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This is a follow up question of "What is the best price-to-value 2000 w pure sine inverter for a mid-2015 Tesla Model S with a DC-DC inverter?"


Question

My understanding is there are (at least) three distinctly different wiring one may use to connect a 1500-2000 w pure sine inverter in to a Model S Tesla: (i) directly to the 12v battery, (ii) directly to the high-voltage DC to low-voltage DC converter, and (iii) directly to the high-voltage battery.

The auxiliary 12v battery one should be fairly "straight forward": One connects to provided cables to the 12v, but this will kill the auxiliary battery in short order if used at 1.5-2 kw.

After over 10 years of Model S and a number of reiterations of its electric design, how to best install a pure sine inverter directly to the DC-DC converter, to the high voltage battery, or otherwise sparing the car's built-in 12 volt battery from "cycling the low voltage battery like mad, and [potentially] suffer low voltage cutoff on the inverter" so as to be able to draw continuous 1500 watts with the vehicle stationary?


Answers sought

Based on this tutorial how to replace a fuse in the DC-DC converter, any explanation about to which part of the converter to connect the inverters cables (or marking them on screenshots), will be much appreciated.


Research (my findings so far)

"The DC-DC converter [is of a maximum of] 2500 watts[, 14 volts and 178 amps output; o]bviously some of that is needed for the car systems." (Understanding the Tesla Model S Power Electronic Components, Weber State University Davis, March 11, 2021, see also, TMC post, Nov. 26, 2016, DarkMatter)

"[I]f you wire [an inverter] in to the [propellant] battery [of the Model S] then [the size of the available wattage depends] on how long you plan to draw high currents for [among many factors]." (TMC post, Nov. 26, 2016, green1)

For a 2000 w inverter "[one would need] 2 awg wire[s], keep the runs short[, and probably at least a 250] amp fuse to allow for surge current". (TMC post, Feb. 27, 2018, n2mb_racing)

"There is a current sensor [in the Model S] monitoring the output of the DC-DC converter which can be viewed by apps such as Scan my Tesla. [¶ I]f the car sees continuous draw of certain current say greater than 7A (or if the DC-DC output power exceeds certain level), the DC-DC converter won't turn off even if the car is in sleeping mode. If that is the case, there is no worry about the cycling of the 12V battery." (TMC Post from February 27, 2018)

The "high-voltage battery" (per Tesla parlance) monitors and charges the led-acid 12v auxiliary battery (the 2021 or '22 and up Model S and X use lithium-ion for the auxiliary as well).

The modification would likely need ca. 8-9 mm diameter cable (+50 mm2), and preferably short between the point of contact of the car and the inverter.12

Images

Schematic view of location of the DC-DC converter:

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Photo of the location of the 1st-gen DC-DC converter in a fire-response extrication video instructions:

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DC-DC converter panel (front view) from a fuse replacement tutorial:

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Schematic assembly view of the DC-DC converter panel:

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Footnotes

1 "[A] 600 watt inverter can perfectly well continuously run with 10mm2 wires[ in a Model S Tesla;] 1000 watts at 12 volts should have 25mm2 and that's getting [a] bit large and expensive already" (mechanics.SE answer, Sept. 24, 2022, juhist)

2 Standard high-voltage harnessing is 8 mm in diameter, or ca ~50 mm2 (Understanding the Tesla Model S Power Electronic Components at 4:00)

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    Did you try asking Prof John Kelley of Weber State University in the link or Rich Rebuilds? There may be Tesla forums with experts that may be able to answer your questions. Ford, GM and Rivian are among ev manufacturers with stock ac inverters incorporated into their vehicles. Perhaps forums there may have info to help.
    – F Dryer
    Sep 26, 2022 at 1:04
  • @FDryer Good for the competition, and thanks for all that! If it comes to that, I may as well try to reach out to the professor or Rich Rebuilds! (I previously tried to contact Rich, but, to no surprise of mine, he never replied — he's kinda famous at this point) Perhaps someone knows of a good video tutorial or a photo one from other forums I failed to dig up if no one could answer it. Sep 26, 2022 at 1:51
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    Be patient as your questions are very technical with many more smart people out here than I can imagine. After all, engineering from many discliplines created Tesla with many auto manufacturers attempting evs. There's a English youtube outfit that does conversions from ice vehicles to evs using Tesla parts. These are the people to seek out, knowledgeable about evs and should be able to analyze your questions and possibly help.
    – F Dryer
    Sep 26, 2022 at 3:14
  • @FDryer I narrowed the scope of the quesitone, hopefully will be easier to answer now. Sep 28, 2022 at 20:58
  • Unfortunately, I think the short answer is no one with a Tesla has connected a large inverter to run off either main power or 12v battery. Voiding warranty for any electrical modifications would be the main deterrent. Outside of warranty would present challenges to anyone with advanced electrical/electronic skills.
    – F Dryer
    Sep 29, 2022 at 1:32

1 Answer 1

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One problem I learned after reading about Tesla's DC-DC converter. Apparently Tesla is accounting for all current draws in software and adding these up. If the current draw from DC-DC converter isn't accounted for, it will detect there's something odd in the electrical system.

So the best you can have is to add the inverter to some circuit that is already accounted for. Like the ~10 ampere cigarette lighter circuit, but you won't get much over 100 watts from that. Or maybe you can use the stereo circuit that should offer more than 10 amps.

Source: https://www.reddit.com/r/TeslaLounge/comments/khs8ya/recommendations_for_2000w_12v_inverter_for_y/

You need to do some research about how you plan to connect this. The car has software that monitors power usage on the 12v systems and will absolutely get angry if it sees a sudden high load where it isn't expected.

Another source: https://teslamotorsclub.com/tmc/threads/dc-to-dc-converter-what-can-it-reasonably-handle-in-terms-of-using-your-battery-as-a-power-source.196187/

So Tesla knows how much power the DC-DC converter is producing. And because every circuit in the car is protected by an eFuse, the car knows exactly how much power is being used. When you tap into 12V under the rear seat, that ends up being an unmonitored power draw. When the car sees the power produced, and power consumed diverge significantly, it assumes something is wrong.

You have chosen the wrong car. Tesla really hates customers, especially those who may want to use the car for something other than its intended purpose. A car by company that loves customers could be for example a Hyundai Ioniq 5 which by the way doesn't require an aftermarket 2000W inverter since it already has 3600W inverter.

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  • Appreciate your time to learn about the peculiarities of this brand, and the answer! "Tesla really hates customers, especially those who may want to use the car for something other than its intended purpose." If I could share my thoughts with you about Tesla, trust me I would. The first source you cited, I found as well, and one of them also summarizes my findings that "people had success on older Model S [(pre-April 2016, or 1st gen)] with a 1500w inverter in the frunk running off the 12v battery, but I [no success] on a 3 or a Y, […] there's load monitoring to prevent it." Sep 29, 2022 at 20:52
  • I have long had a small cigarette lighter 12v port to 120v inverter rated at peak 25 amps, and is rated at 200 w output presumably continuous, and maybe like 300 watts peak. However, because of my old model, the car is not rated for more than 150w's continuous if I'm not mistaken off of the cigarette lighter. (It does the job for even a fast MacBook Air charger, but I'm hoping to make use of the car's power.) Sep 29, 2022 at 20:55

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