True, but the biggest difference is that your car's alternator is internally 3-phase, whereas your in-house power supply is of course single-phase. The 3-phase has much less ripple because one phase is always rising when another crosses the zero point. Single phase crosses the zero point 60 times a second, and is effectively off. This is much harder to filter. The phases are also 120 degrees apart instead of 180 degrees. Also, house current is at 60HZ. Anything above a low idle and your alternator should be above this.

 

Look for something like this: http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=22-508

They used to have a 20 Amp model. Every once in a while I see them on sale for half price. There's many out there, google "switching power supply" .

You're going to have to figure out the minimum size you'll need. Not sure what a modern HU draws, power wise. Guess I could roughly figure 4 x 25W, plus a bit more for internal circuitry and cd, etc. A couple hundred watts, maybe? And that's if you run the speakers off it. If you hook it into your home receiver and let it run the speakers, it wouldn't take much of a power supply to fire the HU up. Even a common 4 Amp linear could probably power the thing. That's why I think a PC PS might be the ticket. The old 300W ones are pretty common and if you have a place to hide it...

The little black wall transformers just don't have the power. Even the larger ones, say 400 milliamps don't put out that much, 12x400E-3=4.8W, so at about 5W you wouldn't have much thump.

A battery has a deadline DC waveform. Any other mechanical power supply that starts off as AC has some form of AC left in it. You might not be able to see it without an oscilliscaope, but it's there. For most things this is "good enough". This little bit of AC riding on the DC line is called ripple, (non-alcoholic). 40mV ripple on a PS is really good. To filter it enough to get down to 30mV might cost a few hundred more dollars. So, even DC has a little AC - just not enough to worry about.

One of the reasons Bob's showing a little concern about the AC/DC thing is that if you take a standard electrical transformer, it's really hard to tell if it's an AC or DC by just looking at it. Everyone that's played around with this stuff has fried something they spent hours and bucks building, by using the wrong one. (Antie up Bob, what kind of board did you smoke?...)

 

I remember being a kid, about 12, and powering a car stereo in the garage off an old model train transformer with a bridge rectifier. No caps, no coils, no vreg. No filtering of any kind. The thing worked fine with no 60hz hum. A friend of my brother's was over one day looking at it and kept saying "I can't believe that thing is working. Where's the filter?"
Don't know why it was so quiet. I've built power supplies since with all kinds of filtering and regulation that were much noisier. Go figure.

 

Use a small dry cell 12 v battery and a trickle/ smart charger. Battery size will depend on how long you want to use the stereo continuously.

 

Most car radios have a good filter (PIE- 2 electrolytic caps, and an inductor) in the 12V supply.....probably explains why you didn't have any 120HZ hum.
The frequency component with a bridge rectifier (full wave) is 120HZ, not 60HZ.

Howdy, I haven't burned up any boards, but I have done a lot of BOOO BOOO's!!

 

Well I have a plug that says 12V DC output.. just wondering lol. I have an old CPU somewhere.. To do the CPU one, where do you tap into the power supply at? And would I have to have the whole case? Or could I get the power box out of there? What do you guys recommend?

 

The normal wiring color code for PC power supplies is yellow +12V, black - GND. Red is normally +5V.

 

Just pull the power supply out of the case, piece a cake. Not very big, has a fan and a cord, ready to go. Might want to install an inline fuse between the PS and the HU, up to you = it's usually a good idea.

 

Bob:

I wrote, "So that I could listen to it, I used a slot car transformer and mounted the whole thing to a piece of plywood and put it on my desk/table.
Ran some speaker wire and hooked up some speakers . . . it worked GREAT!
(The transformer put out [max] 13 volts, 12 volts nominal.)"

Key words were 'slot car' transformer. They not only reduce 120v AC to 12 - 13.2 volts, they convert to DC. (And, that power was fairly 'clean'. No hum, no hiss, from the stereo.)
Heck, I probably still have that transformer in the basement, in a box, back at my parent's house.

That 'Rube Goldberg' setup that I made, worked flawlessly, for as long as I had it connected to the 8 track.

 

that radio shack supply would actually work really well it looks. you have to remember that your alternator is going to put out more than 12V. so really your radio is runing off of like 13-15 V when running. you also have to realize that you're gonna need a LOT of available amperage if you're gonna max our your HU. say you have a 4x50W max. you're looking at 200 watts. thus that power supply would probably be adaquate. actually im pretty glad i read this cause that's the cheapest i've seen a supply that will have enough amperage to run a HU.

i've always that it would be neat to build a box for a pioneer HU and boxes for 3 way 5x7 or something like that and use it for my room stereo. kinda expensive route to go, but hey it would be something to talk about when friends come over. i would suggest to go with the radio shack supply and use that. i dont know if you want to run 10-15 amps through some of those computer cables.

 

Well I've talked to some other people that have done the PC route but with amplifiers and ran subs with it. I'm pretty sure my HU will run just fine. It runs 26wRMSx4 with 50x4 peak. I would go out and buy the Radio Shack one but I already have a power supply.

Ohh and jjoel - not all cars run 13V - 15V like you said. Reality is most run 11.8 - 12.6 or so. And mine usually runs lower than that because I have an amp that sucks way too much juice. But my alternator I'm gonna buy is rated for 210 amperes.

 

I'm thinking that for the price I could get something from here: http://www.pcpowercooling.com/products/

I'm gonna check newegg and see what they've got. Thanks for the help.

 

Not true, the "nominal" electrical system voltage while engine is running is 14V. So, if you are going to use a power supply with a HU, you should set
the power supply voltage to 14V.

 

You'ld be suprised. 300w pc power supply at 12Vdc works out to be 25 amps. I'm pretty sure it's not a good idea to keep it maxed out, but they seem to last a long time. Keeping the wires fairly short helps. In DC, the longer your run, the larger the conductor.

 

I've been looking at the PC power supplies and a lot of them run 18 amps at 12V DC, but there's like 3 sets that run at 18 amps 12VDC. I think I'm just gonna pull the power supply from my old computer.