Charging 2 Teslas in a sequence

[roblab]

I have a hundred amp sub panel in my garage, which supports an electric water heater, a resistance heater, garage door openers, and so forth. Charging on two 50 amp circuit breakers would absolutely cut off the power. Since I have found that my cars have all night, and rarely need over a hundred miles of charge, I just set them at low amps on the dash. They are both charging at 24 amps, and I have never had any trouble or insufficient charge when I went out in the morning. Saves a lot of money on timers, too.

 

[nwdiver]

which supports an electric water heater

Can't help it... gotta plug my favorite energy saving appliance... Sounds like it could save a little capacity too; in heat pump mode it only uses ~2A (500w). You could probably get away with putting it on a 10A circuit, you just wouldn't be able to use the backup resistance elements.

Rheem Heat pump water heater

 

[ai4px]

What kind of upgrade did you look into? Upgrading the Distribution Panel would indeed be VERY costly because it's labor intensive. ~$3k would not be unreasonable. An alternative would be tapping off your meter base. It should be possible to connect a standalone 60-100A breaker directly to your meter base then use that to feed your HPWC. This would also make charging slightly faster and more efficient. Not sure about electricians in your area but my company would be able to do this for <$500. This is what we have to do if we want to install >8kW on a 200A service...

This is an interesting idea... particularly if you tap the TOP two wires instead of the bottom two wires. snicker.

 

[nwdiver]

This is an interesting idea... particularly if you tap the TOP two wires instead of the bottom two wires. snicker.

Sadly the utility will inspect to ensure it's configured correctly before they install their tamper seal. They caught my 'mistake'

 

[eprosenx]

I've searched a little, but I can't quite find the reference. However, @eprosenx has been reading the new electric vehicle code sections a lot and can probably find that. Do you know the line that says an outlet installed for electric vehicle charging has to be the one dedicated outlet on a branch circuit? I think that was recently added to the NEC section 625.

Yup! NEC 2017 (NFPA 70) - Page 515 of the online free access reference (you have to register with an email address to get access).

625.40 - Electric Vehicle Branch Circuit. Each outlet installed for the purpose of charging electric vehicles shall be supplied by an individual branch circuit. Each circuit shall have no other outlets.

While the NEC is murky and unclear on a lot of things, this piece is pretty crystal clear to me!

In reading this thread, clearly the best solution is two HPWC units that talk with each other to keep load managed under a certain level.

It is kind of sad that the "standard" charging method (J1772) is not a little nicer. Right now the Tesla Wall Connector is a pretty amazing deal. $500 for something that can do up 19,200 watts! Supports multiple units sharing out of the box! Has a 24' cable! Is indoor/outdoor rated! The cable has a sleek and compact connector (better than J1772 I think).

The sad part is that it is proprietary. What if you want a second EV that need J1772? You are stuck with no sharing ability...

I think the future is not only "linked" chargers, but also chargers that understand what your current house draw is in total (i.e. CT's on the mains that the data feeds from to the EVSE's). So in most cases you can support both at full bore as long as you are not running the oven and dryer and AC at the same time. In the middle of the night even on a 100a service you could give nearly full power to two cars... The key is that since there is no feedback loop, today, NEC requires us to calculate as if the oven is always running, etc...

 

[eprosenx]

What kind of upgrade did you look into? Upgrading the Distribution Panel would indeed be VERY costly because it's labor intensive. ~$3k would not be unreasonable. An alternative would be tapping off your meter base. It should be possible to connect a standalone 60-100A breaker directly to your meter base then use that to feed your HPWC. This would also make charging slightly faster and more efficient. Not sure about electricians in your area but my company would be able to do this for <$500. This is what we have to do if we want to install >8kW on a 200A service...

Can you confirm that this kind of "tap" is generally done for solar backfeed applications? It sounds to me like the 8kw you refer to is due to not being allowed to backfeed a traditional 200a panel with more than 20% of the overall rating. So 40 amp breaker would be the max for solar backfeed, and then my guess is a further derate to 80% of that due to it being considered a continuous load, so 32a * 240 = 7,680 watts.

I don't see what the benefit for doing this kind of install would be unless it was because the main panel was only 100a rated, but the meter and meter base and the service drop was rated for 200a and so you would be creating a second "service disconnect" with its own "panel" just to serve the car charging?

This would totally work, but I wonder how often you find a scenario where the service drop and meter base is already rated for over what the inside panel are rated for? (perhaps this is really common since I don't think they really make meters below a 200a rating anymore I don't think?)

I do totally agree that the labor involved in swapping a service panel out is a lot! Often the wires are not all of sufficient length and they need to be extended, etc... Though often these service upgrades are a really good thing since they replace old and questionable ancient panels with new and modern ones that are easier to get parts for, etc....

 

[ai4px]

I think the future is not only "linked" chargers, but also chargers that understand what your current house draw is in total (i.e. CT's on the mains that the data feeds from to the EVSE's). So in most cases you can support both at full bore as long as you are not running the oven and dryer and AC at the same time. In the middle of the night even on a 100a service you could give nearly full power to two cars... The key is that since there is no feedback loop, today, NEC requires us to calculate as if the oven is always running, etc...

What you speak of already exists ... the Smart EVSE from Netherlands has a current transformer and will adjust the pilot signal accordingly to limit current draw. You could hook up several each with it’s own CT. No need for them to comunicate with each other

 

[nwdiver]

Can you confirm that this kind of "tap" is generally done for solar backfeed applications? It sounds to me like the 8kw you refer to is due to not being allowed to backfeed a traditional 200a panel with more than 20% of the overall rating. So 40 amp breaker would be the max for solar backfeed, and then my guess is a further derate to 80% of that due to it being considered a continuous load, so 32a * 240 = 7,680 watts.

I don't see what the benefit for doing this kind of install would be unless it was because the main panel was only 100a rated, but the meter and meter base and the service drop was rated for 200a and so you would be creating a second "service disconnect" with its own "panel" just to serve the car charging?

This would totally work, but I wonder how often you find a scenario where the service drop and meter base is already rated for over what the inside panel are rated for? (perhaps this is really common since I don't think they really make meters below a 200a rating anymore I don't think?)

I do totally agree that the labor involved in swapping a service panel out is a lot! Often the wires are not all of sufficient length and they need to be extended, etc... Though often these service upgrades are a really good thing since they replace old and questionable ancient panels with new and modern ones that are easier to get parts for, etc....

As you described the limiting component is the panel bus. If you've got a 200A main you cannot back feed >40A of solar (40A Breaker 32A Solar really...) even though the service is more than capable of back feeding >60A (~15kW) of solar. I've helped install 3 systems that exceeded the bus rating. For car charging it would get a bit trickier since you're not back feeding... Might need to upgrade the meter base or downsize the 200A main breaker to 100A... either would be cheaper than replacing the main panel.

Wish I had a better picture... this is 22.8kW of solar landed directly in a 400A meter base. The smaller meter on the left is the production meter. There's 2 11.4kW inverters feeding a dedicated 'back feed only' 150A sub panel.

 

[Rocky_H]

The sad part is that it is proprietary. What if you want a second EV that need J1772? You are stuck with no sharing ability...

Then you should get one of these from Quick Charge Power
80A home charger, HPWC, High Power Wall Charger, Tesla
They take Tesla wall connectors and replace the cords with J1772 handles, so they still have the same power sharing functionality.

 

[miimura]

Then you should get one of these from Quick Charge Power
80A home charger, HPWC, High Power Wall Charger, Tesla
They take Tesla wall connectors and replace the cords with J1772 handles, so they still have the same power sharing functionality.

They also sell a lower priced 40A version. The cable and J1772 handle are cheaper and lighter because they don't have to handle the full 80A current, but the Wall Connector box is the same.

 

[gfb107]

If you want to charge an J1772-capable EV from a (stock) Tesla Wall Connector or UMC in North America or Japan, use one of these: JDapter Stub (Tesla Charge Station Adaptor)

 

[eprosenx]

Then you should get one of these from Quick Charge Power
80A home charger, HPWC, High Power Wall Charger, Tesla
They take Tesla wall connectors and replace the cords with J1772 handles, so they still have the same power sharing functionality.

So are these people buying Tesla HPWC units retail and them modifying them or do they have some source for the base parts and doing some custom manufacturing?

I know the HPWC is actually made by Delta electronics.

Making an officially supported J1772 unit that could talk to HPWC units would be a brilliant idea. A huge deal for some folks homes and businesses.

Of course, if you sold a J1772 version, then there would be no much reason for folks to buy the proprietary Tesla connection one.

 

[Rocky_H]

So are these people buying Tesla HPWC units retail and them modifying them or do they have some source for the base parts and doing some custom manufacturing?

Yes, they buy the real one for $500 and modify it. That's why theirs costs about $999. They have that full $500 parts cost before their other parts and labor cost get added to that for the conversion. And that's why you can also buy the spare replacement cables with the Tesla handles on them--because they are removing one of those and reselling it for each one of those wall connectors they buy and convert. It's still a good deal, though, for high power ones because the Tesla wall connector is such a good deal to start with. A Clipper Creek J1772 unit that can use a 100A circuit is $2,195.

 

[eprosenx]

Yes, they buy the real one for $500 and modify it. That's why theirs costs about $999. They have that full $500 parts cost before their other parts and labor cost get added to that for the conversion. And that's why you can also buy the spare replacement cables with the Tesla handles on them--because they are removing one of those and reselling it for each one of those wall connectors they buy and convert. It's still a good deal, though, for high power ones because the Tesla wall connector is such a good deal to start with. A Clipper Creek J1772 unit that can use a 100A circuit is $2,195.

Makes sense.

But talk about a mess. I presume they kill the UL listing of the device to do the modification and I am sure Tesla won’t support it anymore, so that would give me great pause and not make me want to buy one.

 

[Duckjybe]

I have dual HPWC's running off a 50A breaker at 40A. One problem I ran into over the winter was at very cold temperatures (-35 C) neither car would charge at the split 20A for some reason when both were plugged in. The solution was to only charge one car at a time. I contacted Tesla as I believed it was a software problem either in the HPWC's or the car. I never followed up but I hope it gets resolved. We will see next winter if we get temps that low again.

 

[brkaus]

They also sell a lower priced 40A version. The cable and J1772 handle are cheaper and lighter because they don't have to handle the full 80A current, but the Wall Connector box is the same.

Note if you get the 40a one, the other, even if not modified must also run 40a max.

They do sell this - JDapter Stub

But I’m not a fan of lots of connections.

 

[eprosenx]

I have dual HPWC's running off a 50A breaker at 40A. One problem I ran into over the winter was at very cold temperatures (-35 C) neither car would charge at the split 20A for some reason when both were plugged in. The solution was to only charge one car at a time. I contacted Tesla as I believed it was a software problem either in the HPWC's or the car. I never followed up but I hope it gets resolved. We will see next winter if we get temps that low again.

Wow! That is a fascinating edge or corner case you found! I would push on Tesla to figure it out.

I wonder if the batteries were too cold and so they needed more than 20a to run the heaters to get them up to a safe temperature at which to charge?

-35C is pretty cold!

 

[Duckjybe]

Wow! That is a fascinating edge or corner case you found! I would push on Tesla to figure it out.

I wonder if the batteries were too cold and so they needed more than 20a to run the heaters to get them up to a safe temperature at which to charge?

-35C is pretty cold!

Yes I think it had something to do with amount of current used for battery heating and signalling between car and HPWC.

 

[tga]

Yes I think it had something to do with amount of current used for battery heating and signalling between car and HPWC.

I don't think it's a software issue. How long did you leave them each pulling 20A? The battery heater can pull around 6kw; at those temps I've plugged a cold-soaked car into a 30A circuit, pulled 24A for a while (at least an hour or 2) without any increase in charge level. Once the battery warms it should start to charge slowly. As it continues to warm, the charge speed will improve.

The trick is to plug in and start charging as soon as you get home while the battery is still warm, or just be patient.

 

[FlatSix911]

Can't help it... gotta plug my favorite energy saving appliance... Sounds like it could save a little capacity too; in heat pump mode it only uses ~2A (500w). You could probably get away with putting it on a 10A circuit, you just wouldn't be able to use the backup resistance elements.

Rheem Heat pump water heater

Can you elaborate on the benefits ...