PSU tier list 2.0

[turkey3_scratch]

Capacitors are confusing. They store energy, they filter ripple... I just have trouble trying to piece this all together. I never quite understood why the terminology "discharge" is used either.

 

[tiny voices]

Discharge makes perfect sense in this context. Capacitors hold a charge. So if you are getting rid of that charge, you are discharging them.

 

[turkey3_scratch]

But a discharged capacitor has the same amount of charge as a charged capacitor.

 

[tiny voices]

I don't believe so.

 

[stavrosmast]

1-0

 

[Darkbreeze]

But a discharged capacitor has the same amount of charge as a charged capacitor.

Definitely not.

http://www.repairfaq.org/sam/captest.htm

 

[turkey3_scratch]

http://amasci.com/emotor/cap1.html

Every bit of charge that's injected into one terminal *must* be forced out of the other terminal at the same time. The amount of charge inside the capacitor never changes. The net charge on each plate is cancelled by the opposite charge on the other plate. Capacitors are never "charged" with electric charge!

Therefore, during the "charging" process, energy is placed into the capacitor. Capacitors store energy, not charge. When we "charge" a capacitor, we give it a charge of energy. But because we use the word "charge" to refer both to electric charges and also to quantities of energy, our capacitor explanations are nearly impossible to understand. "Charging" a capacitor means injecting electrical energy into the device.

However, if we consider the capacitor as a whole, no electrons have been put into the capacitor. None have been removed. The same number of electrons are in a "charged" capacitor as in a capacitor which has been totally "discharged."

It's the truth. A discharged capacitor has the same amount of charge as a charged capacitor.

 

[Darkbreeze]

Your source is faulty/misleading.

Capacitors are sort of like batteries
—
both store electrical energy, but they work
differently. A battery uses chemicals to produce electrical energy and release it very
slowly through a circuit, sometimes taking several years to disperse all the energy (in
the case of a watch battery, for instance). A capacitor, which stores energy in t
he
form of an electrostatic field, generally releases its energy much more rapidly
—
often in seconds or less. This can make a large, charged capacitor extremely
dangerous if used or handled improperly.

 

[turkey3_scratch]

No, my source is not faulty. It's written by electrical engineer William Beaty, professor from the University of Washington, who writes articles on electricity misconceptions. Capacitors store energy, not charge. Charge has to flow through a capacitor to energize the capacitor, charge does not actually build up inside.

Ask the people on Jonnyguru. They also say capacitors store energy and not charge.

And in your quote above, it says right there a capacitor stores energy in an electric field, not by charge buildup.

 

[Darkbreeze]

It is essential - for your safety and to prevent damage to the device under test as well as your test equipment - that large or high voltage capacitors be fully discharged before measurements are made, soldering is attempted, or the circuitry is touched in any way. Some of the large filter capacitors commonly found in line operated equipment store a potentially lethal charge.

This doesn't mean that every one of the 250 capacitors in your TV needs to be discharged every time you power off and want to make a measurement. However, the large main filter capacitors and other capacitors in the power supplies should be checked and discharged if any significant voltage is found before touching anything - some capacitors (like the high voltage of the CRT in a TV or video monitor) will retain a dangerous or at least painful charge for days or longer!

A working TV or monitor may discharge its caps fairly completely when it is shut off as there is a significant load on both the low and high voltage power supplies. However, a TV or monitor that appears dead may hold a charge on both the LV and HV supplies for quite a while - hours in the case of the LV, days or more in the case of the HV as there may be no load on these supplies.

The main filter capacitors in the low voltage power supply should have bleeder resistors to drain their charge relatively quickly - but resistors can fail. Don't depend on them. There is no discharge path for the high voltage stored on the capacitance of the CRT other than the CRT beam current and reverse leakage through the high voltage rectifiers - which is quite small. In the case of old TV sets using vacuum tube HV rectifiers, the leakage was essentially zero. They would hold their charge almost indefinitely.

 

[turkey3_scratch]

Yes darkbreeze, your source is the faulty one. The person who wrote that has misconceptions about how a capacitor works, hence why he says "drain the charge".

Maybe the more skilled of electrical engineers and scientists gain their extreme expertise not through classroom learning. Instead they gain expertise in spite of our K-12 classroom learning. Maybe the experts are experts only because they have fought free of the wrong parts of grade school science, while the rest of us are still living under the yoke of the many physics misconceptions we were carefully taught in early grades.

 

[turkey3_scratch]

Charge flows through a capacitor to "charge" or "discharge" it; when one leaves, another enters (though it leaves because another charge entered, they are directly related).

 

[Darkbreeze]

No, my source is not faulty. It's written by electrical engineer William Beaty, professor from the University of Washington, who writes articles on electricity misconceptions. Capacitors store energy, not charge. Charge has to flow through a capacitor to energize the capacitor, charge does not actually build up inside.

Ask the people on Jonnyguru. They also say capacitors store energy and not charge.

Semantics. You're using loosely exchanged terminology as a sticking point. Energy, voltage, charge, all are stored power. But I think you know that. If you don't, then you're trying to learn something above your head. If you do, then you're arguing a moot point. Capacitors store energy/voltage/charge, period, and regardless of what William Beaty might have to say on the subject. Tell William to explain to the families of people who have died from touching the wrong caps how there was no charge in them.

 

[turkey3_scratch]

They do store charge, but then amount of charge that is stored never changes. That is why defining a capacitor as "storing charge" is silly, because it always remains the same amount.

Beaty knows they have charge inside, he is not happy with the definition of a capacitor.

 

[Mousemonkey]

Back in the good old days when cars used points instead of electronic ignition it was possible to have some fun with the capacitor from the rotor, getting a whack from one of those would soon edumacate you on how much energy a cap can store!

 

[turkey3_scratch]

Oh yeah, I believe it. Electrocution is the 3rd most common cause of death in the workplace.

 

[Darkbreeze]

It does change. If it didn't, then the Institute of electronics and electrical engineers would not have specific guidelines for discharging capacitors before work on or around them was conducted. That's like me saying that 90% of vehicles do not have a motor. Technically, they do not. Motors are electically powered. ENGINES produce power by internal combustion. Technically, I'm correct, but half the world relates to what creates power/torque as the "motor", so it's simply semantics.

As to whether it stores/depletes, that's just a fact and your William Beaty is spreading a dangerous misconception that, based on that notion, would indicate that discharging a high voltage capacitor is a nonsense procedure, which of course it is not. I trust the entire governing body of electrical engineers far more than I do one electrical engineer.

These are directly from the IEEE.

An electrical device that can store energy in the electric field between a pair of closely spaced plates

A capacitor is charged up much faster than a battery, and is discharged just as quickly.

When current is applied to the capacitor, electric charges build up on each plate. Each plate has the exact same amount of charge, but one plate has positive charges and the other negative charges

The battery must be removed from the circuit to discharge the capacitor.
When this happens, the capacitor acts as a battery and provides energy to
the circuit.
•
As time increases:
–
The amount of charge on the capacitor plates decreases (as in graph above)
–
The current (rate at which charges move) through the circuit decreases
–
At the beginning, a large number of charges want to get out, because there is a lot of
repulsion. As more charges are removed from the plates, the remaining charges repel
each other less, so they move slower and less current flows through the circuit.


Charge continues to flow until the voltage on both sides of resistor is equal. In this example, that means 0V when the capacitor is fully discharged

 

[turkey3_scratch]

William Beaty is not saying that discharging is not important, he's explaining what discharging actually does. It is a release of energy.

Charge does leave the plate, but another charge enters the other plate. It is incorrect, though, that as time increases the amount of charge on the plates decreases; the charge on one plate decreases, and the charge on the other plate increases, meaning a net change of 0. The amount of energy in the fields decreases. Charge does not build up on both plates, one charge enters plate A which causes a charge to leave plate B. This causes one plate to have an excess of electrons, and the other plate to have an excess of protons. In the end, the amount of electrons and protons are the same inside the capacitor, but the distribution of them about the two plates has changed. The amount of electrons in one plate may change, but in total for the entire capacitor it is the same.

 

[Darkbreeze]

Quoted directly from your William Beaty, and directed towards the subject that initially brought this up which is that pressing the power button DOES in fact discharge the capacitor, at least for OUR purposes, whether the electron and proton count changes or not.

A capacitor is briefly connected to a battery, so energy is stored in the capacitor. If the leads of the capacitor are now touched together, charge moves from one plate to the other. Does the capacitor now contain less charge? Yes, because its plates are now uncharged.

 

[turkey3_scratch]

Do you have a link to that quote?

Here is another quote by him:

Another one: if you "charge" a capacitor, you move charges from one plate to the other, and the number of charges within the device as a whole does not change. Or from an engineer's perspective, you drive charge through the capacitor, which causes potential across the plates to rise. But capacitors have exactly the same total charge within them whether they are "charged" or not! Whenever we take an electron from one plate, we put an electron onto the other plate. When we speak of "charging" capacitors, we've suddenly stopped talking about charge, and started talking about electrical energy. A "charged" capacitor has quite a bit more energy than an "uncharged" one (but exactly the same net-charge, and the same quantity of + and - particles inside it.) This basic concept is very important in understanding simple circuitry, yet it is rarely taught. The misleading term "charge" stands in the way of understanding. I suspect that students are not the only ones being misled. Many teachers misunderstand simple physics, and they believe that the purpose of a capacitor is to store electric charge.

The total charge inside a capacitor never changes. The total charge in the plates of a capacitor does change, but the net total change of charge for the entire capacitor is 0 because of this cancellation of one plate having what the other doesn't have. When one plate has an excess of electrons, this creates strong e-fields because the electrons are forced apart from their excess of protons in the other plate.

Source: http://amasci.com/miscon/eleca.html#charge

If William Beaty did say your quote above, then in fact he spoke in terms of the misconceptions he teaches about, so he made a mistake himself (mortals!).

 

[turkey3_scratch]

I believe you that holding the power button does discharge a capacitor. But the trouble arises because the term "discharge" has multiple meanings, and in this case refers to loss of energy rather than the loss of net charge.

 

[turkey3_scratch]

Darkbreeze, I found the source of your quote. You left out the rest of it:

a problem with the word "charge": A capacitor is briefly connected to
a battery, so energy is stored in the capacitor. If the leads of the
capacitor are now touched together, charge moves from one plate to the
other. Does the capacitor now contain less charge? Yes, because its
plates are now uncharged. No, because the total quantity of electrons and
protons never changed (each electron that left one plate ended up on the
other plate.) A "charged" capacitor contains exactly as many electrons as
an "uncharged" one. Charge imbalance is called "charge", but electrons
and protons are also called "charge."

Source: http://www.electrical-contractor.net/ESF/Why%20Electricity%20is%20Impossible%20to%20Understand.htm

When he says "Does the capacitor now contain less charge? Yes, because its plates are now uncharged." he is using the word "charge" in its second context, the context of energy, or what he calls charge imbalance. As he says, charge refers to three things, which is why it's easy get confused with: "net-charge, to quantities of charged particles, and to "charges" of energy"

Now it all makes sense why this debate even exists. When I speak of charge, I refer to protons and electrons. But when y'all were speaking of charge, you were referring to charges of energy. So yes, there is less charge in a discharged capacitor if we define charge as a charge of energy, but there is the same amount of charge if we define charge as protons and electrons. It's all very confusing because so many things refer to the word "charge".

 

[Darkbreeze]

I didn't LEAVE OUT, the rest of it. I posted the relevant part. The point you are trying to make has no bearing on the purpose for which this was brought up. The fact is, capacitors DO discharge, in the manner in which they are being CLAIMED to discharge. Nobody is saying that if you press the power button with the unit unplugged, it's going to deplete the capacitors electrons or protons. They are simply saying that the relevant power that is existing in the capacitor at that time, which may not allow either volatile memory or the bios rom to "reset", by whatever name you want to refer to it by, even cheese if you want to call it that, will in some cases do so by using that method. That is all. It's unrelated to whether or not the capacitor still has x amount of electrons or protons still present on one or the other plate.

 

[turkey3_scratch]

Yeah I know, I agreed to that initially, but then the topic swayed over to a different topic of discussion of disagreement.

Are we at agreement that a discharged capacitor has the same amount of electric charge as a charged capacitor?

 

[turkey3_scratch]

Anyway, different subject, this Sama Forza 800W is quite nice http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=468 and it should be hitting the North American market eventually. It's one of the most attractive power supplies I've seen. It's just that, it's another expensive Titanium unit. I'd like to see this company make some Gold units to compete with the G2. That's what I want all companies to do.