AC vs DC?

[steven]

I am getting ready to join the ranks of Lightning owners tapping their batteries through the 240v truck bed socket. My electrician explained there is more risk to the truck from power faults doing it this way than there would be using the HIS and Charge Station Pro. Here is the electrician’s explanation:

With the truck powering the house, you’ll see we have opposing bonded neutral connections. Since the truck’s chassis is insulated from earth by the tires, it doesn’t have a reference to earth ground. This creates that parallel ground path I’ve mentioned, since electricity wants to take the path of least resistance to ground. The X’s in boxes along the return path show how it can “crash” into itself along the way. This crashing is usually evident in real life by equipment blowing up because of the amount of energy sustained in a fault.

If I understood his explanation, with the CSP / HIS power from the truck is supplied using direct rather than alternating current, reducing the risk from the neutral bonded ground in a power fault.

From what I gather, neutral bonded (grounded?) generators are common, maybe even the rule. Sol Ark supports generators. Are there other hybrid inverters that do? Are there other bidirectional charging stations that use DC in their V2H transfers? Anyone have any idea how much more risk there is to the truck using AC and the 240v output socket rather than DC through the CSP to the Home Integration System?

 

[Ssob]

First of all, I'm not an electrician, but I have researched this because I have an F150 hybrid with the 7.2Kw onboard generator. My understanding is that one can use the 240V AC outlet of the PowerPro to feed back to the house, within the constraints of the current limits of the circuit. However, as your electrician points out, and does a good job of illustrating, there is a problem with how the neutral is bonded at the truck versus the house. The good news is that the truck has protection to prevent the damage from occurring if one just makes the connection between the truck and the house - see the second video, below.

To make it work requires the use of a transfer switch that breaks the neutral/ground bond at the house, relying only on the neutral bonding at the truck during the use of the truck as a generator. When the transfer switch is applying grid power (normal state) the ground-neutral bond is restored at the house and the connection to the truck is opened. The first video is a good explanation of what would be required to safely make it work.

Steve

 

[steven]

Thanks for your reply. If I understood my electrician, just breaking the neutral bonding at the house might not be enough to protect the truck. I have Lightning and solar with a 260ah battery backup. up to a point, maybe somewhere around the 9.6 kw it can supply, it looks like the truck can protect itself. But one possibility the electrician suggested was a battery runaway. And since the truck is not really grounded because it sits on inflated tires if a fault generates more voltage than the truck can handle wouldn't its circuitry be toast? In the case of a Lightning, would there not also be the danger of a fault-sparked battery fire for trucks parked in a garage?

So how much safer would a DC vehicle-to-home hookup be than using the 240v Pro Power outlet? I know some DC based EV bidirectional chargers are coming on the market. Any way F150 hybrid owners could use them (to power a house) if that is warranted from a safety perspective?

 

[Ssob]

Okay, so your situation is different. Without batteries in the situation, the solution identified in the video, above, doesn't have the same risk as having batteries that can "runaway." I don't have the cred to second guess your electrician and you have to trust that he/she knows what they are talking about.

 

[MR Fiso]

@steven - How did your situation work out? I now have a 9.6kWh Platinum and have considered my options. The electrician I would like to use has not responded to my messages, but he may not be comfortable to implement this kind of work.

That said, the core concepts are taken care of by anyone who knows how to install a solar / battery installation with switch over. They know the correct gear to use and install.

I know that Sunrun and QMerit may be expensive. But it might be worth it in the long run to both protect your very expensive truck and what ever you plug in on the opposite side.

I may just opt to plug the FCSP unit in as a stand alone and upgrade later to auto switching power. I can always run some long extension cords to the ProPower sockets for critical power items (fridge, freezer, etc) off direct connections. Gas furnace may not be an option unless electrician has an solution for that without a full critical loads panel / bypass switch answer.