Adding an amp on a Prius: must it have voltage regulation?

[garypear]

Will adding a medium priced amp, hooked up directly to the 12v battery, cause the sound level to change, even slightly, in response to ICE kicking in/out and/or other changes in the Prius drive mode?

In discussing adding an amplifier, the install shop suggested it might be important that the amp I use have the ability to maintain a constant output (wattage? voltage?) in response to varying voltage the amp might receive. Keep in mind the amp will be hooked up DIRECTLY to the 12v battery's positive terminal.

I responded that I'd have thought that pretty much any decent amp would have that ability, and he said no.

After considering it, I hypothesized that the reason the average amp need not be able to do that is in most cars the amp is always receiving either a constant 12v (running off the battery when the car is off) or a constant 14.4v (running off the alternator when the car is on).

Question 1: How constant is the voltage running through the Prius 12v system? Does it jump up to 14.4v whenever the car is running? Does the voltage change back and forth when the ICE kicks in and out, etc.?

Question 2: Assuming the answer to question 1 is no, the voltage is not constant, and I choose an amp that does NOT have the ability to maintain a constant output in response to varying voltages, what audio problems/results might be encountered? According to a "level 2" tech support guy in Kenwood's car audio dept., it would only be a problem if the wattage demands of the speakers being powered were high enough, but he didn't have the time to fully explain why that's the case.

It occurred to me that the fact that the factory radio's sound level doesn't change is not the final answer to the question because a proper install of an amp requires power be taken directly from the battery. Even if the Prius designers incorporated a voltage consistency fix farther down the electrical stream, the voltage directly out of the 12v battery might not be constant.

[bobc]

Gary,

When I have a chance (if someone doesn't post it first), I'll check out the voltage readings over the course of the ICE turning on and off.

I know nill about this stuff but isn't the draw that the amp imparts on the battery fairly low unless the stereo is really cranked up loud? I can do a test on my newly installed amp and see.

Also, just to throw this out, when in the store purchasing my new speakers and amp, I noticed that Monster sells a capacitor to put in line between the battery and the amp to assist when the amp requires peak power. Would this help?

To answer your question in bold at the beginning of your post, I haven't noticed any change in sound level in my system but I'll listen closer to it in over the next couple of days. I do play my system relatively low on the volume scale. BTW, my amp is hooked up directly to the battery...

Cheers,
-bob

[garypear]

Hi Bob,

Thanks, please let me know what you found out. Also, can you tell me how you or your installer dealt with the following adding an amp related issues?

1. 12v amp on? From where did you hook that up to the amp.
2. Touchscreen beeps: Did the volume of yours increase after the amp was installed? If not, was it because special care was taken to remedy/prevent that result?

Thanks again.

Gary

[ken1784]

Question 1: How constant is the voltage running through the Prius 12v system? Does it jump up to 14.4v whenever the car is running? Does the voltage change back and forth when the ICE kicks in and out, etc.?

Following is the spec about DC-DC converter from Toyota Tech Manual.

input voltage: 168-300V
output voltage: 14V
output amp.: 100A max

The output voltage is very consistent and no relation with ICE running in READY mode.
In ACC or IG-ON mode, the voltage is raw 12V and battery never been charged.

Regards,
Ken@Japan

[bobc]

Hi again Gary,

I installed the system myself.

The remote turn on for the amp comes from tying into the wire that supplies power to the OEM head unit when the power button is pressed on(ACC mode). I was following your thread earlier about tying into the antenna amp and from that, this seemed to be the best solution.

Yes, my beep volume did increase. There was an earlier post in this forum about that happening. One poster sugggested that the owner go back to the installer and they could easily remedy this by altering the freq. cutoff (I think) on the amp. No specifics were given, tho. The person did this and it took care of the loud beeps. I'll have to post this question so someone can fill me in on what I need to tweak.

-bob

[garypear]

Hi Ken,

Thanks for that info. Sounds promising regarding my concern but when is it 14v and when is it 12v?

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Hi Bob,

Sounds like a winning answer regarding the 12v amp on problem.

Is that the line that is actually providing power to the radio? I know for an amp it's two separate hookups: a power line that is led to it directly from the battery and the 12v on which (ideally) is led to it from the head unit.

Does the decision to use that line make it necessary to pull the radio out when you otherwise wouldn't have to to add an amp (or even XM?) Is it obvious which line that is?

Please keep us posted regarding solving the beep increase problem. My concern with an amp frequency tweak: would that solution inhibit using those settings on the amp to send different signals to different types of speakers (such as a subwoofer, front tweeters?)

Thanks.

[DanMan32]

You would have more power fluctuations caused by too much resistance in the feed wires from your power source to your amp, than at the power source itself. The capacitors or secondary batteries are usually to accomodate the amp's large but fluctuating draws than the power source fluctuation.

Ken, I'd like to know where you got your info. The DC/DC output is fused at 100A, and it seems Toyota providea aprox. 20% margin between max draw and fuse value. For example, outlet is rated 120 watts or 10A, yet it has a 15A fuse. Typically alternators output 80A, and I have seen that figure someplaces, though I can't remember where.

ICE wouldn't be a factor, as it is started using the HV battery, as the other motor is. There is no alternator providing 12V charge current like conventional cars, it is done in the inverter using the HV battery coverted down to 12V using a switching power supply cirucuit.

[ken1784]

Hi Ken,

Thanks for that info. Sounds promising regarding my concern but when is it 14v and when is it 12v?

READY: 14V
ACC: 12V
IG-ON: 12V

Regards,
Ken@Japan

[ken1784]

Ken, I'd like to know where you got your info. The DC/DC output is fused at 100A, and it seems Toyota providea aprox. 20% margin between max draw and fuse value.

The spec is came from Toyota Tech Manual CDROM for NHW-20 Prius (P/N 7A04700).
It contains Theory of Operation, Service info and wiring. It's all written in Japanese. :-)

Again, the output spec of the DC-DC converter is 100A max. no matter how much rated fuse is installed.

Regards,
Ken@Japan

[bobc]

Gary,

Here's my voltage numbers which equate to Ken's. These are from putting the meter right on the battery:

Car is off: 12.4v
in ACC mode: 12.4v
Ig-on: 12.4v
Ready mode, ICE off: 14.0v
ICE on: 14.0v

These are one time readings, so who knows what happens over the course of a daily drive but as per Danman's comments, I would suspect that the voltage is pretty well regulated and maintained. I've intently listened to the stereo system that last couple of days and there's no fluctuations/degradation from potential voltage fluctuations, which was your initial concern.

Also, with regards to draw on the battery from the amp, I cranked my stereo up to 65 and the voltage reading didn't budge From an electrical engineering friend, he said that car amps really don't draw much unless one is playing at ear splitting levels or driving huge subwoofers. He went on to admonish me about getting sucked into the marketing scheme that one has to upgrade the OEM speaker wire because they can't handle the load and using 8 gauge wire for the amp... Something about Ohm's law and how little wattage is really going through these wires...

As for your other questions, the power for the amp is coming directly from the battery. As Danman and my friend stated, this provides for clean power to the amp and is not affected by other loads turning on and off if the amp was powered from elsewhere in the car.

The turn on for the amp comes from the ACC ON wire heading into the OEM head. Yes, the radio really does have to be taken out, as per Jon at PriusXM's instructions, to get to this wire. I'm sure someone else could easily find this wire elsewhere inside the car (OK, it's at Junction Connector J19) but since I had the radio out, it was already accessible. It's the only Gray wire coming out of the OEM radio (Standard radio)...

As for the louder beeps, again from my friend, any tweaking of the frequencies at the amplifier will degrade the sounds coming from the speakers. More on that later....

Hope this helps!

Cheers,

-bob