What happens when you seriously increase capacitance?

[chipper]

Re: What happens when you seriously increase capacitance?

One or more components in the compensation network in the feedback loop compensates for the RC network formed by the ESR and the capacitance of the output capacitor. A large increase in the capacitance is likely to cause changes in the regulator's response to load transients or even cause the regulator to oscillate.

Anybody know what the opposite senario would produce if you intentionally dropped some of the capacitance values? I would imagine that the regulator could overheat and produce shut down symptoms. Especially seeing as there don't seem to be any really close "dropping" choices from say : 1000uF to 470uF / 330uF / 220uF being the case. Any in betweens?

[chipper]

Re: What happens when you seriously increase capacitance?

Back to the front:

""Say you replace 6.3v 1000uF capacitors at RAM slots with premium brand 25v 4700uF or greater, what could happen? has anyone tried increasing capacitance all the way to failure? if so what is the failure that happens?""

~~~~~~

Here is what happens because the voltage is too high:

[erosion 1]
The aluminum oxide layer slowly 'dissolves' into the electrolyte over time until an equilibrium is reached.
[ BTW: This is where the shelf life rating of caps comes from. ]

[erosion 2]
Ripple currents strip the aluminum oxide layer into the electrolyte due to the rapidly changing current direction. (Basically by electrolysis.) Some of the ions (charged particles) drift into solution and go too far from the dielectric to be replaced when the current direction reverses. The layer becomes thinner and thinner over time.

[rebuilding]
DC voltage replaces the layer. (Basically by more 'normal' electrolysis process.) The constant non reversing voltage in the correct direction builds up the layer (until the electrolyte runs out of ions.) - This repairs the damage done by both erosions.

=> "electrolysis", hence *electrolytic* capacitor.

[ I really don't know where this came from but I remember it as a thumb rule from way WAY back in electronics school. I've heard it now and then in other places. - Not really the sort of thing that comes up much, ya know? ]
-
The working voltage (circuit voltage) needs to be no less than (approximately) 1/3 of the rated voltage of the cap.
- Because:
If you don't have at least that much voltage the DC current isn't strong enough to rebuild the oxide layer. Since it isn't being replaced, erosion 1 and erosion 2 eventually destroy the oxide layer to a point of no return.

The oxide layer is an insulator and -IS- part of the dielectric.

As it becomes thinner and thinner:
(dielectric) the capacitance value is going to go down, eventually drastically.
(insulator) the current is going to rise, eventually drastically. This is going to overheat the internals of the cap and eventually the internal materials (including the electrolyte) will break down. The cap may form gas and vent, it may fail open, it may even short under these conditions.
~~~~~~
All of this assumes the failing cap doesn't cause another component failure somewhere else in the circuit.

[ Somewhere in the forums someone disassembled a cap that failed this way and posted pics. You can SEE that the 'paper' between the foil layers is brown and burned from the heat. It looks very much like paper that was left on a stove long enough to get brown, going for black, but didn't quite make it to flames.]

Your 25v cap should not be used in a circuit with less than about an 8.3v working voltage. (So that voltage would be just dandy on a 12v rail but no where else on a MoBo.)


~~~~~~~~~~~~

Capacitance too high is a different animal.
It really depends on what the rest of the circuit does.

Throwing the circuit out of balance have been covered.
[Adding to that if you go too far off the design value you may inadvertantly create a resonate circuit by the interactions with other components. Having a component intended to remove ripple voltages behave as a part time oscillator is not generally considered effective.]

Excessive charge current has been covered.

There is another one.
-
Higher capacitance caps take longer to charge and discharge and that can affect timings.
-
That bigger bucket from the past post isn't taller it's bigger around.
How high (deep) the water is in the bucket represents the voltage.
- Let's say that bucket needs to be 3/4 full to be at the circuit's working 'voltage'.
When you first start the computer that bucket starts filling and the BIOS runs the motherboard through POST checks. The BIOS gets to the check for the 'voltage' in that bucket (or rather the attached circuit) and it's not filled to 3/4 full yet.
-> POST Error -> lock-up or shut down. - NO GO!
----- And that's not going to change until you replace that cap.

~~~~~~~~

If you know what the working voltage in the circuit is, then you can make voltage changes safely by following the 1/3 rule.

As they age the capacitance of electrolytic caps goes down...
.. and .. they have a 20% tolerance in the first place.
---
So: If you raise the capacitance only one step you are (almost) always safe because as the cap ages it will be moving INTO the original operating range of the original cap anyway. [This assumes the original cap was a good choice in the first place -and- that it wasn't already raised once during a prior re-cap job.]

.

I see you have changed your opinion about 10fold on the subject of installing higher voltage caps , since you swore up and down and even repeatedly called me a "MORON" for having said so myself on other threads here in the forum. Stating that I had nothing better to do than to hang around in forums and such.

To quote you a bit , you specifically said that capacitors "cannot" increase in voltage while they are on a redundantly controlled circuit of "any" sort , therefore capacitors "are not going to have too much voltage buildup" as a result. [HERE YOU ARE : saying that 1/3 voltage increases when replacing is a good guide and that capacitors that have higher voltage limits will cause the capacitor to work abnormally]

"I think some deleting is in order on your previous threads about my opinions and observations."

How you could go into explicit detail to say "NOW" , that "other" integrated circuits could be adversely effected by "any" overvoltage that may occur , is beyond my comprehension , "creating inherent circuits" and effect timings?

I had tried to suggest , being that everyone seemed to be against me on my opinions , that it would not be a good idea to move the voltages up unless you knew for sure what reactions could occur as a result.

Suddenly , you are Albert Einstein (outside my email box alerts) , with information in hand to say that a capacitor will break down and "burst" as a result of it being used in a circuit that is basically prone to keep filling up the available "bucket space" in the capacitor which leads to "X" over time.

Since you are Albert himself - I would like to add a few "simple electrical" questions that I think you should easily be able to answer immediately to quell the boiling blood in my veins "over-time".

Since also that your knowledge of electrolyte and such is extensive - here they are ( I expect an immediate answer in less than 4 hrs. )

WHO INVENTED THE COMMON BATTERY?

WHAT IS THE CHEMICAL CONTENT OF AN AUTOMOTIVE BATTERY?

AND WHAT ARE THE EXACT CHEMICAL PERCENTAGES OF THE AUTOMOTIVE BATTERY LIQUID FILL?

I could simply answer these questions here myself , or put them immediately into a new thread to prove my point and knowledge. Even though I agree with what you have "NOW" chosen to say , I must say you have done a masterfull job of contradicting your previous threads and insults about me.

THANKS FOR THE INFO

[PCBONEZ]

Re: What happens when you seriously increase capacitance?

This conversation is about capacitance.

The other is about voltage.

You chipper, DON'T KNOW THE DIFFERENCE.

[999999999]

Re: What happens when you seriously increase capacitance?

Anybody know what the opposite senario would produce if you intentionally dropped some of the capacitance values? I would imagine that the regulator could overheat and produce shut down symptoms. Especially seeing as there don't seem to be any really close "dropping" choices from say : 1000uF to 470uF / 330uF / 220uF being the case. Any in betweens?

It depends entirely upon why they chose the value they did.

Often with electrolytics, they don't choose a uF value based on circuit need, they choose it to get an optimal price per build to achive low ESR. In other words, don't choosen lower uF if it results in lower ESR, but if you can choose lower ESR and it is also lower uF and the switching frequency is realatively high, it can work fine, even better.

Now back to the generic ideal- unlike a motherboard/other manufactuer, you are not producing enough quantity for a few cents differrent to matter much. Your time and labor are worth far more at a scale of 1. Choose the largest cap that will fit without being excessive in uF value increase. Choose the highest quality, lowest ESR and highest lifespan vs temp that the budget also accepts. If you know for certain that a specific timing of a circuit depends on a certain uF value then ignore this, but such circuits are very rate today and such timing capacitors aren't the type that tend to need replaced at all.

In other words, look at the board cap position and max it out, get the largest value the diameter and height clearance will allow. In theory someday this could exceed tolerances like inrush current, but in practice it hasn't happened yet.

[PCBONEZ]

Re: What happens when you seriously increase capacitance?

Many 9's you are wasting your time.
Chipper is a lost cause.
- Actually believes that if you use caps with a higher voltage rating the caps will store more energy and the voltage in the circuit will go up resulting in damage to the gear.
- Refuses to accept any other idea.

.

[i4004]

Re: What happens when you seriously increase capacitance?

he doesn't have a multimeter to check it?
he can't charge the cap and then check its voltage?

[999999999]

Re: What happens when you seriously increase capacitance?

Many 9's you are wasting your time.
Chipper is a lost cause.
- Actually believes that if you use caps with a higher voltage rating the caps will store more energy and the voltage in the circuit will go up resulting in damage to the gear.
- Refuses to accept any other idea.

.

They won't store more energy. That's what the uF value signifies. They won't store more voltage than the peak in circuit, similar to what a lesser cap would.

Voltage is only a max rating within reasonable limits, like you can use DDR400 memory at DDR333 if you chose to.

[kc8adu]

Re: What happens when you seriously increase capacitance?

yes chipper needs a remedial electronics course.
if he chooses to read and absorb here he gets it free.
i wonder what itt tech or rets tech charges nowadays?

[chipper]

Re: What happens when you seriously increase capacitance?

Many 9's you are wasting your time.
Chipper is a lost cause.
- Actually believes that if you use caps with a higher voltage rating the caps will store more energy and the voltage in the circuit will go up resulting in damage to the gear.
- Refuses to accept any other idea.

.

"HERE IS WHAT HAPPENS WHEN THE VOLTAGE IS TOO HIGH" : your #62 post right here above.

[chipper]

Re: What happens when you seriously increase capacitance?

yes chipper needs a remedial electronics course.
if he chooses to read and absorb here he gets it free.
i wonder what itt tech or rets tech charges nowadays?

2 sinking in the same boat , is not better. Read #62 above about how overvoltage can occur.

[999999999]

Re: What happens when you seriously increase capacitance?

2 sinking in the same boat , is not better. Read #62 above about how overvoltage can occur.

Your local library has some books on basic electronics that you need to read. A capacitor can only create a voltage potential, charge, as high as the circuit it is in produces. The voltage rating of the capacitor has no effect on this, it only determines how high a circuit voltage it can tolerate before it potentially fails due to the dielectric not sufficiently insulating it.

Similarly, if you put "Z" speed rated tires on your car, that does not make the car go faster than S rated tires, it only allows the car to go faster than 112MPH while staying within the safety margin of the tire.

You might consider testing this yourself, it's a rather trivial thing to take out a capacitor and replace it with one having higher voltage rating. Without testing you have not applied any kind of scientific method to validate your hypothesis.