Leaky caps replaced

the-one1

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I just replaced 12 caps on a p3 mobo i got for free because the old ones were all F___ed up and blown. They were 1000uF 6.3v caps. The new ones I put in are 2700uF 6.3v.
I was reading up on replacing caps and they mentioned that as long as the volts are equal or higher , then its fine.
But what about the capacity of the caps, it wont do anything bad if its higher will it?
thnx
 

Ice Czar

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relocated to Electronics

I dont think you have a problem (but Im relocating it never the less, because Im not positive)
but would have advised you ask this question before replacing the caps :p
 

CleanSlate

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Well I'm not an electrician but I've taken engineering physics 2 (electromagnetism and light) and here's what my book says:

charge = capacitance * voltage

So in this case you're increasing the charge sent by 2 and a half times by each capacitor, which I think might be a bad thing :p. My guess is that you'd fry your motherboard if you flipped the switch because the charge it's expecting would be alot lower than what it would actually get.

~Adam
 

Ice Czar

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hmmmm....good thing i relocated this :p

http://www.badcaps.net/tips/

Now that you've got all your equipment lined out, you need to make sure that you've identified ALL your bad caps and located NEW replacements for your board. VERY IMPORTANT: UNDER NO CIRCUMSTANCE SHOULD YOU CHANGE THE CAPACITANCE RATING OF THE CAPACITORS UNLESS YOU KNOW WHAT YOU'RE DOING!!! DOING SO MAY HAVE TRAGIC RESULTS FOR YOUR BOARD!! Some will argue this point to death, but the way I see it is this.... The engineers that designed these boards know far more than all of us put together about this. Unless there was a factory revision that changed the capacitance rating, I think it's safe to assume the engineers knew what they were doing. Remember, the reason for the failure was NOT the capacitor's value, but rather a poorly manufactured capacitor!!

However, increasing the rated voltage is OK. The only thing the capacitor voltage rating means is the amount of voltage the capacitor was designed to handle. Increasing this value is OK, but NEVER decrease the voltage!! For example, it is safe to replace a 6.3v capacitor with a 10v capacitor, but NOT visa-versa. The only thing increasing rated voltage will do is enable the capacitor to handle a little more voltage. One more thing, NEVER cannibalize your replacement capacitors from some old motherboard you have in your junk pile!! You might be using capacitors that are in worse shape than the ones you're removing! You will also need the long and straight leads on the new capacitors! The holes in the motherboard are extremely small and delicate!! Trying to stuff a bent up, solder blobbed, and short lead into those holes is very difficult and can have fatal results if a mistake is made!!
 

the-one1

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Thnx for moving this, I was looking for the forum.
Anyways, too late about flipping the switch, its on and has been running for a couple of days now just fine ( i hope). Ran it through sandra burn in wizard 100 times and no lock up. Played Need for Speed 5 and no lock up. Overclock from 600 to 800, no lock up. No buldging caps either. Isnt the job of a cap to smooth out the power so there are no spikes?
 

CleanSlate

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The job of a cap is to build energy and then let it go quickly thus allowing your circuit to have a clean amount of energy higher than your power source. I'd suggest not running it like that, you really are sending alot more power than necessary through those caps and I doubt it will last, whatever it is.

~Adam
 

BlindedByScience

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CleanSlate said:
The job of a cap is to build energy and then let it go quickly thus allowing your circuit to have a clean amount of energy higher than your power source.

~Adam

Not exactly.....best analogy I can think of is that "big" electrolytic caps are like electron "buckets"....the current fills the bucket, and when the load asks for a sudden splash of current, faster than the hose can fill the bucket, the bucket gets partially drained and satisfies the load, while the "hose" fills the bucket back up. The small, "high speed" caps on the motherboard do a very different type of job, btw.

...two things;

First, increasing the value of the caps capacitance will quite probably de-tune the board such that it will no longer pass FCC emission tests. Probably not a big deal....

Other point is that it's not uncommon for folks to use the value they get the best deal on, price wise. Such is often the case in manufacturing.

Biggest concern I can think of off the top of my head is that the inrush, or initial surge of current required to chage those babys is now at least twice what it once was. However, if you didn't slag your power supply by now, you're probably fine....:D Once running, they don't draw any more "current" than the ones you replaced...and, actually are probably doing a better job of filtering the DC supply on the MoBo. Probably.....

My $00.02 - It's running.....no worries.

Good luck - B.B.S.
 

BlindedByScience

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CleanSlate said:
I'd trust BBS before me, he's alot more experienced.

~Adam
...naah, I've just blown more stuff up....:D

2X in value doesn't worry me.......now, 10X could be a very different story.

Regards - B.B.S.
 

joecool234

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Electrolytics are generally used for cleaning the power supplied to ICs. If you use a higher rating for these caps, you should be fine. A higher capacitance might make the caps less effective for filtering high frequency crap, but if the board is stable you should be OK.

Bulky electrolytics like the ones you are using are usually just used for charge storage. The larger the value, the better the storage, the better off you are.

Anyone ever tinker with car audio amps? When hooking a sub up to a car, a huge cap is generally required. Without it, your lights will dim each time the bass rumbles. The cap, as stated above, is a "charge bucket." The bigger the cap, the more current that can be supplied to the load. This is why cructhfield sells a .5F cap for like $150 and a 1F cap for $400. You can use either, but the bigger one is better.
 

dualblade

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can someone explain why larger caps are a problem? since devices request current, won't the cap just deliver whatever the device needs, regardless of how much electricity is stored? i would have thought that a cap would be sized just larger than the largest possible current draw the circuit is designed for (to build in buffer room), and any larger than that would be unnecessary but not undesirable. unless my understanding is flawed, a cap is not an all-or-nothing device (anotherwords, it doesn't either deplete itself or deliver no power, it's based on the pull of the circuit itself)
 

The Brain

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dualblade said:
can someone explain why larger caps are a problem? since devices request current, won't the cap just deliver whatever the device needs, regardless of how much electricity is stored? i would have thought that a cap would be sized just larger than the largest possible current draw the circuit is designed for (to build in buffer room), and any larger than that would be unnecessary but not undesirable. unless my understanding is flawed, a cap is not an all-or-nothing device (anotherwords, it doesn't either deplete itself or deliver no power, it's based on the pull of the circuit itself)

Speaking as someone who has designed power distribution networks in the past, I feel that I am qualified to answer your question.

There is really two different answers to your question. The first answer assumes that the larger capacitor has the exact same properties as the original capacitor except that it has higher capacitance. The second looks at what other capacitor properties change along with its value.

For identical (but different value) capacitors, several things will happen:

- The higher capacitance means that the power system can handle larger voltage transients. (This is good)
- The higher capacitance means that more charge is requires to "fill" the capacitor at power up (This is bad, and has been mentioned before). However, this should not hurt the power supply but might, in the extreme case, cause the voltage to rise to slowly to correctly power up the computer.
- The change in capacitance will probably also affect the EMI generated by the computer but probably will not affect actual performance.
- In the extreme case the change in capacitance load could cause the DC-DC controller loop to become unstable. (This is very bad as the board will no longer work). This one is unlikely.

For different capacitors, the following things may occur:

- All of the above listed items still apply
- The capacitors will likely NOT be low ESR type. This means that their frequency response will be different (slower). In general motherboards are designed with some head room so you can often get away with this. However, you do lose headroom. It is possible that you will no longer be able to push the motherboard as hard and remain stable. (ie heavily overclocked and heavily overvolted).
- The capacitors ripple current rating will probably be different. If you exceed the ripple rating of the new capacitor its life span will be shortened.

Basically what I am saying here is that correct operation depends on more then just capacitance. In fact power distribution systems are typically designed to have a certain ESR first and then to have sufficent capacitance second. The only reason that people can swap "lesser" components in during repairs is that the motherboard is designed with some headroom.
 

the-one1

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Thnx guys.
BSS and BRAIN explained everything I wanted to know.
Very edu-macational.
I guess I'm fine then
The main reason why I chose 2700uF was that my bro-in-law gave a whole strip of them to me for free. They are three times the size of the oem and was a very tight fit for the slot P3. It didnt boot up at first, I thought the surgery was a failure, but it turned out the cpu wasnt pushed in deep enough, it was very tight indeed.
If it ever blows up, I make sure to note it in the forum.
:)
 

aL Mac

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I think it was a very bad idea to change the cap...

it could affect time constants of waveforms etc.. t = R * C..

Why not replace it with the right value anyway.
 

Whatsisname

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Their only job is to store it. Releasing it quickly or not is up to the engineer.

CleanSlate said:
The job of a cap is to build energy and then let it go quickly thus allowing your circuit to have a clean amount of energy higher than your power source. I'd suggest not running it like that, you really are sending alot more power than necessary through those caps and I doubt it will last, whatever it is.

~Adam
 

mattg2k4

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Not to mention the resistance and inductance of the cap.

I think that the 2700uF caps will probably work fine and cause no problems, but there's always a small chance they will (by drawing more current than designed), and if they are not low ESR caps like computers normally have, it might mean things aren't quite as stable.
 

gee

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If at all possible, replace with the exact same cap... If you can figure out the manufacturer and the capacitor's part number, then find an equivalent part with the same voltage rating and ESR.

The switching power supplies / VRMs / etc on your motherboard have their control loops designed to suit the characteristics of their output capacitors... when you start changing capacitance values or capacitor ESR, then you can change the control loop characteristics.

This can cause bad transient response (which could make a high overclock not work as well) or even worse, it can cause instability and blown CPUs/DDR/etc.

Higher voltage capacitors have higher ESRs. It's entirely possible to have a 6.3V cap work just great, but have a 10V cap run hotter due to ESR and fail right away...
 

plot

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i have electrolytics that are rated +-80% of what there printed value is supposed to be... so if the caps you had before are +80% and the ones you have now are -80% you're overlapping anyways. should be no big deal... hell, in lab alot of times we just go through plugging in caps to see which value works *best* after trying the initial calculated capacitance... no biggy.

it's ESR and the likes you need to worry about.
 
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