How to calculate power consumption (amp hours) for a car stereo?
Submitted: Saturday, May 31, 2008 at 21:45
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Mark O
I want to calculate actual power consumption of my car stereo, for the purposes of planning a dual battery kit.
1. The head unit says "4 x 52W". I've only connected 2 speakers to it. I'm guessing "4 x 52W" is the peak. Assume 100W? Probably too much but anyway...
2. The standalone amp says "4 x 50W RMS". Assume 200W?
Can we now calculate the power consumption? I've used a few web calculators that indicate 300W RMS equates to 14.5A (ref:
Car amp calculator)
So to calculate amp hours, I've done: 14.5A x 4 hours x 2 days = 116AH (amp hours) used. This seems massive to me ... and of course would add heaps to the battery requirements (ie. $$$!) of a dual battery project.
Have I got it right? Am I better off going to an auto-elec and getting them to physically measure the power usage? I do have a multi-meter, but it won't measure amps that high.
Thanks in advance for any pointers here.
Reply By: Member - Olcoolone (S.A) - Saturday, May 31, 2008 at 22:28
Saturday, May 31, 2008 at 22:28
Very hard to do with a stereo system, depends how efficient everything is.
The only sure way would be us an amp meter but that would only give you a guide, you might have to use something like a data logger and play you typical music at your typical volume for a set time and then calculate the average current draw per hour.
Again using an amp meter would only give you a peak reading not an average reading unless it has an average function.
With car audio power out put don't think what they say is is what it is.
Also as the battery decreases in charge so does the voltage, when the voltage goes down the current goes up.
We had a Yamaha 6.1 AV amp rated at 100 watts true RMS for each of the six channels and the advertised power consumption was 710 watts, we then brought a Cambridge Audio 7.1 AV amp that is rated at 100 watts for each of it's 7 channels but the power consumption is 1400 watts....some of the reviews out of the UK have tested the Cambridge at 198 watts RMS per channel.
So if you used the RMS power out put as a guide the Cambridge would be
miles out.
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