Car stereo amperage


Feb 12, 2007

I'm wondering how much a car radio/stereo player/amplifier will take electricity (I mean those which you have in your car). You do know those ones? I can't explain more.
It's a cheap one an the amplifier is normal 4x45W.
I'd like to use one not-in-a-car and don't know how strong power supply it needs. Might it be 10A? 15A?

Thanks in advance.


Mar 17, 2006
Depend on the speakers you put in and the output level you listen to.

average probobly 5 to 10 amps. crank it high 'till you hear distortion and you'll be making 8 - 12. By then your car stereo will shutdown or die if not the speakers that gave in first.

Unless your absolutely regulating 12V DC then your at the mark. but car battery put out 14.5 at full charge to around 11.0 with all your equipment running. In anycase I don't think you'll be making 10 amps constantly. thats too load to listen too in close proximity.


Oct 28, 2006
I'd steer away from using a car amp for "non-car use" - car amplifiers aren't especially good quality (sonically), and they're quite inefficient (use a lot of power, and generate wasted heat)

If u insist on using a car amplifier -

-If your amp draws ~ 15A, get a 18-20A power supply. The current drawn isn't continuous, it spikes and dips according to the music you play, and the volume. e.g. Low volume = less current, bass transients and techno music = a lot of current drawn. You need to overrate the PSU substantially, to allow for these spikes - not doing so will cause the power supply to burn out with extended use, or may constantly trip its overload protection mechanisms. (If you amp draws less, than over-rate proportionally - for 5A draw, 8A PSU, 10A draw, 14A PSU)

-To ensure you reach the amps max power and efficiency, use a 13.8-14.5V supply voltage. Do NOT exceed 14.5V. As rexter said, the actual battery voltage is higher than 12V. ~14.1V is ideal.

-Use a "low noise" power supply, or a transformer based alternative. Some of the cheaper switchmode power supplies give out really dirty voltage - this comes through the speakers as hissing, pops, high pitched squealing, clicks etc.

-Make sure you use big thick power cables from the PSU to your amp


To calculate approximately how much current an amplifier draws -

Total Power / Supply Voltage = Current; then increase by 20% to allow for inefficencies.

So for 4x45W:

180W / 13.8V = 13.85A
13.85 X 1.2 = 16.6A MAX

It does seem like a lot, but it isn't continuous, and most car amps will never reach their "labeled power" without heavy distortion, so in effect, the max current draw will be ~13-14.5A, as you said, so use a 16-18A PSU.

Hope thats clear enough



Dec 3, 2007
By the way, if you are talking about the head unit ie. the car stereo itself doing the amplification, then the 45w story is horse manure as you can only get maximum 22w (RMS) out of 12V. This 45w or whatever is the absolute peak rating similair to PMPO (Permissible Maximum Power Output (me thinks)).

Car audio amps obviously offer much higher outputs than the head unit can but that is due to the switched mode power supplies within these amplifiers which boost the input voltage allowing for much higher amperes to be drawn. Head units do not have this feature (none that I have ever encountered).

Why I am saying this is that you do not need such a powerful power supply,check what the fuse rating is on the head unit and add a few more amps to that and thats what PSU you require (excluding other additional equipment which may draw more power. My head unit uses a 3 amp fuse in line with the main +12v supply.

Do not use the fuse rating of lets say the yellow or orange wires as these are to protect the head unit from blowing while switching on numerous amplifiers etc.

Years ago when I was a kid I was powering a cheap head unit with a cheap PSU, I blinked and the head unit blew up, all capacitors were well, visibly damaged! The voltage regulation and filtering was inferior.


Aug 18, 2012
HELP! I have a 94 conversion van that has 6 speakers. A couple of the speakers were blown and the others didn't sound great. I bought 6 new speakers (250W) and installed them. The two front speakers sound great. The back four don't. How come? Do I need an amp or what? The radio in the van is after market and was installed by Best Buy about 10 years ago. New radio? Let me know.


Jan 2, 2013

I'm in a similar situation, where I have done a custom car audio install and want to power 2 out of 3 amps from household 240v connection. I have done the maths that technology-sponge recommended but totaled a 115(*1.2) amp draw which i'm not sure is right. is it possible to have someone help me out with the maths / what equipment I should be using.

Here is what I would like powered off the 240v line.

PA660.4 - 2 ohms: 75watts x 4 chan.
PAD1000.1 - 2 ohms: 800 watts x 1 chan.
PAD4000.4 - 4 ohms: 125 watts x 4 chan.

I've been looking at something like this 13.8V 40A Switchmode Laboratory Power Supply here would it work or just fail entierly?

What's your thoughts?
I was hoping to not use a car battery charger as this defeats my intended outcome. Also I will have a Rockford Fosgate 2 Farad capacitor between whatever I have to provide power and the actual system.

Thanks in advance :)
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