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

marcmerlin

Member
Jan 12, 2016
98
113
Cupertino, CA
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/attac...v_and_high_voltage_power_on_model_3-pdf.3090/
Thanks. It's a long document, what part was what actually helped?
I'd think that if you disconnect 12V from both sides (battery and DC-DC side), the car should fully lose power and forget the old battery. Are you sure that it's not enough?
 

marcmerlin

Member
Jan 12, 2016
98
113
Cupertino, CA
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
Interesting, I didn't think about those, but I am dealing with 200A, I'm not sure a few of those, even in parallel, are going to do the trick. (3000W inverter at 12V is actually 250A)
Other people who worked on this talked about a bypass relay once the inrush is over, and honestly you need a solid piece of copper for 200A, so I'm not sure there is any way around that.
 

9-Volt

Member
May 15, 2019
327
163
Vancouver
Thanks. It's a long document, what part was what actually helped?
I'd think that if you disconnect 12V from both sides (battery and DC-DC side), the car should fully lose power and forget the old battery. Are you sure that it's not enough?

All of the (13) steps outlined to disconnect the high voltage power, and then the reverse to reconnect the high voltage (and 12V), were required.

Sorry, I thought you'd already tried disconnecting the 12V and it didn't work. The guys in the shop fully disconnected the battery for 24 hours and it still wasn't enough to make the car think a new battery was being hooked up. Worked instantly after following the steps above, and no problems since, so I think the key is a disconnect/connect of the high voltage.
 

marcmerlin

Member
Jan 12, 2016
98
113
Cupertino, CA
All of the (13) steps outlined to disconnect the high voltage power, and then the reverse to reconnect the high voltage (and 12V), were required.

Sorry, I thought you'd already tried disconnecting the 12V and it didn't work. The guys in the shop fully disconnected the battery for 24 hours and it still wasn't enough to make the car think a new battery was being hooked up. Worked instantly after following the steps above, and no problems since, so I think the key is a disconnect/connect of the high voltage.
Did you disconnect the 12V from both sides? If you only disconnect the battery, the DC-DC will keep the car alive from the other side.
If the DC-DC trips, or you disconnect it from under the rear seat, and then you also disconnect the battery, the car's computers have no power and absolutely nothing will work, including opening doors (so don't close the trunk unless you want to try the emergency opening procedure).
 

9-Volt

Member
May 15, 2019
327
163
Vancouver
Did you disconnect the 12V from both sides? If you only disconnect the battery, the DC-DC will keep the car alive from the other side.
If the DC-DC trips, or you disconnect it from under the rear seat, and then you also disconnect the battery, the car's computers have no power and absolutely nothing will work, including opening doors (so don't close the trunk unless you want to try the emergency opening procedure).

Not 100% sure, as my audio shop did it, but I think they had the battery out of the car and sitting on a charger. I know they also tried disconnecting the power from under the rear seat (but not sure if the battery was disconnected at that point or not).

Obviously, your mileage may vary as to whether some or all of the steps outlined in the Tesla document linked above are required to clear the 12V error message. I just thought I'd pass along the info that worked for me--as food for thought--in case you can't clear the message and have a known good battery.
 

marcmerlin

Member
Jan 12, 2016
98
113
Cupertino, CA
To close off that discussion on this thread too, please go to How many amps can you get from the 12V system for emergency situations? for how I made it work.
I now have a 2000W inverter that powers on and off at the same time than the car DC-DC system, without the big current inrush that was disabling the car's DC-DC system in a way that it didn't really reset on its own.
Turns out I didn't even need a zener diode, relying on the voltage being high enough at the inverter poles to trigger a bypass relay, was enough.
 
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Reactions: FlatSix911

Ravire

Member
Feb 13, 2020
187
130
Orange County
So forgive me if I’m wrong but in newer model 3s there’s a trailer wiring harness behind the rear bumper can the 12v on this be used as a remote turn on? I believe it leads to vc_left and I have no interest in using a trailer so it would cut down on the amount of work.
 

marcmerlin

Member
Jan 12, 2016
98
113
Cupertino, CA
So forgive me if I’m wrong but in newer model 3s there’s a trailer wiring harness behind the rear bumper can the 12v on this be used as a remote turn on? I believe it leads to vc_left and I have no interest in using a trailer so it would cut down on the amount of work.
do you know what fuse it's connected to? how many amps? by connecting to the DC-DC under the rear seats, you get 200A :)

Marc's Blog: electronics - Using a Tesla Model 3 as Emergency Power Source In Case of Grid Failure
 

Idkorcare

Member
Nov 3, 2019
186
143
Atlanta
So forgive me if I’m wrong but in newer model 3s there’s a trailer wiring harness behind the rear bumper can the 12v on this be used as a remote turn on? I believe it leads to vc_left and I have no interest in using a trailer so it would cut down on the amount of work.

Vc left no longer functions the same way as it did before with one of the last updates, it currently mirrors the dc-dc power and only shuts off when the car sleeps, no clue on the wiring behind the bumper, id check the factory sub first.
 

Ravire

Member
Feb 13, 2020
187
130
Orange County
Vc left no longer functions the same way as it did before with one of the last updates, it currently mirrors the dc-dc power and only shuts off when the car sleeps, no clue on the wiring behind the bumper, id check the factory sub first.
Oh okay I’ll just use the signal turn on then
 

Idkorcare

Member
Nov 3, 2019
186
143
Atlanta
Fwiw straight up signal sense MIGHT also keep the amps on longer than expected. I was using signal sense when the update to vcleft changes how it worked and notices the amps would stay on even tho no audio was playing like while sentry is on or the penthouse is still awake.

i ended up running a relay off the console lights to get a new turn on but others had trouble getting it to work.
 

Ravire

Member
Feb 13, 2020
187
130
Orange County
Fwiw straight up signal sense MIGHT also keep the amps on longer than expected. I was using signal sense when the update to vcleft changes how it worked and notices the amps would stay on even tho no audio was playing like while sentry is on or the penthouse is still awake.

i ended up running a relay off the console lights to get a new turn on but others had trouble getting it to work.
Do the amps staying on longer just hurt range or will it cause any errors due to the power draw. I don’t mind losing a little range while I’m out of the car.
 

Idkorcare

Member
Nov 3, 2019
186
143
Atlanta
you probably wont notice it affecting range, they will just be on. I set off warnings on my car way more than I want to admit installing the stereo testing different things and im pretty sure 95% of the battery errors people were having were caused by running accessories directly off the 12v and letting the car sit, running the battery down just enough(right around 12.0v) that the car thought it was bad and made no attempt at charging it as a precaution.

I also hooked my amps up directly off the 12v battery and it never tossed an error from drawing power off it. But what would happen is once I crossed some current draw threshold, and im talking cranking up the stereo to near full blast for a bit, it would stop charging the 12v battery till I lowered the load.
 

Sartir29

New Member
Jul 29, 2021
3
0
Katy Texas
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)

relay-soft-start.png
Hey Jamie…how did you get the error message on the center console to go away?
 

hamtonp

Member
Sep 4, 2018
177
265
Dallas
Hey Jamie…how did you get the error message on the center console to go away?
When you get this message, this means the 12v is running on it's own. So the HV is not charging the battery. The charging port won't even work.
One way to fix is to disconnect and reconnect the 12v battery. If the 12v has enough juice to power up, everything will go back to normal. If not, you need to charge the 12v battery using an external charger. I would keep it charging as the car boots up. You can disconnect once everything is up and running correctly. You should keep the car awake a bit so it will continue to charge the 12v battery.
 

Sartir29

New Member
Jul 29, 2021
3
0
Katy Texas
When you get this message, this means the 12v is running on it's own. So the HV is not charging the battery. The charging port won't even work.
One way to fix is to disconnect and reconnect the 12v battery. If the 12v has enough juice to power up, everything will go back to normal. If not, you need to charge the 12v battery using an external charger. I would keep it charging as the car boots up. You can disconnect once everything is up and running correctly. You should keep the car awake a bit so it will continue to charge the 12v battery.
Many thanks! That worked. I assume the cause of the problem is related to the new amplifier as mentioned at the start of the thread. I’ll attempt to install the circuit as mentioned previously to try and resolve the issue permanently.
Thanks again!
 

hamtonp

Member
Sep 4, 2018
177
265
Dallas
Yes, the amp is drawing too much too quickly when powering up which drops the 12v battery voltage pass a safety threshold. When this happens, the car disconnects all non-essential devices to preserve the 12v battery including the HV battery which is what charges the 12v battery. Strange but that's what it does.

My work-around is installing a very tiny 12v battery that is always connected to the amp. A solenoid acts as a relay that connects the car's battery and the 2nd battery when I enter the car. I did this before learning about using the resistor to slowly power up the amp. This setup has been working great with no issues for a year now. I guess it doesn't hurt to have an extra battery to help stabilize the voltage when I'm jamming it out.
 

Sartir29

New Member
Jul 29, 2021
3
0
Katy Texas
Yes, the amp is drawing too much too quickly when powering up which drops the 12v battery voltage pass a safety threshold. When this happens, the car disconnects all non-essential devices to preserve the 12v battery including the HV battery which is what charges the 12v battery. Strange but that's what it does.

My work-around is installing a very tiny 12v battery that is always connected to the amp. A solenoid acts as a relay that connects the car's battery and the 2nd battery when I enter the car. I did this before learning about using the resistor to slowly power up the amp. This setup has been working great with no issues for a year now. I guess it doesn't hurt to have an extra battery to help stabilize the voltage when I'm jamming it out.
Question: one concern I have with the circuit with the resistor is the size of the wiring for the 30A relay. The 4 gauge wiring (power) going to 12 gauge (relay) back to 4 gauge doesn’t seem to make sense. Any thoughts?
 

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