AC300 : solar in, AC out vs battery wear


Does AC300 directly convert its PV DC input into AC without using the battery? I understand the excess is stored, but I want to make sure it’s not wasting energy and cycles by loading and discharing the battery at the same time.

I read the batteries of an AC200max would endure excessive levels of wear in case loads are connected on the AC outputs while PV in is active.

The bluetti app of my AC300 shows electricity entering the battery, then reaching AC loads.

I also noticed that the grid and ac out become green under some conditions (ups settings).

Thanks in advance for helping me understand!

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Hi @Derceto , sorry for late reply. Based on your question I went to consult with relevant engineers with following.
In any mode, under any operating conditions, PV charging is enabled in priority when PV energy is available
All UPS modes are based on the presence of utility power, without utility power are entered off-grid with load. When the status turns green, it means that the battery power is not used.


This latest coment flom @BLUETTI confuses me… I use AC300+B300 units and in the manual it states:

Can it be charged and discharged at the same time?
Yes, the unit supports pass-through charging function for both AC and DC

What exactly is meant by “pass through” then? I would expect bypass the battery (for most) when AC/DC appliances are pulling power.

Your answer is vage, I’m not using utility power, so when my solra is producing 1500W and connected appliances pull 1200W I would expect the remaining 300W to be stored in the batteries.

Somehow I get the impression that all 1500W is first going to the battery and then from the battery 1200W is supplied back to the appliances… Please tell me the latest is not true.

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Would be interested in understanding exactly the same for the Ac200max as we have a fridge freezer running constantly on AC from the Ac200max. solar input during the day exceeds the fridge freezers power draw.

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Hi thanks for the answer.

Can you just confirm the scenario where no grid power is available and PV input (1500Watts) is available while AC output is connected to loads (1200Watts).

Is it:

  • the whole 1500Watts are stored in the batteries while 1200Watts are being pulled from the batteries for AC out?
    -1200 Watts from PV input are directly inverted and supplies to AC (bypassing battery charge/discharge) and the remaining 300 Watts are injected in the battery?

First scenario would be a poor use of batteries (conversion loss + wear) while the second one is in line with our expectations (off-grid UPS).

Thanks in advance for the clarification!

I’m unpleased to see the FAQ for both AC200P & Max no longer mention the following - it used to be item #5 back in June this year:

Q5: Can I charge and discharge AC200P at the same time?
A: Yes, but it is not recommended to charge and discharge at the same time in order to protect the battery life.

Now only AC200Max has a mention of it: « Can I charge and discharge at the same time? Yes. »

I’d like a clear confirmation that PV IN doesn’t continuously charge the battery in off-grid situation where appliances are running 24/7. Would defeat the purpose of being a UPS.

Sadly for you the previous FAQ was clear about this: just-in-time PV consumption still involves battery charge & discharge prior to feeding AC out.

Let’s wait for Bluetti’s answer on the matter :+1:

I think bluetti documents that ups is only available when grid power is available. Pass through is a ups feature. So if you are not in ups mode, with grid power being up, there is no ac pass through. I think that pv charging is dc power in and not ac power in so that ac pass through on dc power in isn’t there/possible since dc must be inverted to ac and cannot pass through since it is not original ac in.

I don’t think the ac300 runs like a growatt or sol-ark. I think the pv in power must be stored on the battery first then ac is inverted from the storage available and not directly through pv in.

Which would be very unfortunate and why…? DC from solar to the inverter who creates AC.
Unrequired DC by the inverter can go to the battery.

I don’t understand why they are not absolutely clear about this… I’m getting suspicious at the moment.

Unfortunate because it involves useless battery wear (store and pull energy at the same time).
One battery cycle = having pulled 100% of the battery capacity, in B300 terms that’s roughly pulling 3kWh. It also means 2 baskets of laundry in an average washing machine.

In a previous version of their FAQ, Bluetti recommended against storing and consuming battery energy at the same time (AC200P) due to resulting excessive wear. Given they recommended against it, I want to make sure AC300 is engineered as a “real” solar UPS: invert DC to supply AC loads then only store the excess DC in.

A Victron / Growatt / etc. as mentioned would only store the excess and keep battery wear to its minimum. They are “real” solar UPS devices. I want to make sure AC300 is as “real” as these are.

Even though 3000 cycles is a lot, I just don’t think it’s a good idea / choice to treat a device like a solar UPS while in reality it causes useless wear (+ energy loss due to battery in & out).

About your mention of becoming suspicious, I encourage not to go to that extent quite honestly. I want to trust their reputation first. After all, 3000+ cycles is a lot. Let’s think of it this way: 3 cycles per sunny day means 80% battery capacity is still available after 3-4 years. We purchase a product that has proprietary wires. We know that when an AC300 dies (the inverter and MPPT are the two weakest links in solar generators) then the B300 either needs a new AC300 OR it goes to the bin.

We’ll keep in mind that we buy a product that has 2 years warranty whereas Victron / Growatt / etc wall-mounted devices have 5 to 10 years warranty.

The only Bluetti product with 5 years warranty is EP500pro.

I’m patiently waiting for @BLUETTI 's answer regarding the “solar ups vs battery wear” question.

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I agree with you 100% @BLUETTI please come and enlighten us…

Meanwhile I have decided to do a 3rd setup victron based. Although I started out buying 2 sets of 1xAC300 + 4xB300 for emergency/backup power, I decided to try todo maximum off-grid now.

Hi @Derceto @EchteWappie ,

  1. If there is AC load connected when PV is charging, it can be inverted directly through the bus bar without going through the battery.
  2. When the battery is fully charged and the PV is charging, turning on the AC load will not have any effect.
  3. The APP shows the animation demonstration, the actual internal circuit can be directly inverted output if there is AC load connected during PV charging.

Hope it can help :slight_smile:



Is this the same for the AC200MAX ?

Hi @Chorlton , Yes, also for AC200MAX model.

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Thanks @BLUETTI that is what I would expect. Glad you confirmed that.

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Splendid, thanks. I think this should be advertised as a real plus in favor of AC300.


That’s great , thanks for confirming.

@BLUETTI , With the AC300, when there IS an AC Load, if the batteries are at 100% you mention that there isn’t any effect (assuming bypass of the battery); however, the APP shows an animation with NO PV entering (e.g. 0 watts), as long as the battery is at 100%, therefore it appears that the AC Load IS running off the batteries. When the Battery level goes to 99%, then the PV kicks back in until it reaches 100% and back and forth between 99% and 100%. I didn’t know if this situation is a limitation of the App. In my example photos (below) I would expect at least 235W + wattage used by the AC300 inverter to be displayed on the PV input. (also note, after 23 minutes I just had the 100% drop to 99% and is now charging via the PV)

@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.