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chris-p-bacon avatar image
chris-p-bacon asked

Tesla charging issue - will an autotransformer fix it?

I have a generic off grid 8kw 48v solar inverter that only outputs single phase 240v (L1 / L2 / G). I would like to use it to charge a Tesla, but the US mobile charger (UMC) doesn't like it. At first I was getting a ground loss error, but I was able to get past this by bonding L2 to ground rod. That said, the US UMC is still throwing an adapter fault because it can't properly detect the outlet. It's capping charging at 8a because of this.

I suspect it doesn't like the single phase output and wants 180 degree inverted legs. If I were to run L1 / L2 through an autotransformer, do you think the UMC would work at higher current? I don't care about the neutral / split phase - I just want to be able to pull close to the inverter's max through the autotransformer @ 240v for Tesla charging.

I would run the inverter's AC output directly to the autotransformer, then from autotransformer to load center, and then bond N to G in the load center to appease the UMC's ground check.

Will the Victron 100A model be able to handle close to 8kw @ 240v? If not, then do I have to go the isoloated transformer route?

Autotransformer
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Mike Dorsett avatar image Mike Dorsett commented ·
if your house system is 240V single phase with Neutral ground, then you need an isolating transformer in order to provide the proper split phase with center ground.
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chris-p-bacon avatar image chris-p-bacon Mike Dorsett commented ·

I'm treating the off grid inverter similar to a generator in terms of feeding the auto transformer. It has no feed from shore power. I would run the inverter's L1 and L2 to the autotransformer and only earth ground the chassis of the inverter, which has no separate neutral line and neither L1 or L2 would be bonded with ground at the inverter. Then I would bond the new center tapped neutral with the autotransformer's ground and tie both to earth ground rod.

Similar to this setup:

victron-ground.png


The main thing I'm trying to figure out is why the US Tesla charger doesn't like single phase 240v. I think it's looking for two inverted 120v phases for the 240v and somehow tests ground resistance to give the green light for high current charging.

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victron-ground.png (76.9 KiB)
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