AC current w/ DC voltage cheap lcd power meter?

Thread Starter

bigjoncoop

Joined Feb 1, 2019
178
I was thinking of using an Arduino to make a DIY car audio real time voltage/ wattage meter...

It's quite simple since you just need to measure AC current on the positive lead to the subwoofer and the DC voltage input of the amplifier and multiply the two together in order to get actual wattage. This is exactly how all of the expensive wattage meters work. You can do the same thing with the AC clamp meter and a multimeter.


But I was thinking, for $20 you can buy a LCD power meter online that will show the voltage, power, amperage, etc... but they only come in either AC or DC. So my question is is it possible to use one of these 100a AC meters but with only 12v DC voltage? My guess is no but...

Screenshot_20221107-085932__01.jpg
 

Ya’akov

Joined Jan 27, 2019
6,856
The meter you picture seems to have an inductive sensor, effectively the same as used on an AC only clamp meter. You would have to use one with a hall effect sensor or a shunt for DC. Also, mixing AC and DC is probably not going to make the meter happy.

Even if you got it to operate it probably wouldn’t provide good numbers.
 

Audioguru again

Joined Oct 21, 2019
5,416
What power do you want to measure?
1) Continuous low distortion output power? But music and speech have an average power of 1/10th to 1/5th of the continuous low distortion output power. The level varies all the time.
2) Peak instantaneous power? It is simply double the real continuous low distortion output power.
3) Do you want to include the power produced by the amplifiers making heat?
 

MisterBill2

Joined Jan 23, 2018
13,778
What is the intended purpose of that " a DIY car audio real time voltage/ wattage meter... "???
The normal method used for measuring audio amplifier output power is by measuring the voltage across an accurately known high wattage rated resistor. It works very well if an accurate voltmeter is used.
Measuring the DC input current to an amplifier will never give an accurate indication of the output power unless the amplifier is 100% efficient, which is not likely.
And measuring real time power gives me the impression that attention would not be focused on driving, which I do not support.

So now you know how to accurately measure audio amplifier output power. An ammeter is not involved, only a voltmeter and a resistor.
 

crutschow

Joined Mar 14, 2008
31,123
Measuring the DC input current to an amplifier will never give an accurate indication of the output power unless the amplifier is 100% efficient, which is not likely.
I would be within probably 10% if the amp is Class D, which it could be for the (possibly huge) subwoofer of a car audio system.
 

Audioguru again

Joined Oct 21, 2019
5,416
"Real Time" audio system voltage/wattage is a VU meter that shows momentary voltage/power or it has a peak detector that shows peak voltage/power.

The output power from most car audio systems is constantly varying. Unless the audio is playing the continuous synthesized scream from a fake huge 12 cylinder or fake jet engine.
 
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