AC500+B300S - PV Priority set at 20% - Pulls grid power at 100% WHY?

This is what I want to be able to do . . . I’m trying to pull all energy in from my solar during “sunny days”. So I set to PV Priority at 20%. My thinking is that it will pull from my solar panels (as priority) during the day to power my A/C Loads…then overnight, if the battery gets below 20% > I wanted the unit to pull from the grid until the sun comes back up to take back over.

Here’s my Issues:

  • AC500&B300s is topped off at 100%. For some reason its pulling around 50-60 watts from the grid when the AC500 reads 100% and nothing from my 2400 watts of solar panel supply.
  • If it’s at 100% it stops pulling from my PV/Solar. I want it to power from my solar, like as a “pass-through”. and not waste that free power. But it doesn’t.

Can anyone see what I’m doing wrong with the settings?

I’m thinking the unit may be faulty. I tried to download the firmware updates from the app and all of them always “download failed”.

Does anyone else have these issues? Should I contact Bluetti for a replacement unit?


I have the AC300/4B300 combo set up the same way. I believe the 50 / 60 watt draw maintains the internal draw of display,WiFi, Inverter (on standby) etc. Ince you start drawing a bit more power from the unit, it should switch over to 100 % solar input. Cheers!

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Not your AC500.

I own three AC300s of various vintage and - what appear to be - slightly different hardware and all three exhibit this very same behavior, on both accounts.

When an AC300/AC500 hits 100%, it stops charging and the batteries start slowly discharging, servicing the internal components’ needs.

When the SOC drops below 98% (the average becomes 97.75% in case of a four-battery setup) and the app as well as the touch screen display “97%”, the charging resumes at full throttle once again, and the batteries are charged back to 100%.

In between these two states, the solar charging occasionally also kicks in for brief periods (I use the D300S voltage reducers and I can hear them spinning up periodically - they have a distinctive, high-pitch noise above certain wattage levels) and also see it in the app and the touch screen, however this does not seem to provide the sort of “PV pass-through” you or I would expect. Depending on the load (the shallower/lower the load, the higher the probability is), occasionally it seems to find a sort of “equilibrium” when the incoming PV roughly matches the outgoing load (I only output AC so it is easier to see) but even then, the batteries slowly discharge and the SOC drops to 97%, when the full recharging to 100% kicks in.

The other “issue” you mention is at least as interesting, if not more, and I only realized it recently, after purchasing the 3rd unit and connected it for “grid” charging to one of the other two AC300 units. The two older AC300 units are connected to the “real” (i.e. utility) grid, on two opposite phases, via 30A single-phase L14-30 charging cables.

What I noticed is that when the “downstream” AC300 is in “Load Matching” mode (the solid orange AC icon), and the unit is told explicitly to DISCHARGE (either by being in PV Priority mode and above the configured SOC [your case] or by forcing discharge via the Time Control / Customized UPS mode [my case]) it still picks up a few dozen watts from the “grid”. Although the unit itself shows it is not using any grid power, the outgoing AC load on the “upstream” AC300 clearly shows an elevated load (in the 20 to 50W range), depending on the load on the “downstream” AC300).

Now, I have known it for some time that the AC300 will not show the load used for powering the internal components as part of the load drawn from the grid (i.e. it will show 0 if there is no other load) but I did not expect it to draw grid power even when it is explicitly told not to (and also should not, because it could power itself from its internal batteries or when there is more than enough juice from PV). Still, it apparently does use a small amount grid power practically every time.

The only way to prevent this from happening (apparently) is by physically disconnecting the unit from the grid, and putting it into “Inverter Mode” (light orange AC icon). Not even turning off the “Grid Charging” in the Customized UPS mode prevents this slow trickle of grid power usage.

Finally, the funniest part: I have been using my two main AC300s in Customized UPS mode and “discharging” for months, believing that I was not drawing any grid power in the process, when I evidently was (as it turns out). BUT: I have never been billed by my utility for this usage and it has never showed up in any usage reports. The only thing I can imagine is that this slow trickle of power draw by the two upstream, utility-facing AC300s is below a certain threshold the utility recognizes as actual usage.

I few closing notes:
This ping-pong of bouncing back’n forth between 100% (or any configured SOC(max) and 97% [or configured SOC(max) - 3%] is something the AC300/AC500 regularly does - not only when charging from PV but also when grid-charging.
It also does a similar thing when it is told to discharge, but reaches a configured SOC(min), while connected to the grid: it goes into Pass-through mode “D” (one of the two states hiding behind the green AC icon), lingers there for a while with load seemingly matching the AC load, creating the impression of a “real” pass-through, but the batteries are in fact still slowly discharging until SOC(min) - 3%, at which point it grid-charges back to the configured SOC(min).

In summary, although these things are indeed peculiar, I personally can live with them, especially since I’m not being charged by my utility for that “shadow” consumption (hope it stays that way). The 3% ping-pong instead of proper pass-though is, well, annoying indeed, but I can live with it, especially since I have two full stacks of 4 B300s (not B300Ss :).

Hope it helps. - Gabriel


@toddsworld Under normal circumstances, when the machine SOC is lower than the preset value, the load is powered by the grid bypass, and the machine is charged by the grid and PV together; when the machine SOC exceeds the preset value, the load is powered by the machine battery or PV. AC is not input at all. AC can neither be bypassed for loading nor charging.

Could you please provide me with the SN and the firmware version, then we can push a firmware for you to test.

Check out the video I just posted of my AC300 and how PV Priority is supposed to work Your description of the units behavior on yours does not seem correct:


PLEASE NOTE: I have not been able to upgrade the firmware from my bluetooth, android phone. It always states: “Download Failed”.

Hi Doug, I saw your awesome video. That is exactly what I want it to do and it does do it to some extent. It was just puzzling why it was pulling from the grid sometimes when it was already maintaining 100% battery and I have 2400 watts solar available…why? Also when I’m at 100% battery during the day it stops pulling from my solar panels even when I have a load of about 250 watts. Why not have the available solar pass-through and use that to power the 250 watt load? Why does it turn off the solar and take from the battery. This seems stupid to me, to waste available solar.


As I said above, just because you see a big fat zero next to the Grid icon doesn’t mean the AC300 isn’t pulling any power from the grid. Perplexing but true …

I have the same issue with my EP500 Pro that, every few seconds there is a mains draw of up to 150 watts.
This effect occurs with every UPS setting, regardless of whether it is in time priority mode or PV priority mode.

The answer from bluetti was:
" I’m sorry for the late reply, because I’m on a business trip.
When the load is running or fluctuating, EP500 use the mains (grid)to power the load shortly,then use its battery power the loads."

It seems to be normal…

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I just connected my kill-a-watt to the AC300. It is showing 5-7W on the grid plug, but 290VA, for .02 power factor. Seems there’s some capacitance on the input side. I’ll keep it there and observe. Thanks for the tip.

That’s a good observation.
I have rerun the test as well and the upstream AC300 shows 30~60 W outgoing AC (depending on the load on the downstream AC300 in Load Matching mode) while the latter consistently shows 0 W being pulled from the “Grid” (upstream AC300 in my case).
The kill-a-watt in-between show a more or less steady 20W.

That said, after rereading this thread, @toddsworld’s initial issue was probably slightly different (it sounded like he saw “real” power being pulled by the AC500 - and also indicated as such) when it was not supposed to and probably he expects an answer from Bluetti so I’ll wrap this discussion up here. Apologies if this was a tangent.

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My AC300 was behaving the same way. I have a whole house energy meter and noticed little spikes of grid energy when the batteries were full in PV Priority mode

I never really got an explanation so I leave the grid supply plugged in but turned off and will manage grid charging manually in Winter if needed

My Firmware is up to date

@toddsworld Could you please provide me with the firmware version of the battery pack? The update of the BMS version was pushed to all B300. You can test if you see the update notification and test.