AC/DC converter, large power output

[Phaelium]

Hey<p>Ok I want to know if and where I can get some sort of a converter that runs on house current to power a 12v DC car amplifier to run subwoofers in the house. The amp puts out around 300w RMS and draws quite a bit of current, so I know like a computer power supply probably wouldn't work (or last long). Thanks for your input!

[Chris Smith]

Name some values and specs? A computer supply puts out quite a few amps, some in excess of 20 amps 12v. Then there are large power supplies, and all sorts of other ways to solve your problem.

[Phaelium]

Well I think (not 100 percent sure) that the amperage draw by the amp when the bass hits hard is around 60-70 amps, so its quite high. I have heard of one alternative of having a car battery run it and then charge the battery, but if it isn't being charged all the time then I will probably have a voltage drop on the amp and the subs will start clipping, and I don't know of anything that can charge the battery that fast (other than an alternator, obviously) and doesn't cost a fortune.

[Chris Smith]

70 amps at 12 volts is only 7 amps at 120 volts. A car size battery is good because it will act as a huge cap which will help with the surge factor. A charger/power supply must have close to zero ripple and hum, and there are many supplies that you can make, copy, or buy that will do this fine. <p>This WILL come to some big bucks any way you look at it simply because of the logistics. I can think of a dozen ways to sunday to attack this problem, but all ways will probably come to around $100 no matter which way you go? <p>Check out "pico" on the web, they may have a ready made unit?<p>[ May 17, 2002: Message edited by: Chris Smith ]</p>

[toejam]

I think bg micro has a 12v 25 amp transformer for 20 or so bucksa. two of them paralled plus a 100 amp dide bridge with a .5 mf cap will do it.(don't short the leads)
tj

[Chris Smith]

Thats only 50 amps, and 1 whole farad would be a little better. <p>Point 5 uF [micro farad] is good for a small hand held transistor radio running off a 9 volt battery? <p>But if 70 amps is needed? <p>And a car battery is better, also.

[keymaker]

I know alot of people use computer power supplies... The trick is to buy them from a computer chop shop for $2 each and use 4 of them.<p>The car battery will definately help for the "surges", But will be a load on the supply most of the time.<p>Still advantageous if you ask me<p>I get alot of noise from conventional battery chargers personally<p>Good luck

[toejam]

I have to admit three of those transformers would get you closer to 70 amps and a 1 farad cap may improve the bass response, but thats about 900 watts of continious power.I'd try two first and if not satisfied i'd add another along with more capacitance.
Switching power supplies from chop shops would be a much lighter alternative shipping wise.I have never tried putting them in series, and they seem to favor the 5 volt side when it comes to the high current output.I have repaired some of the larger switchers and they are a bit tempermental and caps in them have a tendency to fail,sometimes with impressive and noisey results.
tj

[toejam]

you got me on that .5 mf cap i really ment .5 farad.

[Chris Smith]

It wasnt toooo far out? <p>Those Caps can run some bucks, while a car battery can run as low as 35 bucks new, and is far more steady in the delivery. <p>Gold Memory type caps werent designed for quick charge and discharge so these tiny type caps are strickly out. <p>The only draw back with lead acid is its less clean and tidy?

[toejam]

I can agree with a battery but for some reason on the more competetive auto boomers, the ultra high value caps seem to hava a fair amount of popularity. I guess if your gonna shoot top performance both a battery and a giant cap would be the choice.
tj

[viveguy]

I have a homebrew 40 amp supply I would be willing to part with.I was going to get into car audio repair but thought better of it.This thing is a monster. It weighs in at about 50 pounds.If you want to talk about it,contact me off of the board at [email protected].<p>Al

[toejam]

i'm serious here, with all the shipping charges for these heavy transformers being a major cost consideration, i would consider lookin fer a used welder Ac being fine, and a ten amp variac.that would cost about 40-60 bucks.for the welder,and the variac maybe 50 or less if you look around a bit.Large 100 000 mf caps can be found in surplus outlets reasonabaly inexpensivly as well as 100 amp diodes or scrs which can be made into diodes by connecting the gate to one of the other thingies.that stick out of it.By using the variac, you can get at least 100 amps at 12-15 volts d.c.,more if you desire.that would give you plenty of headroom.
tj

[Chris Smith]

You still get 10 amps, at any voltage, with the variac!

[toejam]

you plug the welder, which is a transformer into the output of the variac there are 220 volt variacs out there. there are also 110 volt welders out there. ten amps at 120 v == 100 a at 12 v.less effifiency loss of course.now on the other side if you connect to the output of the welder to the input of the variac what you say is true.