DC to AC inverter input capacitor question

Discussion in 'General Electronics Chat' started by sdowney717, Apr 22, 2015.

  1. sdowney717

    Thread Starter Member

    Jul 18, 2012
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    I am going to replace the input capacitors on the 12 volt side.
    They are currently some cheap china brand and are 3300 uf 16v.

    I will definetly up the voltage to like 24 vdc. There 12 of these.

    Would increasing the 3300uf to a higher value help with surge or be worth doing?
    I have seen where some people are putting a farad or more on the DC wires going into the inverter to help with surge starts. Although if they are wider they might not fit the board. They can easily go taller about 1/2 inch. Right now they are about 1.25 inch tall and 1/2 inch wide.
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    More capacitance isn't necessarily better. What problems are you trying to address?
     
  3. sdowney717

    Thread Starter Member

    Jul 18, 2012
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    Since they are getting replaced, now is the time to make any changes is all.
    I will likely just replace again with 3300 uf, but make them 25v.
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    using higher voltage electrolytics will not make anything better, it could fail sooner due to the fact that electrolytics are made to operate at a certain volotage, and if used at a lower voltage, will fail, not enough voltage to maintain the electro chemcal reaction.
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    Wow. I never heard of that one before, but that doesn't necessarily mean anything these days.
     
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  6. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    Me neither. If this is the case; electrolytic capacitors should also have a minimum voltage rating... which I've never heard of either.
     
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  7. Papabravo

    Expert

    Feb 24, 2006
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    Ciao blocco!
    Great reply.
     
  8. kyu9971

    Member

    Mar 28, 2015
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    I did not think there was a minimum voltage of work , but only a maximum tolerable
     
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  9. sdowney717

    Thread Starter Member

    Jul 18, 2012
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    I bought these Nippon, got 30 of these 25v 3300uf for about $15.
    I read these are a good brand to use. NEW NOS should be fine.
    they are 16mm wide and will just barely fit.
    The current 16v ones are 13mm wide.

    I watched a lot of inverter repair videos on youtube and 25vdc was said to be a much improved choice over 16v for a 12v inverter.

    The original caps say LESR Ricon 3300uf 16v
    Who knows how LESR they really are! I have been reading bad things about LESR china caps, that they aren't.
    Maybe going to these higher volt ones will compensate for that?
    [​IMG]
     
  10. OBW0549

    Well-Known Member

    Mar 2, 2015
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    I've been in electronics for over 50 years and I've never, NEVER heard of anything like this. Got any references to back up these remarkable assertions?
     
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  11. alfacliff

    Well-Known Member

    Dec 13, 2013
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    only about 50 years of experience. remember when electrolytics were marked in working volts dc, as well as maximum volts? after a number of years (less lately, someone changed the chemical mix) electrolytics used at lower voltages than they are rated start fading. in Yeasu microphones, a 1 mfd cap in series with the mic element fades to a few pf after about 5 years. a 50 volt electrolytic used at around 5 volts max. other places too, such as 12 volt supplies with caps rated at 35 volts and used at 18, fade to nothing after a few years.
     
  12. dl324

    Distinguished Member

    Mar 30, 2015
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    When buying capacitors, you should note lead spacing, diameter, and height.
    Just goes to show you can't believe everything on the internet. Everyone has a right to their opinion, but that doesn't mean it's right...

    ESR will change over the life of the cap. It isn't a problem until it gets too high.
    Higher voltage rating in smaller package and unbelievably cheap prices don't necessarily increase reliability or performance.
     
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  13. OBW0549

    Well-Known Member

    Mar 2, 2015
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    As you wish, although this is the very first time I have ever heard anyone claim that "electrolytics used at lower voltages than they are rated start fading", or anything remotely similar. And everything I have experienced as a design engineer, and everything I have ever read, says exactly the opposite.
     
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  14. alfacliff

    Well-Known Member

    Dec 13, 2013
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    then someone needs to do a failure analsys on the electrolytics. I change caps in switching power supplies and other stuff every day with the same fault, low capacitance, and usually bad ESR. usually with the rfated voltage on the cap nowhere near the voltage across it.
     
  15. Papabravo

    Expert

    Feb 24, 2006
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    An empirical correlation between two things is not proof of causality. I suggest you offer a stronger theoretical basis for your statement in order to retain some credibility. Like maybe a manufacturer's application note or white paper.
     
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  16. ian field

    Distinguished Member

    Oct 27, 2012
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    If you use an aluminium electrolytic at significantly less than its rated voltage. The caustic electrolyte etches the formed oxide dielectric, this effectively reduces the distance between the plates and increases the capacitance. If you then apply the full rated voltage, the thinner dielectric will pass high leakage current until the dielectric is formed to its normal thickness - assuming it doesn't heat up and burst first.

    More important parameters to 'improve' on are; temperature rating - you should be able to get 105 deg-C, and ESR which you should look for the lowest value you can find.
     
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  17. OBW0549

    Well-Known Member

    Mar 2, 2015
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    Well, "someone" has-- namely, just about every major manufacturer of electrolytic capacitors, along with major users, has published data on capacitor reliability as well as recommendations for temperature and voltage derating.

    Googling on the terms "electrolytic capacitor life vs voltage" and "electrolytic capacitor derating guidelines" brings up an ENORMOUS amount of material, none of which supports your claim that operating electrolytics at voltages below their rating reduces their life.

    Those are the typical failure modes when aluminum electrolytics are operated at too high a temperature (which can be exacerbated by excessive ripple current), not when they are operated below their rated voltage.
     
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  18. ian field

    Distinguished Member

    Oct 27, 2012
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    The formed oxide dielectric etches thinner in the caustic electrolyte, thinner dielectric is basically less distance between the plates, which means higher capacitance.

    You can subsequently form such capacitors back to their original rated values, but you have to limit the forming current to avoid overheating.
     
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  19. OBW0549

    Well-Known Member

    Mar 2, 2015
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    Agreed; and that goes double for electrolytics that have been in storage, unpowered, a long time.

    Looking through my junk box, I see a Sprague 1500uF, 63V electrolytic that was manufactured back in 1978, when Jimmy Carter was president. It's never been used, never had any voltage applied to it. I wonder if it's any good...
     
  20. ian field

    Distinguished Member

    Oct 27, 2012
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    My capacitor re-former was originally designed for measuring high voltage zeners - if I described its workings, that would be the end of the thread.
     
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