capacitors question regarding power supplies?

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 stoped 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

Update:

the power supply still throws out the correct amount of voltage and powers the router, however the blown cap seems to control the ampage as the suply is giving out 0 amps and making the router not go into the ready state in other words the power light on the router is not changing to green and is staying RED

8 Answers

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  • 1 decade ago
    Best answer

    You can add smaller value capacitors join in parallel to make a 300uF or higher replacement capacitor if the position is allowed to install. The voltage rate of replacement capacitors must be equal or higher than the original one.

  • Ecko
    Lv 7
    1 decade ago

    A capacitor is not expensive. Get the right one so it will fit in. Old ones from the junk box may not be the same as expected. Additionally the power supply is probably a switch mode, may need a capacitor with low ESR (equivalent series resistance). First remove the gunk it put around, which is conductive. It can't hurt to try a new capacitor, but the replacement needs to be the same value really so it will fit in. If you are talking a 330uF that is the same as 300uF. The voltage is important and the ESR might be. Actual capacitance values vary quite a lot anyway. Specs may be -50%/+100% - it is not unusual. There is a good chance it won't work with the new capacitor - well it doesn't work now does it? Once you get a good look at it you can search for the brand and type (data sheet or spec) and determine if it is a low ESR type.

  • 1 decade ago

    Without seeing the exact circuit, it is hard to say.

    A capacitor could be used for numerous things on the board. Just because it is near the outlet cable does not indicate it is being used for circuit "power". When you state it is "next" to the outlet cable I assume it is not directly connected to the "outlet cable"; therefore, it could be used for anything.

    A capacitor is most commonly used as a filter. It can "smooth" a rectified voltage ripple to create a nice looking DC voltage, or it can be used for noise reduction.

    If it is a smoothing capacitor, you could put the same or larger size capacitor, with the same or larger voltage rating, in place of the toasted one. Chances are, you are using a Wall-wart ( the ugly black box that connects to the AC outlet), and the smoothing would be taken car of there, so I doubt it is a smoothing capacitor.

    In the case of a filter, it could clean the input voltage and would be a simple capacitor connected from Vin to GND, to reduce external Noise. Or it could be a low/high/notch filter. In either of these methods, you should replace it with the same value of capacitance(parallel combination works too).

    Chances are pretty good that the capacitor is not the only source of malfunction. Check for a fuse or a burnt trace.

  • 1 decade ago

    The capacitors serve two purposes.

    1 is to smooth the current coming out of the transformer after the rectifier as the sinusoidal wave is now more of a swa tooth and DC powered devices need a constant voltage over 5.5 Volts TTL so the capacitor "FILLS" this gap in the saw tooth to try to get totally even voltage:Without a regulator ( and many don't) it is not likely to be a steady voltage.It also helps prevent the peaking of the output over the designed rating.

    2 It forms part of the DECAY circuit. This is the circuit that not only stops a sharp peak on initiation ( see above) but allows the charged capacitors in the regulating or smoothing circuit to discharge WITHOUT accumulating a voltage above the rated capacity.

    So you need to ascertain if the capacitor is part of the smoothing circuit or part of the decay circuit. If it is part of the decay circuit it indicates there is a problem elsewhere in the power supply probably a fault in the rectifier which is permitting reverse voltage.

    If it is part of the smoothing circuit it could indicate a fault either in the transformer or in the cascade/avalanche diode which prevents over voltage.

    The blown capacitor is mearly a symptom of a more serious condition.

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  • Roger
    Lv 7
    1 decade ago

    As long as the capacitor has the same value or larger and is equal to voltage rating or larger it will be alright. The capacitor removes ac ripple. I would check to make sure that some else didn't fail. Capacitors tend to short and it may have damaged some other component.

  • 4 years ago

    Use 3, 6, 9, or 12, not 10. Your power supply is 13.8 volts, not 12. 4.5 x 3 = 13.5 volts, close enough. Series circuit of 3 leds, add another series 3 at a time until you have what you need.

  • Anonymous
    1 decade ago

    the device might not work properly since the amount of current discharge is different. i advise you to get one in the nearest hardware store

  • 1 decade ago

    replace with same value or with nearest one it will work !!

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