Series caps
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I think there is confusion about connecting caps in series. Yes, two 1F
caps in series = 1/2F...but so what? If you charge a single 1F cap with 1
amp for 1 sec, it will be charged to 1 volt. If you charge two series 1F
caps with 1 amp for 1 sec, you will measure 2 volts. The total charge
transferred is the same, (coulombs = amps x seconds), and the current is =
in a series circuit.
This means you could connect two 2.5 volt caps in series to achieve 5 volts.
In practice, they should be charged individually, because mismatch in
capacitance will result in one of the caps reaching full rated voltage first
if charged in series. Charging further would overvoltage the lower
capacitance unit. So charge them individually, then series them to run the
load. No loss of stored charged occurs when they are used in series.
A good analogy is that you do not lose battery amp-hour capacity by
connecting them in series.
Hope this helps,
Ray McArthur
caps in series = 1/2F...but so what? If you charge a single 1F cap with 1
amp for 1 sec, it will be charged to 1 volt. If you charge two series 1F
caps with 1 amp for 1 sec, you will measure 2 volts. The total charge
transferred is the same, (coulombs = amps x seconds), and the current is =
in a series circuit.
This means you could connect two 2.5 volt caps in series to achieve 5 volts.
In practice, they should be charged individually, because mismatch in
capacitance will result in one of the caps reaching full rated voltage first
if charged in series. Charging further would overvoltage the lower
capacitance unit. So charge them individually, then series them to run the
load. No loss of stored charged occurs when they are used in series.
A good analogy is that you do not lose battery amp-hour capacity by
connecting them in series.
Hope this helps,
Ray McArthur
Comments
rjmca wrote:
>
> I think there is confusion about connecting caps in series. Yes, two 1F
> caps in series = 1/2F...but so what? If you charge a single 1F cap with 1
> amp for 1 sec, it will be charged to 1 volt. If you charge two series 1F
> caps with 1 amp for 1 sec, you will measure 2 volts. The total charge
> transferred is the same, (coulombs = amps x seconds), and the current is =
> in a series circuit.
This doesn't feel right. Caps are not batteries, there are charge issues
involved because energy is being stored, not generated.
> This means you could connect two 2.5 volt caps in series to achieve 5 volts.
> In practice, they should be charged individually, because mismatch in
> capacitance will result in one of the caps reaching full rated voltage first
> if charged in series. Charging further would overvoltage the lower
> capacitance unit. So charge them individually, then series them to run the
> load. No loss of stored charged occurs when they are used in series.
>
> A good analogy is that you do not lose battery amp-hour capacity by
> connecting them in series.
Bad and confusing analogy actually. A battery generates its charge, the
cap simply stores it. This topic makes me uncomfortable as there is something
that I know I'm missing. Series caps will drop the capacitance (and storage
capacity) by the formula Ct = 1/(1/C1 + 1/C2). That is the rule, I
believe it,
I've seen it in practice. This leads me to believe that putting caps in series
to increase voltage will lose total energy. We are seeing charge
transfer, it
is not like two batteries in series whose total potential difference is actually
greater. This charge transfer must be the source of the system total
charge
loss. I believe the total (-) charge on the one cap will be filled with the
(+) charge holes no the other cap, result, loss of 1/2 of the charge.
In short, will someone test this? My brain hurts.
DLC
> Hope this helps,
> Ray McArthur
--
Dennis Clark http://www.verinet.com/~dlc
dlc@v...
Just to confuse the issue :-) There is a HV pulse circuit called a marx
bank, in which capacitors are charged in parallel and discharged in series.
If one charges N capacitors to V volts in parallel, one can get N x V volts
out when the bank is discharged in series. Technique is used in pulsed
lasers, pulsed x-rays, EMP weapons(!) etc. Acts kinda like a battery...
-B
At 01:56 PM 5/4/2000 -0600, you wrote:
> Bad and confusing analogy actually. A battery generates its charge, the
>cap simply stores it. This topic makes me uncomfortable as there is something
>that I know I'm missing. Series caps will drop the capacitance (and storage
>capacity) by the formula Ct = 1/(1/C1 + 1/C2). That is the rule, I
>believe it,
>I've seen it in practice. This leads me to believe that putting caps in
>series
>to increase voltage will lose total energy. We are seeing charge
>transfer, it
>is not like two batteries in series whose total potential difference is
>actually
>greater. This charge transfer must be the source of the system total
>charge
>loss. I believe the total (-) charge on the one cap will be filled with the
>(+) charge holes no the other cap, result, loss of 1/2 of the charge.
>
> In short, will someone test this? My brain hurts.
Bob Tilden rntilden@l...
High Energy Physics Group
Northwestern University
Rechargeable batteries are sometimes modeled as *huge* capacitors in high
powered battery systems analysis. There is no charge lost, or energy lost
when going to the series connection.
Applicable formulas:
Q (charge, coulombs) = current x time
on a charged cap: Q=C x V
cap energy=(C*V**2)/2 that's voltage squared.
GE Labs in Schenectady, NY, at one time did lightning testing on power
distribution components by charging caps in parallel, then discharging them
in series; made a he.. of an explosion!
Regards,
Ray McArthur
Original Message
From: Dennis Clark <dlc@v...>
To: <basicstamps@egroups.com>
Sent: Thursday, May 04, 2000 3:56 PM
Subject: Re: [noparse][[/noparse]basicstamps] Series caps
> Ray,
>
> rjmca wrote:
> >
> > I think there is confusion about connecting caps in series. Yes, two 1F
> > caps in series = 1/2F...but so what? If you charge a single 1F cap with
1
> > amp for 1 sec, it will be charged to 1 volt. If you charge two series
1F
> > caps with 1 amp for 1 sec, you will measure 2 volts. The total charge
> > transferred is the same, (coulombs = amps x seconds), and the current is
=
> > in a series circuit.
>
> This doesn't feel right. Caps are not batteries, there are charge
issues
> involved because energy is being stored, not generated.
>
> > This means you could connect two 2.5 volt caps in series to achieve 5
volts.
> > In practice, they should be charged individually, because mismatch in
> > capacitance will result in one of the caps reaching full rated voltage
first
> > if charged in series. Charging further would overvoltage the lower
> > capacitance unit. So charge them individually, then series them to run
the
> > load. No loss of stored charged occurs when they are used in series.
> >
> > A good analogy is that you do not lose battery amp-hour capacity by
> > connecting them in series.
>
> Bad and confusing analogy actually. A battery generates its charge, the
> cap simply stores it. This topic makes me uncomfortable as there is
something
> that I know I'm missing. Series caps will drop the capacitance (and
storage
> capacity) by the formula Ct = 1/(1/C1 + 1/C2). That is the rule, I
> believe it,
> I've seen it in practice. This leads me to believe that putting caps in
series
> to increase voltage will lose total energy. We are seeing charge
> transfer, it
> is not like two batteries in series whose total potential difference is
actually
> greater. This charge transfer must be the source of the system total
> charge
> loss. I believe the total (-) charge on the one cap will be filled with
the
> (+) charge holes no the other cap, result, loss of 1/2 of the charge.
>
> In short, will someone test this? My brain hurts.
>
> DLC