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Electrolytic capacitors: Opinion required please

Discussion in 'General Electronics Discussion' started by Ray Pooley, Oct 3, 2018.

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  1. Ray Pooley

    Ray Pooley

    Jun 3, 2017
    Hi all

    Is there any difference between these two capacitors other than their physical appearance. See attached.

    Are they different types internally?

    They are both 120mF 450v 105C

    Are they interchangeable?

    Reason for asking is that I replaced the fat one with the longer one and sparks flew when I switched it on.

    I did use soldering acid on the board while soldering the capacitor in and it was still a little wet when I removed the new one
    after the blow.

    But the soldering acid doesn't conduct electricity so why would it short?

    Thanks for your input.

    PS. Ignore the scribblings on the paper. That's a fuse spec.

    Attached Files:

  2. dave9


    Mar 5, 2017
    No, swapping one with the other of the same specs should not cause sparks. What device are you repairing, and a schematic wouldn't hurt if you have one.

    Where did the sparks come from? It does seem possible that you have created a short somewhere during soldering OR possibly there was a different fault already?

    Were you trying to repair something that stopped working and assumed it was the capacitor at fault when it might have been something else that failed?

    Was the fuse blown and you put a new one in?
  3. kellys_eye


    Jun 25, 2010
    Providing you adhere to the polarity......
    and there isn't another fault external to the capacitors.
    HellasTechn likes this.
  4. Ylli


    Jun 19, 2018
    Soldering acid? I sure hope you mean flux.
    duke37 and davenn like this.
  5. Ray Pooley

    Ray Pooley

    Jun 3, 2017
    No. That was the thing. Pics of board attached. See the scorch mark between the terminals? it's isolated on the board and the terminals are about 10 mm apart. No chnace of shorting them out.

    Attached Files:

  6. Ray Pooley

    Ray Pooley

    Jun 3, 2017
    Polarity was fine. Thanks.
  7. Ray Pooley

    Ray Pooley

    Jun 3, 2017
    No. AG Soldering Acid. Cleans oxidation from the terminals and solder. This stuff. Like I said it's non conductive so I can't see why it would short out.
  8. BobK


    Jan 5, 2010
    Never heard of soldering acid, but, if it is what is in acid core solder, then it should not be used for electronics.

    davenn likes this.
  9. davenn

    davenn Moderator

    Sep 5, 2009

    don't use it for electronics

    use proper rosin cored solder :)

    As others have said …. if the values of the 2 caps are truly the same 120uF and 450V
    and you can absolutely and utterly guarantee that you have reversed the plority, then you have made some other mistake
  10. dave9


    Mar 5, 2017
    First, I assume the dark mark was not there until after you powered it on with the new capacitor?

    Second, I would take my multimeter probes and stick them in a pool of that solder flux to see if it's conductive.

    Third, I would not leave wet flux behind either way, but especially with a highly active acid flux. I do have a lot of old tarnished parts whether they were cannibalized from old trash or very old surplus from electronics merchants, and do rarely use zinc chloride acid flux, but it's petroleum based and I use it sparingly and always clean residue off promptly after soldering (and never on multi-strand wires where it can wick up the wire and do damage long term). I would not use it unless the corrosion was bad, which is unlikely on a tinned PCB trace and capacitor leads.

    Point being, I would get some mildly active rosin core flux and try to use that whenever possible.

    With no wet flux left behind I could better tell if the capacitor itself vented out the bottom to cause the wetness. If it did not vent out the bottom then the only conclusion I can make is that the flux is conductive.

    Is the flux water or petroleum based? If water based, as it reacts with the metals it's going to produce metal salts which make the flux conductive... possibly not highly conductive, but you have that cap at a place in the circuit where it's going to see over 300V.
    Last edited: Oct 3, 2018
  11. duke37


    Jan 9, 2011
    All acids are ionic and conductive.
    If they leave a wet deposit then that will be conductive. Wash it with water, then de-ionised water, then IPA. Dry.

    Only use cored solder made for electronics use
  12. kellys_eye


    Jun 25, 2010
    That burned board? Pure carbon?
  13. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir Ray Pooley . . . . .

    To err is human . . . .and I think that you have erred .

    That product brand offers either rosin flux based or acidic / base active agents .
    In your situation, the choice ended up in a strong base active agent that is dissolved within a
    isopropyl alcohol solvent / vehicle.
    The active ingredient is being
    TRIETHYLAMINE . . . . . . .with its NOISH identifier being 612-004-00-5
    You can research it at.

    " The substance is a strong base, it reacts violently with acid and is corrosive to aluminium, zinc, copper and their alloys in the presence of moisture. "

    " It is recommended to clean residues with ethyl alcohol or isopropyl alcohol ."

    The position that you had the board in for soldering probably resulted in a drain thru to the side of the board that is burnt. Either it was still moist or had a conductive caustic salt deposition on that area.
    With the probable 360VDC plus voltage across the board on power up, there was a flashover, with your end result.

    Look at the other offerings of that brand and you will see the rosin based FLUXES, instead of the ACID or BASE derived mixes of SOLDERING " ACIDS " .

    73's de Edd
    Richard9025 likes this.
  14. Audioguru


    Sep 24, 2016
    I used 450V capacitors with vacuum tubes 55 years ago. Maybe the replacement capacitor was old and in storage so long that it lost its "forming". I looked up forming and it said a very high current could flow causing heating of the chemicals inside causing gasses inside to cause an explosion. Then the heat of forming burnt the board.
  15. dave9


    Mar 5, 2017
    In an aqueous solution. I just tested a tin full of petrolatum based zinc chloride (acid) flux and it shows infinite resistance, even with the meter probes as near together as I could get without them touching.

    I also had the same result with a petrolatum based ZnCl₂ tinning flux with 4-8% tin in it (Oatey #95), no measurable conductivity.
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