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Sub install - Need 12 volt sense or cap with auto on from charge voltage....

Discussion in 'Gen II Prius Audio and Electronics' started by sorka, Dec 4, 2011.

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  1. sorka

    sorka Active Member

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    Wordy title :)

    I'm installing a bazooka 10" sub in back. Clearly I'm going to need a cap given the size of the accessory battery. Looking for 1 to 2 farads.

    The thing is I do NOT want the sub powered unless the car is in powered on mode. i.e. when I pull up and turn the car off, I want the sub to turn on even if I still have the stock stereo going. I've prewired the the speaker level inputs from the JBL amp under the passenger seat. But I need a 12 volt wire that is only powered when the car is in powered on mode as a sense wire to the sub.

    Another alternative would be a cap that doesn't pass voltage out or charge unless it senses charge voltage, i.e. 13.5+ volts vs 12.5 volts for a fully charged but not currently charging battery.

    Also, a lot of the caps have voltage displays which obviously can't be powered on when the car is off or it will drain the battery, so the cap either needs to also have a sense input or needs to deactivate itself if it doesn't sense charging level voltage.

    I'd really like to avoid running a wire from under the front dash if possible but will if necessary. It would be cool if the amp had a 12 volt wire that only get's power when in powered on mode or if there's another wire in the back. There's a harness with lots of wire's coming off the 12 volt battery. Perhaps one of them?
  2. sorka

    sorka Active Member

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    Oh, and any ideas for the cap location? I really don't want it visible so was think of placing it under the cargo area, but would need some sort of shielded quick connect/disconect so I could remove it when I need to pull the tray out.
  3. sorka

    sorka Active Member

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    Well, scratch the cap idea for now. I'm assuming the inverter will pump out more than enough juice to smooth out any instaneous draws, so I'll try it first without one. If my interior lights don't dim to the beat, then I won't need a cap.

    Just need a 12 volt wire that is only on in power up mode.
  4. KK6PD

    KK6PD _ . _ . / _ _ . _

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    Try the cig lighter, they turn off when the car is powered down. If you have the JBL system, there is a sense wire going to the Amp. Caps are not necessary, good luck!
  5. sorka

    sorka Active Member

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    Let me rephrase for clarity. I need a 12v line that is powered *ONLY* in powered on mode, not accessory mode. The power ports are powered when the car is in accessory mode or above. I don't want to run the sub unless the inverter is charging the battery.
  6. jpadc

    jpadc Type before I think too often

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    I don't know of any such line that is powered only when the car is on. Clearly there have to be some including one or more that open relays for the HV battery. Not sure you want to tap into those, however.

    Many of us have one of these units installed

    Automatic Power Off Switch

    that we use to make sure an inverter only runs in power on mode, not accessory mode. Not a cheap option, but will accomplish your goal. It also can be connected directly to the battery in the back so you do not have to run a 12 volt line up to the front of the car.
  7. V8Cobrakid

    V8Cobrakid Green Handyman

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    a cap in a prius... for a 10" sub... lol...

    automatic power off switch... good idea... i'd say it's worth the money (i'll save up for one... i can find 101 uses for that!)
  8. sorka

    sorka Active Member

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    Thanks! That should do the trick. I guess I'd set it for 13.05 volts and 0 minute delay.
  9. sorka

    sorka Active Member

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    Yea, silly in a prius given the inverter provides about 3x the instantaneous draw of a typical truck alternator.

    I've had this sub and a 4 channel amp in another car which has a combined 1000w RMS and with the right music, the lights would dim when at idle.

    I check the prius last night my graphing Fluke meter and the voltage never varried by more than a few hundreths with big base notes so any cap would be a waste of money.
  10. V8Cobrakid

    V8Cobrakid Green Handyman

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    when i had my sub hooked up... (i wasn't very informative last night.. i appologize)... i used to be able to turn it up to the point where you couldn't see traffic out of the rear view or the side mirrors. you could see traffic.. but it was dancing to the music ;)

    too much testing and too much joy riding ,while testing, eventually ripped that sub apart... oops... then i patched it... eventually my amp shorted. there wasn't enough cooling around the amp. so.... the lesson is (and i've seen a lot of rigs on here) is to add a 12v fan or something to the amp or compartment it's in. some people mount it in the lower compartment (as i did)... it gets warm down there...
  11. R-P

    R-P Member

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    Newby alert...

    The inverter is switched on via the CAN-bus I guess? No supply-line to be stolen from there?

    I do remember making a unit (from an electronics magazine) that switches OFF if the battery voltage drops under 11.8V, and this could be reworked to switch off at <13V and on >13.5V, but this was probably a decade ago and the chip used was already hard to come by back then...
    That 60$ unit doesn't sound that bad compared to the work done and the components used in my 'battery drain preventer'.

    I do wonder about the comment about the inverter being able to supply more than a truck alternator though. I got warned today by a Toyota hybrid master tech not to plan too much amplifiers due to this inverter. Then again, this is on another forum where many run several kW's of amplifiers:cool: so maybe he mistook me for one of them. I asked what kind of amperage I could siphon without undermining the normal workings of the car but haven't heard back from him yet.

    I've been a Prius owner for 12 hours now, so don't be too harsh on me with regards to reading first instead of posting ;)
  12. V8Cobrakid

    V8Cobrakid Green Handyman

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    maybe a cap would reduce possible damage to the inverter... long term.

    i've been able to pull a constant 950 watts or so.. but that's it. the fuse for that line is rated at 100amps. everything rides on it though.. (about 300watts of computers).. if you pull too much, it "dips out"... the car still works fine.. it's just that 12v line. you'll see the mfd reboot and such. do that too many times and you'll mess something up (or so people warn... i've done it a lot with use of my inverter)

    how many watts do you plan on producing? rms and peak
  13. KK6PD

    KK6PD _ . _ . / _ _ . _

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    At this point I can only add one word.

    Tinnitus!

    It's a bitch!
  14. R-P

    R-P Member

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    I have 3 amps of 500Wrms and one of 600Wrms: Helix H400's and H1000, but not all will be used at the lowest impedance, so lets say 1000Wrms. But my aim is SQ rather than SPL, so headroom is more important than actually turning up those 1000W completely.
    But haven't looked into the speakersizes, so no idea whether my Dynaudio kit would fit (MW170's for front, active and MW150's in the back, passive, for the Volvo I was going for a centerspeaker in the navigation-cavity, but I'll drop that in the Prius, tweeters: whatever I can get my hands on (I have Rainbow's for in car use, but also home Elac's and Dynaudio's), maybe even (temporarily) re-use the Prius ones if they are any good.).

    No rush... Just interested in the theory behind it all.
  15. V8Cobrakid

    V8Cobrakid Green Handyman

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    ok... those details will be useful.

    what head unit do you plan to use?
  16. R-P

    R-P Member

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    May buy another AVX33 (JVC) so the front will also fit in my Volvo ;)

    Have been looking at Helix PP50 on Ebay, as they seem to be a neat piece of kit (DSP, 5 channel amplifier that hooks up after the OEM headunit and you can download EQ settings for very many cars: I guess they measure different cars for e.g. their cabingain and thus make a vehicle specific EQ-file that you can download on the net and upload into the amp via USB :D)
    I liked it for it's possibilities, but I already had the amps for the Volvo, the subchannel isn't powerful enough for my Aliante and I didn't want to integrate it with the OEM radio, so there really was no need to covet it. Now there is...;)

    But if and when that time arrives, I think it best to make a new thread about it instead of stealing another mans thread. :eek:
  17. Calle

    Calle New Member

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    Absolutely incorrect. You certainly do need a cap in a Prius for even SMALL sub setups. The other thing is that the prius converter will not provide 3x what a truck alternator will. It will provide about the same- 100amps or so. You said that you monitored the DC/DC voltage during bass beats and it did not vary. That is great, but unfortunately has nothing to do with current. If your sub is hitting, and the lights are dimming, that means that your power source is unable to provide enough instantaneous power to run the load at 100% irregardless of the voltage remaining steady. I experienced this in my Prius prior to installing a capacitor. The Prius uses a switching DC/DC converter to power the 12V system and it is not capable of providing a high wattage sub with enough juice in certain conditions. It does not act the same way an alternator does nor does it act like a stereo would if it were run directly from the battery..A battery is essentially a giant capacitor, however it is of no help in acting like one in car audio because your alternator-or in this case your converter-is running at a higher voltage which means instead of the battery handing out power to your components and potentially acting like a cap, it is instead being charged. The OP said he wanted a cap because the Prius battery was so small. It wouldnt matter if it were a big battery because it cannot function as a cap if there is a power supply running in parallel with it at 14V. So, just because the voltage stayed steady, the current demands are not being met by the prius converter, and the only way to combat this is by installing a capacitor. As far as sizing, all of the general guidelines that the car audio manufacturers suggest are way off as it pertains to capacitor sizing. As a general rule, you would need about 3,500uF - 6,000uF per amp (assuming we are working in this voltage range). That being said, for a 1000w RMS system, a 248,000uF to 426,000uF capacitor will suffice, or you can cut those values in half and use two smaller caps. No need to buy an expensive car audio brand. Goto Mouser.com and search for aluminum electrolytic caps they have thousands in stock. (248,000uF = 0.248 farads)

    The OP also said he wanted a way to only have the system on when the car is in READY mode. This can easily be achieved by finding a relay at mouser.com that activates at ~13v. All you would need to do is take any power line, run it into the relay, and on the other side you have your amp remote wire. When the car is in accy mode, the relay will not have activated but once the car goes into READY mode and the converter kicks on it will activate because the voltage req will have been met. Or you can use a standard Auto Zone 12V relay in the same manner but with a resistor in parallel so you slightly lower the voltage it sees just enough to where it will pop when the converter punchs on.
  18. Calle

    Calle New Member

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    Sounds really cool, but you have a limitation and that is the Prius DC/DC converter....It can only provide 100 amps before the fusible link blows and it will not provide you with 14v at higher loads so your effective usable wattage is about 1200 watts I'd say...Your other problem is that those 1200w have to be shared with things other than your stereo such as all of the electronics, the blower motor, headlights, brake accumlator, windshield wipers. Driving at night w/your lights on coupled with the AC or heater on low and the Prius 12v base load, you are talking about 30 amps already being used just to get yourself down the road. That leaves you with 70 amps or about 900 watts and at those numbers you are pushing the envelope. The only way to run a 1500w audio system in a Prius would be to have your amplifiers hooked up to seperate 12V batteries, or some other external power source such as a load sharing DC/DC switching or linear converter...Food for though.
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