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Powering an amp with a PSU

Last response: in Components
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June 5, 2012 8:52:56 PM

A friend is planning to power a car amplifier with a PC PSU. Does anyone here have any experience with this sort of thing?

It's a 800W max amp and he's planning to connect a pair of 250W(each) subs and some crappy speakers(probably 25W or so). How many watts would be enough to power this setup?

I checked out a couple of videos and forum posts, but I couldn't find any information for this particular setup.

Thanks!

EDIT: I'd like to add that this amplifier(like most car amps) does, in fact, run off of 12V DC, which a PSU can supply via its main 12V rail. Please do not comment if you do not know what you are talking about.

More about : powering amp psu

a b ) Power supply
June 5, 2012 9:15:03 PM

Hi :) 

Look up Ohms law...also car electrical systems run on 12 volts....and Psu`s dont...

All the best Brett :) 

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a b ) Power supply
June 5, 2012 9:23:32 PM

Great! When you figure out how to get a 110v power supply to run a 12v car amp, let me know, I could use some help figuring out how to get an old psu to run my solar landscape lights.
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June 5, 2012 9:23:33 PM

Brett928S2 said:
Hi :) 

Look up Ohms law...also car electrical systems run on 12 volts....and Psu`s dont...

All the best Brett :) 


I think he is trying to hook the amp up to household electronics and using PC PSU's to convert the house power to 12V DC
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a b ) Power supply
June 5, 2012 9:24:52 PM

Wouldn't it make more sense to run the car amp off the cars 12v battery? :bounce: 
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a c 1200 ) Power supply
June 5, 2012 9:26:52 PM

psufan836 said:
A friend is planning to power a car amplifier with a PC PSU. Does anyone here have any experience with this sort of thing?

It's a 800W max amp and he's planning to connect a pair of 250W(each) subs and some crappy speakers(probably 25W or so). How many watts would be enough to power this setup?

I checked out a couple of videos and forum posts, but I couldn't find any information for this particular setup.

Thanks!

Is the amplifier 800 Watts Peak or RMS?

A reputable name brand 850 Watt or greater PSU with a single +12V rail should work.
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a b ) Power supply
June 5, 2012 10:13:17 PM

Of course a car battery with at least 500 cold cranking amps would be the way to go. LOL
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June 5, 2012 10:36:33 PM

ko888 said:
Is the amplifier 800 Watts Peak or RMS?

A reputable name brand 850 Watt or greater PSU with a single +12V rail should work.


Thanks for the answer!
It's a Kenwood KAC-7201(150x2 RMS, 800 peak). Does it have to be such a high wattage? Can a lower-watt PSU pull it(e.g. 600-700W), i.e. would the speakers work at lower-than-max volume, or would the amp just not work?
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a b ) Power supply
June 6, 2012 12:29:01 AM

I got a look at the instruction manual for that amp. It carries a pair of 30A fuses (60A total). That means the cabling and power supply must be capable of delivering that 60A. That equates to 720W on the +12V rail which will probably be a 750W power supply. Of course, you can install lighter cables and smaller fuses if you wish. Like a pc, the amp will only draw as much as it needs but with lighter fuses, cabling and power supply you're more likely to blow something sooner.

The biggest problem you're going to have is tranferring the high current load from the power supply to the amp. In cars that supply is fed through heavy duty cabling (80-100A cables) connected directly to the battery, if not connected to the main fuse box. In a pc power supply the high current is split between a number of smaller cable capable of carrying no more than 5A each, some high power power supplies have heavier cables capable of about 10A per cable.

It should be noted that when a car engine is turning over the alternator actually raises the car electrics voltage up to 13.5V, whereas pc power supplies sit around 12V and drop slightly with higher loads.
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a c 1200 ) Power supply
June 6, 2012 2:56:10 AM

psufan836 said:
Thanks for the answer!
It's a Kenwood KAC-7201(150x2 RMS, 800 peak). Does it have to be such a high wattage? Can a lower-watt PSU pull it(e.g. 600-700W), i.e. would the speakers work at lower-than-max volume, or would the amp just not work?

I was going with an assumption of 800 Watts RMS because you didn't specify it in your original post.

The Kenwood KAC-7201 specifications say that the current draw is 43 Amps at an operating voltage of 14.4 Volts that works out to 619.2 Watts.

On a 12 Volt power source it would be 51.6 Amps.

You really don't want to be triggering the PSU's over-current or over power protection circuits.

A 650 Watt PSU is too close to the borderline. Don't go any lower than a good 700 Watt PSU with a single +12V rail rated at least at a continuous current rating of 58 Amps or greater. If I were doing this I would go with an 800 Watt PSU that has a single +12V rail with continuous +12V current rating of 66 Amps or greater.

You will need to aggregate all of the yellow wires of all the cabling together into one power connection point because those are the +12 Volt wires. You will also need to aggregate at least the same number or more of black wires together for the ground. You should be using at least 10 AWG or thicker cabling from the power supply to the amplifier.

Modifying the PSU's wiring is going to void the PSU's warranty.
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June 6, 2012 4:18:13 AM

Ok I did this project it does not work.. I mean it gets sound but nowhere near enough I even tried using 2 power supplie combined got louder but still not usefull. I ended up using a rack mount 1000 watt pa amp a friend gave me with a low pass filter on it or was it high pass lol I forget. i now have a dual 12 inch car sub as the sub in my home theater setup lols its stupid loud can break stuff.. Ended up with a Crown CE1000 about 200 bucks you will be allot happier and its made to do the work. Also you will get to learn how to wire Nutrix Spekons LOL I had to :p 
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a c 1200 ) Power supply
June 6, 2012 5:06:03 PM

thently said:
Ok I did this project it does not work.. I mean it gets sound but nowhere near enough I even tried using 2 power supplie combined got louder but still not usefull. I ended up using a rack mount 1000 watt pa amp a friend gave me with a low pass filter on it or was it high pass lol I forget. i now have a dual 12 inch car sub as the sub in my home theater setup lols its stupid loud can break stuff.. Ended up with a Crown CE1000 about 200 bucks you will be allot happier and its made to do the work. Also you will get to learn how to wire Nutrix Spekons LOL I had to :p 

It definitely works if you know what you're doing.
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June 7, 2012 3:20:18 PM

Ok let me rephrase then a 1000 watt power supply will not give you the same ammount or quility of power as a the amp I mentioned that has power supply and amp combined into 1 and is about the same price.. Car amps can pull huge ammounts of amps when hitting long and low I had my powersupplies going into protect mode when turned up much so it sounded loud enough. Soooo anyway I loved doing the project it was quite fun also learned how to combine two power supplies while I was at it. LOL you can even find my threads on here asking for info on how to do this. As a proof of concept yes it can be done but it is really not a good long term answer... Easy to try though take you power supply short green to black (to turn on power supply) and connect yellow wire to pos and black to neg on amp see what you get out... Good Luck

Thent
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November 14, 2012 1:41:43 PM

psufan836 said:
A friend is planning to power a car amplifier with a PC PSU. Does anyone here have any experience with this sort of thing?

It's a 800W max amp and he's planning to connect a pair of 250W(each) subs and some crappy speakers(probably 25W or so). How many watts would be enough to power this setup?

I checked out a couple of videos and forum posts, but I couldn't find any information for this particular setup.

Thanks!

EDIT: I'd like to add that this amplifier(like most car amps) does, in fact, run off of 12V DC, which a PSU can supply via its main 12V rail. Please do not comment if you do not know what you are talking about.



Iv been running car sterios ... various decks and 2 amps .. 1 is a 400watt amp other a200watt. Iv found trhat as long as you run the amp and deck of seperate rails of the power supply it lasts so far indefinetly. Iv blowen a few 400watt psu's tho and ended up making the most of a 880watt power sup that has caused no drama and the system cranks harder than most home sterios and sounds amazing. altho it all looks a bit dangerous to people when they first see it. now im running the sterio of a car batery and a few solar panels I put in series. works great too... until the sun goes down and the battery goes below 10 volt haha.

main problem tho was when the sterio was cranked near 100 percent of it volume the power supply wires heat up way to much and I have had them start smoking. :) 

and the sub connected was a blapunk 1200watt
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November 14, 2012 1:45:06 PM

pauls3743 said:
I got a look at the instruction manual for that amp. It carries a pair of 30A fuses (60A total). That means the cabling and power supply must be capable of delivering that 60A. That equates to 720W on the +12V rail which will probably be a 750W power supply. Of course, you can install lighter cables and smaller fuses if you wish. Like a pc, the amp will only draw as much as it needs but with lighter fuses, cabling and power supply you're more likely to blow something sooner.

The biggest problem you're going to have is tranferring the high current load from the power supply to the amp. In cars that supply is fed through heavy duty cabling (80-100A cables) connected directly to the battery, if not connected to the main fuse box. In a pc power supply the high current is split between a number of smaller cable capable of carrying no more than 5A each, some high power power supplies have heavier cables capable of about 10A per cable.

It should be noted that when a car engine is turning over the alternator actually raises the car electrics voltage up to 13.5V, whereas pc power supplies sit around 12V and drop slightly with higher loads.




you are completly correct about the cables. :)  iv had mine smoke up haha
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