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Old 5th December 2006, 06:13 PM   #1
impsick is offline impsick  United States
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Default question on caps

ok im new to this, so my head is full of crap right now from trying to soak up all that i read.
anyways say a project calls for a 25v 100uf cap and all i have is a 16v 100uf. or say it calls for a 50v 100uf, and all i have is a 50v 470uf. how much would this effect the project, and is there like a rule or margin we should stay within?

if someone can clear that up for me i'd appreciate it.
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Old 5th December 2006, 06:23 PM   #2
Vikash is offline Vikash  United Kingdom
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You're asking for trouble if you don't know what you're doing and start substituting higher voltage caps with lower ones. At best you will lower the life of the cap, and at worst they will explode and can potentially hurt your body parts!

The second question is pretty daft and it should be obvious that you can't randomly substitue values with what you have available unless you really know whay you're doing. Remember that caps have tolerances so if you're using a cap value that is quite close than it may not have much impact. In your case, I would stick to the design until you're famililar with why a particular value has been chosen.
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Old 5th December 2006, 06:31 PM   #3
Nordic is offline Nordic  South Africa
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Caps often form filters in combinations with neighbouring resistors/impendances, which are very value specific.

As for tolerances, if you have a 50V supply for instance, haveing only a 50v cap is bad news, as your mains power will make it fluctuate well above and below this point (i'd say battery circuits could be excluded for the most part.

In power supply comopnents (I.e. not signal path) going a value or so larger would probably not hurt in the band of frequencies we are dealing with. If it calls for 50v, that is the minimum you should use.
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Old 6th December 2006, 04:38 AM   #4
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As long as it's not just a smoothing cap, don't substitute.

If something like a schematic calls for a 10,000F, and you have a 11,500F cap - (same voltage rating of course...)(...I don't think anyone makes/ever made a 11,500F cap...but
something near and above 10,000F) - and it fits in the PCB or what ever, It probably wouldn't be a problem.
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Old 6th December 2006, 05:48 AM   #5
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in the fewest words...

stay at or above the voltage given on the original called-for cap...

yes you can vary you cap values with little consequence. we're talking, i dunno 10%?

you can get assortments real cheap at a surplus store or ebay. when i need a new value of something, i buy 10 times more than i need, so i'll always have a collection of parts...
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Old 6th December 2006, 08:09 AM   #6
impsick is offline impsick  United States
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COOL. THANKS
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Old 6th December 2006, 08:09 AM   #7
impsick is offline impsick  United States
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COOL. THANKS ALL. GOOD POINTS. SO ITS COOL THEN IF I REPLACE 50V 1000UF CAP WITH A 2K RESISTOR RIGHT? HA HA JK. THANKS AGAIN.
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Old 7th December 2006, 02:32 AM   #8
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Old 7th December 2006, 12:52 PM   #9
CarlosT is offline CarlosT  United States
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If an amp calls for let's say 1,000uF 50V for the power decoupling caps, is it generally safe/recommended to go up to let's say 1,200uF, 1,500uF or even 1,800uF? This seems to be the gist of what I'm hearing.

What is gained from going up in capacitance for this function?
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