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Cap Life Span ?

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iso9001

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Hi,

I'm using electrolitics on my power supply and I keep seeing "cap life" all over the place. I understand as they were out the esr will change and whatnot. But I was wondering,

If I have a 5V supply and a 47uf 50V rated cap is it going to last longer then say a 47uf 16V cap ?

Obviously the 50V cap will be bigger but does it effect the life span at all ?

Thanks
 
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Because more current go's through the cap and that create's heat and draw's alot of energy.

The reason the make it bigger is to increase life spand.
 
Since both caps have the same capacitance value, they will have the same current in the circuit.
47uF is such a low value that the current through it will be very small anyway. It certainly isn't the main filter cap in a high-current rectified supply but you don't say if your supply is linear or is a high frequency switcher. The capacitor will have a high current in a switching supply and a larger cap would run cooler because its size dissipates heat better than the small cap.
A 16V cap at the output of a 5V linear supply would probably outlast you. :lol:
 
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Ya but he did not say what type of amp's he want's to run on the power supply either. You can of have to give us more info.
 
The higher voltage cap should last longer, and also perform better - higher voltage caps have lower ESR to begin with. It's common to see capacitors with higher voltages than required in power supplies for this reason.
 
Sorry about the lack of info, but its a pretty simple deal.

5V DC, the circuit draws a total of 150mA max, this is for supply filtering/smotthing.

I was just wondering cause cap space is not an issue and the drice for a 16V 47uF cap is the same as a 50V uF cap, so I was wondering which is better.

But since apparently the ESR is lower for higher voltage caps, thats probably the route I'll go.
 
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I would have to disagree with you nigel because the bigger the caps the longer the last but the higher voltage the faster the cap's life reduce'es.
 
Actually, it is the heat that does the damage.
The internal temperature will rise faster with
more ripple. If you have a choice between
caps, go with the more costly (which usually
translates to a lower ESR. Failing that,
the higher voltage ratings will have much
more headroom.

<als>
 
The cap in question is at the output of a 5V regulator isn't it? Then it won't have any ripple and will be cool.
47uF is too small to be the main unregulated filter cap with the 150mA load.
 
The load is usually ~50ma, 150 is a worst case.

33uF and 47uF have been working great. I have a .1uF on the supply off all the ic pins for high freqs. But this is a noisy enviorment and I noticed a huge difference with the caps aposed to without.

How can I figure out what cap value is "right" depending on load ?

The output is from a regulator, but its in a sealed system that i have no idea where its really coming from, could be a reversed zener for all i know, but I'de assume its a regulator.

It looks like 2 to 1 for high voltage caps. Anyone else ?

Is 5000 hours being VERY conservitive with my load and voltage? I want this thing to last as long as possible. I'm now thinking its not such a big issue. Its just that the 5000 hour thing is nagging me a little.
 
iso9001 said:
Is 5000 hours being VERY conservitive with my load and voltage? I want this thing to last as long as possible. I'm now thinking its not such a big issue. Its just that the 5000 hour thing is nagging me a little.

It's not a big issue at all!, don't worry about it!.

Capacitors mostly fail in switchmode designs, it's VERY rare to see one fail in a conventional PSU - I wouldn't expect them to fail during the life of the design (and probably not in your life either?).
 
About 5 years ago many Chinese caps were faulty and companies were formed and guys got rich doing nothing but replacing them in many products.

The value of filter cap to reduce power supply noise depends on how many 555 timers and old TTL IC's that are making their huge supply-current spikes during their switching. Of course the switching frequency is important too. A 555 clocking a TTL syncronous counter chip will produce enormous supply-current spikes. Then you might also have TTL gates or decoders making spikes plus perhaps a multiplexed LED display.
 
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