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## Introduction: Car Amplifier and Subwoofer Powered by a Computer Power Supply

Background Information:

For starters, your car amplifier is meant to receive its voltage from a 12 volt DC source which is your car battery. Common households use approximately 120 volts AC. So you can see that we two problems. The first is that we need 12v and not 120v, if this was the only problem it wouldn't too hard to solve. However the real problem is that we need DC electricity instead of AC. So why not use a simple transformer, like a cheap laptop charger that supplies 12v DC?

The problem with using some type of transformer is not that it puts out 12v but its the amperage. A typical car amplifier requires anywhere from 10-30 amps. (You can check how much amperage you need by looking at the fuses usually located close to the inputs on your amplifier.) So if you were to use a simple transformer that delivered 12v DV, it would most likely work at very low volume but it would get destroyed by the power needs once the volume starts to get louder and the amplifier requires more amperage. So, do they make transfers at a high amperage at 12v DC?

Yes, but they are often very expensive, easily on the upwards of a few hundred bucks for a quality one. So what's the best solution thats also more economical?

The best solution is to convert a computer power supply (CPS) to work at 12v DC and deliver high amounts of amperage. This is the most effective and possibly also the simplest way to get your amplifier working at full capacity. The process isn't too complex, it would be beneficial to have some knowledge of basic electronics and circuitry, and also be able to solder.

Tutorial:

To begin, first know how many amps your amplifier needs. Do this by looking online or checking the fuses on your amp. Ideally you would want to exceed the amperage on the fuse so that your not constantly working the CPS too hard. This is the one i used, its rated at 24 amps for the 12v output. (http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=2475867&CatId=1078) Once you have your CPS, search the serial number with additional words such as pinout to locate your models pinout sheet. Its typically not too hard to find pinouts of a CPS. Once located, you want to find the pin that says something like "PS_ON" or "PS_OK", typically located on the "Main Power Connector" plug. Most of the time the wire will be green but I have seen a few that have been purple or other different colors (typically older power supplies don't use green). Once you've located that wire, connect it to any of the black ground wires. What this does is allows the CPS to turn on properly. So once you've connected these two wires, try to turn on your CPSband it should work.

Now that you have your CPS working, unplug it and take the cover off. The orange wires usually supply 3.3v (good for wiring any LEDs if you want) and the red wires usually supply the 5v source, both in DC voltage of course. If your only using the CPS to power your amplifier, then trim all the orange and red wires. KEEP the Yellow and Black wires, those are the ones used to supply the voltage and ground the amplifier. Once down, group all the yellow and black together separately. I used zip ties so they weren't a mess.

I STRESS that it is needed to wire all the yellow wires and all the black wires to the amplifier. When running this high of voltage, just one or a few wires going to the amp may work great at first but it will lead to problems. Think about the wire thats used to connect the amplifier to your car battery, those wires are thick. Its not only a strong fire hazard but also keeps the voltage flow more open and puts less stress on the amplifier by wiring them all together.

Now you need to find a way to attach a bundle of wires to a small terminal on your amp. The best solution i found was to use a fork wire terminal for two reasons. (1) it makes a great connection. (2) it doesn't look sloppy. You can buy these at your local hardware store, automotive store and just about anywhere that has a hardware section. I would encourage you to solder the wires together into a bundle before crimping to terminal on. This ensures that every wire is connected and makes it hard to pull the wires out from the terminal. For extra precaution i heat shrinked the connection as well.

Additionally, you will want to bridge a wire from the 12v source on your amp to the "REM" or "REMOTE" terminal on your amplifier as well. This bridge allows the amplifier to turn on.
So connect the 12v, ground and REM wires to your amp and it should be good to turn on. Don't connect it to your subwoofer right away though.

Now, give it a try.

Be careful, electronics can be fragile in the right environment and you don't want to damage something and spend hours or maybe days trouble shooting or having to re-buy something. There's no shame in posting a comment if your unclear about something and need help.

I have had offers to build the CPS unit already converted and ready to hook up. I have no problem doing this for a bit extra than what it costs for materials and shipping. Send me an email to work something out.

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## Questions

My subs not really getting any power and I don’t understand why. I connected all the yellow and black wires like you said. I have a 500w power supply 800w amp and the subs 400w. I figured the 500w power supply would be enough to power the one sub?

This is an awesome tip thanks. I did take the PSU apart , and I only used 1 yellow (12v) and 1 Black (Ground) works a treat :D

oh I forgot to mention that my amp is 4000w monoblock running two 1400w pioneer,, and another CPS running a pioneer carrozzeria double din with 4 mids connected to it, the reason I need to connect this capacitor thing is that I want to be able to switch on/off my monoblock using car stereo remote so I have to connect them all together on CPS

hi guys since I'm new here. i like this method n I've been using it since 2014. since some receivers do not have deep bass which is my favourite like 32 hz.,my question is can I connect a capacitor since my monoblock is too big (car capacitor to my CPS)

To clear some thing up, you can group all the yellow and black cable together as they are all connected together inside the PSU on the common 12V rail, you are better off connecting the cables together as this means the current isn't just taken from one connection on the PCB inside the PSU it also should keep the voltage stable and stops the wires from becoming overloaded. Cars use thicker cable due to the high amount of current being drawn from the battery lower voltage appliances tend to draw more current then higher voltage ones, it also helps reduce voltdrop. Someone has said that CCA is what you want to look for on a car battery this is incorrect as Cold Cranking Amps are for when the car is cold and you try to start the engine its designed for a very short duration while keeping a voltage of 12V, the actual battery usage you need to look at is measure in Ah these are usually much smaller then the CCA and are the rating you can safety continuously draw from a car battery. Note for the writer its a great article but i wouldn't recommend soldering then crimping, solder is very soft and will become loose after a while your better off crimping stright on the copper.

Hi. I have recently hooked up my Amplifier to a PCU. But I only used one black and one yellow wire of the PCU to power it. You said to connect all the yellow wires to each other and all the black wires to each other, and to use them that way. But when I asked if I must connect the yellow and black wires together (Like you did) on Yahoo Answers, people told me I will blow my amp and PCU if I did that. Why I don't know.... Can you please tell me if I will blow it or not.
My PCU supply's 14A on 12V+
It's a 450W

14 replies

Thats a great question. After some additional research, it appears that the standard wire size for a computer power supply is 18awg. According to various sources, it seems that 16A would be the maximum for an 18awg wire.

However, there is a lot of information that skews this 16A rating. Each situation has their own variables that need to be considered specifically for that application.

Personally, i have had this set up for about two years now and use it daily. I've also built many more of these conversions and have never had or heard of any problems.

This question leads me to wonder why the power cable in your car for an additional amplifier is so huge (like 4-8awg). It just doesn't add up to me, why you would be able to use an 18awg wire in your house and then have to use something like a 4awg wire in your car.

Theres clearly something i'm missing here, ill keep doing some research in my down time and see if i can figure this out.

In a car, the power run is usually 10 feet or more. Over longer distances, you'd require a thicker wire to maintain good amp draw. That's also why you'll often see smaller gauge ground wires right next to the amp. The shorter the run, the smaller you can go with the wire. That applies to both the positive and negative, by the way. If you have one of the various cars with the battery in the trunk, and you're connecting your amp just a couple of feet away, you can safely use significantly smaller wire. There are some tables online that can help you with this, and they take into consideration your amp draw and the distance to tell you which gauge of wire is ideal.

Thicker conductor is necessary for higher current, whereas thicker insulation is necessary for higher voltage. A car battery only supplies 12 volts, but it can pour out an enormous 200 amps. The current from the outlets in your walls probably won't ever exceed 15 amps, since that's what most household circuit breakers are rated for. However, the 110 volts needs more rubber around the wire.

Wire gauge also changes for the length of the connection. If you're just running a short connection from a power supply directly to an amplifier on top of it, you can get away with a slightly lower gauge wire. However, when wired up in your car, the wire has to worm its way from the battery and through the chassis and into the trunk. This extra distance will benefit from a thicker gauge to keep the wire from heating up.

This is why jumper cables are made with such thick wire. 200 amps going across ten to twenty feet requires a lot of copper.

A typical car battery puts out 500-600 amps. Look for the CCA Cold cranking amps...on the battery.

Hmmm.... Yeah you're right. Maybe the power cables in a car is so huge because the car's battery Amp's are way bigger than the 16A of a CPS. I've read that a normal car battery gives round about 30A out. Thus the cable's need to be bigger to carry that type of current. Otherwise the cables could over heat and short out. Imagine 30 Amps running through a 18awg wire in a car.

A car battery typically puts out 500 to 600 amps. Read your battery look for its CCA (Cold cranking amps ) Amp power wires are so big because the distance from the battery to your amp, would overheat a smaller wire due to the resistance of the wire and the load ( your amp) being at a distance. The smaller length wires on a psu work because the distance has fews ohms of impendence.

Actually I'll give you a big hint.. there is a diffrence between House/Home electronics and Car Electronics.. It's called the Alternator.

Basically car electronics are typically 'over engineered' because unlike house hold appliances which typically can be certain that they are going to get a constant supply of power that isn't surging all over the place a Car can't.. you can actually watch this on (older) Cars simply by watching the Battery meter if your alternator starts to flux, the volts being thrown out by your battery also begins to flux as well, not to mention that cars have FUEL in them and are on rubber tires and don't ground easily.. it's better to over engineer their requirments there then to go 'oh damned we just blew up the car'

as for the actual output on the White PSU 12V and it's output Has any one actually bothered sticking a multimeter on a SINGLE plug and seeing what it's throwing out? My Multimeters dead atm so I can't.

An electrical component only draws the amps it needs as dictated by its impedance, and a car's rubber tires do not affect its ability to ground because it doesn't get electricity from the power grid. Its ground is its chassis, which is connected to the negative terminal of the battery.

Is your multimeter dead because you bridged a high amperage power source with it? Using the unfused side of a multimeter to short a circuit which could potentially deliver over 20 amps is a bad idea.

The potential for current spikes from the alternator is a good point, though.

Si mon carnalito I have four of the 12v yellows connected together reading 13.4

Yes thats correct that they can give out something around 30A.

However though, the amount of amps running through the cable will only be what is needed by the amplifier at that instant. Especially for a smaller amp that would only require something like 15 or 20A at max. The size of the wire required even for a small amplifier is still something like 4 or 5 times bigger in diameter.

It might be partly due to the fact that the wire is running a long distance and that there would be a small voltage drop due to inefficiency with a small wire. However the increase in size due to the voltage drop would not account for that big of an increase of size for a wire only like 10-15ft.

Thicker wire has less resistance. Less resistance menas better sound.

The length of the power wire used in a car is different

Hey, a question, if u have two 25a fuses on a four channel sony xplod 500 watt xm-504z, would u have to get a power supply to equal both fuses or just one? I want to bridge a 10" 300 watt sub and connect two speakers, how much amperage would i need, equal one fuse or both?

Im looking at this psu, what do u think? http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=8438086&CatId=1079