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Pc power suply to power car amp?
Redseven80:
Ok the 12vdc amp is 300w
sub 400w / 3 ohms what will that combination be in amps?
richms:
Depends if its a sony 300 watts or a rockford fosgate 300 watts since all manafactureres fudge there figures one way or another.
Best to look at the fuse requirements for the supply to the amp.
Also the power figures for the actual subs are the only area where there is more BS then the amps power figures.
So long as the amp isnt distorting, the sub should be fine. If the sub starts to disrort its generally just it reaching the end of its travel and not likly to cause it to burn out quickly.
General rule, if the sound coming out of it is clean, then nothings being stressed.
elvis:
--- Quote from: Redseven80 on May 24, 2005, 02:27:58 am ---Ok the 12vdc amp is 300w
sub 400w / 3 ohms what will that combination be in amps?
--- End quote ---
As above, is this 300W "max" (PMPO - Peak Mean Power Output) or 300W RMS (Root Mean Square)
http://en.wikipedia.org/wiki/PMPO
http://en.wikipedia.org/wiki/Root_mean_square
My two speakers are 120W PMPO. RMS values are probably around 20W at most. For my 200W power supply, this sort of draw is peanuts.
As for your max ampage draw, that should be clearly labelled on the amplifier, if it has passed all of your local safety certifications.
richms:
If only it was that simple.
The facts are, normal unclipped music material has a RMS:Peak ratio of about 10dB - slightly lower on stuff heavy in the bass, and more on vocals. Your amp needs to pass the peaks of the music undistorted, whereas the total power used from the powersupply is the average. The car amps have a DC-DC voltage step up in them which averages out the powerdraw nicely.
So, your 120w peak speakers, on normal music will be outputting about 12 watts RMS, quite loud as anyone that owns some mcintosh audio gear with wattmeters will tell you ;)
Most sony and other mid to lo-fi stuff measure it with a single tone at 1kHz at medium distortion levels (0.5-1%), and the sine waves RMS is only 3dB less then the peak power they will get from the voltage in the amp, so they get another 7dB on that rating over what you will actually be pushing thru it with normal music material.
If your not entering bass sound offs, you wont be playing anything remotely like that, so your 300 watts becomes something closer to 30.
PMPO is BS'd furthur by measuring the instantanious power as the amp swings from its maximum positive voltage, to the maximum negative voltage, as fast as it can, something that you will never use when driving speakers with audio (Unless you want to blow up your tweeters)
however, as amps use the output devices in linear mode, they disappate heat - allow for 50% efficiancy generally, perhaps less in a car amp since it has a switchmode voltage step up to waste more energy, so your (30 by 2) 60 watts of audio is actually 120 watts in from the power supply, with about 60 watts of heat into your cabinet, crude maths, but likly close enough to get you there.
In addition, the 300 watt car amp is most likly measured at 14.8 volts, which is the maximum charging voltage you will see in a car when its either really cold or really hot (Cant remember which) - and you are only giving it 12 volts, so the power output will not be near what they claim.
Anyway, the PC PSU _should_ have overload protection, and overheat protection, so if the amp does start to suck the juice too much, the PSU should shut down, but no guarentes naturally.
Perhaps put a blade fuse inline to the amp thats one step below the max 12 output of the PSU?
BobA:
I agree a properly protected PC supply (separate) can power a car amp if power draw is matched or protected properly but you guys are forgetting the other part of the question. He also has an electric car seat for the driving cab. This means motors as well as the car amp.
BobA
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