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# Power car amp from PC PSU

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Hi all.

Can anyone please help me with the following: I want to power a car amp from my mains power supply (220V, 50Hz). I have read and searched around, but haven't found anyone that could really tell me exactly how to do this. My idea was that I take a powerful PSU, about 600W or so and strip all connectors off and connect the yellow wires together and the black ones and connect it like that. However, I read somewhere that you could also "bridge" two PSU's together by connecting all yellow wires from both PSU's and all black ones. They mentioned using diodes on the yellow wires rated at at least 10amp or so.

Can anyone please tell me how I could do this by using one or two PSU's or would you suggest another method. I'm on a very tight budget and can't afford the large, proper high current ac/dc converters.

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ok first of all, how much does the amplifier draw in amps (the fuse rating is a good indicator of what it is) or check how many watts the amp it is. then divide the wattage by 12, you will get the amperage draw (this would obviously be at maximum volume)

second of all, once you have found that, u will need to see how many amps you can draw from the 12 volt rails of your power supply. the equation 600/12 = 50A would not be right, as that 600w counts for the 5 and 3.3 volt rails, which will not be used here. on most PSU's there is a label which will tell you the amperage of the 12v rails, and as far as i know its per wire, so if it says something like "+12v = 8.2A" thats the maximum you can draw from each wire, hence the diodes, so they dont cancel each other out, once u have found the amperage, multiply that by the number of wires, noting that there must be the same amount of ground wires (must also have diodes) as there are power wires.

third of all, a computer power supply isnt a very rugged source of power, an amplifier really needs a beefy source of around 13.8volts
it will work, but it will not be very efficient, and will most likely be short-lived. when the power supply makes a sound reminiscent of a cap gun going off, you have blown the output capacitors and the power supply is pretty much finished. i have tried to use a 300w psu to power a small car radio (no cd or tape, just radio), it had a capacity of 8.2amps at 12v, but i still blew it! because they aren't solid enough.

best bet is to get a small car battery (or even a 12v motorcycle battery), and a charger. or order a 20amp 13.8v power supply for AU\$99.95 (works perfectly) from www.jaycar.com.au and that should have enough grunt to power any amplifier up to 300w. if you arent in australia it is ok, as you have 220V as we do (actually 240v but there is really no difference), just buy it, change the plug or use an adaptor, so there will be no problem with mains voltage.

Warning: if you are intending on using a large 4 channel amplifier it really isnt worth the trouble, as any power supply capable of powering a large amp like that will be expensive, large, and heavy.

you never know u may be able to power it, i just need to know the amplifiers power, the amperage of your PSU's 12v rail

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Hi Frank,

You can use two PC-PSU

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yeah i think ive just had bad luck with the PSU's, that 5+5+3.3 sounds pretty good actually, nice work Ante, cos that gives 13.3 like u said, but its not voltage that worries me, admittedly, it wasnt a 300w now i think of it, it was actually a small mini-ATX 80w power supply, with 2.7A on the 12v rail, and it was a cheap CD/tuner

how many amps can u pull with the 5+5+3.3 setup safely?
would a 300w psu be enough to power a small BOSS CD/Radio head unit, that is probably about 4 x 35w - obviously theoretically it could run 2, but im making room for heat dissipation and that so yeah, was thinkin of settin that up in my shed.
set that up with 2 x 6 inch's inside and 2 outside the shed
that would be all i would be running

btw if u start to overload the PSU 12v rail, do they tend to start poppin capactors, or do they just fail?

sorry to hijack the thread but its the same thing
thanks
ben

and to Frank, the only concern is the small gauge of wire that will be connecting the amp (18 gauge) to the psu, unless, you modified the PCB and allowed it to fit 8 gauge straight from the PCB.
i only recommend the battery as u will be able to run any amp you want and not have to worry bout blowing a PSU up
and u will avoid having to control the volume around the PSU's amperage.

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Hi Ben,

The maximum current will depend on the three PSU

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I'm gonna play around with it and see what I can come up with.

Really appreciated!

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