Question about capacitor size vs capacitance

[Eric Bauld]

I have been getting myself into electronics for some time as a hobby.
And often run into questions I am unable to answer with just search
engines. This is one of them.

I am getting my head wrapped around the storage capacity of capacitors
in relation to volts and amps. But one thing I cannot figure out is
capacity VS size.

I have a few large capacitors, one from a microwave, a bunch I believe
from stereo amplifiers, another is a motor start capacitor... all
currently completely discharged.... of course.

The have the following capacitance and approx dimensions. uFarads,
Voltes, (Inches)
Microwave: 0.8 uF 1200v 5'x2'x3' Oval-ish shape
Stereo: 12000 uF 71V 2.5'x1.5' Cylinder
Motor Start: 40 uF 340V 7'x5'x4' (approx) Box shape (its huge)
And there are super caps which are fairly small about 1v to 5.5v and
can store a full Farad

What interests me the most that I have had trouble organizing is the
differences in these caps any why.

Ex: The Stereo Amp capacitor is tiny compared to the motor start
capacitor but is 300 times the rated farads and the large one is only
about 4.8 times more voltage ability.

The microwave I can see being large basing its construction so that It
does not break down at high voltage. But the difference between the
motor start being VERY large, but only having very tiny capacity in
comparison.

What is the reason for this ? Can it output its energy faster? Does it
actually store more ? in some round about kind of way and my
understanding that the Farad capacity of a capacitor is not really how
"MUCH" energy a cap can actually store ? Or is it so the capacitor can
handle a large amount of amps passing THROUGH its structure ? Where
the stereo cap would be relatively low amps ?
And then there are car audio capacitors which advertise anything from
one F to 12F and higher, I don't have any of these but I have learned
their advertised capacities are often quite wrong. And these are also
quite large. How do these compare to the very large motor start
capacitor ? Both are large, one has 40uF other has 1F.

- E
Any reading material that would help with this or explanations would
be great.

 

[Barry]

"Eric Bauld" <eric@bauld.com> wrote in message
news:14b4cded-664b-4f45-9faf-2e4d6ecdb1a1@x8g2000prh.googlegroups.com...

I have been getting myself into electronics for some time as a hobby.
And often run into questions I am unable to answer with just search
engines. This is one of them.

I am getting my head wrapped around the storage capacity of capacitors
in relation to volts and amps. But one thing I cannot figure out is
capacity VS size.

I have a few large capacitors, one from a microwave, a bunch I believe
from stereo amplifiers, another is a motor start capacitor... all
currently completely discharged.... of course.

The have the following capacitance and approx dimensions. uFarads,
Voltes, (Inches)
Microwave: 0.8 uF 1200v 5'x2'x3' Oval-ish shape
Stereo: 12000 uF 71V 2.5'x1.5' Cylinder
Motor Start: 40 uF 340V 7'x5'x4' (approx) Box shape (its huge)
And there are super caps which are fairly small about 1v to 5.5v and
can store a full Farad

What interests me the most that I have had trouble organizing is the
differences in these caps any why.

Ex: The Stereo Amp capacitor is tiny compared to the motor start
capacitor but is 300 times the rated farads and the large one is only
about 4.8 times more voltage ability.

The microwave I can see being large basing its construction so that It
does not break down at high voltage. But the difference between the
motor start being VERY large, but only having very tiny capacity in
comparison.

What is the reason for this ? Can it output its energy faster? Does it
actually store more ? in some round about kind of way and my
understanding that the Farad capacity of a capacitor is not really how
"MUCH" energy a cap can actually store ? Or is it so the capacitor can
handle a large amount of amps passing THROUGH its structure ? Where
the stereo cap would be relatively low amps ?
And then there are car audio capacitors which advertise anything from
one F to 12F and higher, I don't have any of these but I have learned
their advertised capacities are often quite wrong. And these are also
quite large. How do these compare to the very large motor start
capacitor ? Both are large, one has 40uF other has 1F.

- E
Any reading material that would help with this or explanations would
be great.

For one thing, the type of capacitor and how it is manufactured is
important.

The capacitor from the stereo is an electrolytic capacitor. It packs a
lot of capacitance in a relatively small volume. The size goes up with
both capacitance and voltage rating. Most electrolytic capacitors fall
into the range of 3 to 6 volts minimum to 500 volts maximum. They are
polarized, except the seldom used non-polar electrolytics which
internally are two back-to-back electrolytics. Electrolytic capacitors
can be made of aluminum or tantalum with the tantalum capacitors being
physically smaller (and more expensive).

The microwave oven capacitor is most likely a film dielectric capacitor.
Again the size goes up with both capacitance and voltage rating. Film
capacitors generally start at 50 volts and go up from there. Voltage
ratings of over 1000 volts tend to be uncommon expensive. They are
non-polar.

The motor start capacitor is most likely a film capacitor, although
nonpolar electrolytics are sometimes used with a low duty cycle. They
are rated for AC voltage, but can be used at significantly higher DC
voltages.

The supercaps currently pack the most capacitance per volume. They are
all low voltage units, generally 5 volts or less. In some senses they
are more like batteries than capacitors.

For any given capacitor technology (i.e. aluminum electrolytic,
polypropylene film, mica, etc.) the volume is proportional to the charge
the capacitor can store which is the product of the capacitance and the
working voltage (Q = C*V).

I have written many posts on electrolytic capacitors in the past. If you
are interested in reading them, put electrolytic capacitor and my surname
into a Google search to find them.

Dr. Barry L. Ornitz WA4VZQ my_ham_call_letters@live.com

 

[Eric Bauld]

On Mar 21, 11:42 am, "Barry" <n...@nospam.org> wrote:

"Eric Bauld" <e...@bauld.com> wrote in message

news:14b4cded-664b-4f45-9faf-2e4d6ecdb1a1@x8g2000prh.googlegroups.com...



I have been getting myself into electronics for some time as a hobby.
And often run into questions I am unable to answer with just search
engines. This is one of them.

I am getting my head wrapped around the storage capacity of capacitors
in relation to volts and amps. But one thing I cannot figure out is
capacity VS size.

I have a few large capacitors, one from a microwave, a bunch I believe
from stereo amplifiers, another is a motor start capacitor... all
currently completely discharged.... of course.

The have the following capacitance and approx dimensions. uFarads,
Voltes, (Inches)
Microwave: 0.8 uF  1200v 5'x2'x3'  Oval-ish shape
Stereo: 12000 uF 71V 2.5'x1.5' Cylinder
Motor Start: 40 uF 340V  7'x5'x4' (approx) Box shape (its huge)
And there are super caps which are fairly small about 1v to 5.5v and
can store a full Farad

What interests me the most that I have had trouble organizing is the
differences in these caps any why.

Ex: The Stereo Amp capacitor is tiny compared to the motor start
capacitor but is 300 times the rated farads and the large one is only
about 4.8 times more voltage ability.

The microwave I can see being large basing its construction so that It
does not break down at high voltage. But the difference between the
motor start being VERY large, but only having very tiny capacity in
comparison.

What is the reason for this ? Can it output its energy faster? Does it
actually store more ? in some round about kind of way and my
understanding that the Farad capacity of a capacitor is not really how
"MUCH" energy a cap can actually store ? Or is it so the capacitor can
handle a large amount of amps passing THROUGH its structure ? Where
the stereo cap would be relatively low amps ?
And then there are car audio capacitors which advertise anything from
one F to 12F and higher, I don't have any of these but I have learned
their advertised capacities are often quite wrong.  And these are also
quite large. How do these compare to the very large motor start
capacitor ? Both are large, one has 40uF other has 1F.

- E
Any reading material that would help with this or explanations would
be great.

For one thing, the type of capacitor and how it is manufactured is
important.

The capacitor from the stereo is an electrolytic capacitor.  It packs a
lot of capacitance in a relatively small volume.  The size goes up with
both capacitance and voltage rating.  Most electrolytic capacitors fall
into the range of 3 to 6 volts minimum to  500 volts maximum.  They are
polarized, except the seldom used non-polar electrolytics which
internally are two back-to-back electrolytics.  Electrolytic capacitors
can be made of aluminum or tantalum with the tantalum capacitors being
physically smaller (and more expensive).

The microwave oven capacitor is most likely a film dielectric capacitor.
Again the size goes up with both capacitance and voltage rating.  Film
capacitors generally start at 50 volts and go up from there.  Voltage
ratings of over 1000 volts tend to be uncommon expensive.  They are
non-polar.

The motor start capacitor is most likely a film capacitor, although
nonpolar electrolytics are sometimes used with a low duty cycle.  They
are rated for AC voltage, but can be used at significantly higher DC
voltages.

The supercaps currently pack the most capacitance per volume.  They are
all low voltage units, generally 5 volts or less.  In some senses they
are more like batteries than capacitors.

For any given capacitor technology (i.e. aluminum electrolytic,
polypropylene film, mica, etc.) the volume is proportional to the charge
the capacitor can store which is the product of the capacitance and the
working voltage (Q = C*V).

I have written many posts on electrolytic capacitors in the past.  If you
are interested in reading them, put electrolytic capacitor and my surname
into a Google search to find them.

        Dr. Barry L. Ornitz     WA4VZQ     my_ham_call_lett...@live.com

Thanks, explains a few items. One thing that stood out. Why would the
non polarized AC capacitor be usable at a "significantly" higher DC
voltage ? I have searched for you posts on caps, taking a read now.

- Eric

 

[Barry]

"Eric Bauld" <eric@bauld.com> wrote in message
news:8306fa2b-bd53-4d7c-9db0-577239d477bb@t19g2000prd.googlegroups.com...

Thanks, explains a few items. One thing that stood out. Why would the
non polarized AC capacitor be usable at a "significantly" higher DC
voltage ? I have searched for you posts on caps, taking a read now.
- Eric

The peak to peak voltage of an AC waveform is 2*SQRT(2) = 2.83 times the
RMS voltage. Also there are spikes on the typical AC line voltage. To
survive these, the capacitor must have a large safety margin. Capacitors
used for across-the-line or antenna coupling service have special
requirements under Underwriters Laboratories' rules that require testing
with high voltage impulses. You can read more about these in
http://database.ul.com/cgi-bin/XYV/template/LISEXT/1FRAME/showpage.html?&name=FOWX2.GuideInfo&ccnshorttitle=Across-the-line+Capacitors,+Antenna-coupling+Components,+Line-bypass+Components+and+Fixed+Capacitors+for+Use+in+Electronic+Equipment&objid=1073753701&cfgid=1073741824&version=versionless&parent_id=1073753700&sequence=1

The selection of the right capacitor for any given application can
sometimes be rather complex. "Real" capacitors always have series
inductance and resistance as well as shunt conductance. ESR, or
equivalent series resistance, is important in electrolytic capacitors,
especially when used in modern switching power supplies. Low series
inductance is important when the capacitor is used in high (radio)
frequency circuits. Audio circuits often require low dielectric
absorption capacitors. As you read more about electronic components and
become more familiar with the terms, this will make more sense to you.
ALWAYS consider safety when selecting electronic components. If you are
unsure, feel free to ask in the various electronic newsgroups. This
knowledge does not come overnight.

Dr. Barry L. Ornitz WA4VZQ ham_call_letters@live.com

I know I am showing just how ancient I am, but I can remember when spam
did not exist and you did not have to hide your email address.