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Discussion Starter #1
I've ordered the Tesla Gen 2 MCU and have asked an electrician to install an appropriate line and NEMA 14-50 plug.

I have a Generac 10kVa backup generator with an automatic transfer panel (ATM) on my home.
This was installed primarily for my sump pumps and fridge. We purposely significantly under-loaded it.

It makes sense to me to have the charger wired to the generator ATM so I can charge my car during a power outage.

However, I'm wondering if that is a good idea as it seems the MCU can pull a lot of peak amps, too.
Although, I can choose when to charge (i.e. not if it is raining and pumps running) although it could all occur in the middle of the night....
Last thing I want to do is burn out the generator then be SOL.

Any thoughts?
 

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If you are using the Tesla MCU, have a NEMA 10-30 or 14-30 receptacle installed next to your 14-50 receptacle, and get that adapter for the MCU. Using the MCU with that adapter limits it to 24 amps (5.8 KW) leaving some head room on your generator for other loads. Use the 5.7 KW charging for normal day to day, and only use the 14-50 receptacle and MCU adapter (7.7 KW) if you really need it and don't have conditions that would make you expect the generator to possibly kick on.

Keith
 

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If you are using the Tesla MCU, have a NEMA 10-30 or 14-30 receptacle installed next to your 14-50 receptacle, and get that adapter for the MCU. Using the MCU with that adapter limits it to 24 amps (5.8 KW) leaving some head room on your generator for other loads. Use the 5.7 KW charging for normal day to day, and only use the 14-50 receptacle and MCU adapter (7.7 KW) if you really need it and don't have conditions that would make you expect the generator to possibly kick on.

Keith

This kind of requires you to know you're going to have a power outage before you actually have it. I can see having the second plug to switch over to if an outage has occurred, but I'd normally charge from the higher output plug, and only switch to the lower if there was an outage and I actually needed the charge. Generators consume more fuel under load, and I wouldn't charge my car that way unless it was an emergency.


This all does assume the EVSE in question is good at blocking the transients that come with power out and restoration.
 

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What model # is your generator? If you have a Generac 10kVa generator that is the 8kW generator which can only produce 7000 watts if you are running NG. That's assuming you actually get the performance that the specification sheet indicates. You lose 3.5% performance for each 1000 feet above sea level. It's a calculation one almost never even mentions except your plans as I 'understand' them will put you at the very limit of the generator with my guestimate of your existing load. Ironically, I'm in the middle of installing a Generac SMM to isolate my Bolt (which arrives Saturday) from the 22kW generator. I would suggest you install an SMM so that it can shed that load automatically, but part of me is thinking it's going to always shed the load because you are at the limit. In any case, just trying to protect your generator. Not sure how clean the power is going to be under that load. I have a lot of questions, and I'm reluctant to say much because I don't want to be a negative nancy. The maximum circuit size for the 8kW is a 30 amp circuit, so technically speaking you can do it. As FiveDoor said above you're going to draw 6kW on a generator that (if on NG) can only produce 7. It's the continuous load aspect too. Just my 2 cents.
 

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Too be electrically "correct" should some type of a selector switch be inserted between the two plugs so you can't have both plugs live simultaneously?
You can have both live at the same time, as in energized. However, the LOAD of the total circuit .... BOTH PLUGS cannot exceed the rating of the circuit breaker and the appropriately sized wire. You can put in multiple plugs onto the same circuit. If you apply a load to both at the same time, the circuit breaker will trip as it should. That's the way it works. No different than a room in your house. You have many 15amp receptacles in that room and I'm sure there are a couple or a few on a single 15 amp circuit breaker. Plug a big power hungry vacuum cleaner in one, a hair dryer in another and a mini arc welder into the third. The circuit breaker will trip to protect the circuit/wiring/you.
 

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You can have both live at the same time, as in energized. However, the LOAD of the total circuit .... BOTH PLUGS cannot exceed the rating of the circuit breaker and the appropriately sized wire.
Yeah - you'd only need some sort of lockout if you PLAN to overload the generator by plugging in more load than it can handle. The purpose of that would be to prevent the circuit breaker from tripping so that, for example, your car would continue to charge at the expense of whatever else was plugged in.
 

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Discussion Starter #10 (Edited)
Well, I was thinking more from an electrical code standpoint, not that I would every try to use both at the same time.
However, your home-circuit analogy makes sense to me

My Generac is about 10+ years old.
Model Number 0058830
The label also states: Amps 83.3/41.7
And: "MAX Load Unbalanced - 50%"

Which makes me think I'm not safely going to get anywhere near 10KVa unless I carefully balanced current draw, which seems unlikely for an emergency backup generator primarily powering sump pump(s).


I really don't have much on this generator; it is primarily to keep my basement from flooding.

I have two sump pumps (one is in an overflow sump as a backup) and they are rated at a Full Load Amps of 10.4 each (120V).
Also, have the fridge at Full Load Amps of 3.2 (120V)
I also have a few circuits on there to keep the basement lights on but otherwise, nothing else that draws significant current

But, if what I'm interpreting is correct, I have 10.4+10.4+3.2 = 24 AMPS (Although second sump pump is a backup; but you never know...)

That only leaves me 17 Amps to play with? That's not much better than my Level 1 charger....
 

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I'm using a SMM for my generator. In my case, without any doubt I have enough capacity to run my charger in all it's glory. However, my EV is a 2nd car for me and before I put it in the face of locally generated power I need to look more closely at the quality of the power it's handing out. I will do that in a week. I also run in a situation where the generator is capable of delivering much more than I need. My whole house was sized for a 17kW. But I follow the one better rule so for $100 more I could buy the 20kW. But then I looked at the 22kW, it has an all aluminum outer shell versus galvanized (could rust) shell. The 22kW actually uses less NG than the 17 and runs quieter. It was $100 more than the 20kW. So, I have a 22kW. I don't want to run my generator at full load or quite frankly no where near full load. My car won't task the generator greatly in my situation. Everyone has a different situation. So, by putting a SMM on mine. Here's what I gain:


I can choose to lock out the EV from generator power. If I want to include the EV during an outage, it's just a simple slide switch.
I can choose to have the EV included in the generator load, but program the SMM to not energize the car until the outage has been 30 minutes or more.
If the EV is on generator load, and the SMM detects that the generator is exceeding it's capacity, it will automatically SHED the EV and keep it offline.


On paper, it sounds super nifty. In reality, the SMM doesn't do a perfect job of shedding. Remember, it has to see the generator struggling and then it reacts. I don't want the generator to be in that situation in the first place.



Without knowing the startup load of your pumps, their true (real world power draw) and seeing the real numbers for load on your generator. And taking into account you have 7kW of usable load if you are on NG (Nat Gas) I'm skeptical that it's the best direction for you. We know, at 24amps, you're going to use 6kW, luckily that is split 3kW per side assuming the LVL 2 chargers do indeed play fair. Like I said, just my 2 cents. I'll upload a picture of my setup with my SMM and offline if you're interested in what I've learned from the SMM versus PMM I can share. This is a car forum so I'm trying to stay on topic. If you are going to do it, you should look at putting slow starts on your pumps. That way, they don't spike during start in current draw. PM me for details.
 

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Well, I was thinking more from an electrical code standpoint, not that I would every try to use both at the same time.
However, your home-circuit analogy makes sense to me

My Generac is about 10+ years old.
Model Number 0058830

Your generator is rated at 29.2 amps maximum continuous load with natural gas and 33.3 amps with propane.
 

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Discussion Starter #13
Well, that sucks. I'm running NG.
So basically, if both my pumps and the fridge are running, I've got enough to light a few lights.
I guess I will leave the EV charging circuit off of the Gen panel. Worst case I can go back to my Level 1 charger and have enough to get to work.

I chose the 10KVa because (1) my primary goal was to keep the basement from flooding, (2) I wanted the generator quite a distance from the house because of noise (and other factors) (3) the house is "all electric" and to go down the slippery slope of running a heat pump, etc was going to significantly increase the cost (the increased cost of the larger-guage copper that was needed was several thousand dollars by itself).


Oh well, the likelihood of my EV becoming non-functional due to a power outage is still pretty low....
 

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^ I modded my OEM Volt EVSE back in the day to run off 240VAC.
That was a more involved and less safe mod that relied on the ground circuit and one 120V hot side to power the electronics inside the EVSE. If you tried to run it on a GFI circuit... pop!


The mod for the current OEM Bolt EVSE is super easy and safe as it was designed to run off 120 or 240VAC. No disassembly required, no cutting PCB traces, no soldering like on the old Volt EVSE.


Have fun!
 

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I took delivery of my Bolt today and got half of the Level 2 charger installed today as well. This is in the garage, bringing a 100 amp service into the garage to this sub-panel. From this I'm going to power:
30 amp RV circuit.
50 amp RV circuit.
20 amp receptacle.
50 amp circuit for EV1 - the JuiceBox Pro 40 you see in the picture.

I haven't strapped the conduit down, and the main run isn't in as you can see. But this is the SMM I talked about, that will load shed or lockout the EV charger if needed. It runs in series to the charger.
 

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