A question about Capacitors

Discussion in 'General Electronics Chat' started by KM Photography, Nov 15, 2014.

  1. KM Photography

    Thread Starter New Member

    Nov 15, 2014
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    This may have been answered before. I'm currently working on a Photogenic Powerlight 1500SL Studio Strobe Light. I have found a bad capacitor. This is my first time replacing a capacitor, usually it's as simple as replacing a fuse or fixing a solder joint. I would assume this cap is Non-polar since it is 200uf 200VNP 250VDC, However when you look at the tabs that hold the leads in place there is a "-" on one of the tabs and a dot on the other, which to me would suggest it's polarized. Below are some photos of the cap in question, any help would be greatly appreciated! DSC_0212.jpg DSC_0217.jpg
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Looks electrolytic (polarized) to me!

    Take a look here for instance. I would use a cap rated to a higher temperature (105°C versus 85°C) if I could, with same or higher voltage rating and same or slightly higher capacity.

    Finally, be sure the replacement has the right diameter and lead spacing. It looks like you could use one quite a bit taller, but a larger diameter would be a very tough fit.

    How did you decide the cap was bad? Just curious. I'd highly consider replacing ALL the electrolytic caps. It will only add a few dollars to your project.
     
    Last edited: Nov 15, 2014
  3. KM Photography

    Thread Starter New Member

    Nov 15, 2014
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    But the VNP stands for Volts Non-Polarized, correct?
     
  4. KM Photography

    Thread Starter New Member

    Nov 15, 2014
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    Well I was testing the flash, and after each flash smoke would come out of the unit. Hoping it left a mark I took it apart to see where it was coming from but to no avail, so I hooked the connectors back up and left the unit open, plugged it in (carefully) and flashed it a few times. I saw smoke rolling from underneath this capacitor. If you look at the lead with the "-" on it, that is where it was starting to explode.
     
  5. ISB123

    Well-Known Member

    May 21, 2014
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    VNP-Vertical Natural Plate
    Its just more robust electrolytic capacitor.it has higher voltage breakdown so it can sustain overvoltage.
     
  6. KM Photography

    Thread Starter New Member

    Nov 15, 2014
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    Okay so this cap is actually polarized and more than likely the lead with the "-" is the negative lead, because there are no other markings indicating positive or negative.
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Read this data sheet. It explains the VNP marking.

    Can you find a data sheet for the one you are replacing?
     
  8. KM Photography

    Thread Starter New Member

    Nov 15, 2014
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    I wish I could find the data sheet. This product is about 10-15 years old.
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    These caps might be used for some type of voltage doubler, common in flash units. The big caps are for the high voltage storage. Since the polarity is reversed as the voltage is doubled (or quadrupled, or...), a non-polar cap is reasonable but not common.
     
  10. KM Photography

    Thread Starter New Member

    Nov 15, 2014
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    If I posted a picture of the circuitry, would that help? Unfortunately, I haven't been able to find any schematics on it.
     
  11. KM Photography

    Thread Starter New Member

    Nov 15, 2014
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  12. ian field

    Distinguished Member

    Oct 27, 2012
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    NP on the label and no obvious "bar" to mark negative strongly points at non-polar, but I'd expect one with those ratings to be a lot bigger.

    The arcing at the solder joint could be the whole extent of the problem - I'd make some attempt to test the capacitor, assuming it isn't shorted - I'd be interested whether it had more leakage one way than the other.
     
  13. KM Photography

    Thread Starter New Member

    Nov 15, 2014
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    I believe it's shot. I didn't see any actually arcing, just smoke coming from underneath the cap. If you look at the lead it's burnt around the body of the cap. If it was just arcing at the solder point, I wouldn't have had to heat the solder to remove it.
     
  14. KM Photography

    Thread Starter New Member

    Nov 15, 2014
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    Not to mention, it smells like a burnt capacitor. They have those rich smells that smells like a coal tar pit.
     
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  15. GopherT

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    atferrari, Sinus23 and KJ6EAD like this.
  16. atferrari

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  17. GopherT

    AAC Fanatic!

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    One who makes things easier - pretty much sums up my life.
     
  18. KM Photography

    Thread Starter New Member

    Nov 15, 2014
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    Lol thank you Gopher. I did happen to give some advice for pictures. I'm using a Nikon D3300 to take my photos, however you can still get a decent quality photo with even the most basic point and shoot camera. I put that advice on the forum you linked to me.
     
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  19. ian field

    Distinguished Member

    Oct 27, 2012
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    Just had a proper look at the posted photo - those burn marks look a lot like rivet failure where the leads come through the seal and attach to the solder lugs.

    Obviously not good enough to repair the capacitor to return to service - but you can partially re-form the rivet heads with the point of a screwdriver if you tap the handle with a bit of weight.

    That should restore good enough contact so you can do some tests to determine whether leakage is significantly more with one polarity than the other.

    The Ohms ranges on an analogue meter such as an AVO 8 should give you some indication - when you apply the prods to the capacitor lugs, the pointer should "kick" to nearly 0 Ohms and slowly sink back to infinity. If it sinks very slowly one way round - that's leakage.
     
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