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Registered Member #1822
Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300
I recently modified a PC powersupply to run a subwoofer and even though it has built in overcurrent protection I would like to know when it is running over 90% capacity so that I know when to turn it back a bit. My idea was quite simply to measure the voltage drop across a very small resistor but, the drop would be very low and I am not sure how I could measure that with any accuracy. Can anybody point me in the right direction?
Registered Member #3989
Joined: Thu Jul 07 2011, 05:10PM
Location: In a van down by the river.
Posts: 52
The peaks of the bass coming from the speaker will cause a bunch of current spikes with the bass notes and drum beats and make it hard to read with an ammeter and resistor because a heavy duty ammeter is going to have such a slow response. In my estimation of what you are doing I would recomend using a small 12v battery in parallel with the load (preferably of the sealed lead acid type but a lawn tractor battery would probably be ok too) to buffer the power supply, this would have the effect of averaging or smoothing the load on the supply and make it easier to accuratly read the ps output level with an ammeter. You then put your ammeter in series between the battery and power supply to read the current going into the battery. This will make your amp and psu last longer and run cooler. It will also improve the sound (and filter noise) because the battery is a giant capacitor from which to draw instantaneos peak power during the bass thumps as well. This is the method I use, as I often use car amplifiers inside my house. I have an automotive style ammeter that can directly read up to 250 amps (it's for testing starters, my power supply can only make about 75 amps).
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Austin the Ozone wrote ... ...I would recomend using a small 12v battery in parallel with the load (preferably of the sealed lead acid type but a lawn tractor battery would probably be ok too) to buffer the power supply, ... It will also improve the sound (and filter noise) because the battery is a giant capacitor from which to draw instantaneos peak power during the bass thumps as well.
That's also why ultracapacitors in the 1-5 farad range are popular accessories for loud car stereos. In cases where at moments of peak demand, the supply voltage would otherwise sag due to resistance of wires between car battery and the amplifier.
For metering the DC current, how 'bout a conventional current shunt (say, 50 mV at 50 A ) with appropriate d'Arsonval meter movement? For example:
You're right, you can also use a known length of copper wire as the current-sensing shunt.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Rather than a current-limit sensor, consider a distortion sensor,
If you compare the output (via a resistive divider) of your PA with it's input then the difference will be the distortion. (Your PA may be inverting or non-inverting, slightly different circuitry) There's always a little distortion, ignore it,
when the audio clips or gets severely distorted the comparator will give a large output which could power a led for example.
P.S. a black-box that samples a PA input and output with variable feedback (potentiometer) and inv/non-inv selection could be used to test all your amplifiers.
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Over Current Indicator
