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Question about capacitors

Discussion in 'General Electronics Discussion' started by Scout, Dec 19, 2012.

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  1. Scout

    Scout

    15
    0
    Jun 9, 2012
    I need to replace a few:
    1000uf 16v
    470uf 35v
    680uf 25v

    according to my ruler they are about 10mm x 25mm in size and rated for 125 degrees

    first it seems most of the replacements I find geared toward lcds are 105 degrees I know they are not ideal but are they acceptable?

    and

    many are also 10mm x 16mm is that acceptable and in general does the physical size matter or as long as tolerances are correct and they will fit in the board will they work?

    and i was told higher voltage ones are fine is that correct?

    Thanks in advance
     
  2. GreenGiant

    GreenGiant

    842
    6
    Feb 9, 2012
    size isnt a huge deal, you can usually bend the leads to get them to fit in the same spot so long as there is the room on the board.

    what type of capacitors are these?

    I would get capacitors that have the same or higher voltage, any lower and you risk blowing them out

    The 105 degrees Vs 125 degrees shouldn't make too much of a difference but I can't promise that
     
  3. Scout

    Scout

    15
    0
    Jun 9, 2012
    Thanks for reply
    they are electrolite capacitors from an lcd monitor.

    They are just some I found on ebay for cheap. If I knew that it was for sure the problem I would buy better ones to ensure that they last longer but so far I've had bad luck when it comes replacing capacitors in attempts to repair lcds and the capacitors I'm replacing physically look fine.I dont have a cap tester just a multimeter to test them and they seem to test fine with multimeter but from what i understand that just means they are not shorted

    (Btw monitor is flashing like a strobe light and I ruled out inverter and backlight as problem)
    Im hoping it's the power board because there are like 50 ,and just guessing cause not in front of me, 47uf caps on the mainboard.
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    11,513
    2,651
    Nov 17, 2011
    What matters are capacity, voltage rating and temperature.

    Size is, as GG wrote, not important as long as you can make the capacitors fit the available space.

    Higher voltage ratings are generally o.k., but also generally these caps are bigger.

    As to the temperature rating: I'm sure the manufacturer of the monitor had a reason to use 125 ° capacitors. He wouldn'T use them otherwisem because they are more expensive. Using 105 ° capacitors will work, but these will loose capacity much faster and you're going to have to replace them again.

    From my point of view this is economizing at the wrong end
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    You can use electrolytics rated for a higher voltage than the original, as long as you can make them fit. Higher-voltage components generally have better performance than lower-voltage components of the same capacitance, and will generally last longer.

    Electrolytics are not operated at their "rated" temperature. The rated temperature is simply the temperature at which they are supposed to last their rated lifetime, which is often only 3000 hours [Edit: or less; Steve has seen as low as 500 hours, maybe even less]. Every ten degrees Celsius lower than the rated temperature should roughly double the life expectancy.

    So if the capacitors run at 55 degrees Celsius, a 105 degree capacitor is rated for 50 degrees more, or five decades, so it should last 2^5 times (32 times) longer than its rated lifespan. A 125 degree component has seven decades of safety margin so it should last 2^7 times (128 times) longer.

    Also, capacitors with higher temperature ratings ARE designed to run at higher temperatures, and will generally be of higher quality.

    Two other important specifications for electrolytic capacitors that are used in power supplies and other power circuitry are ESR (equivalent series resistance) and ripple current. These are not normally marked on the component but you can find them out if you have the manufacturer's name and the capacitor "series", which is usually a two-letter or three-letter identifier marked on the capacitor.

    Download the data sheet for the capacitor range, locate the specific part you have, and check the ESR and ripple current specifications. Your replacement must be rated for at least the same amount of ripple current, otherwise it may overheat and fail, and should be specified for the same or lower ESR. (In some circuits, using a capacitor with MUCH lower ESR can cause instability and malfunctioning.)

    Also, electrolytic capacitors are not all created equal. As with rechargeable batteries, there is some creativity involved in specifications from budget manufacturers. You should always buy reputable brands - UCC (United Chemi-Con), NCC (Nichicon), and Panasonic (Japanese) come to mind - if you want the device to operate properly and last a long time.
     
    Last edited: Dec 20, 2012
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
    2,837
    Jan 21, 2010
    I've seen as low as 500 hours for sure, and I think I may have seen lower.
     
  7. Jotto

    Jotto

    120
    0
    Aug 24, 2012
    Are you working on a Tatung monitor?

    They always seem to have one odd ball capacitor. Best place I have found for a variety of capacitors is B&D Electronics.
     
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