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Aftermarket Sub-woofer Amplifier Installation using DC-DC +12v Power Source

Discussion in 'Model 3: Interior & Exterior' started by Jamie Sibley, Apr 18, 2019.

  1. Jamie Sibley

    Jamie Sibley New Member

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    I have identified the cause of the "Cannot Maintain Vehicle Power" error when installing aftermarket amplifiers and drawing power from the CD-CD terminal under the rear seat. The cause is the DC-DC converter tripping when first powering on and trying to charge up the large input capacitors present inside the amplifiers. The large capacitance causes a high current spike on the converter, immediately tripping a current fault= and preventing it from powering on. Since the dc-dc converter turns on a few times over night to keep the 12v battery maintained, if it is unable to start up, the 12v battery discharges, giving the "Cannot Maintain Vehicle Power" error. I was able to trigger this error much more often by using an aftermarket 1 farad capacitor in parallel with my amplifier, vs without the capacitor, giving weight to the argument that the capacitance is the cause of the error. Using a cheap amplifier with a small input capacitor will probably avoid tripping the dc-dc converter, but any high-quality amplifiers, or stiffening capacitors will likely cause a lot of problems.

    The solution to this is to use the attached simple circuit when drawing power from the DC-DC converter. The circuit works by limiting the inrush current to 12 amps when the DC-DC converter comes online by placing a 1 ohm resistor inline with the amplifier. However, this resistor would quickly overheat when the amplifier was in use, so a bypass relay is powered from the accessory 12V line coming from VC-Left. The car turns on the acc signal about 3 seconds after powering up the DC-DC converter, giving the amplifiers plenty of time to charge the input capacitors.

    The only items needed are a 12v 30A automotive relay (amazon-link), and an approximately 1 ohm ignition resistor (amazon-link). If you are running a very high powered amplifier(s) , you may want to use 2 x 30A relays in parallel to avoid damaging a single relay.

    I have am currently using this circuit in my Model 3, with a 800w Kenwood amplifier and a 1 farad stiffening capacitor. I have verified that it does allow the DC-DC converter to power-up without any error messages.

    (Image-Link)

    [​IMG]
     
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  2. Daniel in SD

    Daniel in SD Well-Known Member

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    Why not just connect directly to the 12V battery?
     
  3. Jamie Sibley

    Jamie Sibley New Member

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    After reading this on another forum, I decided to not make any attempt at going through the firewall and connecting directly to the battery since most amplifiers and stiffening capacitors have some current draw, even when shut down.

    "Concern: Customer states car needs service/contact Tesla service alert is on.
    Corrections: 12V Battery and Fuses General Diagnosis
    Inspected 12 volt battery assembly, found aftermarket camera's installed and connected
    directly to the battery. Due to the consumption monitoring capabilities of the model 3 this
    installation directly at the battery will lead to alerts and or loss of 12v. Replaced 12 volt
    battery as one time good will. Disconnected aftermarket power wires from 12v battery."

    (Link) to original thread.
     
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  4. JPP

    JPP Active Member

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    There was (?still is) an issue connecting loads directly to the 12V battery in the Model 3 (search these forums). It causes depletion of the 12V battery and faults/errors (maybe due to the same process as above). Those of us with dash cams have had to find alternate sources of 12v power.
     
  5. Daniel in SD

    Daniel in SD Well-Known Member

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    Is that true even for loads that are only drawn while the car is on?
    Looks like you've found good solution if so. Though hopefully the electronic fuse on that wire will protect it as you're probably drawing more current than it was designed for.
     
  6. Jamie Sibley

    Jamie Sibley New Member

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    Most dash cams draw about 0.1 to 0.15 A ( 100-150ma) @ 12V when recording with the screen off. My sub-woofer amplifier and capacitor draw 0.008A ( 8ma) when powered off. I suspect that the model-3 12v battery may tolerate a 8ma load when the vehicle is off, but I didn't feel like routing a wire all the way up front, just to find out the battery supervisory system didn't like it. I read somewhere ( can't find the reference) that the DC-DC converter was capable of 150A of output, additionally, the wire gauge on the DC-DC converter would indicate that it should be able to produce 80-100A continuous.
     
  7. snow4us

    snow4us Member

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    I'm looking for a 12 V power source to power my trailer light power module: https://www.amazon.com/gp/product/B00ASY29C0/ref=ppx_yo_dt_b_asin_title_o00_s02?ie=UTF8&psc=1
    There is a guide to run a cable to the 12 V battery, but I would rather keep my wires internal if possible. (here's that guide FYI )

    Is it possible/ advisable to attach the power wire w/ 15 amp fuse directly to the positive dc-dc converter terminal under the rear seat? Any potential problems with this setup vs routing the wire all the way to the 12v battery?
     
  8. MrChoi

    MrChoi Member

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    I purchased a 120A relay found here. I had my amplifier connect first to the dc dc converter but after about 4-5 months it disabled the car due to an internal error. Took it to service center and they changed out the VC left not knowing the cause of the problem was the amp. After I discovered it was the amp causing the fault, I rerouted the power cable directly to the 12v battery. Few months later I get a “maintenance required soon” prompt. Service center said the 12v battery was bad and needed to be replaced. The replacement was not gonna be converted under warranty because of that wire and aftermarket subwoofer/amplifier. It’s been another two months or so and now I have a “replace 12v battery soon.”

    Long story short, I’m testing the 12v battery’s capacity with a hobby charger and redoing the amp wires. I bet you money the 12v battery is still good.
     
  9. LakeWorthB

    LakeWorthB Member

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    Did you have a resistor in parallel to relay to slow inrush current?
     
  10. MrChoi

    MrChoi Member

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  11. derekwatterson

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    It seems like there's a split in the community between who has and doesn't have this problem. I was curious if it's been narrowed down to the amps that cause the issue. Is it a certain size? Do smaller, more efficient amplifiers (like class D) not cause this issue?
     
  12. Wampa

    Wampa Member

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    I have a 640w Class-D amplifier and have had zero issues so far.
     
  13. MrChoi

    MrChoi Member

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    I use a 400w class d amp. Had an issue in the past after about 4 months of no issues.

    Kicker KX400.1 (40KX400.1) Monoblock KX Series 800W Class-D Amplifier
     
  14. Watts_Up

    Watts_Up Active Member

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    I carry often some big bags full of sport equipments in my trunk and I feel that the audio bass sounds get absorbed.

    So I'm considering installing a 5" or 6" subwoofer speaker inside the rear facing part of the central console of my Model 3.

    [​IMG]

    I wonder if this has been tested and if this would be worthwhile?

    - First thing would be to remove the console to check if there is enough space to install a subwoofer

    - I noticed that the Tesla rear subwoofer is 8" so it would not fit.

    So I wonder if I could just disconnect the rear subwoofer speaker and connect a new subwoofer:

    - Does any one know the impedance of the Tesla subwoofer and if it is a single or dual coil?
    Would there be a risk to damage the Tesla subwoofer amplifier?

    Another possibility would be to add a second amplifier for this new subwoofer.

    - Does anyone know how I could connect this new amplifier to the existing Tesla amplifier input?

    I wonder if having a second amplified subwoofer would interfere the sound waves coming from the existing Tesla amplifier?
    How to determine if the two amplifiers would not be in opposite phase?

    - Any recommendation for a good auxiliary subwoofer amplifier?
     
  15. Rpgonzalez

    Rpgonzalez Member

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    Everything still stable with this setup?
     
  16. Dhesi7

    Dhesi7 Member

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    could you help me locate the “12v acc blue wire ?”
     
  17. marcmerlin

    marcmerlin Member

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    Out of curiosity, how does the car decide the battery needs replacing? Is it possible it see this from a low voltage once even though the battery is good? If so, can that condition be reset to let the car verify if the 12V battery is truly going bad, or whether it was a temporary condition?

    Also, if you hit the current inrush from the DC-DC converter that then causes it to shut down for self protection. How does it decide to reset, and how long can it take worst case?
    I can imagine that if it takes too long to try again, even after you've fixed the cause for the shutdown, the 12V battery will discharge too much, causing potential damage to it, or more likely at least the error you describe until the condition is fixed (not sure how you do that, just wait and hope?)
     
  18. marcmerlin

    marcmerlin Member

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    How is your battery? Did you keep driving around for months with the "replace battery" prompt?
    If you didn't replace it, try this:
    1) unplug it from the car entirely
    2) recharge it with a regular charger
    3) plug it back in
    The car will hopefully detect it as a new battery and should not give you the error again until your battery is truly having issues.
     
  19. 9-Volt

    9-Volt Member

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    Just FYI, the above didn't work for me. My audio shop did just that (and more!), but I still had the warning (despite no issues with the 12v when they hooked it up to their charger/tester). They then followed the below procedure I dug up on another forum, and I've had no issues with the warning (or otherwise) since (6 months ago):

    https://teslaownersonline.com/attachments/br-17-17-004_disconnecting_12v_and_high_voltage_power_on_model_3-pdf.3090/
     
  20. linux-works

    linux-works Active Member

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    #20 linux-works, Dec 26, 2019
    Last edited: Dec 26, 2019
    not sure if normal NTC thermistor parts are heavy enough current for you, but that's one trick that home amps use for inrush limiting. those parts are like resistors that change their values as they heat up, so they are higher Z at cold state and lower Z as they warm up.

    might need several in parallel, but then if you get it working, no need for relays or sharp transitions. NTCs are more smooth.

    Varistor - Wikipedia

    How to Use NTC Thermistors for Inrush Current Limiting | Tech Notes | NTC Inrush Current Limiters | TDK Product Center
     

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