Hi team,
I am going to be getting a powerwall 3 in the not too distant future, that is capable of providing almost whole home backup (11kW AC inverter).
Talking to the installer we can either put our car charger on the essential or non-essential loads side of the gateway. I am keen to have the charger on the essential loads so that I can choose to charge the car if I want to, but I also dont want to wake up in a grid outage with an empty powerwall and a partially full car as it started charging at 1am as if nothing was happening.
Is there a way to tell the charger there is a grid outage and not to charge on schedule automatically? But still retain the ability for Solar Diversion and/or manually initiate charging in the app?
At the moment there’s no way to tell the charger whether there is a grid outage or not so we don’t have any configuration to choose behaviour which depends on that. It’s a good idea though so we’ll have a think about how it might be done.
I would agree with you that it’s probably best to put the charger on the essential load side of the gateway so that you have the option to use some of the stored energy to charger your car if you need to.
Assuming you are running single phase. I have 3-phase and in an outage, only one phase is powered by the Powerwall 2 so I cannot power the Evnex X22 during an outage. Actually, this is not 100% true since the X22 can be powered by a single phase and do single phase charging only, but I don’t know how it would act if it was running 3-phase and suddenly 2-phases of power disappeared.
If you have solar diversion active, but do not have a schedule setup on your Evnex charger, then you won’t run the risk of draining your battery unexpectedly, because the only way it would charge your EV would be if solar is being exported to the grid (which cannot happen during an outage) or you manually initiate a charge.
If you do have a schedule enabled and want to charge your EV from your battery during an outage, you could use a single pole, double throw AC electrical switch capable of 240 V/32 A that could physically switch the active going to the Evnex charger between a connection to the back-up side and the non-backup side of your Tesla backup gateway. You would normally leave the switch on non-backup side and during an outage, if you want to charge your EV, switch it to the backup side. Just don’t forget to switch it to the non-backup side after the outage. I presume there is some version of such a switch that is controllable via home automation, but I have not looked. Obviously, you gotta run this by your electrician. Also, when you flick that switch the Evnex charger will momentarily lose power. Might be that you need to switch the charger off first at the breaker, flick the non-backup to backup switch, then after 10 seconds, switch on the charger again at the breaker.
Generally, charging your EV from a battery isn’t ideal. Real world round trip efficiency of home batteries is around 75-80%. Don’t expect to be getting more than 10 kW of EV charge from a fully charged Powerwall (13.5 kW) when you add in losses in the EV charging process.
“Generally, charging your EV from a battery isn’t ideal. Real world round trip efficiency of home batteries is around 75-80%. Don’t expect to be getting more than 10 kWh of EV charge from a fully charged Powerwall (13.5 kWh) when you add in losses in the EV charging process.”
Sorry about being pedantic but this avoids any ambiguity in what you’re stating. And I agree that sourcing EV charging from static battery storage is not advisable, for battery degradation reasons as well as bad efficiency.
Thanks for the responses, just for extra context I have an E7 charger on single phase supply. Definitely not intending to charge the car from the battery on the regular, so if it were to happen I am not too stressed about efficiency, its more if something went really wrong.
I do have a standard 3-pin plug EVSE that can be plugged into a backed up circuit, but it just takes a long time to charge.
I would definitely be keen if you build something and need a tester @TomRose