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Question About Excess Power During Outage Going to EV

We just got a Tesla M3 to replace our 2018 LEAF. We have a single Powerwall and 4kW Solar. Our current car charger is a 14-50 Open EVSE that is not part of the backed up circuits that the Powerwall will power...

Which brings me to my question that I thought the experts here could help me better understand.

If I connect the Mobile connector to one of my 120V plugs in the garage, that is on the back up panel, will it follow the rules in the Tesla App for EV Charging?

I have it set right now to 95% Home Use - 5% Share with vehicle.

99.9% of the time we will charge it with the 240V 14-50 EVSE connection - but during an extended power outage we could switch it over to the Mobile Connector 120V setup and harvest any excess solar production...

How do I am make sure this happens? Do I understand this correctly? Is there anything I need to change settings wise?

Thanks in advance!
 
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jjrandorin

Moderator, Model 3, Tesla Energy Forums
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Nov 28, 2018
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Riverside Co. CA
We just got a Tesla M3 to replace our 2018 LEAF. We have a single Powerwall and 4kW Solar. Our current car charger is a 14-50 Open EVSE that is not part of the backed up circuits that the Powerwall will power...

Which brings me to my question that I thought the experts here could help me better understand.

If I connect the Mobile connector to one of my 120V plugs in the garage, that is on the back up panel, will it follow the rules in the Tesla App for EV Charging?

I have it set right now to 95% Home Use - 5% Share with vehicle.

99.9% of the time we will charge it with the 240V 14-50 EVSE connection - but during an extended power outage we could switch it over to the Mobile Connector 120V setup and harvest any excess solar production...

How do I am make sure this happens? Do I understand this correctly? Is there anything I need to change settings wise?

Thanks in advance!

That should work, but you would have to test it to be sure. It should, though. I do exactly that same thing, except the outlet I put on the backup side is a 14-50, and my (2) tesla wall connectors are on the non backed up side.

I have only tested it a couple of times, but it works exactly like I wanted. In a power outage situation, I could take one of my mobile connectors, my 14-50 adapter for it, plug into the 14-50 I had put on the backup loads side, and keep my solar going by charging my car (I have it set to 92%). In regular operation, we dont use that 14-50, we use the two wall connectors.
 
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If I connect the Mobile connector to one of my 120V plugs in the garage, that is on the back up panel, will it follow the rules in the Tesla App for EV Charging?
I believe the EV charging rules will be followed as long as the Tesla is being AC charged. I think the way this is controlled is with a frequency shift in the power, so that should be detectable both when L1 and L2 charging.
You might want to get a 14-50 plug on the backed up side for your Mobile Connector. At 120 V, you might have a hard time absorbing all the excess solar because of the low charging speed.
 
I believe the EV charging rules will be followed as long as the Tesla is being AC charged. I think the way this is controlled is with a frequency shift in the power, so that should be detectable both when L1 and L2 charging.
You might want to get a 14-50 plug on the backed up side for your Mobile Connector. At 120 V, you might have a hard time absorbing all the excess solar because of the low charging speed.
I don't think I can add another 14-50 plug to the backed up side - I am pretty maxed out on the main panel at this point - and the single power wall is backing up our main home sub panel and a few extra plugs and lights in the garage.

I think I will have to use the 120V plug and see how it behaves - just pulling some juice at peak solar times would be nice and since I only have a 4kW system on the roof and typical house load of .5-.8kw for basic stuff it might just work out...

Thanks for the details.
 
Does anyone else have a single powerwall with a backed up 60a EV charging circuit/Tesla wall connector in California?

I have a single powerwall with the whole home backed up. Our baseline energy consumption is about 750w, and we rarely peak above 3kw usage so we're not usually at risk of overloading the 5kw powerwall output if we were to have an unexpected power outage.

Now, I'd like to install a Tesla Mobile wall connector on a 60a circuit and wondering if it's possible to do that on our backed up circuit.

Advantages would be tracking ev charging usage within the energy side of the app (since putting it in front of the gateway on a non-backed up panel wouldn't have the neurio CTs) and potentially in a longer outage, we might be able to "store" more of our excess solar (4.3 plus 5kw arrays) where on a good production day with a charging powerwall, it would curtail production if producing more than the 3-5kw that could be put into the battery+home load.

I'm thinking with a backed up wall connector, we might be able use it as a load to set it to charge at 2-3kw or whatever rate allows the powerwall to get charged to 100% while curtailing less solar production (i.e. the 9kw array could produce 7kw instead of being limited to 4kw).

The potential problem I see with backing up the EV charger is that if there was a power outage while charging at more than 4kw, it would overload the powerwall and shut it down. (Most of the time we would probably be charging slowly, since we've been getting by ok on a 120v mobile connector set at 10a for the past month since getting the car, but I like the idea of being able to charge at 7kw+ if we needed to turn the car around quickly.)

I know there's a setting about how much battery to use for EV charging versus home backup in my powerwall settings, but I think it can't be set lower than a 5% EV charging amount, right? If it was set at 20% and the powerwall was at 85% when an outage hit and the car was charging via the wall connector at 7kw, would the wall connector stop charging or reduce the rate, or would it just trip the Powerwall off?

It would be great if the wall connector could be set to instantly curtail or stop charging when the powerwall goes to off grid mode if the charging rate was set at more than the PW can provide and require manual initiation at a slower speed and even better if the the wall connector could vary the charging current based on how much solar there is and how much additional powerwall battery charging capacity is left. (I.e. if powerwall is 98% and solar would otherwise get frequency shifted off, the wall charger could modulate charging current to balance consumption with production.)

Hopefully someone here has some answers so I am a little more knowledgeable when I start talking to electricians to get install quotes for the wall connector.

Thanks!
 
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jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
17,521
23,492
Riverside Co. CA
Now, I'd like to install a Tesla mobile wall connector on a 60a circuit and wondering if it's possible to do that on our backed up circuit.

Not with one powerwall, you wont be able to do that. You could do it with a wall connector, but not a 60amp circuit. The circuit would need to be within the amount of power that a single powerwall can provide (30amp max).

You are also mixing terms, as there isnt anything called a "tesla mobile wall connector". There is a tesla mobile connector, which maxes out at 32amp charge rate (from a 40amp circuit) and a "tesla wall connector" which maxes out at 48amp charge rate (from a 60amp circuit).

If you want something on the backup load side its going to be probably a 20amp circuit, either with a tesla mobile connector, and a 240v 20amp outlet, or a tesla wall connector, set to a 20amp circuit.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
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Nov 28, 2018
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Riverside Co. CA
Oops, you're right, not sure how the word mobile slipped in there but my hope/ intention was to put a full 60a wall connector circuit into my backed up panel, provisioned for 50a charging if needed when grid power is active.

A single powerwall can only power a 30amp load max (that is max spec for a single powerwall), and that would include any other loads beside the wall connector.

Your choices, at least as I see them:

1. Do nothing
2. Put a circuit of some size in the non backed up load panel (60amp or otherwise depending on load calculations)
3. Put a circuit that the powerwall could handle on the non backed up load side for charging, depending on load calc, no more than 30amp but probably more like 15amp / 20amp
4. Buy another powerwall, then put the 60amp circuit on the backup load size that you want.

#4 is going to be the most expensive. If you want 60amp charging, you likely need to do #2. #3 is going to be a much smaller circuit than you are asking for.
 
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Agreed.
A single powerwall can only power a 30amp load max (that is max spec for a single powerwall), and that would include any other loads beside the wall connector too.
Agreed.

In my post I mentioned the max 5kw output of the single powerwall.

I'm not expecting the powerwall to exceed 30a output off-grid. I'm wondering if anyone knows if it's within code to have a 60a circuit in a backed up panel and whether the wall connector can gracefully stop charging if it was charging the car at more than 30a during an unexpected grid outage without tripping the powerwall off.

I wouldn't expect that I'd be charging at more than 30a regularly (probably a few times a year) and not when an outage might be expected such as during a wind/fire/flex alert event, but it would be nice to have the option.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
17,521
23,492
Riverside Co. CA
While you could put the 60A breaker in for the wall connector, and use it for the rare instances when you need a big boost quickly, you could finesse this by just continuing to routinely use the mobile connector that you have been using. (I.e. option3 in @jjrandorin's post)

Re reading what I wrote, option 3 was supposed to be "put a circuit the powerwall could handle on the backed up load side" (not the non backed up load side).
 
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Thanks for everyone's input!

I will have to talk with some electricians in the area, and my original powerwall installer about the options discussed above.

As I'm thinking about all of the options, I had a few more realizations;

1) Installing a 14-50 outlet with wiring and a 30 or 20 amp breaker for my mobile connector to run at a slightly faster speed and always charging at 20a or less on 240v is probably only marginally less expensive than installing the 60a circuit with my wall connector, but would allow me to charge the car half as fast and both circuits would still have the possibility of overloading the Powerwall if charging during a sudden unexpected off-grid event (because of other baseline house loads).
2) I already (in my full home backup setup) have the potential to be drawing >5kw at any time during the day which could cause a problem during an unexpected off-grid event. Even though it would be extremely rare for me to be running the oven and microwave and dryer and coffee maker/etc. all at the same time, the net effect would likely be the same as charging the car on the 60a wall connector with a sudden outage. -> The Powerwall would overload and the house would lose power, I would have to manually shed loads (i.e. turn off the charger breaker or unplug the car, turn off the oven, etc.) and toggle the Powerwall off and on to regain power to the house. Since the number of unexpected grid outages we've had since installing the Powerwall in the last 3 years has been <10 and has actually decreased over time with changes that SCE has made, I think this is a risk I might be willing to take, for the improved capability of charging the car faster when needed.
3) Even if charging at <32a most of the time, there's still an advantage to the wall connector since it'll be outside of my house and accessible from the driveway in that we can specify that only our car can charge from it. (Yes, unlikely that another random person would park in our driveway and plug into our charger cable, but people do weird stuff, and I don't want to have to think/remember to flip off the charging circuit breaker anytime we leave the house for a longer period of time or vacation.)
4) The wall connector doesn't offer an advantage over the mobile connector on a 14-50, if trying to use the car battery charging as a load to improve solar capture during a grid outage (with ~9-10kw solar, and a moderately charged PowerWall battery, it's unlikely that we'd want to set the car to charge at greater than 32a(32*240=7.6kw) since the sun going behind the clouds could cause a drop in production and if solar production dipped below 3.6kw (7.6kw car charging + 1kw baseline house load - 5kw Powerwall limit = 3.6kw solar needed at all times during off-grid car charging at 7.6kw) that the battery couldn't replace and would cause an overload shutdown condition.
 

power.saver

Grid Specialist
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Mar 4, 2018
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Arcadia, CA
Thanks for everyone's input!

I will have to talk with some electricians in the area, and my original powerwall installer about the options discussed above.

As I'm thinking about all of the options, I had a few more realizations;

1) Installing a 14-50 outlet with wiring and a 30 or 20 amp breaker for my mobile connector to run at a slightly faster speed and always charging at 20a or less on 240v is probably only marginally less expensive than installing the 60a circuit with my wall connector, but would allow me to charge the car half as fast and both circuits would still have the possibility of overloading the Powerwall if charging during a sudden unexpected off-grid event (because of other baseline house loads).
2) I already (in my full home backup setup) have the potential to be drawing >5kw at any time during the day which could cause a problem during an unexpected off-grid event. Even though it would be extremely rare for me to be running the oven and microwave and dryer and coffee maker/etc. all at the same time, the net effect would likely be the same as charging the car on the 60a wall connector with a sudden outage. -> The Powerwall would overload and the house would lose power, I would have to manually shed loads (i.e. turn off the charger breaker or unplug the car, turn off the oven, etc.) and toggle the Powerwall off and on to regain power to the house. Since the number of unexpected grid outages we've had since installing the Powerwall in the last 3 years has been <10 and has actually decreased over time with changes that SCE has made, I think this is a risk I might be willing to take, for the improved capability of charging the car faster when needed.
3) Even if charging at <32a most of the time, there's still an advantage to the wall connector since it'll be outside of my house and accessible from the driveway in that we can specify that only our car can charge from it. (Yes, unlikely that another random person would park in our driveway and plug into our charger cable, but people do weird stuff, and I don't want to have to think/remember to flip off the charging circuit breaker anytime we leave the house for a longer period of time or vacation.)
4) The wall connector doesn't offer an advantage over the mobile connector on a 14-50, if trying to use the car battery charging as a load to improve solar capture during a grid outage (with ~9-10kw solar, and a moderately charged PowerWall battery, it's unlikely that we'd want to set the car to charge at greater than 32a(32*240=7.6kw) since the sun going behind the clouds could cause a drop in production and if solar production dipped below 3.6kw (7.6kw car charging + 1kw baseline house load - 5kw Powerwall limit = 3.6kw solar needed at all times during off-grid car charging at 7.6kw) that the battery couldn't replace and would cause an overload shutdown condition.
You don't need to worry about #4. During a grid outage, EV charging is limited to excess solar (Solar - Home) or when there is no solar to (PW Limit - Home) so you will not overload the PW. The car will modulate the charging rate to prevent overload.
 
Oh wow- that would be awesome, and what I'd hope would happen, but I haven't been able to find a hard source that would confirm it.

I suspected that if scheduled charging was set to turn on during a time when the powerwall was off-grid, that it would limit total battery usage oer the available settings (i.e. to 5% minimum of the battery, since the slider doesn't allow you to completely turn off charging during off-grid) but it doesn't mention anything about automatically communicating with the charger (via frequency shift?) to make the charger reduce charging current, and whether that will happen fast enough if charging at a high current upon sudden grid outage such that the powerwall doesn't overload and turn off because the car charger tried to obtain more than the 5kw that the powerwall can put out.
 

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