Capacitor dilemma

[Ross Herbert]

On Mon, 18 Feb 2008 11:41:57 -0800 (PST), kayvee <kmvgroups@gmail.com> wrote:

:On Feb 18, 2:19 pm, et...@FreeNet.Carleton.CA (Michael Black) wrote:
:> kayvee (kmvgro...@gmail.com) 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.

 

[kayvee]

On Feb 18, 2:19 pm, et...@FreeNet.Carleton.CA (Michael Black) wrote:

kayvee (kmvgro...@gmail.com) 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.

 

[Michael Black]

kayvee (kmvgroups@gmail.com) 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

 

[kayvee]

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?