Some amps have had around 100,000 uF in the power supply.
A soft start circuit is needed for such a large passive supply.
Come to think about it.
With a sufficiently large power supply, the limiting factor will be the wall socket. Given a dedicated 120 VAC / 15 A circuit .. and using a 0.95 power factor, we'd be looking at 1750 watts... converting to DC... about ~1300 watts dc (ball park).
So, I figure that if we want more power than that (*) perhaps the answer would be to put in something like an Uber regenerator/battery up front that can deliver even more power. Like one of them PS Audio units but with way more cojones. Something that can charge up its battery and caps when the current draw is less than the line capacity and then provide very high instantaneous peaks when needed.
Sure, installing a dedicated homerun with 20A breaker and upgraded romex will do the same thing.. but it will no be portable and likely cost as much.
(*) Admittedly quite a bit, but some amps do have two AC cords... noticed that?
With a sufficiently large power supply, the limiting factor will be the wall socket. Given a dedicated 120 VAC / 15 A circuit .. and using a 0.95 power factor, we'd be looking at 1750 watts... converting to DC... about ~1300 watts dc (ball park).
So, I figure that if we want more power than that (*) perhaps the answer would be to put in something like an Uber regenerator/battery up front that can deliver even more power. Like one of them PS Audio units but with way more cojones. Something that can charge up its battery and caps when the current draw is less than the line capacity and then provide very high instantaneous peaks when needed.
Sure, installing a dedicated homerun with 20A breaker and upgraded romex will do the same thing.. but it will no be portable and likely cost as much.
(*) Admittedly quite a bit, but some amps do have two AC cords... noticed that?
You guys are amazing, this thread has increased my understanding of amps and capacitance massively!
Not to go too far off topic, but looking at the power supply capacitance of my current power amp, I'm a bit confused. I have an Audio Research D-70 60wpc tube power amplifier with a regulated power supply. It has two "big chonky" 800uF 450V caps, and two smaller 1000uF 25V caps, presumably in the high-voltage and low-voltage supplies. Neither of these banks provides anywhere close the capacitance levels you have been talking about here. Is it a case of SS vs. tube designs having different requirements?
Not to go too far off topic, but looking at the power supply capacitance of my current power amp, I'm a bit confused. I have an Audio Research D-70 60wpc tube power amplifier with a regulated power supply. It has two "big chonky" 800uF 450V caps, and two smaller 1000uF 25V caps, presumably in the high-voltage and low-voltage supplies. Neither of these banks provides anywhere close the capacitance levels you have been talking about here. Is it a case of SS vs. tube designs having different requirements?
It's really about the energy storage in the power supply, which is C x V^2 / 2
So tube circuits, using around ten times the voltage of ss circuits,
only need around 1/100 the capacitance for the same amount of energy.
So tube circuits, using around ten times the voltage of ss circuits,
only need around 1/100 the capacitance for the same amount of energy.
Capacitance is inversely related to voltage.
C = Q / V
Q is charge, in coulombs.
As you can see, given a charge, the capacitance drops as the voltage increases.
Why? Because it becomes harder to push the charge across higher voltages... hence the ability to store that charge ( capacitance ) drops.
The really BIG caps (*) in your ARC D70 are measured across 450VDC. Hence the capacitance "drops".... BTW, I got an ARC D70 Mk II myself. Running the Svetlana 6550s now, which are good for 58 watts.
Tubes do have a lot of capacitors (in size) due to the voltages they use. The D70-II has big ones, look at the D120... and the VT200... nowadays they've gone to whole rows of those fast caps. So, even the tube amps have "less" capacitance, they are still storing quite a lot of charge.
C = Q / V
Q is charge, in coulombs.
As you can see, given a charge, the capacitance drops as the voltage increases.
Why? Because it becomes harder to push the charge across higher voltages... hence the ability to store that charge ( capacitance ) drops.
The really BIG caps (*) in your ARC D70 are measured across 450VDC. Hence the capacitance "drops".... BTW, I got an ARC D70 Mk II myself. Running the Svetlana 6550s now, which are good for 58 watts.
Tubes do have a lot of capacitors (in size) due to the voltages they use. The D70-II has big ones, look at the D120... and the VT200... nowadays they've gone to whole rows of those fast caps. So, even the tube amps have "less" capacitance, they are still storing quite a lot of charge.
Probably not the best way to look at it. Capacitance in farads is simply defined as Q/V. Farads are a derived unit.
A capacitor of one farad capacitance will store 1 coulomb of charge for every volt across its terminals. Capacitance does not change with voltage except due to parasitic effects on the dielectric material, which are not of (much) concern for power supply capacitance.
The relevant equation is J=CV^2/2. Thus at higher voltages, much less capacitance is required for the same energy storage. To store the same energy at 70 volts as at 450 volts requires about 41.3 times as much capacitance. 29,000 uF vs 700 uF.
A capacitor of one farad capacitance will store 1 coulomb of charge for every volt across its terminals. Capacitance does not change with voltage except due to parasitic effects on the dielectric material, which are not of (much) concern for power supply capacitance.
The relevant equation is J=CV^2/2. Thus at higher voltages, much less capacitance is required for the same energy storage. To store the same energy at 70 volts as at 450 volts requires about 41.3 times as much capacitance. 29,000 uF vs 700 uF.
^ "Capacitance does not change with voltage "
Huh? C = Q / V
For a given charge, the capacitance varies inversely with voltage.
Re-read what you wrote:
^"... at higher voltages, much less capacitance is required for the same energy storage"
++
Now back to the OP... where does current come from?
Current is flow of electrons... flow of charge ( change of charge ) over time.
I = dQ/dt...
But, fundamentally, let's think in Physics, not engineering... why do we have a flow of charge?
Let say you connect two points in space at different electronic energy levels... one is at a higher charge than the other... when you connect them, they both are now referenced to a common ground, so there will be more potential charge in one than the other... that is, each will have its own Voltage and there will be a difference of voltage between the two.
Recall that voltage is really EMF (Electro Magnetic Force )... it is intrinsically a measure of Potential Energy.
Thus the charge will flow from the point in space at a higher charge (higher voltage) to the lower charged point ( lower voltage ).
The flow of charge from a point of space at a higher energy level to a point of of space at a lower energy level is current.
Everything else is just details....
Of course, the flow of current is opposite to the flow of electrons.... tsk, tsk... engineering details... ;-)
Huh? C = Q / V
For a given charge, the capacitance varies inversely with voltage.
Re-read what you wrote:
^"... at higher voltages, much less capacitance is required for the same energy storage"
++
Now back to the OP... where does current come from?
Current is flow of electrons... flow of charge ( change of charge ) over time.
I = dQ/dt...
But, fundamentally, let's think in Physics, not engineering... why do we have a flow of charge?
Let say you connect two points in space at different electronic energy levels... one is at a higher charge than the other... when you connect them, they both are now referenced to a common ground, so there will be more potential charge in one than the other... that is, each will have its own Voltage and there will be a difference of voltage between the two.
Recall that voltage is really EMF (Electro Magnetic Force )... it is intrinsically a measure of Potential Energy.
Thus the charge will flow from the point in space at a higher charge (higher voltage) to the lower charged point ( lower voltage ).
The flow of charge from a point of space at a higher energy level to a point of of space at a lower energy level is current.
Everything else is just details....
Of course, the flow of current is opposite to the flow of electrons.... tsk, tsk... engineering details... ;-)
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Capacitance is related to the physical object and does not vary (to first order) with operating conditions.
For a simple model, C = epsilon x A / d where epsilon is a constant, A is the plate area, and d is the plate separation.
A real capacitor is more complicated in construction.
Better to view the equation as Q = C x V, where C is a constant.
So for a given capacitor, and capacitance value, the stored charge is proportional to the applied voltage.
For a simple model, C = epsilon x A / d where epsilon is a constant, A is the plate area, and d is the plate separation.
A real capacitor is more complicated in construction.
Better to view the equation as Q = C x V, where C is a constant.
So for a given capacitor, and capacitance value, the stored charge is proportional to the applied voltage.
@tonyEE Sorry, you have cause and effect mixed up. C=Q/V is a definition of the unit called Farads. It is not determinant of capacitance, which is a property of the plate geometry and dielectric. You cannot change the capacitance by changing the voltage, except for some secondary effects that change the plate geometry and dielectric.
Think of what you are claiming. Take a capacitor and charge it with a given amount of charge. This will establish a voltage across the plates of the capacitor. Remove the charging circuit from the capacitor. Now, how are you going to change the voltage? You can't. Capacitance is a physical property of the capacitor. The device obeys the VA laws. The VA law does not alter the capacitance.
Also, energy is not charge alone.
Think of what you are claiming. Take a capacitor and charge it with a given amount of charge. This will establish a voltage across the plates of the capacitor. Remove the charging circuit from the capacitor. Now, how are you going to change the voltage? You can't. Capacitance is a physical property of the capacitor. The device obeys the VA laws. The VA law does not alter the capacitance.
Also, energy is not charge alone.
The electric field is generated by the spatial arrangement of charge. Voltage is the potential (in the vector calculus sense) of the field between two points. Current is the movement of charge. It is possible for charge to move without being moved by an electric field.
Two examples:
1) The static charge on a balloon can be moved physically by carrying the balloon from place to place. This is a current just like "free" charges being moved through a field.
2) Superconductors, where charge moves indefinitely without a voltage difference.
Charge is a fundamental property of sub-atomic particles.
Two examples:
1) The static charge on a balloon can be moved physically by carrying the balloon from place to place. This is a current just like "free" charges being moved through a field.
2) Superconductors, where charge moves indefinitely without a voltage difference.
Charge is a fundamental property of sub-atomic particles.
As another poster reacted, this cause-and-effect seems perverse, but it isn't unheard of. Get an old tuning capacitor from a decades-old radio, the kind with fixed plates meshing with rotating plates and air as the dielectric. Mesh the plates fully (the usual capacitance value here is 455pF), charge to a couple hundred volts, remove the source of voltage, and rotate the shaft so the plates unmesh. The charge remains the same, but as the capacitance goes down the voltage goes up until there's a snap from the capacitor discharging across the plates.
"Where do Amps come from?"
Well... when an N transistor and a P transistor love one another very, very much they cuddle into sockets and get all warm together and then the lid goes on and the lights go out and... well anyway that's where amps come from.
Well... when an N transistor and a P transistor love one another very, very much they cuddle into sockets and get all warm together and then the lid goes on and the lights go out and... well anyway that's where amps come from.
This has been a very good conversation overall. I appreciate the knowledge shown here in a way that is understandable, well at least up to the limit of my understanding.
Another term for voltage can help some. Potential - to do work. It does nothing until current flows.
A capacitor is similar to a bucket of water. Put a hole in the bottom and the depth of water above the hole along with the size of the hole sets the flow rate. Flow is an analogue of current. Size of the hole - resistance to flow. The capacitance depends on the size of the bucket. This where the terms come from but the word potential isn't used very often - it's measure in volts.
Useful if one of your children has a crap A level physics teacher
A capacitor is similar to a bucket of water. Put a hole in the bottom and the depth of water above the hole along with the size of the hole sets the flow rate. Flow is an analogue of current. Size of the hole - resistance to flow. The capacitance depends on the size of the bucket. This where the terms come from but the word potential isn't used very often - it's measure in volts.
Useful if one of your children has a crap A level physics teacher
^
Post #27
Recall that voltage is really EMF (Electro Magnetic Force )... it is intrinsically a measure of Potential Energy.
Post #27
Recall that voltage is really EMF (Electro Magnetic Force )... it is intrinsically a measure of Potential Energy.
Yes, that's true because for a given capacitor design, the capacitance is a constant. The equation states that charge is proportional to voltage. The constant of proportionality is capacitance. Again, neither voltage nor charge change the capacitance. Your original claim that voltage changes capacitance is false.
In a capacitor, the charge cannot change without a concomitant change of the voltage. In order for the capacitance to change, something physical must be done to the capacitor - the plates move nearer or farther, or a dielectric is modified, or the plate size changes, as in the tuning capacitor example above.
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