Can I tap 12volts off the Gen 3 Prius battery for big stereo?

nope, the battery is way too small

 

get tech stream from amazon and a compatible windows laptop.

look through audio threads for detailed advice on large stereos. most end up adding a second battery.

apparently, you're pulling more amps than it is charging? not sure.

 

would be interesting to measure the output vs the input with everything pounding

 

Electric power is not just the Volts. It's the Volts times the Amps. You'll see 14.5V coming out of the inverter into the battery, but how many net amps are you pumping in? That would be amps from the inverter minus amps from your stereo. If the number is negative (as I suspect it is), then no battery will be big enough because your charging is not keeping up with your discharging. It's like if you start with $1000 in the bank and get paid $100 per week but are spending $150 per week you will run out of money in the bank at some point. If you start with $2000 in the bank and nothing else changes you will still run out of money, only a little later.

 

A car stereo that pulls 90 amps.

 

Yeah! Well, some of us really are hard of hearing, I guess. For me 15 Watts per channel is more than enough. That'll be 60 Watts (2 front, 2 rear) at 12V is 5 Amps. Even if we double to 30 Watts per channel it's still under what a cigarette lighter socket provides and should destroy most people's eardrums if the amplifier is a good one.

 

If the audio system is producing 60W RMS audio output, the system will require ~150W of DC power input. At best, the output audio amp is 50% efficient... and then it is necessary to power other components besides the output amp.

The OP is quite a bit off in thinking that the car only needs 25A total, but he could measure the required current using a clamp DC ammeter. For example if exterior halogen lights are on that will take around 10A. If the heater is on that will take 40A for the PTC heater elements plus more current to run the fan. We haven’t even discussed the current to run the many ECUs which probably is another 20A or more.

 

I use a Alpine V9 5 channel class D amp. 100 by 4 and 500 by 1. The Prius charging system doesn't keep up so I just trickle charge it once or twice a week. But least this amp is more efficient at what it draws to what it puts out.

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Yes, I was thinking of a Class AB amplifier. You are right that Class D is much more efficient, 85% or so.

 

The Alpines sound excellent, are very small foot print. I remember when I swapped out my old Alpine class AB for the first series PDX. Midrange sound quality came to life and amp was half the size.

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My amp processor and changer, crossovers.

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Certainly not practical with the stock equipment.

The inverter that keeps the 12 V battery charged and runs all of the 12 V equipment was NOT designed for loads anywhere near what you are putting on the system.

And yes, it is quite common for a power supply to maintain it's rated voltage under a heavy load......as the current available goes down and DOWN as the load goes up. Once you hit the rated wattage, something has to give.

 

You can't do analog (audio) with a class D amp.

 

Somebody needs to tell audiodave.

 

Actually, you can:
Design and analysis of a basic class D amplifier | EE Times
http://www.irf.com/product-info/audio/classdtutorial606.pdf
Class-D amplifier - Wikipedia

The Class D design is more complex than Classes A, AB or B, but at high power levels, the efficiency savings makes the cost of the extra components worthwhile.

 

It's analog in the end. Alpine been using this design for over 10 years with great success. I'm friends with the guy who was apart of it's design.
Only way they'd squeeze that kinda power out of such a small package. Alpine PDX-F9.

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