Power supply, true amperage.

[aj6500]

I'm considering putting a 300max watt audio amp in my cab.  Will a 400 watt 12v computer power supply provide enough true amperage to keep the amp happy?  I know at max the amp will only draw 25 amps, and will spend 90% of it's time at under 12.5 amps.  I know a 400 watt power supply should provide 33.3 amps, but in real life will it work?

[tom61]

Computer power supply are rated in composite wattage, i.e. all wattages added together. Check the label on the PS to see how much amperage it can output on the 12V line.

[StephenH]

Definetly, check the amperage out.   I doubt a PCs supply would supply 33A at +12V.  

I think you may need to get a special supply, that is designed for running car radios from 120V AC.    They may be quite expensive.

Also, you would probably need a really thick wire for that (10 Gauge, or possibly even 8 Gauge)!

[Amra]

People, dont forget Ohms law, you can get Ampres by a small algorithm

Amps = Watts/Volts

Thus a 400Watt PS on a single 12v Line can sustain a maximum of 33Amps.  Granted the Wire for suck a task might be less then par, but it would not be impossible (fairly easily accually) to remove the cover of the PS and snip all the wire and replace with a thicker wire.  Possible even to simply remove the insulation off several of the wires and twist them together, and attach your thicker wire to that (use Heatshrink of course).

So, if you were using a 400Watt PS for a Car amp ONLY, then yes, as long as the draw does not exceed or meet 33 Amps, then you are fine.  This does not garuntee you a constant 33 Amps though, so try and treat that as an overestimate, try not to use more then 20, this way your PS can supply the power without getting the PS too hot, or working it too hard.

I personally try not to use more then 75% of its max capacity, which would be about 25Amps for a 400Watt PS, a PS can comfortably output that, and not have a worry or fear of damaging it or the amp.  So if you plan on pulling 30+ amps, go for a 500Watt PS.  That would give you a max of 41Amps, and so it should be able to do 30 with little problem.  But since you only have a 300Watt PS, I probobly wouldnt use it if the draw could/might get up to 25Amps, as a 300 Watt PS max Amp output is exactly 25, and you shouldnt run a PS at its limit as you can damage the PS or the Equipment.

Otherwise yes, it would work quite well, I myself have a Car Audio system as a stereo running off a Computer PS.  I dont turn it up all the way anyway, because even half way is deafening.  I have one Car amp funning three speakers, two mids+tweeters, and one Sub.  I havent noticed any power related problems.  I use a 500Watt CompUSA Brand PS.

[aj6500]

That's pretty much what I'd figured.  I haven't done much work with PC PS, so I didn't know if they consistently put out the power they are rated at.  I'm planning on combining the outputs into a single wire to run the amp.  It's an old amp that I haven't used since about '94 and has been sitting in my basement.  Now that I think about it, it's rated fro 300wx1 into a 4ohm load.  So actually I figure I'll be maxxing @ 100wx2 into an 8ohm load (house speakers).  I should be between 12 to 16 amps a majority of the time, with occassional burts above.  I've been using an old home receiver to power my juke, but I think using a car amp w/a dedicated power supply might work out better.