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Old 10th August 2005, 11:21 PM   #1
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Default How much capacitance do I really need?

I have a 28v 12 amp SMPS that I am going to power 3 AMP1-B's off of and I was wondering how much capacitance I need. Two of the amps will bi-amp the mains at 8 ohms the other one will handle the subs at 4 ohms.

I just bought 4 27000uf 30v caps, and I was going to use 2 caps per rail. I wasn't sure if the SMPS would be able to cold start all 4 caps for a single rail, so I originally planned 2 per side for now. Fortunately for me, one rail can handle the inrush current of all 4 caps just fine.

So my question is, do I really need more capacitance? I got a good deal on the caps, so it's no big deal for me to order more.

Thanks in advance.
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Old 10th August 2005, 11:28 PM   #2
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I use 4700uf per A....
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Old 10th August 2005, 11:38 PM   #3
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Quote:
use 4700uf per A....
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Old 10th August 2005, 11:48 PM   #4
Stocker is offline Stocker  United States
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that would be shorthand for:

use approximately 4700 microfarads per ampere of load current consumption.
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Old 10th August 2005, 11:56 PM   #5
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Thank you for clearing that up Stocker . So assuming I was to constantly draw the max 12 amps from the supply, that would require 56400uf, which is pretty close to what I have per rail at the moment.

I'm sure I need to consider peeks and such, but I think any more capacitance than I have now is just an accident waiting to happen.
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Old 11th August 2005, 12:03 AM   #6
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If you look in most consumer electronics, reduce the suggestion above by a factor of ten and it's still high! Big capacitors for big bass or certain unusual types of rectifiers. Be sure to also use small value capacitors in the filter (see the "snubberized" thread currently on the main page).

Anyhow, If you are constantly drawing 12A, your ears will be bleeding and you wounldn't notice the difference.

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Old 11th August 2005, 12:30 AM   #7
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Default A cap question

Agreed, all that capacitance is not necessary for performance. However you can get a very significant noise reduction if you set them up with a set of input and output connections. This can reduce the ripple current at the output and lower line related noise, this is worth doing. Check out how the Hypex high quality supply is laid out to get the idea.
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Old 11th August 2005, 01:03 AM   #8
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Quote:
Originally posted by theAnonymous1



Use 4700uf per ampere

Sorry for my bad explication;.
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