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Old 25th December 2009, 17:44   #1
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Default Rolling your own capacitors

In the first place, I dont think one needs a capacitor in an average setup anyway, but thats not the question.

The average branded 1F capacitor costs 40 USD or more.

on the other hand , you can get perfectly good, yet cheap electrolytic/Tantalum capacitors for cheaper.

for example
Digi-Key - 493-3106-ND (Manufacturer - PLG0G272MDO1)

4V, 2700uF. 10 for them ( 5 in series = 20V, 540uF. x2 in parallel = 1080uF)

ESR would be 20mOhms

And this would be very simple. Anyone who knows how to solder could do it. Just remember to use very thick solder tracks to make sure that the resistance is kept to a minimum

would cost just 22$. you'll know thats a true 1F capacitor, It just wouldn't look too good.

How would such a homebrew capacitor compare to a readymade one ?
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Old 26th December 2009, 01:15   #2
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Quote:
Originally Posted by greenhorn View Post
4V, 2700uF. 10 for them ( 5 in series = 20V, 540uF. x2 in parallel = 1080uF)
How would such a homebrew capacitor compare to a readymade one ?
I see one issue.

when a cap dies it shorts. so if there are 10 caps is parallel and one dies the other 9 are shorted out. it is hence better to use better few quality caps than many cheaper caps.
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Old 26th December 2009, 01:46   #3
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I seem to have made a very serious flaw in my calculation !
1080uF is 1mF, not 1F
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Old 26th December 2009, 02:25   #4
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yay, found a feasible option
http://www.nesscap.com/data_nesscap/.../Spec%2002.pdf
http://dkc3.digikey.com/PDF/EU091-GR/1512.pdf
10F, 2.7V.
8 of them in series should come to 1.25F, 23.04$
or if I use 50F , then I'd have a 6.25F capacitor for 53$
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Old 26th December 2009, 07:33   #5
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4V, 2700uF. 10 for them ( 5 in series = 20V, 540uF. x2 in parallel = 1080uF)
When high voltage(say 25V/50V) electrolytic caps (ex. 4700uF or more) are easily available at cheap from your neighborhood electronics shop, is there any reason why you would choose low voltage caps and use them in series effectively reducing the total capacitance?

Also using caps in series would need balancing resistors to keep them in their voltage range; especially if they are rated for low voltages.
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Old 26th December 2009, 08:45   #6
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with 4700u, you'd need more than 200 of them!

Balancing resistors , I did not know about - thanks! but adding them seems fairly easy !
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Old 26th December 2009, 10:40   #7
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Quote:
Originally Posted by greenhorn View Post
1080uF is 1mF, not 1F
the philosophy of using multiple caps in parallel still stands.

Quote:
Originally Posted by greenhorn View Post
yay, found a feasible option
then I'd have a 6.25F capacitor for 53$
a. what are you looking for from your 1F or 6F capacitor? If you are looking at energy storage that is one thing but if you are looking for audio grade caps (see links below) I suggest you stay away from aluminum caps.

Silver/Oil

Solen Electronique Inc.

b. If you want a 6F power cap for your car remember that the same $53 spent on upgrading your big 3 wiring will give better VFM. Power amps have internal caps to take care of most energy needs. A power cap like this will only come into use for instantaneous thumps or to prevent your headlights from dimming on bass transients. Your cost $53. For $65-70 I can get a 5F cap read to install. I dont see much saving for the effort.
5+ Farad Capacitors | Car Audio Capacitors at Sonic Electronix

Quote:
Originally Posted by Digital Vampire View Post
is there any reason why you would choose low voltage caps and use them in series effectively reducing the total capacitance?.
car battery voltages do not exceed 14.4V DC. So a 20V or 50V DC cap is more than enough. A 100V cap will just be 2 times the size of a 25V cap and there will be no perceptable advantage.
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Old 26th December 2009, 15:07   #8
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navin I was looking for power storage. I dont have that big a woofer I need to high pass with a 1.0F capacitor

for the higher value caps, the saving might not be worth it, but for a 1.0F capacitor, 20 USD is worth it for me
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Old 28th December 2009, 10:38   #9
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navin I was looking for power storage. I dont have that big a woofer I need to high pass with a 1.0F capacitor
HPF with 1.0F? What is your target High Pass Frequency, what is the impedance of the component being high passed?
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