Charging and Powerwalls

[Jwolf91]

We are new to the EV world but have owned solar and Tesla Powerwalls for a few years now. Purchased the Powerwalls mostly for backup purposes but also have used them to power the home overnight. Now with time of use pricing and EV charging at night, won’t usually be using them overnight but do want to preserve home backup, in case of grid outage.

So, what I would like to avoid is if a grid outage happens overnight I don’t want the EV to drain the Powerwalls. One option is the new universal Tesla Wall charger, which as i understand it, connects via the app and is able to stop EV charging if the grid goes out. Anyone ever heard of other options? — beside just buy a Tesla!

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[mach-JT]

I have a powerwall and had the same concern. When we installed the solar system and battery, the installer added a sub-panel that is backed up during a grid outage. Our main panel is not backed up so we added the charger circuit to the main panel. Obviously this only worked because of how our system was installed so not sure it applies to your case.

The new Tesla charger wasn't available when we did all this work so not sure on the details of that.

 

[glenthompson]

A lot of it boils down to how often and how long your outages are. Our solar doesn't have battery storage because the house already had a backup generator. Charger is on the non-generator panel as the generator can't handle the whole house. I have net metering for the solar and no time of use charges so doing it that way made economic sense.

 

[Jwolf91]

We don’t have a sub-panel so the whole house is backed up. Have not had too many outages but the ones we have had began overnight.

 

[Hammered]

You put a 'relay' between your EVSE and the panel. The relay has a coil that you power from the utility side of your configuration. You can use 16ga cabling with 5 amp inline 'blow' style fuse (located at the utility power source).

This is a 3 pole contactor, one of the poles is left empty for this use case. Rated to 75 amps of resistance load.
https://www.amazon.com/C25FNF360A-Contactor-Definite-Purpose-104-120VAC/dp/B07PPV12HY/

If there's utility power present the relay is 'on'. If power fails, it opens and the EVSE no longer receives power. I use these for building generator load shedding. They're used to control industrial lighting and motors.

 

[markboris]

I have the same setup as mach-JT with a separate backup panel where the EV charger is connected to the main panel so it will not drain the batteries at night while the car is charging.

I think what Hammered suggested is a great idea to allow you to do what you want.

Also, not sure if your EV charger will do this but my Emporia charger can be set to charge on excess solar only if that is something you might want to have happen.

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