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Changing out Electrolytic Caps for Polymer Ones

Discussion in 'General Electronics Discussion' started by Ernest George, Sep 24, 2018.

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  1. Ernest George

    Ernest George

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    Jul 18, 2014
    Hi guys!

    Long time no post! I bought a new (to me) car and it's got an issue with one of the modules. Some smart fellow took his apart in order to save the $2,000 USD that it would require to buy a new one and he found 3 regular capacitors on the board, one of which was shot. He replaced it and it fixed his problem. Cool beans!

    OK, so I scanned my car the other day and it reports the very same issue and the symptoms are exactly the same. So...I'm planning on going in and finding out what the capacitor values are and ordering up all three.

    This particular module resides in the engine compartment so higher temperatures are encountered. Anyway, one of the caps is 22μF/50v/105°C and they are through-hole regular caps. I was looking at digikey and can get the same thing in a through hole cap (CAP ALUM POLY 22UF 20% 63V T/H) with a higher lifespan etc.

    I don't know a lot about capacitors or the differences between a 'regular' cap and a polymer cap but I do know in the computer industry they went away from 'regular' caps a long time ago.

    My goal is to replace the 3 'regular' caps with really good modern caps that should not need revisiting. Are there any other differences that I'm not aware of or is it just a matter of match the specs and install them?
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Match specs, exceed specs where possible (e.g. max. temperature, max. voltage) and you should be good.
     
  3. MidNor

    MidNor

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    Sep 24, 2018
    Be careful in the old days we use to use caps to protect the circuit. I would say stick with what is in there. Your description sounds like that cap is there for protection.
    Or else you should find the reason for the cap blowing.
     
    Cannonball likes this.
  4. Cannonball

    Cannonball

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    May 6, 2017
    Don't fix it if it isn't broke.
     
  5. Ernest George

    Ernest George

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    Jul 18, 2014
    Thanks everyone - I was able to get the board out today and found 4 capacitors (total) and was able to source identical ones (with higher temperature ratings) in an aluminum poly cap for all 4. So I'm pretty excited about it. Total cost for all 4 caps and shipping was ~20 CAD from DigiKey. I'm pretty certain that will fix the issue (from what a few others have said that did the repair) and that saves me some big $$ - and I get to use my hot air reflow station once again. Thanks again everyone!
     
  6. davenn

    davenn Moderator

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    Sep 5, 2009
    Regular caps ? no such thing ;)
    So I'm not sure what you think the computer industry went away from ??

    Electrolytic capacitors, on the other hand, are still heavily used in the computer motherboard manufacturing industry
    as well as just about every other piece of electronics on the planet :)

    Note electrolytics are polarised caps, are those polymer ones likewise ??


    Dave
     
  7. Ernest George

    Ernest George

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    Jul 18, 2014
    The issues have been solved and the parts have been ordered thanks to the kind folks above. I have not seen a regular electrolytic capacitor in a quality mainboard for more then a decade. It would not surprise me if some really cheap off-brand obscure manufacturer was still using electrolytic ones but all the quality vendors changed over to what they call solid state caps about a decade ago.... (see Taiwan electrolytic capacitor formula theft and the resulting and well-known issue with those caps).

    At any rate, thanks to the folks above I have some new high end caps coming to case this issue once and for all !
     
  8. davenn

    davenn Moderator

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    Sep 5, 2009

    well my top quality Gigabyte MoBo's use standard SMD electro's and they are less than a year old ;)
    and I see ASUS … another top brand are still using electros as well
     
  9. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Electrolytic capacitors with liquid elecrtolyte or with solid electrolyte (polymer) look pretty much the same from the outside. Polymer electrolytic capacitors are typically more reliable than the wet ones.
    Reference e.g. here.
     
    MidNor likes this.
  10. peterlonz

    peterlonz

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    Feb 11, 2010
    Again I note the disparity of views on the subject of caps, their properties, construction, typical use, specs & interchangeability.
    Not sure why the OP needed to use a reflo station for cap replacement, or even if the caps needed to be board mounted. And how did he determine the caps had "failed" obvious visual failure or other electronic test?.
    Still a gutsy effort to attempt this fix, hope he advise how things turn out.
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Possibly they were surface mount capacitors of the sort that are really tricky to desolder and resolder again.
     
  12. Cannonball

    Cannonball

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    May 6, 2017
    Could you explain the difference in polymer capacitors from electrolytic capacitors? What makes them better?
     
  13. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Circuit boards and components in the motor industry usually have to comply with certain specifications, some of which are higher than found in commercial/domestic stuff - specifically temperature ranges.
    Capacitors used in SMPS circuits (on the 'smoothed side') have a tendency to fail more readily but there's no specific reason to fit 'higher quality' devices. Simple 1-for-1 replacement should be more than adequate.

    Out of curiosity, how OLD is the original circuit board? How much longer would you expect to use the vehicle?
     
    Cannonball likes this.
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Polymer capacitors are electrolytic capacitors. It's just that the electrolyte is a solid polymer.

    There is another thread where I went into some detail, but basically they can't leak or dry out, but they have higher leakage than regular aluminium wet electrolyte caps.

    See here
     
    Cannonball likes this.
  15. Cannonball

    Cannonball

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    May 6, 2017
    Thank you for this information. It is good to know.
     
  16. Petkan

    Petkan

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    Feb 9, 2011
    Petkan:
    The most common failure of electrolytic caps is degradation of ESR (equivalent series resistance), especially in switching mode power supplies. It typically leads to higher ripples, nuisance resets etc. The problem is the high frequency of switching making the cap see peak current too many times a second. When replacing a failed electrolytic cap, it is a good idea to add across its leads a ceramic capacitor (to take the peak current away).
    Note that some switching mode power supplies do require minimum level of ripples for proper current mode control.
    Going too far with added ceramic caps may lower the ripples too much. It is hard to overdo it since the ceramic caps with same size have way smaller capacitance. Electrolytic caps in extremely tight enclosures with poor cooling (Apple Time Capsule) tend to require replacement every 2-3 years. Cooling helps
     
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