Incorporating a Lightning into an existing PV system - without HIS

[world2steven]

Very helpful discussion

I'll second that. Thanks! I'm going to pass this to my electrician. I found this with a quick check of Amazon:
10000W Voltage Converter Transformer Step Up/Down 110V/220V Heavy Duty Voltage Converter USB Transformer Power Converter Circuit Breaker
Would all autotransformers be split phase or do we need to look for that? And would 7500w be big enough

Could this be a silver bullet not just for Lightning owners but for those who have EVs with vehicle-to-load capabilities like the Ioniq5? (1.7 kw won't run an AC but 73 kwh could keep a frig going a long time.)

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[world2steven]

I assume isolation transformers, autotransformers and switched neutral transfer switches are all code compliant? If that's the case, would an autotransformer be the most straight-forward, least expensive way to go? 10k watts large enough to cover what the Lightning can supply?

 

[Maquis]

I assume isolation transformers, autotransformers and switched neutral transfer switches are all code compliant? If that's the case, would an autotransformer be the most straight-forward, least expensive way to go? 10k watts large enough to cover what the Lightning can supply?

Put it this way, they can all be installed in a code-compliant manner. The devil is in the installation details.

An autotransformer provides a way to maximize the power available to 120V loads. It does not solve the bonded neutral GFCI tripping problem. An isolation transformer can do both.

The isolation transformer size will depend on how unbalanced your 120V loads will be. If you want to pull all 7.2KW from one 120V leg, you would need a 15KVA transformer. That’s extreme. For practical use a 10KVA should be fine. That would permit over 40A of 120V loads from either side. Total power is still limited by the truck’s 7.2KW limit.

You should work all of this out with the electrician doing the installation.

 

[world2steven]

An autotransformer provides a way to maximize the power available to 120V loads. It does not solve the bonded neutral GFCI tripping problem.

There appears to be a difference of opinion:

Based on the 240V only load test results (https://www.f150lightningforum.com/forum/threads/using-lightning-as-a-generator.14994/post-309716) with the Lightning, I am now also confident you can use an autotransformer instead of an isolation transformer to connect the Lightning to the Sol-Ark generator port with connected ground without issue.

Is v2h8484 saying 'you can get away with connecting a Lightning to a Sol Ark 240V generator port because the Lightning only checks 120V loads for faults?' The link included in the post suggests the tripping is "due to load imbalance", not ground faulting. For us electrical illiterates, this would seem to make sense. How can Sol Ark say they have a generator port if it can't be used with what I assume is a major class of generators, i.e. bonded neutral generators?

 

[Maquis]

There appears to be a difference of opinion:

Is v2h8484 saying 'you can get away with connecting a Lightning to a Sol Ark 240V generator port because the Lightning only checks 120V loads for faults?' The link included in the post suggests the tripping is "due to load imbalance", not ground faulting. For us electrical illiterates, this would seem to make sense. How can Sol Ark say they have a generator port if it can't be used with what I assume is a major class of generators, i.e. bonded neutral generators?

A functional GFCI will trip when any load is applied and there is a neutral to ground connection anywhere downstream. That’s how they are designed to work. An autotransformer does nothing to mitigate that.

That would be a question to ask SolArk.

And I’ll repeat - discuss all of this with the electrician you plan to use for the install. He’ll be responsible for making it work, not some random person on a forum (me).

 

[world2steven]

For my electrical edification:

I’m guessing both switched neutral transfer switches and isolation transformers solve the problem of the Lightning potentially back feeding current from its neutral bonded generator to other components sharing its ground by having their own real earth grounds? So an autotransformer doesn’t or can’t?

P.S. If I am all wet, I am also guessing my misconceptions are shared by other electrically illiterate readers.

 

[Maquis]

For my electrical edification:

I’m guessing both switched neutral transfer switches and isolation transformers solve the problem of the Lightning potentially back feeding current from its neutral bonded generator to other components sharing its ground by having their own real earth grounds? So an autotransformer doesn’t or can’t?

P.S. If I am all wet, I am also guessing my misconceptions are shared by other electrically illiterate readers.

Correct. Switching the neutral eliminates the main panel N-G connection when running on standby power.

The only thing accomplished by the autotransformer is load balancing. The Lightning’s rated output is 7.2KW at 240V. That’s 30A. If you only use 1 side for 120V, you are still limited to 30A so the most power available is 30 x 120 = 3.6KW. A properly-sized autotransformer will allow you to get up to the full 7.2KW from one 120V circuit. This is normally only important when powering RVs from a generator, because their panels are usually wired to use a single 120V circuit. When powering a home, I wouldn’t use an autotransformer because the loads should be somewhat balanced between each of the 120V circuits.

 

[v2h8484]

A neutral forming autotransfomer would resolve the Lightning GFCI issue because it would not have neutral connected to the Lightning. So, the Lightning never sees a 120V load. Here is the basic wiring diagram (Lightning would be the "120/240V Generator" on the left):

You are limited to 7.2kW (30A@240V) by the Lightning so you need an autotransformer that has 30A or greater current capacity. The higher the current capacity the greater load imbalance capacity. Theoretically, you would need a 60A autotransformer to access the full power capacity of the Lightning under the most extreme scenario where you run 7.2kW (60A@120V) of 120V loads all on one 120V leg and nothing on the other 120V leg. It's not a realistic scenario since normal house wiring is unlikely to allow such extreme scenario. Practically speaking, it's unlikely to have imbalance greater than 30A (3.6kW@120V).

The autotransformers found on Amazon and eBay typically have the receptacles wired for European standards so make sure you don't use the them without rewiring or just use the terminal block for wiring.

It's NEC compliant to use an autotransformer provided it's installed properly. However, you should check with an electrician knowledgeable about your local AHJ rules that may have additional requirements.

 

[world2steven]

A neutral forming autotransfomer would resolve the Lightning GFCI issue because it would not have neutral connected to the Lightning. So, the Lightning never sees a 120V load. Here is the basic wiring diagram (Lightning would be the "120/240V Generator" on the left):

You are limited to 7.2kW (30A@240V) by the Lightning so you need an autotransformer that has 30A or greater current capacity. The higher the current capacity the greater load imbalance capacity. Theoretically, you would need a 60A autotransformer to access the full power capacity of the Lightning under the most extreme scenario where you run 7.2kW (60A@120V) of 120V loads all on one 120V leg and nothing on the other 120V leg. It's not a realistic scenario since normal house wiring is unlikely to allow such extreme scenario. Practically speaking, it's unlikely to have imbalance greater than 30A (3.6kW@120V).

The autotransformers found on Amazon and eBay typically have the receptacles wired for European standards so make sure you don't use the them without rewiring or just use the terminal block for wiring.

It's NEC compliant to use an autotransformer provided it's installed properly. However, you should check with an electrician knowledgeable about your local AHJ rules that may have additional requirements.

Thanks! This looks pretty definitive.

 

[Maquis]

A neutral forming autotransfomer would resolve the Lightning GFCI issue because it would not have neutral connected to the Lightning. So, the Lightning never sees a 120V load. Here is the basic wiring diagram (Lightning would be the "120/240V Generator" on the left):

You are limited to 7.2kW (30A@240V) by the Lightning so you need an autotransformer that has 30A or greater current capacity. The higher the current capacity the greater load imbalance capacity. Theoretically, you would need a 60A autotransformer to access the full power capacity of the Lightning under the most extreme scenario where you run 7.2kW (60A@120V) of 120V loads all on one 120V leg and nothing on the other 120V leg. It's not a realistic scenario since normal house wiring is unlikely to allow such extreme scenario. Practically speaking, it's unlikely to have imbalance greater than 30A (3.6kW@120V).

The autotransformers found on Amazon and eBay typically have the receptacles wired for European standards so make sure you don't use the them without rewiring or just use the terminal block for wiring.

It's NEC compliant to use an autotransformer provided it's installed properly. However, you should check with an electrician knowledgeable about your local AHJ rules that may have additional requirements.

Yes, when wired this way, the GFCI tripping in the truck is solved. My previous comments were thinking about a different arrangement.

After thinking about this more, I don’t think it will work unless you use a transfer switch that switches the neutral. Notice that in the diagram, the N-G bond is shown only at the generator. No other bond.

 

[world2steven]

For my electrical education: presumably the Lightning's generator needs to be connected to ground in the circuit because current could be transmitted through transformer induction even though there is no neutral connection? Isn't the idea of a neutral bonded ground to send current back to a safe ground for a stand-alone generator? How does the Lightning sense another path to ground?

 

[ridgebackpilot]

Yesterday I met with two electricians who came to install another Tesla Powerwall at my house. They work for a major solar electrical contractor in my area.

They were quite familiar with efforts to incorporate the F150 Lightning into home solar installations as a backup generator. They were also acquainted with the neutral-bonded ground issue.

They agreed the simplest, easiest, and cheapest way to accomplish this is to install a double-throw manual safety switch that isolates the grid and solar array from the Lightning. They also said the easiest way to solve the ground fault problem is to remove the ground pin from the plug, which we already knew. They seemed to think that the existing grounds at the house would serve to protect the system, including the truck, from any electrical anomalies.

What do you think?

 

[v2h8484]

Yes, when wired this way, the GFCI tripping in the truck is solved. My previous comments were thinking about a different arrangement.

After thinking about this more, I don’t think it will work unless you use a transfer switch that switches the neutral. Notice that in the diagram, the N-G bond is shown only at the generator. No other bond.

The diagram only shows what should be done on the generator side for connection to house wiring (not shown in the diagram) which has its own N-G bond at the main panel. As mentioned in another post, I (and others) have successfully used this setup with N-G bonded 120/240V generators for connection to house wiring.

 

[world2steven]

The diagram only shows what should be done on the generator side for connection to house wiring (not shown in the diagram) which has its own N-G bond at the main panel. As mentioned in another post, I (and others) have successfully used this setup with N-G bonded 120/240V generators for connection to house wiring.

Good to hear neutral forming autotransfomers are still a possibility. It appears there are a lot of possibilities with which even professional electricians may not be familiar. Some questions:

• I assume this type of transformer is readily available?
• Is its use code-compliant?
• Can I get a step-up neutral forming autotransformer? I would like to be able to use the 120v output of my Ioniq5 as input to the generator port of my Sol Ark.

 

[v2h8484]

Good to hear neutral forming autotransfomers are still a possibility. It appears there are a lot of possibilities with which even professional electricians may not be familiar. Some questions:

• I assume this type of transformer is readily available?
• Is its use code-compliant?
• Can I get a step-up neutral forming autotransformer? I would like to be able to use the 120v output of my Ioniq5 as input to the generator port of my Sol Ark.

As you have found, generic ones are available on Amazon but you may need to rewire them. Solar/inverter companies also offer them. Check Victron, Growatt, SolarEdge, etc.

120V generators also work. However, keep in mind that you need autotransformers that have double the power capacity of the 120V generator.

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