I have an AC300 setup that is receiving solar charging and operating in PV priority mode. This unit is serving some of my high-use home grid circuits via a 3-way transfer switch to use the solar when available. When the battery depletes to 20% and there is no solar input I flip the transfer switch to grid and wait for the next sunny day that can charge up my AC300 setup. I’m basically trying to offset some of my electric costs instead of letting the AC300 sit there and do nothing until there is a power outage.
Typically when the AC300 depletes to 20% and the AC charging cord is plugged into my home grid it will charge via AC. Can I leave my AC300 plugged into home grid power while it is serving the circuits in my transfer switch so I don’t have to babysit and flip the transfer switch from generator to grid power when the battery depletes to 20%? I saw a YouTube video https://www.youtube.com/watch?v=FqPJfcWkM3g about setting up the transfer switch (albeit an Ecoflow unit) and a user neocrypto9368 commented stating “You should never plug a Delta pro into an AC outlet to charge while connected to a manual transfer switch as that creates a ground loop and double ground/neutral bond.”
Although it’s an EF unit I think the same concern applies for a Bluetti unit…that an AC300 plugged into grid for AC charging while also plugged into and serving the circuits in the transfer switch, which are also wired to earth ground, will create a grounding loop.
This question (whether AC300 could be connected to both grid power input and also output to a transfer switch at the same time) has been the topic of several threads, with difference experiences reported. There are some AC300 units that cannot safely operate this way (failure modes include over current protection fault and even pop/smoke leading to permanent AC300 failure). I had one such unit that failed this way and Bluetti replaced the unit. Unfortunately the only reliable way (I’ve found) to know whether an AC300 unit would fail this way is to try it.
The double ground/neutral bond is a concern. In my experience (running 24/7 this way for the past few months) it has not caused any problem that I could detect. Single-phase (120V with one AC300) has been working reliably for me in this configuration. Split-phase (240V with two AC300’s) mostly works but has some quirks I’m still working through and don’t have conclusive answer yet.
Thanks. I’m going to be setting it up next week and I’ll be cautious and ready to react if it has any faults or pops or smokes. I’m just trying to put this to use and get some ROI instead of just letting it there until there’s an outage. This guy Jasonoid https://www.youtube.com/watch?v=eiWnqukg9mM talks about this at the 3:20 mark. I can’t tell if he has it plugged into AC as well. Worst case scenario I can be mindful of the battery level and flip the transfer switch from generator to line when the battery gets low.
Yes, it’s much better to get ROI from regular solar generation. In the video you referenced, his AC300 is not plugged into AC grid input (multiple times the video showed that the AC charging cable is not connected, and the screen also showed grid input as inactive/absent).
Here are some notes from my testing simultaneous grid input power and transfer switch connections with several AC300 units.
The AC power input must be from a circuit that is separate from the transfer switch’s circuits (to avoid AC300’s power output being looped back to its power input)
If the AC power input is from a GFCI outlet, the GFCI outlet will trip as soon as the AC300’s power output is connected to the Pro/Tran2 transfer switch. All AC300’s I’ve tried exhibit this behavior.
To test, enable AC300’s power output and connect it to the Pro/Tran2 (it doesn’t seem to matter whether the Pro/Tran2 circuits are switched to “LINE” or “GEN”, but having some output loads might make the testing more realistic). Then repeatedly disconnect and reconnect the power input. The H-Bus Voltage High and pop/smoke failures occur when the power input gets connected (and the relay clicks to enable the power input). In my experience, if an AC300 can go through 10 disconnects/reconnects of power input without failure, the unit seems to be safe to use in this configuration.
As for the double neutral/ground bond connections, it is true that current will flow via both the neutral and ground wires between the AC300 and the Pro/Tran2 (and also between the Pro/Tran2 and your main service panel). I did an experiment where I intentionally disconnected the neutral wire to the L14-30 outlet inside the Pro/Tran2, in order to see whether the ground wire will complete the circuit and conduct the return current (that should have flowed only via the neutral wire). I found that even with the neutral wire disconnected, if the AC300 is connected to grid power input, then the circuits on the Pro/Tran2 (flipped to “GEN”) still work and receive power from the AC300. If I then disconnect the grid power input to the AC300, then the Pro/Tran2 circuits immediately lose power (even though the AC300 still has output power on via battery). But even with the current flowing via the ground wire, I didn’t feel any electric tingling nor shock when I touched the Pro/Tran2 metal enclosure (which is connected to the ground wire). In my setup, the path from AC300 to Pro/Tran2 to main service panel is short (and dry, indoor not outdoor), and this issue with current flowing over the neutral wire has not been a problem for me.
Regarding whether current is flowing over the ground wire (when AC300 is connected to grid power input and Pro/Tran2 transfer switch), I drew premature conclusion in my previous post. I did another experiment where I disconnected both the neutral wire and the ground wire from the Pro/Tran2’s L14-30 outlet. As long as the AC300 is connected to grid power input, the circuits in the Pro/Tran2 continued to receive power from the AC300. It turns out that the circuit still is completed via the neutral wire connection to the grid power input (because AC300 connects its input neutral wire to its output neutral wire). So it’s inconclusive whether any current could flow via the ground wire.
I’ve had my AC300 plugged into grid and it’s been fine. The only downside is that I have it in the basement and there are a lot of things in the basement that I can offset with the unit providing battery power so I can’t just leave it plugged into grid all the time because that basement circuit is also part of the transfer switch. Maybe if we go on a trip I’ll switch over all the circuits except to the basement one or maybe I’ll rewire the circuit so I just leave the one outlet for the AC300 but aside from that I have no issues with ground loops or any of that business that was discussed.
It’s good to hear that it’s working for you. I’ve found that it’s an iterative process optimizing which circuits to put on the transfer switch. I’ve rearranged the circuits on my transfer switch quite a few times already.
Howdy OhioIsEveryWhere!
BLUF: I have my AC300 plugged into grid and feeding subpanels branched off the main (protran model, not that it matters…). It works just fine.
Initially I had the same issue as many others where you would plug the AC300 into the grid (a GFCI outlet in my case), with the subpanels receiving energy from the AC300 and then the GFCI outlet would trip. I replaced the GFCI with a regular outlet and the breaker did not trip and power flowed to the AC300. I put the GFCI back in the circuit, validated again, and it tripped. An extra and unnecessary test, I acknowledge.
The next thing I did was look at how the outlet was wired at the actual breaker. That is where I found a difference. I found that that breaker for that circuit was ‘grounded’ to the neutral bus bar and not the actual ground bus bar. I moved the ground wire to the actual ground. Fixed my issue. Now the GFCI outlet does not trip when the AC300 is connected to grid, and also providing energy to the subpanels.
I would be very surprised if this was not an approved configuration. I am doing almost exactly what you’re proposing - charging batteries via solar during the day (2 1200w strings), and draining the batteries after the sun goes down. I think with 2 B300 I can offset about 50% of my household use 7-9 months a year.
My configuration is nearly identical to this picture (page 6 of this document). The only notable difference is that I’m using a TT30 outlet from my panel and Bluetti’s 30-amp TT-30 cable.
My parameters are: @ 10% - use grid power. @ 8pm, charge to 100%, at 10 pm, run off battery until the following 8pm. It’s similar to PV Priority, but I get the batteries to 100% every night - this way the batteries get lots of cycles. On cloudy days I probably lose a bit (haven’t tested, but guessing about 80% round-trip efficiency) - but as long as I generate > 2 kWh / day from solar, I offset those efficiency losses.
I received a 2nd (refurbished) AC300, which after bench testing, as @terryl mentioned, did the pop/fail when plugged into the TT-30. Still waiting (waiting…) on that replacement @BLUETTI_CARE !
I went the same route with my AC500, but less complicated.
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The Bluetti stacks are next to my Home Theater setup, so all my electronics are plugged directly into it. Then over time I started adding more and more items to the load with a 50amp heavy duty power extension cord hidden behind furniture, running into the kitchen for appliances.
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I got it all balanced out so the batteries never get too low as long as we don’t have more than 3 cloudy/rainy days in a row. If that happens all I have to do it plug the AC500 into the wall outlet, otherwise it’s left unplugged.
I do have to make sure all high power loads are run during the day (dishwasher, laundry, etc.)
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I’m averaging $40/month electric bills while my neighbors are paying +$300/mo. This past month I got it down to $29
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Of course, I’m still looking at 7-8 years before breaking even.
@SpaceBalls After you rewired your GFCI outlet’s breaker, have you tested your GFCI outlet (with a GFCI tester) to confirm that GFCI protection still is working? If GFCI protection still is working and your AC300 no longer trips GFCI, that is really good (I’ve tried multiple AC300 units and found that they’d always trip GFCI if the AC300 is connected to a Pro/Tran2).
@terryl
Ok - I need to apologize.
Summary: My GFCI is tripping.
I’ve had my AC300 using a 30 amp circuit for many months now and haven’t been using the >20 amp plug.
I did “validate” a while back that I wasn’t tripping the GFCI, but I just did a test and it indeed failed.
Not sure what has changed…
I will admit that I may have plugged in the Bluetti to an outlet upstream of the GFCI (same circuit, just closer to the breaker than the GFCI outlet) and it worked fine. But when I plugged it directly into the GFCI, it ended up tripping immediately upon power draw. I even adjusted the amps to 5 on the Bluetti, no difference.
I will have to check into it more when I have time and see what, if anything has changed.
I could have sworn I had solved this…
Again, sorry.
I was doing this when I first stepped into the solar generator world and had extension cords going everywhere but once I learned about the transfer switch it was much more reasonable to have everything down by my load center and out of sight.
The transfer switch is ideal, but for me the problem is locating the AC500 and batteries close to the breaker box, which is on the outside wall of my garage. The gear would never survive being in the garage where it’s extremely hot during the Las Vegas summers. My bedroom is next to the garage but I don’t want it in there either, with the fan turning on and off. Anywhere else and I would need a +150’ heavy duty power cable running around the outside of the house to the breaker box, likely through a metal conduit to pass code inspection.
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Maybe one day, but for now it works just fine for me. Everything but the house ceiling lights and the garage door opener are solar powered. I used only $7.41 worth of grid power last month.
@SpaceBalls No apology needed. I was just surprised by your result and suspected the GFCI might no longer be working. From what I can tell, if AC300 is connected to GFCI outlet as grid input and also connected to Pro/Tran2 at the same time, the AC300 always will trip GFCI. However, I don’t think the tripped GFCI necessarily indicates that it’s a problem with the AC300. I think the AC300 is a common-neutral inverter (grid-input neutral is electrically connected to the inverter output neutral), which means the neutral current could flow via either path. For this reason, the grid-input line (hot) current will not necessarily equal the grid-input return neutral current. The GFCI trips because it detects that the line current does not equal the neutral current.
