capacitor upgrade.

Discussion in 'General Electronics Chat' started by acebodge1, Jun 22, 2008.

  1. acebodge1

    Thread Starter Member

    Jun 18, 2008
    13
    0
    Hiya folks,I repaired the power supply on one of my satellite receivers the other day,by replacing defective electrolytics.The problem is,the receiver will probably need the same job doing in another couple of years.How might i upgrade the capacitors,so the receiver should last a lot longer.For example,one of the capacitors was 470uf/35v,could i use a 470uf/50v?Would the 50volt capacitor last longer than the 35volt version?Or do i have to use the same value,but with a higher temperature rating?
    regards bodger
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If you can fit a higher voltage, higher temp rated capacitor in the same place, by all means do so.

    Use new-stock electrolytics from a major supplier like Farnell - I know they're in the UK, but I don't know the suppliers downunder. If you put in "new old stock", you'll just hasten the time when you'll be making the next replacement.

    Some Asian capacitor manufacturers were using an electrolyte mix that was too strong, which caused their capacitors to fail earlier than they should have due to corrosion. I don't remember which ones, unfortunately - but you could probably discover by doing a search on the Web. Even if I did remember, I wouldn't post it here, as such mentions could lead to liabel suits, which I want no part of.

    Keeping your receiver cool will help extend the life of the caps. Ensure that it is getting sufficient airflow. If you're stacking components, consider adding a cooling fan. You don't have to run the fan at full rated voltage; that can make a good bit of noise. Just run it fast enough to get some air circulating around inside the box.
     
  3. acebodge1

    Thread Starter Member

    Jun 18, 2008
    13
    0
    Thanks sgt,i am a bit naughty for using components that i have pulled from scrap circuit boards,i have a capacitor tester though.I am just wondering ,if just using a higher voltage rating is enough to extend the life of the capacitor?
    Regards bodger
     
  4. nanovate

    Distinguished Member

    May 7, 2007
    665
    1
    Using a higher temp rating will have a greater effect on life than voltage (assuming the voltage rating of the original capacitor was correct chosen).
     
  5. Murod

    Active Member

    Dec 24, 2005
    30
    0
    To make sure that you will have more reliable circuit, you can choose to replace with higher voltage and temperature rating. Just don't change the capacity (uF) value.
     
  6. Norfindel

    Active Member

    Mar 6, 2008
    235
    9
    You could check the voltage at the capacitor terminals, to see if a higher voltage Cap would do any good. Then you can decide if you prefer temp over voltage, or the other way around.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The "rule of thumb" for electrolytic capacitors is to use a voltage rating that is twice the maximum expected voltage across the capacitor in question.

    All capacitors "leak" current between the plates. Electrolytic caps leak more than others. The higher the voltage across the capacitor, the higher the leakage current. This leakage current causes heat. If the heat gets high enough, the electrolyte will boil and the capacitor will explode.

    Testing for capacitance value does not test for leakage current, unless your tester has that as a function.
    In general, the maximum leakage current should be no more than 1mA per 30uF at the capacitor's rated voltage. However, in order to measure the leakage current, you should read it by measuring the voltage drop across a resistor in series with the cap, rather than attempting to read current through the cap, because if the cap fails (shorted) as you're reading the current, you may destroy your meter.

    It is often possible to reform quality electrolytics.
    Here is one method:
    http://www.vcomp.co.uk/tech_tips/reform_caps/reform_caps.htm
    Here is a 50-year-old military manual on using a capacitor reformer, including a schematic of the device:
    http://home2.btconnect.com/gmb/ReformerNo1.pdf
    Or try this Google search:
    http://www.google.com/search?hl=en&q=Electrolytic+capacitor+reforming
     
    Last edited: Jun 25, 2008
  8. acebodge1

    Thread Starter Member

    Jun 18, 2008
    13
    0
    Thanks folks,this is a great site.
    regards bodger
     
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