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

[gpez]

Probably not super helpful for this conversation but maybe for others who come here and are in my situation.

My 14-50 outlet is not backed up as a) I only have one Powerwall and b) my current EV is a PHEV so in a pinch I could charge at 120v/12a on a backed up outlet and of course could just use gas.

 

[BrettS]

just use gas.

Gas? What’s that?

 

[gpez]

Gas? What’s that?

Liquid dinosaurs!

 

[charlesj]

check out this article...

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

Yep, that feature is on my app even though I don't have a Tesla car or other all electric car.
Looks interesting and a good reason the back up that wall charger as well.

I suppose with grid down, one would not be charging the car if that WC is not backed up either. At least with it being backed up it would get some charging..

 

[charlesj]

Gas? What’s that?

Oh, that happens after a good meal that doesn't agree with your intestines.

 

[DonE]

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?

You probably have thought of this, but if you are uncomfortable with the car charging when you are asleep or unaware, you can simply schedule the car to charge at a time appropriate for you. This is done on the touch screen very easily. Good luck!

 

[jrweiss98020]

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.

Back up everything.

Latest car + app software allows you to control car charging based on PW charge level. Set it to 75 or 80%, and you won't draw down the PW with the car charger below that level.

 

[BrettS]

Yep, that feature is on my app even though I don't have a Tesla car or other all electric car.
Looks interesting and a good reason the back up that wall charger as well.

This feature works with communication between the powerwall and the car, so even if I don’t backup the wall charger it would work if I use the mobile charger with a 14-50 outlet (or even if I plug the car into a 120V outlet for that matter). However, it’s also worth noting that the powerwall and the car can’t communicate directly... the communication needs to go through the Tesla servers, so if the powerwall and/or the car has no WiFi or cellular connection then this communication can’t happen. In the event of a large outage that takes down my internet provider and the cell towers then this feature won’t work.

I suppose with grid down, one would not be charging the car if that WC is not backed up either. At least with it being backed up it would get some charging..

Part of my concern is that my solar/powerwall system is sized such that it only meets about 70% of my power needs, but I do a lot of driving and I think most or all of that other 30% is car charging. So I believe that without car charging I’ll be able to run indefinitely on solar, or pretty close to it. But, like I said before, this is my only car, so I do still want to have some sort of charging option when the power is out if I need it. About a month ago they just opened a supercharger like 5 minutes from my house, so assuming that has power I now have another option for charging while the power is out.

 

[BrettS]

You probably have thought of this, but if you are uncomfortable with the car charging when you are asleep or unaware, you can simply schedule the car to charge at a time appropriate for you. This is done on the touch screen very easily. Good luck!

Yeah, that’s an option, but since this is my only car I don’t really like letting it sit with a low state of charge in case I need to go somewhere unexpectedly. And it’s not so much that I’m uncomfortable letting the car charge when I’m asleep... I do that all the time. It’s more that after I have the powerwalls I’m concerned that if the car is charging at night and there is a power failure it will drain the powerwalls and I’ll have no power for anything else.

The more I think about it, the more I think it makes sense to just not back up the wall charger. That way when the power fails I know the car will stop charging. If I need to charge and think I can spare some power for it, then I can use the 14-50 outlet. If I don’t need to charge then I don’t need to worry about it.

 

[BrettS]

Back up everything.

Latest car + app software allows you to control car charging based on PW charge level. Set it to 75 or 80%, and you won't draw down the PW with the car charger below that level.

Right now that doesn’t support the model S. They say model S is coming, but no one knows when. Additionally I have an older AP1 model S and I think there’s at least a chance that the older cars may never be supported. Plus, as I said above, this requires that both the powerwall and the car have an internet connection, which may not be guaranteed during a natural disaster or a widespread power failure.

I think the software option is great and it’s definitely a step in the right direction, but it’s not a perfect solution yet.

 

[CrazyRabbit]

OpenEV Store - All Products
can control charge current thru wifi, local not web server based, works with internet down.

 

[jrweiss98020]

Right now that doesn’t support the model S. They say model S is coming, but no one knows when. Additionally I have an older AP1 model S and I think there’s at least a chance that the older cars may never be supported. Plus, as I said above, this requires that both the powerwall and the car have an internet connection, which may not be guaranteed during a natural disaster or a widespread power failure.

Does it require an Internet connection, or only communication via the local net? I can understand why Storm Watch requires the Internet, but the charging limiter should work without it...

 

[CrazyRabbit]

local net, so you can access and make setting with internet down if you are HOME.

 

[BrettS]

Does it require an Internet connection, or only communication via the local net? I can understand why Storm Watch requires the Internet, but the charging limiter should work without it...

I could be wrong on this, but I don’t believe the charger and the car have any way to communicate directly. Technically they could, assuming they are on the same WiFi network, but I don’t believe that they operate that way. The powerwall and the car talk to each other through Tesla’s servers.

Even the phone app keyless entry option for model S and X cars goes through Tesla’s servers and requires an internet connection for the car and the phone to work. (The model 3 and model Y use Bluetooth and don’t need an internet connection for keyless entry with your phone).

 

[BrettS]

OpenEV Store - All Products
can control charge current thru wifi, local not web server based, works with internet down.

Yes, I realize that there are connected chargers, but I was talking about the new option that allows the powerwall to talk to the car to limit charging during a power failure.

 

[CrazyRabbit]

i don't know if tesla's software is cloud based or not.

 

[R1Bill]

When you charge a Li-ION battery it's only about 85% efficient. So, if you're doing it twice, now you're at 72% efficiency. That alone would make me shy away from using my powerwall to charge my car unless it was an emergency, my power rate was really high and/or I had a lot of surplus energy. On top of that, every charge/discharge cycle reduces the remaining life of your powerwall's batteries. I would definately have a charging circuit put on it in case of an emergency though.

 

[cwied]

When you charge a Li-ION battery it's only about 85% efficient. So, if you're doing it twice, now you're at 72% efficiency. That alone would make me shy away from using my powerwall to charge my car unless it was an emergency, my power rate was really high and/or I had a lot of surplus energy. On top of that, every charge/discharge cycle reduces the remaining life of your powerwall's batteries. I would definately have a charging circuit put on it in case of an emergency though.

I think the main reason to have a charger on the backed-up side isn't to use it to charge from the batteries, but rather to charge from solar. It's helpful to be able to soak up extra solar production during the day so the Powerwalls don't have to shut solar down when they get full. Of course, a 14-50 would probably be plenty for these purposes.

 

[BrettS]

I think the main reason to have a charger on the backed-up side isn't to use it to charge from the batteries, but rather to charge from solar. It's helpful to be able to soak up extra solar production during the day so the Powerwalls don't have to shut solar down when they get full. Of course, a 14-50 would probably be plenty for these purposes.

It’s an interesting thought, but I’m not sure it really makes much of a difference in my case. Normally I can just send any excess production back to the grid, since I have net metering. In a grid down situation I don’t think that I’ll have any excess power anyway. Without car charging my system should come pretty close to meeting my power demand, or maybe even be a little low.

 

[aesculus]

Without car charging my system should come pretty close to meeting my power demand, or maybe even be a little low.

That's how I designed mine too. Seemed like the best price/performer.