AC300 : solar in, AC out vs battery wear

@BLUETTI The number 2 point you have stated does not appear to be accurate in practice as the PV input stops accepting power when the battery reaches 100%. Please see the screenshots @wtytke has provided above. There is ~1.7KW coming in continuous via solar, but the AC300 does not accept it until the battery storage drops to 99%. This indicates repeated cycles of drain and charge cycle on the battery storage even when steady power is available via PV input. I am seeing the same behavior he has documented here.

Exactly the same on the Ac200max as well.

A cycle is supposed to represent a 100% discharge/charge operation. So SOC changing between 99% and 100% continually would add up a to a single cycle after 100 occurrences. In some input/load/storage ratios these 1% cycles could add up to a complete cycle in under a day.

@BLUETTI It would be preferable if PV input was not shut off for AC and DC output and only prevented from topping the battery when SOC reaches 100%.

Bluetti warned that the app’s animation & on-screen values are not 100% matching the blackboxed electric reality happening within the device.

Testing this with AC300/500 is actually quite easy using one of those:

Clamping this on the battery cable will quickly show how much current flows in/out of the battery.

Anybody has one of these amp meters?

Please see this thread I started and answer from Bluetti

I do not know if there could be a firmware solution.

I hope Bluetti can give insight and advise.

Hi @stumped , The machine supports charging and discharging at the same time, you can connect an AC port load.
The power generated by the PV will be given to the load and can also be divided a little to charge the battery. You have this question should be you do not connect the load device.

We suggest that you can connect a 1600W load, the PV can be utilized. The machine does not turn off the AC and DC output, it just turns off the charging input, because the battery cannot be overcharged, it is fully charged when it reaches 100%.

@BLUETTI, what @stumped and I am trying to say that when there is an AC and/or DC Load and the batteries are at 100% and the PV INPUT power is GREATER than the AC & DC load then the load should be powered 100% by THE PV INPUT and NOT the batteries.

Asking the question another way – WHY is the PV Cutting off completely when there is an AC (or DC) Load to power?
Can’t the MPPT direct the excess PV power to JUST THE LOAD and NOT the Batteries when the batteries are fully charged?

Asked even another way – When the batteries are at 100% , and there is an AC (and or DC) Load, AND there is more than significant PV input, then the PV excess power should BYPASS the fully charged batteries, and then power the AC Load WITHOUT using the batteries, at all.

Hope that clears up the question.

I think only the ep500pro does this

I read somewhere before that there is pass through and true pass through with bluetti.

For sure the pv should not be cut off just because rhe battery is 100% and should continue to pass straight to ac load.

May be there is a good reason why that is not possible.

Almost everything I read on MPPT’s in general will redirect the excess solar input to the Inverter and shut off the power to the batteries when they are full (float). The batteries will only begin to be utilized if the PV input is lower that the AC Load + Power to run the Inverter, such as a cloud passing by.
That is not how the AC300 is behaving, I would like to know why, besides the excuse to protect the batteries. The MPPTs in the AC300 should do that AND direct “opportunity loads” to the inverter, thereby passing the batteries.
Bluetti could easily double the life of the battery (at least in my case) if the batteries were not constantly being drained.


The AC300 user manual is inaccurate. Where it mentions pass-through in the FAQ it should say “limited pass-through” and then detail that when the batteries are fully charged pass-through does not apply for AC and DC outputs.

This is a serious limitation and had the Bluetti documentation been accurate I likely would not have purchased.

@stumped, I guess the only option at this point, knowing that the batteries will constantly be used even if they are at 100% charged is to supply enough “off-grid” load to the Bluetti AC300/500 system daily to use a majority of the batteries by morning so that they charge to 100% at the latest possible time before dusk the next day. Therefore, you will know that you are keeping to just one battery cycle per day.
I just started using my system (owned for 3 weeks) with 4x batteries and fine tuned it where I would use only about 33% overnight and it would charge back up to 100% by 1pm-1:30pm. Because of knowledge gained from this conversation, tonight, I added my 500 watt window AC that I use overnight for 8hrs which should bring me to about 40-50% by morning which I should be able to charge back up to 100% by 5pmish the next day. Oh well, live and learn, at least I get 30% back from the purchase via Fed Tax credit.

I wouldn’t say the manual is inaccurate, you’re assuming that pass-through automatically means bypassing the battery but they wrote it as to mean that the energy generated by any sources can be passed to any output. I agree that they ought to clarify this with more detail for those more technical inclined people.

So to be clear… the pv input is sent straight to AC load with remaining sent to battery before 100%? So this is not a problem or extra wear on the battery until 100% charge.

Then at 100% pv load is cut completely off and AC load is put onto the battery until it drops to 99% then Pv takes over again?

Can anyone with an ep500pro also confirm this happens or does that handle it the same as hybrid inverter chargers.

What about ac500?

Maybe ep500pro will be better for me than ac500.

One other question. What happens if you change you soc to 95% in the options on ac 300 you can instruct max charge to be only 95% …maybe with that 5% of buffer the mttp and inverter may allow true pass through?

Just an idea.

@Newsolarfan, I strongly believe that the AC Load is ALWAYS pulling off from the battery and NEVER from the PV input, whether at 1% to 100%. The MPPT’s charge up the batteries while there is PV input (in PV priority mode), until the batteries reach float (100%). Then the PV is cut off completely while the batteries discharge to a level that = 99%, THEN then PV turns back on to charge the batteries to 1% (which is usually a 25 minute cycle). Unfortunately, the AC/DC Load is always pulling from JUST the batteries.
As for the grid AC input, I do not know if there is true grid AC passthrough (I only charged the batteries once with AC Shore power).

As for the 95% setting, I will probably try that out next week (with the custom settings, since PV Priority only allows for Min setting not max,) I want to fine tune the usage this week with an Air Conditioner at different settings.

But I suspect that the AC Load will pull form the batteries and the PV will charge the batteries, still, So, if the PV input shuts off at 95%, then drops to 94% and goes back and forth in the same amount of time (in my case 25 minutes) as with the 100% and 99%, then that observation will help support the theory that the batteries are ALWAYS being used, unless I am missing something.
OR, If the PV stays on, and does NOT drop to 94% in the expected 25 minutes (in my case), then that observation would help support the theory that there is a PV passthrough., correct?
Assumption in both cases, PV input will always be great enough to run the AC Load + Inverter draw. Also the 25 minute cycle is when I usually have 1500 to 2000+ Watts PV input.

Yes please try with 95%

I think up until 100% energy will pass directly to the load. I hope so anyway.

I am not an expert but i was told a battery is unable to accept charge and discharge at the same time.

So what may appear to be coming from the battery is flowing from pv or ac in reality up until 100% which when charge is shut off the load starts flowing from battery. This part should be improved if possible. Im not sure if they can or not via software.

The 100% pv shut off is something that bluetti could maybe fix.

It was once on the documentation under ep500pro a mention of true pass through. But i cant see it now. I hope i didnt dream it. If someone has ep500pro can they comment of the 100% pv shut off.

I could be wrong about all of this of course lol.

Please let me know how you get on with your test.
I guess the idea of amps uclamp meter on battery cable will tell for sure.

@Newsolarfan, Ok, since I want to know now, also; I just changed my mode to Customized 5-90%, hopefully it remains sunny (I am currently at 44%) but there will be storms at 2pmish, and I usually shut off my PV when there is lightning, we had a strike in my neighbors backyard a week ago (wiped out 3 of my security cameras, outdoor music system and other things, but the PV was isolated and all is ok with the expensive items). I should know by this evening.

IF Battery (1-4) SOC <100%, THEN (Battery charge subroutine), ELSE set PV input = supply power to AC/DC Load only.

Instead of:
IF Battery (1-4) SOC <100%, THEN (Battery charge subroutine), ELSE set PV input = 0

(or something to that effect).

Okay great that will be very interesting to know.
Hopefully with a little buffer it may not switch the pv input off.

@Newsolarfan, @stumped, @BLUETTI,

I want to preface, UNLESS I MISSED SOMETHING (eg. a setting, a hidden menu etc.), then I discovered more questions than answers. And I must have missed something because I am sure SOMEONE would have mentioned this somewhere on some AC300 forum.
FIRST, Based on my test, I want to answer the primary question. I am now almost positive (until I get access to a clamp Ammeter to verify) that the AC300 AC Load ALWAYS pulls directly from the batteries at ALL times, even when it is charging via PV <100%.

SECOND, (and like I said, unless I missed something), you can NOT change the HIGH SOC to only charge to a value that you set. After I set the HIGH SOC to 90%, I saw the batteries charge all the way up to 100%, when I got home I went through the menu system and took the attached Photo. When you set the SOC high to a value, say 90% then the connected PV will continue to charge the batteries to 100%, it just will not use Grid Power. If you turn off the Grid AC (which is a setting in this customized menu), then this setting would simulate PV Priority mode, and just charge by PV the entire time. Setting at a lower value (<100%) does NOT stop charging the batteries at that SOC value that you enter. This discovery left me flabbergasted, I thought that you could set a true SOC limit. If anyone knows how to set a true SOC to where the batteries will not charge past that set value, please let me know.
Sorry Everyone, this result was not what I was expecting.
You can’t set a high SOC, and the batteries are most likely being drained at all times without PV Passthrough at any SOC (except at 100% because the PV is then cut off).