Electrolytic Capacitor 500 uF vs 470 uF

Discussion in 'General Electronics Chat' started by Gdrumm, Jul 20, 2015.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    I have a bunch of 470 uF capacitors, but no 500s.

    It's for a Dell motherboard, with 2 bulging caps near the fan.
    Can I use the 470s?

    As I understand it, the voltage is not an issue.
    The old caps are 6.3 v, and the new ones are 25 volts.

    Thanks for any feedback.
    Gary
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,526
    2,369
    Electrolytics usually have a tolerance of -0% to +100%.
    They are not precise components!
    25v are fine.
    Max.
     
  3. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    Thanks Max,

    What about 500 uF vs 470 uF?

    Gary
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,526
    2,369
    I don't see a problem when you get into those values and typical applications.
    Max.
     
  5. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    3,572
    2,535
    I concur... normally caps in a motherboard are used as bypass, so their value is not critical... but, if the 500 µF failed, why not use the next available upwards cap value instead, say 680 µF? They probably failed because they were being worked too hard (I'm talking about their duty cycle, though I'm not sure what the correct terminology is).
    See this conversation I had a few months ago, regarding that issue.
     
  6. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    I do have some 680's, but they aren't new.
    The 470s are new, so maybe it would be best to go with those.

    I advised the owner that he really needs to buy a better computer anyway, this one is getting "long in the tooth" as they say.

    Thanks for all of your help.
    Gary
     
  7. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    you need matching voltage + capacitance.
    If you dont have the correct ESR the circuits on the board MAY not work, PC not starting up. Besides its nearly impossible to desolder them. Multilayer.
     
  8. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    684
    36
    Desldering wasn't too bad, but soldering in the replacements was difficult.
    I still struggle to get the holes cleaned out enough.

    I tried my solder sucker from Radio Shack, and that didn't help.
    I finally got them started, but realised I left the leads too long.

    Anyway, I'm going to put it back together this afternoon.
    Wish me luck.

    I did use 2 new ones, 25v 470 uF.

    Thanks so much
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,526
    2,369
    Remember electrolytic capacitors are NOT precision components, especially for those values, you should be OK.
    Max.
     
  10. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    783
    Electrolytic capacitors are "formed" during manufacture - that's a process of electrolosis that forms an oxide layer on the positive foil, the electrolyte is caustic and etches away the oxide very slowly. It is the leakage current that exists in all electrolytics that sustains the oxide layer.

    If you take electrolytics that have been stored a long time, its often necessary to "re-form" them by charging them slowly up to their rated voltage with a current limited supply.

    The reason for this; caustic etching - the oxide layer got thinner and can't handle the rated voltage. In actual fact, the oxide layer is the distance between the plates in the capacitance calculation, as the oxide gets thinner, the capacitance increases. So running 25V caps at that low a voltage will result in a significant capacitance increase.

    Capacitors usually have pretty wide tolerances - can be as much as -50%/+100%.

    Having said all that - motherboards usually call for low ESR electrolytics - you should replace them with the closest equivalants you can get hold of.
     
Loading...