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Help finding alternatives to this non-existent capacitor!

Discussion in 'Datasheets, Manuals and Component Identification' started by Protonus, Aug 3, 2015.

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  1. Protonus

    Protonus

    9
    4
    Feb 18, 2015
    I need help finding an alternative to 4 (two per board) failed capacitors I need to replace, that are seemingly non-existent! Pics below.

    The capacitors are 63 V, 10,000uF, rated for 105 C. Standard Radial Solder Lead style, aluminum electrolytic.
    They are made by Nippon Chemi-Con, and they are KMG Series capacitors (their general purpose series).
    The plastic disc at the top of the cap is embossed wtih "13D68" - perhaps a date code?

    The special thing about these capacitors is their width. They are approx 25.7mm wide (and 50.5mm tall, which is common height). I have not found any other capacitors with the 63 V, 10,000 uF rating, in this width - looking for alternatives on digikey and elsewhere. All of them are either 30mm or 35mm wide. And looking at the pics I'm attaching below - I don't have room for a 30mm wide cap. I bought high quality (low ESR, higher operating hours, etc) replacement caps without even thinking about the package size, and they were 35 mm wide. You can see how much wider they are in a picture below.

    These caps are out of an amplifier board, from a SoundBridge brand 12" powered subwoofer that's about 10 years old. I have two of these amplifier boards - both of them had cap failure on these 2 caps - so I'd prefer to get better quality replacements. This sub was only sold in very low quantity and pretty much put on clearance immediately thru Woot.com - you can read a little about it here: http://www.woot.com/forums/viewpost.aspx?postid=360217&pageindex=1

    An interesting note is that printed underneath all the components on these boards is the value of the component soldered there. As you'll see on these boards, underneath the caps after I desoldered them, it said they should be 63 V, 4,700 uF ? That might be a clue here?

    I don't know enough about circuit design to know what alternatives I have here?
    I'm figuring it might be possible to use a different value cap - I know usually stepping up in voltage or capacitance is OK, but not down? The only other option I came up with is to use one of the larger 30mm wide caps I found, and run leads to it, and mount it perpendicular to the board, floating over the other components (wasn't even sure the best way to do that?). This doesn't seem like a great idea either, especially in a subwoofer amp which will be vibrating all the time.

    I contacted Nippon Chemi-Con's USA office and they can't find a KMG series cap in this size either, even in their older paper catalogs. Nor do they have a cap in this value, at 25mm width. I sent them these pics and info to their engineering department so they can investigate further because they're as curious as I am! I'm leaning towards these caps either being fakes, or misrepresented/labeled?

    Anyways, thanks to ya'll in advance for your suggestions!

    How the board looked to start (you can see one of the caps is swollen enough at the top to tear the plastic jacket on it):
    [​IMG]

    Caps desoldered, showing the 4,700 uF rating underneath:
    [​IMG]

    Cap pic 1:
    [​IMG]

    Cap pic 2:
    [​IMG]

    Cap pic 3:
    [​IMG]

    Comparison of new replacement caps, being 1 CM wider than the old ones (the old one is in the lower right!)
    [​IMG]
     
    Last edited: Aug 4, 2015
  2. davenn

    davenn Moderator

    13,930
    1,981
    Sep 5, 2009
    hi there

    they may have discovered that after these boards were in service for some time they started getting fault reports
    and it was traced to the smaller value caps so were replaced with the 10,000uF ... just one possibility

    the 4700 or even the 6800 63V would be physically smaller than the 10,000uF ones
    The 6800uF ones could be a good tradeoff


    Dave
     
  3. Protonus

    Protonus

    9
    4
    Feb 18, 2015
    That seems like a reasonable deduction. But it doesn't address why these 10,000uF caps are physically smaller in width than any I've seen for sale, any idea there?

    So it would be electrically OK to exchange these caps out for ones with a smaller capacitance rating, as long as the voltage rating is the same?

    My knowledge of circuitry is rather pragmatic, I don't know enough of design to know when things like that are OK. I normally try to replace everything with identical values when I repair boards.
     
  4. shrtrnd

    shrtrnd

    3,827
    522
    Jan 15, 2010
    I don't know, but here's my guesstimate in the cap width question.
    Capacitor manufacturers get orders from product companies for components that fit the boards their designers come up with.
    They'll make you whatever you want to get the contract order if the price is right.
    I too have often found odd-sized caps on printed circuit boards that I couldn't easily find exact physical-size replacements for.
    I assumed that the product manufacturer specified the odd-size to fit their particular product circuit board.
    May not be accurate, but that's my reasoned explanation for odd-ball sized caps.
     
  5. Protonus

    Protonus

    9
    4
    Feb 18, 2015
    Just following up here. The amp is fixed! Working great, so happy to have bass again!

    The new 6,800 uF caps I ordered above, worked great. So thank you very much for the advice here on choosing a suitable replacement. In fact, as you read on, these 6,800 uF are likely overkill now.

    An interesting addendum to the story, I have two of these amps, so 4 of these caps. I recently picked up an Peak ESR70, so I could start measuring ESR (and capacitance) for checking boards for failing caps. I decided to try it on the old caps, the "10,000" uF ones.

    The visibly failed cap, the one that was bulging, measured at only 3,600 uF, which is certainly low. It was certainly bad.

    The other 3 caps though, that looked OK? All 3 of them measured within 10% of 4,700 uF! I think it's no coincidence, particularly since the board itself was marked with 4,700 uF. Which would mean that all of these caps were badly mislabeled (they claimed to be 10,000 uF)!

    I'll consider that mystery solved, though it seems awfully terrible to me.
     
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