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Old 20th February 2009, 12:30 AM   #1
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Default How do I connect a Small capacitor

I got a 220V Capacitor (330UF).

Car amplifier connected to a Computer Powersupply 12V 60A Rail.

And Basically I want to hook a capacitor to kill most of the voltage drops and ease the load on the PSU.

However Im not sure how its done. Ive put in a picture.. do i do as wired in diagram 1 or 2?

Thanks!

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Old 20th February 2009, 09:06 AM   #2
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Parallel ... with the as close to the amp as possible.
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Old 20th February 2009, 09:26 AM   #3
albin is offline albin  United Kingdom
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Default parallel

Diag 1.....with shortest length wires.
regards
Max
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Old 20th February 2009, 10:39 AM   #4
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Although a 330uF, 200V capacitor won't do anything at all!

You'll need at least a 22,000uF @ 25V capacitor to have any useful effect.
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Old 20th February 2009, 12:21 PM   #5
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Oh thanks people, Im not exactly sure on the UF I'll check it later on.
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Old 20th February 2009, 05:27 PM   #6
Pafi is offline Pafi  Hungary
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I'd rather say 500,000 uF (at least) if you want significant effect! (If anything is needed.)
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Old 20th February 2009, 05:39 PM   #7
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F is way too much. A computer PSU will never handle the inrush current.

10,000 uF to 22,000 uF is more than adequate for this purpose.
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Old 20th February 2009, 06:03 PM   #8
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Does the 12 rail of a computer power supply really put 60 A? Sounds way to high. Computer power supplys put most of the current out on the +5V (3.3). The +- 12 V are much lower current. So most of that power supply is not even being used. Also do you have bad things happening as a result of using a switching power supply? If so, some value of cap could help, but switchers dont like to start reliablly with a lot of capacatance on the output. so you may run into problems. Best idea is to find a linear supply. Can you get your hands on a 15V transformer? That plus a few other parts and you could build your own from scratch.
Good luck;
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Old 20th February 2009, 08:43 PM   #9
Pafi is offline Pafi  Hungary
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Quote:
A computer PSU will never handle the inrush current.
If that's true, then it's unusable for a high power car amp. In this case no capacitor has any benefit. 22000 uF is nothing, if the purpose is to help to a 60 A supply. But I'm not sure if that PSU won't handle the inrush current. It's not a big deal. For example my 14V 60A SMPS doesn't have any problem with some F of capacitor.

60 A for 0.02 sec with 2 V drop is 0.6 F, so significantly less then this is obviously not effective. 22000 uF can assure eg. 4.4 A for 10 ms with 2 V drop, wich is in other words: nothing.
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Old 20th February 2009, 08:54 PM   #10
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That is true, and generally a computer PSU is unusable to power a car amp of any kind. The problem is that those 60A is not on a single rail, nor is it all available for the 12V output. You'd normally see 30-40A of that 60A available to the 12V outputs on a 1000W PSU. Much of the available current is reserved for the CPU power only and much is reserved for 3.3/5V output.

If you connect a F cap directly on the skinny 12V rail of a computer supply, best case scenario is that nothing happens and the PSU detects a short and shuts down. Worst case scenario is that you'll have a massive meltdown and possible explosion.

Quote:
Originally posted by Pafi
60 A for 0.02 sec with 2 V drop is 0.6 F, so significantly less then this is obviously not effective. 22000 uF can assure eg. 4.4 A for 10 ms with 2 V drop, wich is in other words: nothing.
There's absolutely zero reason for more than 22,000uF ... it's a SMPS not a battery. It will not see a voltage drop because the PSU is specifically built to compensate. As I already stated ... there's absolutely zero reason for more than about 22,000 uF for this purpose. If the desire is to have maximum effect out of the amp, one should get a proper power supply instead of a computer PSU. (Or even better get a real amp instead of a car amp).
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