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Need help Today! Capacitance! Electronics Gurus?

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Crashman   08-02-2002 at 02:11:32 PM

OK, I need to change 3 capacitors on a motherboard. These are 6.3v 1500uf capacitors. I can't find any of that specification for sale. I could use "better" capacitors, but I don't know which way to go with the values! For example, would a 25v 2200uf capacitor work? These are the filter capacitors for the CPU power. Please help!

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Quetzacoatl   08-02-2002 at 02:30:46 PM
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they'd definately filter the voltage, but may have too much pull-down resistance to allow enouhg through. Your best bet may be to combine a smaller capacitor, and run another one with a combined capacitance of 1500uf in a series circuit. Try to get as close as you can though, or you'll blow out the motherboard instantly.

"When there's a will, there's a way."

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Crashman   08-02-2002 at 02:34:46 PM
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Got any good sources for capacitors? Radio Shack and Parts Express do not have these values.

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Crashman   08-02-2002 at 02:36:18 PM
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Cold you explain a little more? For instance, what if I used a 1500uf 25 volt instead of 6.3v? Is that just the max rating, or does it add more load to the circuit?

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Quetzacoatl   08-02-2002 at 02:41:35 PM
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I took a few electronic courses in High School, so I learned a bit about PCBs and such. I think *about 75 percent sure* that a 1500uf 25 volt capacitor is it's potential tolerance, but it also adds more load, hence a greater drop on the amps. You could test this theory easily, just by making a simple light circuit, running with capacitors and resistors. I wouldn't try it on the motherboard until you get it straight though, there may be too much pull down resistance with a 25 volt capacitor.

"When there's a will, there's a way."

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Quetzacoatl   08-02-2002 at 02:42:33 PM
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Do you have a Circuit City near you? They carry *some* electronic parts. I know my Radio Shack can order resistors and capacitors, but they don't always carry them in stock.

"When there's a will, there's a way."

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Crashman   08-02-2002 at 02:46:49 PM
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I checked their online database, that was no go.

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Crashman   08-02-2002 at 02:47:45 PM
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What about something with similar voltage and less capacitance, like a 1000uf 6.8v?

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Quetzacoatl   08-02-2002 at 02:52:54 PM
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That would work, but don't forget, you get less capacitance, hence less of an ability to absorb the possible voltage spikes. I still think the way to go may be running a series circuit with say...oh wait a second, I have a better idea now. Try this.

Your circuit starts where the 1500uf capacitor was supposed to be. You could run a parallel circuitry (kind of like DC DDR), with two capacitors equalling 6.3 volts and 1500uf. For example, they would both run at 6.3 or 6.8 volts, but have a combined capacitance of 1500uf. Like, if you ran two capacitors, one with 1000uf, and the other 500uf, connected in a parallel circuit to where the 1500uf belonged. That way, your voltage remains the same, causing no drop in resistance while yielding you the necessary capacitance.

"When there's a will, there's a way."

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Quetzacoatl   08-02-2002 at 02:55:54 PM
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*shrugs* i'm not sure where else you could find the necessary parts, save a computer shop that could purchase the parts from a catalog. If worse comes to worse, you could *carefully* tear the necessary capacitors off another motherboard or circuit board...just have to look around.

"When there's a will, there's a way."

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Crashman   08-02-2002 at 03:00:33 PM
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It uses three in parallel already, so if I could find two 2200uf 6.3v and leave the third out, that would probably work also, but I doubt they would be any easier to find.

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Crashman   08-02-2002 at 03:01:56 PM
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Hey, I wouldn't really have a problem if I used too much capacitance at the proper voltage would I? Like, say, 3 2000uf 6.3v units would have more capacitance, but wouldn't the pull down be similar?

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Quetzacoatl   08-02-2002 at 03:04:09 PM
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Yeah, I believe your total capacitance is a little more tolerable than the actual voltage it's running at. I still am not sure why you can't find them at Radioshack, I know I could get some there.

"When there's a will, there's a way."

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Quetzacoatl   08-02-2002 at 03:07:00 PM
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Hmmm...yes, that would yield 6000uf, at 6.3v. Probably more capacitance than you need, but your pull down would remain the same, which is more important in the end. I don't think the extra capacitance would be a problem.

"When there's a will, there's a way."

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Crashman   08-02-2002 at 03:07:24 PM
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They only carry maybe 200 different values, this doesn't seem to be one of them. Maybe if they carried 2000 different values they would have them!

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Quetzacoatl   08-02-2002 at 03:12:05 PM
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Hmmm, yeah. Heh, that sucks, all those capacitors, and none of them are near 1500uf.

"When there's a will, there's a way."

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svol   08-02-2002 at 04:08:06 PM
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Someone that works at my school told me once that the uF is more important then the V value. I can't help you any further cause I don't have any school books till the vacation is over, there where some chapters about capacitators in it, but we didn't had a test about it, so I don't remember much about it.

I'm sorry I can't help you any further.

My watercooler contains so much water that the moon has influence upon it :eek: .

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Crashman   08-02-2002 at 04:58:33 PM
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A TV repair man just told me that the voltage is actually a max value, not a set value. I always used to think this, but I see evidence otherwize. Anyone else care to share?

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jihiggs   08-02-2002 at 05:08:27 PM
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have you tried your local frys? the one in my area has several racks with components, at least one full rack dedicated to caps.

how do you shoot the devil in the back? what happens if you miss? -verbal

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Crashman   08-02-2002 at 06:07:08 PM
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Yeh, right, my local Fry's. Never even seen one, not even in Detroit. The closest major city is Lansing, and even they don't have one. What is Fry's, a west coast chain?

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jihiggs   08-02-2002 at 06:38:30 PM
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i guess so, it used to be incredible universe.

how do you shoot the devil in the back? what happens if you miss? -verbal

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lakedude   08-03-2002 at 12:17:42 AM
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Sorry so late getting 2 cents in. Been staying out of "Other" because it is usually so stupid. Voltage on caps and fuses is max rated. You can use a 250V fuse in a 12V circuit no problem but you can't go the other way. A cap becomes better and better the closer you can get the plates to one another, unfortunately the closer they get the easier voltage could cause a spark from one plate to another. If say two pie plates are 6 inches away from one another the voltage rating could be very high because it takes a lot of emf to jump a spark 6 inches, esp from a flat surface. A spike or point will allow the electrons to collect in one spot and makes a jump easier. Moving the plates closer increases capacitance but decreases voltage rating. Filter caps are a funny business as there is more to them then just voltage and capacitance. In a computer you have all kinds of unshielded high freq energy floating around and you don't want any part of the power supply acting as an antenna picking up these stray signals. Filter caps on a mb must not only have the capacitance to do the filtering with a high enough voltage rating to not burn up but also must be able to respond quick enough to filter very high frequencies. This is why you will see tons of smaller caps right next to the filtered part instead of only one big one at the ps. The big ones filter out larger low freq ripple and the smaller caps filter out the high freq stuff picked up in the wires themselves between the ps and end user on the mb. Anyway I don't have enough info or knowledge to really answer fully. Sorry I couldn't be more help. LD

Give me fuel, give me fire, give me that which I desire.

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orbz   08-03-2002 at 02:10:39 AM
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Are you looking for something like <A HREF="http://www.mouser.com/index.cfm?handler=displayproduct&&lstdispproductid=520468" target="_new">this</A>?

<i>Nichicon UPW Low Impedance 105 Degree Radial Aluminum Electrolytic Capacitors
Mouser Part#: 647-UPW0J152MPH
Mfgr. Part#: UPW0J152MPH
Supplier: Nichicon
Category: Capacitors, Aluminum Electrolytic
6.3V 1500uF 10x20</i>


<i><font color=blue>The only difference between 200 fps and 300 fps is the blink of the eyes.</font color=blue></i>

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Crashman   08-03-2002 at 02:48:00 AM
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Perfection! I'll order them ASAP!

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