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A question about capacitor's in a power supply

nay27uk

Dec 19, 2009
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Dec 19, 2009
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In the output stage of a power supply what would changing one electrolytic capacitor for a different value do. I have a D-Link DSL-2640B wireless router that stopped working and after taking the lid off of the power supply I see one of the electrolytic capacitors right next to the outlet cables has blown, it is a 300uf electrolytic, and I was wondering if I don't have a spare 300uf in my junk pile what will it alter if I replace it with the next nearest capacitor I can find give or take a few Uf.

This one is very strange as the power supply is still outputting the correct amount of voltage and powering up the router I.e all lights on the router light up however the said cap seems to have something to do with amperage as the supply is outputting 0 amps under load and is making the power light on the router stay red and not change into ready mode (green) so my assumption is the supply is not giving enough amps to kick something in due to the blown cap.

so again my question is will replacing the cap with either a smaller or larger Uf rated cap harm anything, I am assuming as I have narrowed this down to controlling output amperage that it will alter the amount of amps outputted with different values of cap.
 
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Resqueline

Jul 31, 2009
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Blown caps is a modern phenomenon, and it won't do replacing it with just about any brand of cap.. Modern power supplies and electronics place high demands on the ripple current capacity of the caps. The exact capacitance value is not important however because of the high switching frequency of the psu.
You have some detective work head of you. First you find the brand and type (2-3 letters) of the original cap. Then you google this to find a datasheet, noting the ESR and ripple current values. Then you start searching the potential suppliers for a better cap. The bigger case cap you can put in there the better because they have potential for a lower ESR, higher ripple current capacity, and thereby a longer lifetime. Capacitance has only third priority.
For example, I have found the Panasonic FM to be the best type that RS-Components can offer.

The operation of the router is not related to any current limitation btw., rather than a high ripple voltage that constantly resets the cpu.
 
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