Connect with us

Capacitors

Discussion in 'General Electronics Discussion' started by Robert Byrne, Nov 10, 2015.

Scroll to continue with content
  1. Robert Byrne

    Robert Byrne

    20
    3
    Nov 10, 2015
    Guys
    Might be a silly question, I know that it's possible to get a shock from a capacitor, how bad can they get? Is there a way of removing them from a breadboard when testing without getting a shock?
    Hope that makes sense.
    Thanks
     
  2. Minder

    Minder

    3,007
    640
    Apr 24, 2015
    Depends how large they are (capacitance wise) and what voltage they operate at, usually a short circuit with a jumper is fine, it is when you get the many 1000's of μfd's and high voltage, you may get zapped, Many cases there is a bleed off resistor to discharge them.
    If you use a screwdriver for the big ones, it usually results in a need to regrind it.!!!
    (ask me how I know!).
    M.
     
    Robert Byrne likes this.
  3. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    Capacitor shocks can be down-right nasty!
    Something as minor as a little buzz in your fingertip to a sudden very strong shock through your body causing a burn on entry and exit, causing muscles to contract and possibly stopping you heart.

    The problem with a capacitor is that it is very capable of outputting an immense amount of current in a moments notice. There is a reason Capacitors are using in High-Voltage applications like defibrillators, rail-guns and simulated lightning!

    Unplug the device. Attempt to power on the device while it's unplugged.
    If you are not familiar with what you are getting yourself into, let it sit for a few hours. (Caps self-discharge... if you wait long enough, they will loose a lot of their charge. More-so if the designer had included a discharge path)
    Once inside do not touch ANY conductive part of the board.
    Do your research, scout the board and make note of voltage ratings on capacitors and how things are laid out.

    * Get a multi-meter with an alligator clip or use another method to leave one of the probes connected but unattended. This will let you use ONE hand, preferably the right hand to use the other probe to test various parts of the circuit.

    Capacitors are quite capable of spot-welding themselves to conductive objects. Some people may just tell you to short the leads together with a screwdriver or similar. It's hard to advise this, but it would most certainly ensure that there is 0 charge left in the capacitor. Safely doing this would require a power resistor with an appropriate Ω and Power rating to discharge the cap without burning out.
    If it's discharged, you can remove just fine. The real danger of these things is accidentally touching both leads at the same time! This is why I say not to touch ANY part of the circuit board... because one lead could be connected to a trace that you are unknowingly holding with your finger on the edge of the board.
    Take it from someone who shocked themselves with a disposable camera flash... I was holding the little metal tab used as the negative terminal on the battery. Big mistake.
     
    Robert Byrne likes this.
  4. Robert Byrne

    Robert Byrne

    20
    3
    Nov 10, 2015
    Guys thanks very much, I just don't understand capacitors at all. Can I get a shock by touching the body of the capacitor? Some of them say 16, 25 and 50v, what exactly does that mean? I'm starting a project soon and it requires capacitors, that's why I ask, I'm alittle worried lol
     
  5. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    I guess I should mention, this isn't a scare tactic, but beginners should be weary.
    Take a look at the voltage on a capacitor and ask yourself if you think it would hurt ;)
    If you know what you are doing and can identify problematic capacitors, you can avoid them, work around them, and deal with them safely.
    That camera flash that got me. I knew it was life but figured holding what I thought was ground would be safe. Assumptions are always a bad thing XD
    The cap at the time was rated at 330V and was probably sitting pretty close to 300V when I touched it.
    It even had enough charge left over to spark when I touched a screw-driver to it.

    And no... this was not recent.
     
    Robert Byrne likes this.
  6. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    The body is usually just isolated housing. I have yet to be shocked by touching the case in addition to any other part of the circuit, but it's reasonable to expect not to be.
    It's not a promise though. Circuits do funny things all the time.

    Remember this though. A capacitor, like a battery, needs a circuit to discharge.
    If you are floating in the air, and you take your thumb and touch one of the leads from a fully charged 100V capacitor, you won't get a shock. You've provided an 'entry' into your body, but no exit.
    This is why I had suggested using only one hand with a multi-meter, so you don't accidentally give an exit and entry point with both your hands.
    Please note that this is not a golden rule, and dealing with high frequencies will behave differently.
     
  7. Minder

    Minder

    3,007
    640
    Apr 24, 2015
    Touching just the body is usually no problem, it is placing a hand across the two terminals that you get the zap from, fortunately these terminals are often close together and it is just one hand that gets it.
    When I was a young apprentice, we used to charge up a large cap using a megger and leave it on the forman's bench, he caught on quickly.
    The voltages are the ratings at which they can be operated at, so for low voltage ones you should not have any worry.
    M.
     
    Gryd3 likes this.
  8. Robert Byrne

    Robert Byrne

    20
    3
    Nov 10, 2015
    Brilliant thank you very much, I'll have do alot of research on capacitors to try understand them. I think the biggest capacitors I'll be using would be 50v 4.7uf or 16v 470uf, although I'm unsure which is the bigger
     
  9. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    Think of it like a thickwalled little water balloon (High pressure, low capacity) and a thin walled large water balloon (Low pressure, high capacity)

    There are two specific traits. The voltage on one is rated higher than the other, but the other has 100 times more capacitance!
     
    Robert Byrne likes this.
  10. Robert Byrne

    Robert Byrne

    20
    3
    Nov 10, 2015
    I'm sorry for all the questions, I just can't get my head around that at all, I may have a look for a food book that I can study. I can see now that one has higher voltage and lower capacity but just dont understand, is there an easy way to understand them.
     
  11. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    We can try to word it differently ;)

    Well. We can compare to an air tank.
    Voltage = Pressure
    Capacitance = Capacity

    High numbers of one or the other can be a little dangerous, high numbers of both are much more dangerous.
    In reality, it's a little more involved...
    As electrons flow in one side of the capacitor, they force electrons out the other end as they charge.
    There is a special dis/charge curve that shows that this happens easily at first, then gets more difficult as the capacitor charges. When it's charged, there are a number of electrons that were forced out of one side, and an excess on the other. This is a charged state.
    The capacitor will try to equalize itself by repelling electrons out the side that has the excess amount so that they may flow through your hand or other conductive path to get to the side that is missing electrons.
    They are so dangerous because unlike batteries that rely on a chemical reaction to make this 'pressure' the capacitor is completely capable of unloading at a moments notice.
     
    Robert Byrne likes this.
  12. Robert Byrne

    Robert Byrne

    20
    3
    Nov 10, 2015
    Thank you very much for your time and patience with me, you have been very helpful. I always struggled with these when I was in college too, I thought now I'm older it might get easier lol. Kind of getting it now tho
     
    Gryd3 likes this.
  13. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    It's not the most accurate description, but it should help you start out.
     
    Robert Byrne likes this.
  14. davenn

    davenn Moderator

    13,657
    1,888
    Sep 5, 2009
    I need to add an important bit of info, that so far hasn't been mentioned.
    Everyone has been commenting on the energy a capacitor of a certain voltage and capacitance can store/release

    You need to understand that the voltage rating printed on the side of a capacitor has a totally different purpose
    This voltage rating is the maximum voltage that the capacitor can sustain BEFORE electrical breakdown of the dielectric
    material between the plates occurs.
    so consider that a 50V cap ( depending on the circuit it's in) may not have 50V across it, there may only be 10V

    The dielectric is an insulator between the capacitor plates. It may be made up of many different types of materials
    eg ... wet paper, dry paper, mylar, ceramic, air, vacuum to name a few. each of these dielectrics have different properties
    that determine the use of the capacitor in a particular place in a circuit

    variable capacitor with air dielectric


    varc01.jpg

    electrolytic capacitor ( wet paper dielectric)

    electrolytic_construction.jpg

    Ceramic dielectric cap

    Ceramic_disc_capacitor.jpg


    cheers
    Dave
     
    Harald Kapp, Robert Byrne and Gryd3 like this.
  15. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    If you are playing with circuits on a breadboard, what voltage are you using? In most cases, there will be no voltage larger than that across any capacitor. The exception is boost circuit like the photoflash Gryd3 mentioned. These will create larger voltage from small ones, and generally store this voltage in a capacitor.

    So, unless you are building boost converters, you are perfectly safe if the voltage you are using for power is < 30V.

    Bob
     
  16. hevans1944

    hevans1944 Hop - AC8NS

    4,537
    2,113
    Jun 21, 2012
    Depends on what you mean by "understand". There is some math associated with describing how capacitors behave. You can rote memorize the formulas and that will probably be enough to get you by, but deeper understanding would come from a good physics course. Here is an excellent web site for beginners.
     
    Robert Byrne likes this.
  17. Robert Byrne

    Robert Byrne

    20
    3
    Nov 10, 2015
    Thanks for the reply, the most I'll be using is 12v DC, its for a model railway.
     
  18. Robert Byrne

    Robert Byrne

    20
    3
    Nov 10, 2015
    Is there much difference in ceramic and standard capacitors? Are they for different uses?
     
  19. hevans1944

    hevans1944 Hop - AC8NS

    4,537
    2,113
    Jun 21, 2012
    There is no such thing as a "standard capacitor". Ceramic capacitors are useful up to about 0.1 μF capacitance and as low as a few pF. They are available with various temperature coefficients (capacitance versus temperature) that can be important if used in tuned circuits. A ceramic capacitor is often used in parallel with an electrolytic capacitor for power supply by-pass purposes because they have a lower effective series resistance (ESR) at high frequencies.

    The capacitor type is typically sorted by the dielectric used: ceramic, plastic, mica, air, vacuum, electrolyte separating a thin oxide film, etc. Within those broad categories capacitors can be sorted by electrical characteristics such as temperature coefficient of capacitance, maximum working voltage, maximum current versus frequency, leakage current at DC, effective series resistance versus frequency, and (of course) capacitance. Physical size can be almost anything, from a chip a few millimeters on a side to huge power-factor correcting capacitors several meters on a side.

    For hobby use, you are likely only to need ceramic, plastic, electrolytic, and perhaps air variable and mica capacitors if you plan to play with RF..
     
    Gryd3 and Robert Byrne like this.
  20. Robert Byrne

    Robert Byrne

    20
    3
    Nov 10, 2015
    Brilliant thank you, sorry when I said standard capacitors I meant the standard shape, round bodied. Just need to figure out which values I need for my projects.
     
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

-