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samsagaz 28th May 2005 08:03 PM

12V Power Supply ?
I searched the forum and i found someuseful posts but cant find the right answer...

im learning electronics in home (i buy 2 books and i study from it). :)

im an DIY learn too

first, sorry for my english, im from argentina and my english is not very good. i already learned how biasing transistors, and im study right now how AC signals works in transitors....

my main objetive is create an 4x100W RMS Car amp.

so its 400W of power, at 12-14V its 12V*xamps = 400W => xA=400W/12v => i need like 33A.

is possible to get that from an simple car batter? when i goto and design my amp i need to use the source of 12V? or i need to use some kind of inverser so ill get more vols?

hope you guys understand my question... i serached google and the forum but cant get the right answer abt how many volts i will need and how it work :D


Nelson Pass 28th May 2005 09:37 PM

The simple answer is yes, but it assumes something like
100% efficiency from the amplifier and/or switching supply
that converts the 13.8 Volts froma car battery to what you
want. Also, be advised that a car battery will only do this
for a short while.

samsagaz 28th May 2005 10:25 PM

i fount this in another thread..

its the switching supply that i need? this schematic will be useful?

when you say that the battery only do this
for a short while.,u mean with the car engine turned off, right? i mean if i have my car engine running i never will be out of power, right? :D

kilowattski 29th May 2005 08:45 AM

As long as your car is running your alternator will charge the battery. BTW, building that SMPS is not a trivial project. You will need to wind your own transformers.

AndrewT 29th May 2005 10:31 AM

your battery behaves like a very large capacitor supplying the shorter term peak demand and smoothing the alternator's 3 phase AC supply.
The demand from the 4*100w amps will peak at about 600w and your inverter must meet this as a minimum. The continuous demand could be a lot less than this.
The alternator must ultimately meet all these power demands. How big is it? Amps & volts should be in the manufacturers spec.
A 50A alternator is only 690VA and it has other power supply requirements to keep the car running.

rinox 2nd June 2005 09:41 PM

I heard some strange things in this post about power needed by the amp... I don't undertaind.... Pass Lab is a pure class A?
If the answer is yes... ok don't think to put it in your car, but if it is class AB pushed to class A for few watts, maybe it's not so difficult to make an SMPS for it.
May be you can change the bias of the amp without big change in sound, I really don't remember very well the schematic of Pass Lab, but I don't think it's so hard to do it.
Let's ask the guru about this point.

samsagaz 2nd June 2005 10:24 PM

well. if i can build an SMPS i can use an gainclone in my car, right?

Nelson Pass 2nd June 2005 11:05 PM


Originally posted by samsagaz
well. if i can build an SMPS i can use an gainclone in my car, right?
Not in this forum you can't.


samsagaz 2nd June 2005 11:11 PM

ok :)

Stuart Easson 2nd June 2005 11:33 PM


You may not be completely aware of where you are asking the questions. Here in the PassLabs section of DIYaudio, we tend not to emphasize the use of gainclones too much. They are less DIY and more complete in and of themselves and as such are great projects for someone just starting or looking for a lot of output for minimal effort.

In PassLabs land we tend to the larger, more (dare I say it) manly amps that have huge transformers, massive heatsinks, consume vast amounts of electricity and ideally require at least 2 beefy people to move them. As such they are not ideally suited to the automotive environment.

There are other more suitable sections of diyaudio, such as solidstate, car audio and chipamps, wherein lengthy discussions of the virtues of this chip versus that, and their suitability for car use would be welcomed.



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