led says so, also tested with volt meter batt volts 13.9 good, will it last or should i convert to
    your full Bridge Rectifier, Thanks again. Dullspark.
     
  10. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Pop goes the cap's.. ;) But good job all-in-all. :)
    Those diodes are no doubt good, they just need a lot better mounting method than the charger seemed to employ.
    I'm sure a datasheet somewhere specifies the necessary clamping force, which I'm quite sure is quite high.
    I've seen real big thyristors mounted like that between two heatsinks, and they employed a number of conical/cupped constant-force discs.
    This was to ensure a constant clamp force regardless of temperature & coefficients of expansion.
    If you have a setup that ensures a high, even, and constant clamp force on all 6 diodes I'm sure it'll last.
    Also remember that aluminum alloys have an oxide layer that can promote poor electrical contact (= extra heating).
     
  11. dull spark

    dull spark

    33
    0
    Aug 8, 2011
    thanks Dave, your diagnosis was correct, 2 cooked diodes=1exploded capacitor, heat sink set up was designed by a chimp,thanks again, Des.
     
  12. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    12/24 volt charger

    Hi Des.
    Sorry to here it ended that way, if you feel up to it some time you could try a square package bridge rectifier at least 35 amps and maybe a bit more, and a 105 Deg C electrolytic capacitor, as for the two single diodes i know they make them up to 10 amps, silicone axial lead diodes that is, beyond that the really heavy ones are stud mount anode and cathode, they go up to hundred's of amps and volts.

    If you used it for some time in the past and it worked fine, then there might be a short somewhere, or another components failing or failed, its how much patience you have, and that if you want to repair it.

    At times with the way some things are built today, i ask myself with some things i do is it worth bothering.
    Tomorrows another day, better for you i hope. Dave. :)
     
  13. dull spark

    dull spark

    33
    0
    Aug 8, 2011
    Hi Dave,
    Thanks for your sound advice,later on I will follow it to the T. meantime I need the charger to keep a big 12v battery charged, I use this battery as a power pack for testing, vehicle equipment, and for messing around, I am sure the charger failed because some of the diodes were barley contacting the heat sink, the heat sink is a 6 inch sq piece of alloy 1mm thick, the diodes are held in pairs against the plate with little 2 inch brass strips which had lost their spring tension due to high temp, if you seen it up close you would condem it as a dangerous setup, Des
     
  14. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    12/24 volt charger

    Yes i can imagine, 1mm thick plate that size wont be able to dissipate the heat very well, probably not adequate for the job, if you give it another go rivet on a thicker plate or bolt on an external heat sink, air cooled if you wanted 120mm pc axial fan would work well, if you used a thermal switch, say 40 Deg C contacts normally open, closing on temperature rise, then the fan only comes on when needed, the thermal switch bolts to the H sink add a little thermal grease as an interface heat conductor, any way good luck with it Des. Dave. :)
     
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