Pretty sure that explaining my base case will derail the entire thread, but it here goes
I have a Victron Multiplus II 3000VA + 3.200W PV + 5kWh 48V BYD battery.
The Victron has an UPS function, that works wonderfully:
- The grid and heavy loads are connected to the AC In of the Inverter. The critical loads are connected to the AC Out of the Inverter. In the event a grid blackout, everything upstream of the AC In goes dark, but everything downstream of the AC Out lives on.
- I connected most of my house (almost every circuit, except for 5 or 6 heavy loads) to the AC Out of the Victron.
- This way, in the event of a grid blackout, I retain functionally of 95% of the house. At least during the day because, at night time, the 5kWh BYD won't last for long
Cue in the next brilliantpiece of hardware I have in the garage: a Tesla Model S with a 100kWh battery.
I feel rather stupid to have a 5kWh house-backup system that, however,will dry up quickly, while having a massive 100kWh-battery-on-wheels parked in the garage.
With a 12V grid-tie inverter, in case of a prolonged blackout, I would connect it to the battery poles of the Tesla (been pocking around, and can do it rather easily) and to a socket connected to the AC Out of the Victron.... to keep the "Victron-BYD-UPS" going for longer.
What I won't do:
- Tap into the 400 VDC system of the Tesla.
- Use the Tesla 12VDC power source has a permanent solution. I would only tap itin case ofprolonged grid blackouts.
What I wouldn't like to the:
- Have a transfer switch. Definitely not amanual one. Could consider an automatic transfer switch, tapping/sensingthe AC In of the Victron... still.... I feel that a 12VDC grid-tied inverter would be a "cleaner" solution. The problem is that there seems to be no such an inverter
(at least not with an output higher than 250W).
Other dead ends:
- I also tried to find a 12VDC to 48VDC converter, to connect the car battery to the BYD busbar.
Victron has some DC/DC converters, but with a 12VDC input, they only output a max of 24VDC so they're a no go.
Daygreen seems to have some 12VDC to 48VDC, however, I would it them to go all the way up to 51V or 52V, in order to charge the BYD (that has an operating voltage range of around 51V to 55V). So, I think they also don't fit the bill.
Many thanks for your help!
In case of a multi-day blackout, I could even drive out to a Supercharger, to go and get some more electrons for the house