Connect with us

Higher than rating capacitance

Discussion in 'General Electronics Discussion' started by Wrenchead, Nov 6, 2020.

Scroll to continue with content
  1. Wrenchead

    Wrenchead

    9
    1
    Nov 6, 2020
    What if my 470uf-16v cap measures 750uf?
     
  2. Technomaniac

    Technomaniac

    100
    12
    Oct 31, 2020
    Is it made in China ?
     
    davenn likes this.
  3. Wrenchead

    Wrenchead

    9
    1
    Nov 6, 2020
    No name or origen.
     
  4. dave9

    dave9

    1,175
    315
    Mar 5, 2017
    If there is no name (or brand symbol) on the capacitor, it must be low enough grade junk that nobody wants responsibility for it. Even so, in many applications the exact uF value is not critical, especially when up in the hundreds of uF range where it is unlikely to be used for timing purposes. Even so, the potential low quality aspect could result in poor leakage, ESR, or lifespan that causes problems...

    Best to stick with major brand caps of the correct type and that adhere more closely to its specs.
     
    davenn likes this.
  5. Technomaniac

    Technomaniac

    100
    12
    Oct 31, 2020
    I suppose that you discharged it before testing ? Think about buying from a different supplier...I was once told that the Chinese do not have the recipe for making good electrolytics, that was learned over time by the established manufacturers in UK, Europe, US and Australia, who would have all been talking to each other, comparing notes. The Chinese electros seem to have a much shorter life in my experience, at least here on the Tropic of Capricorn. The Japanese make good ones, ELNA are fantastic.(If they're still around, of course) ... I notice all of my Chinese resistors in stock have tarnished pigtails after some years, while much older Philips examples will solder beautifully. Sure, you can scrape the leads before use, but how well has the internal construction stood up ? I can remember we used to buy EM410 one amp 1000v silicon diodes a thousand at a time at a little over a cent each, and the advertising said that they had SOLID SILVER LEADS !
     
  6. Technomaniac

    Technomaniac

    100
    12
    Oct 31, 2020
    Have you noticed how many sellers there are on the net auction sites, all selling the same products, at about the same price, and then you see a cheaper one? Have wondered if factory seconds/rejects out of the bin in the back lane behind the factory are being scavenged by the poorer citizens and put on ebay.. I bought a batch of 24 to 12v regulators in beautiful diecast finned enclosures, and EVERY ONE failed, max life a couple of months, some failed at power up. No way to get warranty replacements. I was frustrated with one seller, who asked me "Could you Google it?" Probably little understanding of English, and probably drop-selling the stuff anyway.
     
  7. Wrenchead

    Wrenchead

    9
    1
    Nov 6, 2020
    The specifics are, I am trouble shooting a chess computer from the 70's. The 2 470 caps are showing a low esr ( around .12). There is also a 2200uf cap with a capacitance of over 3500, and a high esr, .25. I know that one is bad. Just wondering why all the high capacitance levels. Just a hobby, for fun during the pandemic.
     
  8. Technomaniac

    Technomaniac

    100
    12
    Oct 31, 2020
    If you're measuring ESR with the cap in situ, there may be another connected in parallel, though it may be some distance away. Computer Grade electros are high quality and unlikely to be very far off-value.
     
  9. Wrenchead

    Wrenchead

    9
    1
    Nov 6, 2020
    The caps are off the board. I checked them with a dmm, and an Atlas 70 esr. I don't have access to any lab type meters.
     
  10. ratstar

    ratstar

    485
    20
    Aug 20, 2018
    I reckon you got lucky. :)
     
  11. bertus

    bertus Moderator

    2,515
    980
    Nov 8, 2019
    Hello,

    Read this :

    Electrolytic capacitor properties
    Aluminium electrolytic capacitors provide a much higher level of capacitance for a given volume than most ceramic capacitors.
    This means that high value electrolytic capacitors can be relatively small. This is a significant advantage in many instances.

    Electrolytic capacitors are polarised, i.e. they can only be placed one way round in the circuit.
    If they are connected incorrectly they can be damaged, and in some extreme instances they can explode.
    Care should also be taken not to exceed the rated working voltage. Normally they should be operated well below this value.

    The electrolytic capacitor has a wide tolerance. Typically the value of the component may be stated with a tolerance of -50% +100%.
    Despite this they are widely used in audio applications as coupling capacitors, and in smoothing applications for power supplies.
    They do not operate well at high frequencies and are typically not used for frequencies above 50 - 100 kHz.

    From this page:
    https://www.electronics-notes.com/articles/electronic_components/capacitors/electrolytic.php

    Bertus
     
  12. Wrenchead

    Wrenchead

    9
    1
    Nov 6, 2020
    Thanks, Bertus. That would explain the high capacitance. Probably should just use the old idea to change all caps first, especially this old. Just wondering.
     
  13. Technomaniac

    Technomaniac

    100
    12
    Oct 31, 2020
    Just make sure that the quality of the new ones exceeds the quality of the original ones.
     
  14. Wrenchead

    Wrenchead

    9
    1
    Nov 6, 2020
    Yeah, thanks, I started collecting caps from the board, and they are all over the place; T.I., Acrolytic,(Taiwan), mystery no names.
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,505
    2,852
    Jan 21, 2010
    If your capacitor has very high leakage, capacitance meters that use the time taken for the capacitor to charge to a certain voltage from a constant current source (or variations of that) will read a higher capacitance because they mistake the leakage of energy from the capacitor as increased capacitance.

    This is often seen in very old capacitors in valve equipment, less so in newer equipment, but not unheard of.
     
  16. Wrenchead

    Wrenchead

    9
    1
    Nov 6, 2020
    Thanks Steve, that also is the case with this equipment, very old( in electronics years) I am still learning a lot about these older components.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-