Adding another 12v

While I always recommend keeping your Prius in Ready if you use any electronics, be sure that if you add a second battery inside the passenger compartment, that it also be AGM and externally vented to keep (you and) your passengers safe.

If you are mounting it under the hood, that kinetik hc600 seems fine.

 

Actually it is an AGM Lead Acid battery, not a dry cell. I have no trouble, so long as you are not having passengers in the same compartment as the battery, it would be irresponsible to put others at that risk.

Kinetik HC600 (KHC600) 12V High Current Car Audio Power Cell

All the reviews on that page mention putting it in the trunk or under the hood, not in the passenger compartment. The Prius has no trunk. Just keep it in READY, then you have a huge High Voltage battery powering your sound system.

 

While I have never upgraded the radio in any car I ever owned, I do find that the Gen 1 Prius could power 13.75 V., 71-74 A. ~ 1 kW, I seem to recall that my Gen 2 (like yours) had a 100Amp fuse from the Inverter, so I think you are about twice what a Prius will produce. Best of luck.

 

Amps times volts equals watts
74 A * 13.75 v = 1017.5 watts from a Gen 1
100A * 13.75 v = 1375 watts in a Gen 2 (you do not really want to get this close to the fuse blowing)

On a Prius, it is all DC, so I do not think RMS has anything to do with it.

Root mean square - Wikipedia, the free encyclopedia (warning, chock full of math)

 

...waaaaaaait... so if I'm planning to run a smaller 1500 rms system...this is something I should pay more close attention to?? I don't want to ruin my 12v...should I look into adding this 2nd 12v as well??

Two of these Kinetik HC600 would be the same seem to be a better deal than a Optima Yellow top.

 

Just remember that an amplifier is not 100% efficient. An AB might be 30% efficient while a class D might be 90%. So to get 1000W out, you need 1000/0.9 = 1111W input at 90% efficiency. 3333W at 30% efficiency.

The 100A fuse means the inverter can give you about 1300W to power your amp. You will 100% need to run a new wire from the inverter to the back. If you were to power it from the high voltage battery, you would have about 28KW (28000KW) available to you.
The power output versus input however assumes you are running in a DC signal to the amplifier and the battery is dead. Then you could only pull 1300W. And you wouldn't hear anything because DC makes no pressure changes in air. Send in an audio signal and you are looking at a very small fraction of the time the signal is on, so a very small fraction of the time the output is at high power. We are talking nano-seconds and milliseconds. Other times there is 0 current draw (well, plus quiescent to run the amp itself which should only be a few tens of milliamps).

The whole point in upgrading the battery is so that the battery can take the abuse and act as a reservoir. It is like having a garden hose filling up a small kiddie pool. The kiddie pool gets mostly full and then the battery is fully charged. Stick in a kid or dog or something else and have them start splashing. The pool will lose water when they go crazy, but the average input of the garden hose will keep the pool full.

The Prius has an advantage in that it can supply that 1300W anytime. Idle, in park, driving down the road, wherever. In a normal car you have an alternator. This generates power by rotating a shaft through magnetic fields. The intensity of the output current is proportional to the magnitude of the magnetic field and the rotation of the shaft. So when you are at idle, an average car will produce about 20A to 30A of power (~300W). When you are running in a low gear down a highway at a high speed, you will probably be producing the rated output of 100A to 150A or something like that. The point of the battery is again to take the hugely wavering output and in average it is enough to power everything.

So you will have no problem playing 2000W, 4000W or more audio through the Prius' electrical. You will not be able to play those competition sound tones. Not the music ones, the ones where just one tone is emitted and measured. The whole purpose is to test the actual output of the system for minutes. But... none of those cars can either continuously. They have so many batteries that the thousands of watts are pulled from the batteries and they slowly die. After a few more minutes the batteries would be dead and they would be stuck with a 30A to 100A alternator output unable to charge the batteries and power the system.

Now that the math is out of the way, I can say that the only reason for doing this is to show it off to people ignorant of math, physics, and electronics. Which is the majority of car shows. If that is the goal, then go for it. Shiny things bring in the people. I know it, I have had a car featured at SEMA.

When you talk with people, it is about 70db which is 0.1mW. That's 0.0001W. A standard headunit is 55W which on the standard sound analogy scale is louder than a machine gun but just a bit quieter than an average rock concert around 138db. A siren on the top of a police car or something is closer to 150db which is 1000W. Try being trapped in a small room with a police siren blaring at full blast. Your ears will explode. A jet engine is 10000W and 160db.

So the 2000W system will look cool. It will sound nice at normal volumes if you buy good equipment. And it will produce 1300W continuous forever (rock concert), a police siren for an hour or two with a big battery, and a jet engine for a few songs (if your speakers cone doesn't separate and/or melt due to friction).

 

I think it is worse than you describe, as a Gen 2 Prius only charges the 12 volt battery at 13.8 volts. Patrick Wong (if I remember right) estimates that a full charge of the Prius 12 volt battery takes 8 hours, if they start adding more 12 volt batteries, they need another 8 hours charging for each one. So what ever noise they are making, they will need to leave their car on for 16 hours to make it again.

Sure makes the stock unit sound attractive.

 

It is a 36Ah battery for those with the SKS system in the GenII. It would take 1 hour at 500W to charge it from 0% to 100% if it was 100% efficient. If we assume 50% efficient charging, 1300W available would still charge it in an hour.

However, you can't just dump charge into a battery. You would have to raise the input voltage really high to get it to charge at that rate. You can charge an SLA at 16v or 18v to make it charge faster. You are supplying a constant voltage and the battery is drawing the current it can to charge it. It will not draw all the current available, only what it can draw. Same reason why everything you plug into your house's electrical outlet doesn't explode or melt instantly. The power company can give you megawatts of power, but it is a constant voltage and you draw the current you need to power your device. Not the current available on the grid. That would be a short.

It takes 8-16 hours to charge a SLA, no matter what. You can hook 10 of them up in parallel, and it would still take 8-16 hours to charge. Hook 100 of them in parallel and it still takes 8-16 hours to charge. As long as the charging current is less than 100A, it will work.

But that is besides the point. The only time the stereo will be above 1300W where the battery is no longer being charged by the inverter but then being discharged is when it is louder than a police siren constantly. Music is a frequency and amplitude modulation on the electric input. Even in a really loud song, the loud parts (like a booming drum, or scream) are not common. And even if the whole "song" is a big drum with screaming, there is modulation in the frequency/tones and then the duty cycle of them. For simplicity lets say a 50% duty cycle tone. At 2000W, 90% efficient, we are looking at 2200W input power. 1300W comes from the HV battery through the inverter. 700W comes from the battery. But it is only 50% duty, so really it is 1100W average. For 50% of the time, it will be drawing 2200W of power. 1300W will come from the HV battery, 700W from the 12v battery. Then it is off. All 1300W could potentially be used to charge battery or other energy storage devices. Then on and 700W draw from the 12v, then off and charging. This is why people use capacitors near the heavy hitters because they charge as fast as they can. An unlimited capacitor can draw hundreds of amps in nanoseconds. Usually they fuse and limit, but you can charge a cap faster than a battery. So 700W @ 13.8v is about 50A. You need that for 50% of a 48KHz signal, or 50% of 20uS (microseconds), equalling 10uS. So your capacitor would have to be able to stay in the 13.8v to 12v zone supplying 50A to 60A continuously for 10uS, then be able to be recharged in the dead time of 10uS. Common car audio amps are 1Farad which is more than enough for that small of a signal. Even at 90% average duty of 18uS discharge it is fine.

So the battery will not be depleted fully if done carefully. If done improperly and loud music is listened to for prolonged periods stressing the battery banks and not the inverter, then more idle driving time may be needed. But a 2000W system with a human inside the vehicle will not be able to kill the Prius' system.

 

...whew. Good short informational read. So, its over kill to use the Prius 12v plus the Kinetik HC600 on the systems that I will be using w/ 1500RMS (non-competitive system - Just (2) class D amps - (1) 2-channel for the 2 subs and (1) 4-channel for the components). I may be way off beat from what you read, but are you saying with the current Prius 12v and a decent Capacitor, I should be just fine?

 

I haven't had a chance to read all the posts here (or that much interest either) but 2k1Toaster's posts reminds me about "stereo drag racing" (CNN.com - A car stereo that can kill you? Cool - Jul. 2, 2003). Mythbusters did an ep where they took a different approach as I don't think they had the $ or expertise to compete via electronics.

See Annotated Mythbusters: Episode 58: Shattering Subwoofers and Rough Road Driving for a description. They built a 51" diesel powered speaker. The ep was pretty funny, like most.

 

Something not covered here as far as I can see is that the Prius battery of whatever make, OEM, Optima or other are rated with an amp/hr capacity typically in the Prius 35 amp/hr this is at a given rate of discharge in hrs usually 20 hrs this equates to a discharge rate of 1.75 amps. If the battery is discharged at 50 amps rate it will not have a 35 amp/hr capacity, it will probably be more like 20 amp/hr capacity depending on the type of battery.

 

For those looking for somewhere to mount an extra 12 volt battery there is for the none US versions an ideal place. This is inside the front bumper on the transmission side of the car.

In the US version this space is used for the hot water thermos, but in all other versions is empty and there is enough room for a 100 amp/hr agm sealed battery if you wish to go that high.

The under hood jump point "the ideal place to connect" is within 18 inches of this space.