Connect with us

Capacitor dilemma

Discussion in 'Electronic Basics' started by kayvee, Feb 18, 2008.

Scroll to continue with content
  1. kayvee

    kayvee Guest

    I have this circuit that I am trying to make and it calls for a 47uf
    and a 68uf electrolytic capacitor. Now unfortunately, in the smallish
    town I live in the only store to buy components is what used to be
    Radio Shack. There they only sell 100uf and 220uf and 470uf
    electrolytic capacitors. I understand that if you run two capacitors
    in series the total capacitance is (1/C1) + (1/C2) = (1/Ctotal).

    Now, from my calculations I found that two 100uf capacitors in series
    makes 50uf, and a 100uf and a 220uf make about 68uf. Will it run
    exactly as if it had one 50uf and one 68uf or will this effect my
    circuit and I should I wait for my next trip to the big city to buy
    the right ones?

    Also I have the equivalent in ceramic capacitors lying around which
    would give me the right rating, but the diagram calls for
    electrolytic? Can I use them instead?
     

  2. YOu need to step back, and show us the circuit. Because while you may
    be fussing over getting the exact values, the reality of the specific
    circuit may mean that you don't need to fuss. In other words, what
    the capacitors are doing in the circuit will define whether or not
    you need them to be exact.

    In some cases, they will need to be or less exact. In other cases,
    you can use some different value and compensate by changing a resistor
    or two. In other cases, it won't matter because the exact value is
    irrelevant, since it's not determining timing or frequency.

    And the larger the value, the far greater likelihood that it doesn't
    need to be specific. Indeed, once you get to electrolytics, they are
    generally quite wide tolerant capacitors (unless you pay for high
    tolerance), so a little bit off there won't matter.

    Note, once again, that there really is never a reason for polarized
    capacitors. They are specified because the way the capacitors are
    made result in polarized capacitors, and making the capacitors that
    way is the only way to get high capacitance in a reasonably small
    package. Once you get into the tens of uF, you have little choice
    but to go with an electrolytic, and hence they will be polarized, and
    you have to put them in the proper way.

    Hence any time there is a polarized capacitor, it doesn't matter if
    you don't put a polarized capacitor in there. Chances are really
    good you won't find a non-polarized in that value, and if you do,
    you won't like the size or even cost.

    As for using ceramic capacitors, you may want to redo your math.
    Unless you actually have 1uF ceramic capacitors, and that is stretching
    things, you won't have ceramic capacitors in a high enough value to
    get what you want. Even if you have 1uF ceramics, you'd need 47
    and 68 in parallel to get your needed 47uF and 68uF, and you won't
    want that. Chances are good that the ceramics you have on hand are
    actually lower in value than 1uF, so you'd need even more. I point
    this out because people often get confused by component values.

    1uF = 10 times .1uF
    1uF = 100 times .01uF
    1uF = 1000 times .001uF

    Michael
     
  3. kayvee

    kayvee Guest

    I am testing the required capacitance of tattoo machine I am doing the
    wiring for. http://content.answers.com/main/content/wp/en/3/35/Tatgunschem.png
    This machine will be switching on and off at about 120hz, will be
    running on a 12V power supply and has 2 coils drawing the power. The
    capacitors are used to stop the arching of electricity when the
    armature bar ('c' in the diagram) pulls away from the contact point.
    Now I understand the the higher the capacitance, the less arching, but
    this slows down the frequency, so I am trying to find the right
    capacitor for my specific machine, but 100uf is just too high.

    Also, I think you are right about the ceramic capacitors.
     
  4. Ross Herbert

    Ross Herbert Guest

    :On Feb 18, 2:19 pm, (Michael Black) wrote:
    :> kayvee () writes:
    :> > I have this circuit that I am trying to make and it calls for a 47uf
    :> > and a 68uf electrolytic capacitor. Now unfortunately, in the smallish
    :> > town I live in the only store to buy components is what used to be
    :> > Radio Shack. There they only sell 100uf and 220uf and 470uf
    :> > electrolytic capacitors. I understand that if you run two capacitors
    :> > in series the total capacitance is (1/C1) + (1/C2) = (1/Ctotal).
    :>
    :> > Now, from my calculations I found that two 100uf capacitors in series
    :> > makes 50uf, and a 100uf and a 220uf make about 68uf. Will it run
    :> > exactly as if it had one 50uf and one 68uf or will this effect my
    :> > circuit and I should I wait for my next trip to the big city to buy
    :> > the right ones?
    :>
    :> > Also I have the equivalent in ceramic capacitors lying around which
    :> > would give me the right rating, but the diagram calls for
    :> > electrolytic? Can I use them instead?
    :>
    :> YOu need to step back, and show us the circuit. Because while you may
    :> be fussing over getting the exact values, the reality of the specific
    :> circuit may mean that you don't need to fuss. In other words, what
    :> the capacitors are doing in the circuit will define whether or not
    :> you need them to be exact.
    :>
    :> In some cases, they will need to be or less exact. In other cases,
    :> you can use some different value and compensate by changing a resistor
    :> or two. In other cases, it won't matter because the exact value is
    :> irrelevant, since it's not determining timing or frequency.
    :>
    :> And the larger the value, the far greater likelihood that it doesn't
    :> need to be specific. Indeed, once you get to electrolytics, they are
    :> generally quite wide tolerant capacitors (unless you pay for high
    :> tolerance), so a little bit off there won't matter.
    :>
    :> Note, once again, that there really is never a reason for polarized
    :> capacitors. They are specified because the way the capacitors are
    :> made result in polarized capacitors, and making the capacitors that
    :> way is the only way to get high capacitance in a reasonably small
    :> package. Once you get into the tens of uF, you have little choice
    :> but to go with an electrolytic, and hence they will be polarized, and
    :> you have to put them in the proper way.
    :>
    :> Hence any time there is a polarized capacitor, it doesn't matter if
    :> you don't put a polarized capacitor in there. Chances are really
    :> good you won't find a non-polarized in that value, and if you do,
    :> you won't like the size or even cost.
    :>
    :> As for using ceramic capacitors, you may want to redo your math.
    :> Unless you actually have 1uF ceramic capacitors, and that is stretching
    :> things, you won't have ceramic capacitors in a high enough value to
    :> get what you want. Even if you have 1uF ceramics, you'd need 47
    :> and 68 in parallel to get your needed 47uF and 68uF, and you won't
    :> want that. Chances are good that the ceramics you have on hand are
    :> actually lower in value than 1uF, so you'd need even more. I point
    :> this out because people often get confused by component values.
    :>
    :> 1uF = 10 times .1uF
    :> 1uF = 100 times .01uF
    :> 1uF = 1000 times .001uF
    :>
    :> Michael
    :
    :I am testing the required capacitance of tattoo machine I am doing the
    :wiring for. http://content.answers.com/main/content/wp/en/3/35/Tatgunschem.png
    :This machine will be switching on and off at about 120hz, will be
    :running on a 12V power supply and has 2 coils drawing the power. The
    :capacitors are used to stop the arching of electricity when the
    :armature bar ('c' in the diagram) pulls away from the contact point.
    :Now I understand the the higher the capacitance, the less arching, but
    :this slows down the frequency, so I am trying to find the right
    :capacitor for my specific machine, but 100uf is just too high.
    :
    :Also, I think you are right about the ceramic capacitors.

    That url doesn't work for me. I think this is the url you should have posted
    http://explanation-guide.info/meaning/Tattoo-gun.html

    It is hardly what is known as a "schematic" as commonly found in electronics. It
    attempts to be a "pictorial schematic" but it fails even in that regard. There
    is no mention of any capacitors or other components so we really need to see the
    complete circuit schematic using the usual symbols for resistors, capacitors
    etc.
     
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

-