Should my car charger be backed up by my powerwalls or not?

[BrettS]

I have a 2015 Model S60 with dual chargers. I also have my HWPC connected to a 100A circuit, so the car charges at 80A.

I’m putting in a 15.12kW solar system with 4 powerwalls (it’s scheduled to be installed on June 22) and I’m trying to figure out what to do with the car charger.

Originally my plan was to just back up the whole house, including the car charger. But I think there’s a worst case scenario where I get home from a long trip late at night, plug in the car and go to sleep. Then the power fails and the car keeps charging and drains the powerwalls and I no longer have enough power to get through the night.

If the power fails after the car finishes charging there’s no problem, or if I’m awake when it fails then I can manually stop the car from charging and there is no problem, but I don’t like knowing that there is still a potential situation where I could have a problem.

My model S is my only car, so I do still want the ability to charge it in the event of a power failure, but I want to be able to control exactly when that charging happens.

So I’m thinking I can either leave the car charger configured to be backed up and hope the worst case scenario doesn’t happen. It sounds like there is something in the works that would allow the powerwall and/or the car to control or throttle the car charging when the power is out, but that’s not available for the Model S yet. If and when it’s available for my car it sounds like it might solve my problem, so I’d just have to wait it out knowing that I have some risk until then.

Or I could put the car charger on the non backed up panel, so the car would stop charging during a power failure and then I wouldn’t have to worry about it draining the powerwalls. If I did that I think I’d also install a 14-50 outlet that was backed up, so when I do want to charge the car during a power failure I could plug the mobile charger into that outlet. Perhaps a little less convenient than just being able to use my existing charger during a power failure, but at least there’s a little more peace of mind that the car isn’t going to accidentally drain the powerwalls.

What are your thoughts?

 

[boaterva]

I have the WCs not backed up and then can always plug them into a dryer circuit if we are without power for days and have enough solar to maintain PW levels. I’d rather have that than take the chance on the PWs being taken out by the cars especially when there’s no way to get the power back to the PWs from the cars.

Even when the software control of car charging is in place I’d rather have full control of it myself since car charging is usually full before a power loss and you have the backup of another outlet as you say.

 

[patrick40363]

I have a 2015 Model S60 with dual chargers. I also have my HWPC connected to a 100A circuit, so the car charges at 80A.

I’m putting in a 15.12kW solar system with 4 powerwalls (it’s scheduled to be installed on June 22) and I’m trying to figure out what to do with the car charger.

Originally my plan was to just back up the whole house, including the car charger. But I think there’s a worst case scenario where I get home from a long trip late at night, plug in the car and go to sleep. Then the power fails and the car keeps charging and drains the powerwalls and I no longer have enough power to get through the night.

If the power fails after the car finishes charging there’s no problem, or if I’m awake when it fails then I can manually stop the car from charging and there is no problem, but I don’t like knowing that there is still a potential situation where I could have a problem.

My model S is my only car, so I do still want the ability to charge it in the event of a power failure, but I want to be able to control exactly when that charging happens.

So I’m thinking I can either leave the car charger configured to be backed up and hope the worst case scenario doesn’t happen. It sounds like there is something in the works that would allow the powerwall and/or the car to control or throttle the car charging when the power is out, but that’s not available for the Model S yet. If and when it’s available for my car it sounds like it might solve my problem, so I’d just have to wait it out knowing that I have some risk until then.

Or I could put the car charger on the non backed up panel, so the car would stop charging during a power failure and then I wouldn’t have to worry about it draining the powerwalls. If I did that I think I’d also install a 14-50 outlet that was backed up, so when I do want to charge the car during a power failure I could plug the mobile charger into that outlet. Perhaps a little less convenient than just being able to use my existing charger during a power failure, but at least there’s a little more peace of mind that the car isn’t going to accidentally drain the powerwalls.

What are your thoughts?

My whole house is backed up including the charger. Don't over think it. If a bad storm is coming you will not be plugging in the car any way.

 

[StealthP3D]

My whole house is backed up including the charger. Don't over think it. If a bad storm is coming you will not be plugging in the car any way.

A "bad storm" is not the only reason why power might be lost.

 

[boaterva]

Won’t be plugging cars in? Tesla has said for years that cars should be plugged in 24/7. I never unplug mine. If I ran around unplugging them at every rainstorm with a chance of thunder/lightning, wouldn’t make sense.

Still rather have the guaranteed backup power and not have the cars drain the power.

 

[CA-Gbm84]

I think this has been a common question and Powerwall recently received a new feature that addresses this by allowing you to set the % of Powerwall that you want to ensure is kept available for the home.

Setting to 100% will mean the car will not charge at all during an outage, except for surplus solar that would have otherwise have been curtailed... (requires smart inverter frequency control)

Not available on Model S (yet) but will be in the future - so you may want to plan around that end state

Vehicle Charging During Power Outage | Tesla Powerwall.

 

[tomas]

I agree with keeping charger off the circuit. The only thing in proposed plan I’d question is the 15-40. Depends on your driving habits. For me, I seldom have the car below 150 miles, and I seldom drive > 100 per day. So I would be perfectly OK with 120 power in rare instance of charging off power walls.

 

[StealthP3D]

I agree with keeping charger off the circuit. The only thing in proposed plan I’d question is the 15-40. Depends on your driving habits. For me, I seldom have the car below 150 miles, and I seldom drive > 100 per day. So I would be perfectly OK with 120 power in rare instance of charging off power walls.

If I needed to charge from a Powerwall I would want to conserve as much energy as possible. Charging from a 120V outlet is not nearly as efficient as a 240V outlet. Doesn't Powerwall have 240V output.

 

[jboy210]

My charger is backed up. But, since I only plug in the car immediately before I charge I can manage when it pulls power from the solar and PWs very easily. This is because I work from home. Which seems like it may be the default for many jobs.

 

[aesculus]

FWIW I also elected not to back up my WC. I leave my car plugged in 24/7 too but worry about that midnight to 7 am event I was not aware of.

Plus I have my car charge at 72 amps and I was uncertain how that would be negotiated with the PWs. I don't want to constantly have to futz with that and prefer my charging to take place at the max rate to insure the charging gets done in time. In the rare case I need to charge from the PWs I can plug into the wall and just trickle charge. The nearest SC is downhill from me so I need almost no energy to get there.

 

[CrazyRabbit]

check out this article...

Tesla releases new feature to charge your car with Powerwall during power outages - Electrek

 

[jjrandorin]

check out this article...

Tesla releases new feature to charge your car with Powerwall during power outages - Electrek

OP mentioned that, but its not available for OPs model s yet (and I wonder if it ever will be for cars of that year / equipment).

OP, My EV is a model 3 so I dont charge as fast as you mention, but I have 2 powerwalls instead of your proposed 4 and my solar is also about half of your proposed solution (8.7), so our situation is almost exactly the same just the scale is different.

I chose to do what you mentioned, which is NOT put the tesla wall connector on the backup circuit, and ask for a 14-50 outlet to be installed in the garage that is on the backup side. That outlet is for the express purpose of being able to plug in the car using the mobile connector if there is an outage, and I have "extra" solar.

The feature that works to curtail the charging levels was not available when my powerwalls were installed in january, but like you, I wanted no worry about plugging the car in at all times and the car draining the batteries in a power outage.

During a power outage, I would only want to charge my car from "extra" solar that the batteries would not be able to absorb because they were full. The new setting seems to address that, but I have doubts that it will ever become available for older model S.

The potential downside of putting it outside the backup is, more boxes on the install (you end up with a "critical loads" backup panel that includes every circuit except for your wall connector), and also, if tesla ever sets up some sort of vehicle 2 grid (V2G) type setup, which I hope they eventually do, I suspect that the wall connector would need to be on the backup circuit to enable that function.

Pure speculation on my part, nothing more, on the V2G thing, but it makes sense that, at some point anyway, tesla would allow people with powerwalls (and thus, gateways that prevent power backfeeding during a power outage), the ability to use their car batteries as a supplement to their powerwalls in an emergency situation. Lots of people keep thinking that tesla will do this with the car without powerwalls, but I dont see it since they have no proof that a person can disconnect the grid safely, etc.

If you have powerwalls though, you already have permits for battery storage on site at your home, AND already have a proven, permitted ability to make a micro grid, so it seems like a no brainer that your car could supplement it in an outage situation like a mode similar to stormwatch, that only kicks in in certain circumstances. Anyway, if they ever do that, Its my guess your wall connector would need to be on the backup side to make it happen.

its also my guess that you would need different charging equipment in the car, which they would likely not retrofit, so....

Shrug... lots of words to say...

I went with the WC not being backed up and the separate 14-50, and would still do it that way even with the new setting that works for my car. I want the full control of knowing when the car would and would not charge, especially if there was a power outage when I slept, rather than depending on "a setting" not to drain my battery in such a situation.

 

[CSFTN]

I have a 2015 Model S60 with dual chargers. I also have my HWPC connected to a 100A circuit, so the car charges at 80A.

I’m putting in a 15.12kW solar system with 4 powerwalls (it’s scheduled to be installed on June 22) and I’m trying to figure out what to do with the car charger.

Originally my plan was to just back up the whole house, including the car charger. ..

What are your thoughts?

My 2C opinion, also my plans:
Don't Powerall the WC, but have them install a 6-20 and connect that to the Powerwall. So you have something 240 but low enough amps that it shouldn't matter to the Powerwall.

 

[BrettS]

Thanks for the replies everyone. A couple of quick notes. My model S is a 60, so it’s got a pretty small battery, but I do take longer trips routinely and often pull into the garage with the car at only 20 or 25%. (And occasionally with it even as low as 5 or 10%). If the car is at 20% and I charge up to 90% that’s 70% of my 60kWh battery or 42kWh. Definitely enough to nearly drain all four of my powerwalls. But again, that’s only if the power fails at the start of the charge and I am asleep and don’t notice it. Since the car charges at 80A it only takes about 2.5 hours to charge from 20% to 90%, so the window for the power to fail and cause a problem is pretty low.

My main breaker and a few other breakers are installed outside my house by the meter. Then there is a sub panel in my garage that has the other 90% of the breakers. The car charger is on that sub panel. I think that entire sub panel would be backed up, so they would probably have to take the car charger circuit out of that, run it outside the house to where they are installing the new equipment and put it in a non backed up panel there. Then the new 14-50 outlet could go in the sub panel in the garage where car charger was removed. Since the panel is already in the garage it would be pretty quick and easy to just drop in the outlet.

But all that said, I do question whether it’s worth all the extra work to move circuits around and such for a situation that isn’t too likely to happen and may be mitigated with a software solution in the near future. (Although as one person mentioned I do wonder if the software solution will ever be available for my AP1 model S)

 

[aesculus]

The potential downside of putting it outside the backup is, more boxes on the install (you end up with a "critical loads" backup panel that includes every circuit except for your wall connector),

How did you avoid a "critical loads" panel?

They had to install one in my case even if I did back up everything because the meter panel breakers could not be isolated without it. So the WC just stayed in the original main panel and everything else did get put into the backup panel.

 

[jjrandorin]

How did you avoid a "critical loads" panel?

They had to install one in my case even if I did back up everything because the meter panel breakers could not be isolated without it. So the WC just stayed in the original main panel and everything else did get put into the backup panel.

I didnt.. I have a critical loads panel with all my circuits in it except for the Tesla wall connector. My main panel is basically empty except for the main 200amp breaker, my wall connector, and the breaker that goes to the critical loads panel. They even put the blanks back into my main panel to cover up the empty slots, and painted the inside of it so that it was a uniform color without me asking about that.

 

[aesculus]

I think that entire sub panel would be backed up, so they would probably have to take the car charger circuit out of that, run it outside the house to where they are installing the new equipment and put it in a non backed up panel there.

They can easily install a tiny breaker panel for the WC adjacent to your larger panel.

 

[CrazyRabbit]

... My model S is a 60, so it’s got a pretty small battery, but I do take longer trips routinely and often pull into the garage with the car at only 20 or 25%. (And occasionally with it even as low as 5 or 10%). If the car is at 20% and I charge up to 90% that’s 70% of my 60kWh battery or 42kWh. Definitely enough to nearly drain all four of my powerwalls. But again, that’s only if the power fails at the start of the charge and I am asleep and don’t notice it. Since the car charges at 80A it only takes about 2.5 hours to charge from 20% to 90%, so the window for the power to fail and cause a problem is pretty low.
....
(Although as one person mentioned I do wonder if the software solution will ever be available for my AP1 model S)

4 powerwalls can only deliver 80 amps and your car will cause your powerwalls to overload. perhaps you can upgrade to a newer "charger cord" where you can limit what the car takes with a app.. would be good to have with the grid down so you could limit the current to what the solar can deliver so you are not charging from the powerwalls in a outage.
i think they will eventually update your software, the chargers already have this logic built into them, but don't hold your breath.

 

[DHevey]

I have done both. I had a 1410 outlet run from both the protected panel and the unprotected panel, and I switch back and forth, depending on how I want to charge on any given day. I m in net-metering area, so it doesn't really matter how I charge, but I like the flexibility of being able to charge from either source.

 

[BrettS]

They can easily install a tiny breaker panel for the WC adjacent to your larger panel.

It’s my understanding that there will already be a panel for non backed up loads by the meter anyway, so may as well just run the one circuit for the car charger out there rather than installing a whole new tiny panel in the garage, but I guess I’ll see what they say about it when they come out.

4 powerwalls can only deliver 80 amps and your car will cause your powerwalls to overload. perhaps you can upgrade to a newer "charger cord" where you can limit what the car takes with a app.. would be good to have with the grid down so you could limit the current to what the solar can deliver so you are not charging from the powerwalls in a outage.
i think they will eventually update your software, the chargers already have this logic built into them, but don't hold your breath.

That’s a good point and maybe it makes the decision of not backing up the car charger that much easier. I’m using the Tesla HPWC, so I can limit its charging current with jumpers inside the unit, so I could back it down to only charge at, say 60A, but I hate to lose the ability to fast charge when I need it.

The more I think about it the more I think it makes sense to just not back up the car charger and add a 14-50 outlet so I have the option to change when the power is out if I want to do so.