Energy Products

12V jump start TEG?

If the emergency disconnect for the TEG is ever engaged (by the fire department or anyone else), when the system is reconnected after whatever precipitated the emergency, grid power is required for the TEG to startup again, even if there's plenty of juice in the Powerwalls or available from the inverter. This is straight out of the installation manual, confirmed by Tesla and observed by me during testing. If the grid is out (an entirely viable scenario), to get going again the installation manual says a "12V Jump Start" must be given to the TEG. But it doesn't explain how. Does anyone know the specifics? The best I got out of Tesla support was that I had to call their emergency response team in such a scenario -- which is ridiculous.


  • Seems like such an unlikely scenario. I wonder if any TEGs have ever been disconnected by the fire department when there is no grid power.

    Perhaps if the roof is on fire, but there are far larger problems that will have to be dealt with.

    As for connecting 12v, looking at the Powerwall installation guide, it shows on page 31 the 12v connections in the Gateway. I'd be very careful, as there are lots of exposed AC connections in the gateway. These same connections should be available on the side of the Powerwall as well and are shown on page 84.
  • Thanks for those pointers, I’ll take a look.

    One of the major goals for me was to be independent of the grid and external intervention to the least extent possible. I live in area where the infrastructure is horrible; we even lost 911 capability once. If I’m truly isolated, I don’t want my system ever becoming unusable due to a silly design choice. (I feel the same way about an Internet connection being required to make configuration changes — that’s just silly too.)
  • Is that 12V connection within the PW or the TEG? I've never pulled the panel off the TEG, and the prospect of pulling the case off a PW seems pretty daunting.

    In case of a grid failure, I plan to go to my main and sub-panels and shut off all breakers not going to critical loads. If that's done, I should have no problem keeping daily energy needs below about 15kWh. My very "smart" home has parasitic loads like there's no tomorrow...
  • In the TEG. Looked at the drawings in the installation manual and see what they’re talking about. Still not exactly clear how I’d do the jump of I had to. A car battery with leads (how?) going to that 12V pin and the negative where?

    Completely silly that Tesla DESIGNED it to require manual intervention by them this way in this scenario.
  • @greg - both TEG and PW. The PW generates the 12v to power the TEG. There are four low power wires (12v and data) that connect between the PWs and the TEG.

    @BLD - I've not seen any reports here in the forums about it, and you'd expect to if it occurred. I expect if there were real occurrences, Tesla would make an easy to access user-accessible 12v connection. It really wouldn't be that hard to add such a connection yourself. You might wait (perhaps a very long time) until such an event actually occurs.
  • @"" could you elaborate on “not that hard” with a detailed suggestion? 12V source - car battery? Positive connector in TEG - clear enough from the manual, but what about the negative connector? What pins/connectors/wires would you use?

    I just don’t understand why Tesla made it this way. An external power source from the Powerwalls and inverters should not be necessary to bootstrap the system. Makes no sense to me.
  • If it's not clear to you from the manual, I hesitate to offer more advice. For me, it would be trivial to tap into the +12 and ground wires that go to the 4-pin connector - either at the gateway or behind the side panel of a Powerwall. Any 12v source should work. You might contact an electrician to do this work if this doesn't make sense.

    Before connecting 12v to those wires, I'd make absolutely sure they don't have 12v on them. It's possible you might damage the electronics if you connect your own 12v source while the Powerwall is producing 12v. It's likely protected, but you're doing something that is not documented or recommended by Tesla.

    I expect the reason Tesla designed it this way as there has never been a need to do what you're attempting to do. I don't understand why you are so worried about something you've never encountered. I could be worried that the 2x4s in the wall might crack and the Powerwall would fall off the wall. Seems about as likely as needing to insert 12v into the system.
  • The only way I can think of that would result in the need to jump-start the TEG would be if the PW was depleted to "zero" (in reality, there's a 5% reserve), then had no PV source (or grid) to recharge it for whatever time it would take for the system to deplete the 5% (~.675 kWh) reserve due to internal parasitic loads.

    If the grid's down in a non-PV scenario, the PW will provide back-up power until it's depleted. It's done its job. If the outage lasts long enough to deplete the reserve, so it needs a jump-start, it looks like setting up a convenient jump-start port would be a prudent action to take.

    Me? I'd instead put a small, (1kW?) solar PV system together with the PWs. The TEG will then have a near daily source of energy ready to keep at least some energy in the PWs, eliminating the need for a jump-start.
  • The TEG takes about 2 watts. At fully depleted (when actually have 5% or 675 W left) that should last 337 days. Probably less due to internal losses, but at least 150 days.

    If you don't have solar or grid for that long, I expect you have more serious problems to address.
  • I may be wrong on this, but end up with the same numbers!

    The Neurio current monitor in the TEG takes < 2 W. There are some additional Tesla electronics, and I expect they may take another 2 W or so, with perhaps a peak of 10W for a very short period when connecting/disconnecting from the grid. Tesla doesn't spec this, so it's my estimates. Anyway, when nothing is happening (99.99% of the time), it is likely taking about 4W.

    That said, if you have 2 Powerwalls, then you have twice the power from my prior estimate. The end result would still be about 337 days of power, which I'm still estimating is closer to 150 days with internal conversion losses, and some margin when it gets close to a real 0% SOC and unable to generate 12v.
  • Folks -- it does not matter how much charge the Powerwalls have, if the emergency disconnect is engaged and then later disengaged after the emergency is past, the TEG will NOT come back up unless there is GRID power (see page 33 of the installation manual). I have explicitly tested this with the installer. The ONLY other option according to the installation manual is to provide a 12V jump start. I live in an isolated coastal area where the infrastructure is total crap, and the loss of all power and communication is a very real possibility; it has *happened*. It is not at all out in the realm of la-la land that I might have reason to emergency disconnect my system during a grid outage. And it's further not out in la-la land that said emergency could be resolved during the grid outage. In that scenario, I am STUCK without a "12V jump start," even if the Powerwalls are 100% full! TeslaTap, it sounds like you're just as surprised that the TEG won't come back up just from the Powerwalls as I am.

    Now I agree that the second scenario of running the Powerwalls themselves down to true zero during a grid outage is extremely unlikely -- but that is not my primary scenario of concern (even though the fact that it's even a remote possibility still seems like a silly design -- if I have power from any source, grid, solar or battery, I should be able to bootstrap, period).

    Regarding the wiring for the jump start, sorry, TeslaTap, I don't know why I didn't see the Ground terminal labeled on page 45 before. Yes, you're right, it's obvious. But I still wouldn't mind a suggestion for the easiest types of cables/connectors to go from the posts on a 12V car battery to those terminals.
  • @BLD - I see what you're talking about, but I read it differently. This seems to only apply to the optional installation of a remote disable switch (page 32) AND you manually disable it and the grid is down and you then reenable it without the grid. Then 12v external power is needed.

    Not sure of the purpose of this remote disable as it is not installed by Tesla. So you added the remote disable switch? What are you using it for? It appears as part of the design to purposely turn off the 12v from within the Powerwalls. It might be useful for Tesla engineering, but don't see much other value. The manual doesn't explain why anyone would install it either.

    The remote disable is not the emergency disable switch that a firefighter or someone else would disable the system. That manually cuts the AC between the grid and the solar/Powerwalls.
  • If you land the powerwalls to the internal distribution bus w/o going through the solar disconnect some jurisdiction may require the powerwall disconnect switch.
    The jumper is shown on page 47, I’m sure you can figure out the polarity with a ohm meter if not marked on gateway.
  • I don’t know why you would ever want to disconnect your powerwalls with the remote disable switch in a power outage now that you know a jump start is required. Opening the main breaker on the GW will disconnect you. But if your power goes out, you can bet I’m gonna be running over to your house to throw the switch!
  • @"" that remote disable switch is precisely how Tesla implemented the emergency first responder disconnect for my system.

    Cutting grid AC is not sufficient to deenergize the home — the batteries must be disconnected too (and then with no AC at all, the inverters will shut off along with the PV).

    But I’m almost positive even opening the main breaker on the TEG has the same problem: closing the breaker won’t bring the system back online without the grid or that 12V jump start.
  • @BLD - Interesting. Sounds like your local building code requires this. Mine and others I've seen have a big emergency AC cutout switch next to the gateway. The box is huge (1ft x 2ft) with a huge lever. I can also disconnect the Powerwalls and solar via the breakers.

    That explains why everyone here, including me, have been confused about your need - it's different than everyone else :)

    Ok, I hope you have enough info now to connect up a 12v battery if you ever need it.
  • I could have gone with the giant knife-arm disconnect as well. However, I also had the hard requirement that the disconnect be secure. Those knife-arm disconnects cannot be locked in the open position, so any clown can walk along and pull it. In order to meet county code and have it be secure too, I had to have a disconnect switch small enough to go inside a box that could be locked with a Knox padlock for which only the fire department has a key. So another silliness -- only the fire department can get at that disconnect. *I* have to do it the old-fashioned way by going to the room where the TEG and Powerwalls are and flipping the breakers.

    But I'm pretty certain that you folks with the knife-arm disconnect will be in the same boat as I. First responders arrive, pull the utility meter and pull your knife-arm disconnect. When the emergency is over and you push your knife-arm back up, the TEG will not restart until the grid is restored too (or you provide a 12V jump) -- just like in my case with the low voltage disconnect. I'm almost (but not 100%) certain that the installer and I tested this too, but I will confirm later.
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