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Old 6th November 2001, 08:36 PM   #1
Ignite is offline Ignite  Canada
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I have a friend who wants to use his old car subwoofer amp as a subwoofer amp in his house. And he has less money than I. So I'm wondering about the lowest possible cost power supply for it. The easiest would be using a computer switching power supply or two (can you just attach the leads of two power supplies to the power connections on the amp to supply more power?) because we have them in abundance from computer projects. I know this will work, but unless we can use more than one computer power supply somehow a single one won't provide enough power. It's rated at 400W total RMS power into 4 Ohms, but that's all I know. What are his options?
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Old 6th November 2001, 11:53 PM   #2
bawang is offline bawang  Malaysia
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Why don't you just use a car battery (say of size at least 70Ah) and construct a simple charger for it? I've done this before, and it worked. Anyway, from the way I see it, computer power supplies won't do the job as the current available at the +12V output is too small for the car amp. That amp will need at least 20A at normal (read: not too loud!) listening levels. Lead acid battery chargers are easy to make (if you have the required transformer) and simple.
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Old 7th November 2001, 05:35 AM   #3
Ignite is offline Ignite  Canada
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I have 2 P/S units capable of 15A at +12V.
Could I use them both?
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Old 7th November 2001, 08:50 AM   #4
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well if you choose to do this you will need to consider the following............ you'll want to limit the current that the amp can draw to about 28Amps to ensure that the switchers in the PSU's dont overload and some sort of soft start circuit if the amp doesnt already have one...... the 12V line on a computer is generally rather noisy cause it usually only runs motors etc ........... almost all computer psu's also require a minimum current draw at all times on each of the voltage rails......... they also often have massive turn on current draw so if using 2 or mor check if a single wall socket will handle it ....... if you want to run more than one computer psu then you will have to be aware of the following.........the mains power inputs for the psu's will have to be wired in parellel which can be done in many ways...... you can pull the cases off the psu's and run copper wire Earth terminal of one psu to the corresponding terminal on the other psu then make a new case for the supply or you can use a mains splitter cable (it has one wall socket plug and 2 IEC sockets on the other end)

if you need to use 2 wall sockets, you have 2 options......
buy a power distribution board worth $100's or buy a 20Amp extension cord and the the required plugs/sockets (they only need to be 10Amp rated) and wire it as follows .....

. . . wall socket --------|. . .|-------- PSU 1
. . . . . . . . . . . . . . . . . .|. . .|
. . . . . . . . . . . . . . . . . .|----|
. . . . . . . . . . . . . . . . . .|. . .|
. . . wall socket --------|. . .|-------- PSU 2

ignore the periods ... i had to use them cause it doesnt like spaces.

just be careful of the above procedure ... in some countries this could be extremely dangerous if done incorrectly.
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Old 21st May 2002, 08:50 PM   #5
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Ignite-

I'm thinking of doing the same thing. Any success??

Phil
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Old 22nd May 2002, 07:25 AM   #6
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Paralleling two powers supplies will not work. One reason both power supplies have to be the same, so one will be hotter than the other. Second each power supply will destroy the other power supply. Wire can not take it. Even if you use huge wire. The power supply will not provide all the power. Third your amplifier will be very noisy too. Fourth, power supplies will not turn on because theres no load.

Your best bet is buy a few seal acid batteries. Then put them in parrallel to increase current capacity. Second, build a charger for the batteries.
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Old 22nd May 2002, 12:59 PM   #7
paulb is offline paulb  Canada
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Parallelling power supplies can be done in some cases, but trying to do it with two switching supplies is just asking for trouble.
I agree with the charger idea: note it will be much cheaper to buy a battery charger than to build one.
However, you may not be able to run the charger when the amp is running because of the effect on the sound quality.
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Old 23rd May 2002, 12:53 AM   #8
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Yes generally speaking, parallelling outputs from separate psu's is a bad move SMPS are (in my opinion) temperamental at the best of times, i would not parallel the outputs from the 2 psu's. You can buy 13.8V power supplies capable of 50A or more so this would be a better option.
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Old 14th June 2002, 08:56 PM   #9
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Thumbs up woohoo!

Well, I went and bought a 450Watt PC power supply for ~$90CAD that supplies 20 amps on 12V. It works quite well with my HT sub. The amp is a Rockford Fosgate punch150HD(150WRMS into 8 ohms bridged, 75x2WRMS at 4 ohms .05% THD+N).

If anyone attempts this, you may notice noise making it's way into your speaker from the supply that changes pitch based on load. I didn't notice this at first because bridging the amp does a pretty good job of cancelling it out. All you have to do is supply a load on the +5V line(as to not drain power from the amp). As the load increases, the whine's pitch increases, and it's Volume decreases, until it's gone! I ended up using a small light bulb and it did the trick nicely.
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Old 14th June 2002, 11:04 PM   #10
jleaman is offline jleaman  Belgium
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Default True true

Verry true i fix them pos's and hate it because there tricky the little est bit of dirent value in one resister and the thing squeeks like a pari of bad breaks on a car hehe I HATE THAT SOUND

LOL

Jason
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