Mixing electrolytic capacitors

Discussion in 'General Electronics Chat' started by Gdrumm, Oct 6, 2014.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    I have a roadside pickup eMachine that has 2 bulging caps, 6.3 volt, 1800 mfd.

    I don't have the exact caps, but can I put two caps in series?

    I have (2) 16 volt 1500 mfds, plus (1) 50 volt 330 mfd, plus (1) 35 volt 300 mfd.

    So, a 1500 + a 330 = 1830 with higher than required, and non matching voltages.

    And another set, of 1500 + a 300, with again slightly higher and non matching voltages.

    Sounds logical to me, but I thought I had better run it by you guys.

    Thanks,
    Gary

    Just found 10 pieces the right size, from China for $1.32, with free shipping.
    I think I will wait a couple of weeks, and fix it right.

    It's still an interesting quetion though.

    Thanks
     
    Last edited: Oct 6, 2014
  2. Lestraveled

    Well-Known Member

    May 19, 2014
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    First, you would put them in parallel, not series.
    Second, mixing caps in parallel is fine, just so long as the lowest voltage is higher than you need, (greater than 6.3 volts).
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    Thirdly, replacing one 1800uF/6.3V with one 1500uF/16V is acceptable in a power supply.
     
  4. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Good information, and thanks for the refresher on Series and Parallel.

    I might go ahead and give it a shot, while I have two weeks to burn.

    I appreciate the feedback.

    As always,
    Thanks,
    Gary
     
  5. takao21203

    Distinguished Member

    Apr 28, 2012
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    in most cases, almost any similar part will do.

    If it is a special low ESR capacitor, you need to know some circuits indeed are picky and wont work right if you use different caps. The circuit WOULD WORK, but the error detection shuts it off.
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    Oops. I didn't read the part "roadside pickup eMachine".
    That is a different beast. The switch-mode supply on a computer mother board is a different story. They commonly have a number (6 or 7) such capacitors in parallel and require low ESR capacitors. Replacing through-hole capacitors on a multi-layer board is a pain and require the right tools and expertise and lots of patience. But it is doable. I have done a few myself.
     
  7. Lestraveled

    Well-Known Member

    May 19, 2014
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    What is a "roadside pickup eMachine"???
     
  8. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Sorry,
    It's a cheap computer made by eMachine that I found on the side of the road.

    This one has Vista Home, with 2 gigs of ram, and an 80 GB hard drive.

    The bad caps were on the mother board.

    Gary
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
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    Those values sort of hint at ultra low ESR, the values are typical of what you're likely to find on a PC motherboard.

    Scrounge some scrap MOBOs from a repair shop - you'll probably find 6.3V caps at least pretty close to the values you need.

    Bad caps is a common failure on MOBOs - so you might have to weed through a few.
     
    Gdrumm likes this.
  10. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Update,
    I scrounged, and found an old MB with the exact caps.

    Now for the lesson of the day.
    Don't drill the holes on the MB so the caps will go in easier............


    I mean I measured the wire of the cap, and found it to be .034", so I got my pin vise, and a .035" drill, and drilled out the holes, thinking this would help me install the replacement caps easier..

    I learned the hard way, that this action removed some of the metal to which the pin anchors to the board.

    I like to never got the final pin soldered in.

    Thanks for your expertise, again,
    Gary

    Update,
    PC is up and running.

    Thanks,
    Gary
     
    Last edited: Oct 11, 2014
  11. ian field

    Distinguished Member

    Oct 27, 2012
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    PC MOBOs are usually multilayer. so some through hole vias connect to tracks buried inside the PCB layers.

    If you run them through with a pin chuck and remove the via - you can isolate buried tracks that are next to impossible to patch with a repair wire.

    Re-tin the salvaged capacitor leads and run the solder off the ends as you hold the capacitor up vertical, this should drip the blob off onto the tip of the iron, with an even layer of solder on the lead, you can see how straight it is.
     
  12. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Good tip.
    Sounds similar to what I finally did.
    With solder on the capacitor leads, I got them thru the holes, then added solder to them again.
    While holding the iron on the leads, I pulled them back thru the holes slightly, then removed the iron.
    I finally got enough of the lead to make a solid grab inside the hole.

    I got lucky.
    One of them took about 10 tries before it finally grabbed.

    Thanks for the tip.

    Gary
     
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