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Old 26th October 2009, 10:16 PM   #1
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Default Class D car Amp and Computer Powersupply?

Ok so basically.. I use the 12v+ @ 60A Rail on my computer PSU to my car amp, It works great, I added all the 12v+ and ground/negatives and my PSU has alot of protection circuits so nothing for me to worry about, anyway I connected the 12v+ Senseline and from 12.00v on my multimeter, it now reads 12.48v which is awesome, Ive had it like this for a few weeks and I've seemed to notice whenever I switch on my psu after an hour or longer rest, the voltage comes up as 12.48v then at idling (No music playing) it slowly drops/flutuates down to 12.44v and stay there, If I bump before it drops down to 12.44v, it drops down abit quicker, My question is concerning why is this happening? I kinda thought maybe as the amplifier warms up the load on the sense line is decreased and the PSU drops the load abit? Oh and one more thing, Since I connected this senseline im getting way less voltage drop and im loving it, anyone care to explain to a newbie what this actually does?

EDIT: Another question... Don't really need this answering if your sick and tired of it, but yeah I was thinking of buying a 1-2F Capacitor and connecting that into my rig, Capacitors have extremely low ESR and will help me when my amplifier requests instantanous power and lessen voltage drop.. but then again, My PSU is not a car chassis, Its pretty much less then a foot away in length to my amplifier with approx 7gauge wiring (if you add all those 18AWG wires up), Did I answer this question myself to some extent?

Thanks!

Last edited by icecoolwas; 26th October 2009 at 10:25 PM.
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Old 26th October 2009, 10:44 PM   #2
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Both questions seem more relevant to the power supply forum than the class D.

Anyways, the second question is easy to answer ... it won't make the slightest difference soundwise if you have giant cap or no cap between the PSU and the car amp since the amp is already running on a switchmode supply internally and is impervious to voltage drops on the supply. However, a very large cap between the amp and the PSU may overload your PSU during start ups, so I'd recommend not using one.
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Old 27th October 2009, 02:54 AM   #3
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The sense line is meant to compensate for the voltage drop along the wire(s). Since all wires have some resistance (not a perfect conductor) there will be some voltage dropped across it,the heavier the load,the more voltage is 'lost'. If the sense wire were connected at the 'near' end (at the PSU) it would only compensate for the internal wiring losses (pcb traces,etc.) and you just have to live with the bit of loss along the wires. If you connect it at the 'far' end(the load) it will compensate for the loss along the wires by increasing the voltage output,to maintain a steady voltage at the sense point,effectively canceling out the voltage loss along the wires.
Clear as mud?
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Old 27th October 2009, 10:05 AM   #4
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Yep Yep, great answer.. now only need to figure out why its flutuating after a cold-start.

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Originally Posted by DigitalJunkie View Post
The sense line is meant to compensate for the voltage drop along the wire(s). Since all wires have some resistance (not a perfect conductor) there will be some voltage dropped across it,the heavier the load,the more voltage is 'lost'. If the sense wire were connected at the 'near' end (at the PSU) it would only compensate for the internal wiring losses (pcb traces,etc.) and you just have to live with the bit of loss along the wires. If you connect it at the 'far' end(the load) it will compensate for the loss along the wires by increasing the voltage output,to maintain a steady voltage at the sense point,effectively canceling out the voltage loss along the wires.
Clear as mud?
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