buying caps for a car amp

[phaseform]

I've just got a 12v car amp which I want to power using a 12v Dell Server PSU. I've read that the server PSU wont output peak voltages very well due to being a regulated supply, so I wanted to add some caps to the amp power input. I've been looking around on ebay and it seems the power capacitors for car amp are reasonably expensive, at least $50, and often don't meet specs. I was thinking of using 3 super caps available from jaycar (CAT.NO: RU6705, 1 Farad 5.5V Super Capacitor) in series to do the job, but thought I'd share my plan here in case I'm missing something important.. I haven't seen examples of people using normal caps in car amps before..

[Psi]

Those caps are intended for clock backup and wont be able to handle the current needed for your amp.

The easiest/cheapest way is to put a 12V SLA battery across your 12V.  It will basically be float charging all the time from your 12V psu.
Any peak currents the amp needs come out of the battery.
http://www.jaycar.com.au/Power-Products-Electrical/Storage-Batteries/SLA-GEL-Rechargeable/12V-6Ah-SLA-Battery/p/SB2485

You also get a auto system that will run for a little while when the power fails
Just be sure you don't keep running the battery flat. They don't like that, you want the battery to stay charged.

You only need those large farad automotive caps if you want to run massive bass with huge subs.

[phaseform]

cool thanks for the reply Psi, I might just see how the PSU goes alone to start with since I'm worried what would happen if the SLA was drained too much then connected to the PSU n I can't be bothered with anything too complicated. Little Surprised high current caps are hard to find, for me at least

[DanielS]

Little Surprised high current caps are hard to find, for me at least

They are not hard to find: take a bunch of 2200-4700µF 16V low-ESR caps, put them in parallel, done. For $50, you can put together a fairly beefy capacitor bank.

You may need to implement some form of current-limiting during power-up though since the power supply might not like having over 100mF on its 12V output during soft-start since the ATX spec only requires correct operation up to 10mF on all rails.

[djQUAN]

I have done a bench supply using a 57A 12V Dell server PSU and it does not like large caps on the output. It shuts down as it sees a short at turn on. Even a single headlamp bulb triggers its protection circuit when cold.

If you precharge the cap though, it would run normally.