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Capacitor question...

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Old 04-27-2010, 07:18 AM
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pb1592
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Default Capacitor question...

I'm working on a 'homebrew' RC project circuit (airplane) and need clarification about capacitance if someone could help... It is OK in any situation to use multiple caps in PARALLEL (assuming they all have the same mfd/voltage rating) to maintain the rated voltage and to INCREASE CAPACITANCE additively for all the caps used in the circuit? For example, if all caps were rated at 5V, 1mfd, and ten of them were ran in parallel, that would be the EXACT same thing as using ONE 5V, 10mfd cap, right?

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Old 04-27-2010, 07:28 AM
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Default RE: Capacitor question...

That is correct
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Old 04-27-2010, 08:12 AM
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Default RE: Capacitor question...

Furthermore, is it ok to use a higher VOLTAGE rated cap? For example, if the circuit needs a 10V 50MFD cap, is it ok to use a 20V, 50MFD cap?
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Old 04-27-2010, 08:40 AM
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Default RE: Capacitor question...

Yep, it's ok. Also, the caps don't have to be the same value (uF) - they'll add up anyway. 10uF & 4.7uF in parallel = 14.7 - like adding resistors in series. Sometimes a designer will use different values on purpose - like 10uF, 1uF, and 0.1 or even 0.001 - each cap works best at a certain frequency when bypassing power supply lines, etc. Using the multiple values will help create a broad-band low impedance. There's more to it than that, but if you're just looking for large amounts of capacitance, then adding up multiples of the same value is no problem.

Another thing to watch - with most electrolytic caps (the larger values you're mentioning) it's best not to have the actual applied voltage much over 60-70% of the rated voltage, they'll last longer that way. If you have 5V caps, for instance, I wouldn't use them much over 3.5 volts or so in circuit. I think cap vendors will say 80% or so, hence the 6.3V caps (used on 5V circuits), etc.

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Old 04-27-2010, 10:03 AM
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Default RE: Capacitor question...

Thank you so much for the quick responses. This is exactly what I needed to know. Thanks!

-Brian
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Old 04-27-2010, 01:08 PM
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Default RE: Capacitor question...

Just to clarify,

If i had a 35 Volt 4700mfd cap, i could parallel 4 of them into a circuit that called for a 18800mfd, 20 Volt cap, correct? Assume the caps have a 20% tolerance.
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Old 04-27-2010, 01:41 PM
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Default RE: Capacitor question...

Yep - you'd have an 18,800 uF 35V cap at that point. Should be fine.

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Old 04-27-2010, 02:33 PM
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Default RE: Capacitor question...

Thank you!
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