AC500 does small (but noisy) charge cycles in Standard UPS mode

I recently got an AC500 230V EU version with 2xB300S set up in Standard UPS mode running about 200-500W loads most of the time, Silent Mode is OFF.
It’s working fine but I’ve noticed that it gets noisy every once in a while.
It turns out that it slowly discharges to 99% (even with a 100W load with AC plugged in), and then starts charging at max possible speed (3000W in my case) which is weird and emits unwanted noise.
Is there any workaround for that?
As a suggestion - is it possible to fix it so it doesn’t discharge to 99% under AC power or make charging past 99% slower so it doesn’t need max fans?
IOT 9041.02, ARM 4048.02, DSP 4047.03, BMS 1022.08, Serial 2232000277763

Hi @AlexxV , The machine has no-load power consumption, so it is normal to have a slow discharge. Fan start is also normal, the machine to 3000W charging this will certainly activate the fan, you can turn on the silent mode to see.

It’s not about no load discharge:
I have it plugged into AC and it still discharges to 99% and then charges back.
Also, I need that 3kW charging in case I have a power outage.
So the only option is toggling silent mode ON and OFF manually which is not that handy because that means I have to keep track of it manually all the time.
The suggestion would be to add an option to auto-enable silent mode when above 98% charge levels - it would still charge fast but won’t be noisy under normal operation.

Check if you have an option to lower the utility power charging amps. It will not fix the battery draining and recharging but should lower the charging watts.

Well, I need that fast charging in case I have an outage and need to get it charged back. And it’s not a moot point as we tend to have 8-16hr outages every day so I need every single amp of charging power when that happens.

Actual problem is that it drops to 99% charge level all the time while being plugged into utility AC

And what I’m saying is if these 99%-100%-99% cycles are required to save battery life or something - then pretty please make 99% to 100% charge use less amps than the rest 0% to 99% charge to save on fan noise.

This behavior is a limitation of the design that Bluetti chose. When the unit is turned on, the internal electronics ALWAYS use power from the battery instead of from utility power. When this drained the battery to 99% it will get recharged. So in UPS mode it will continuously do these cycles.

I got the same problem with my AC300:

Some possibilities you can consider:

  1. Try the settings to make the charging silent by enabling silent mode or limiting AC charging amperage. You mention that you need fast recharging after a power failure, you can consider to manually putting AC charging to fast in these occasions and then putting it back to silent after it has been recharged.
  2. You can use a regular UPS to power your devices during short power outages and manually turn on your AC500 to power that UPS in case of extended outages. This reduces your AC500 to an extended power bank. You will have to check that the UPS has enough capacity for your intended load and if the UPS is silent. This is how I use my AC300 now.
  3. Return your AC500 for a solution that does not have this limitation. If you’re in the EU you have 14 days to try online purchases and return it for a refund, no questions asked. You only get a full refund if the unit only has traces of use required for testing if it fits your needs. The shop where you bought it may have additional services for returns, like free return shipping. But it should not interfere with your EU rights. If you return it is your responsibility that the unit arrives undamaged and not lost. So if you use a parcel service make sure everything is very well packaged and fully insured to protect against shipping damage and loss. Contact the shop where you bought it for details on the procedure. You must let them know that you want to return your items.

It looks like this is a major issue. My EB3A lasted 1 day in UPS mode and then pass out, dead. I think this continuos 99% to 100% charging cycle is not healthy for the unit. I’m waiting for a replacement but I am afraid I won’t be able to use it as a 24/h UPS… That’s a pity because I choose this solution just for this UPS function attracted by capacity and battery life which is not comparable to any UPS.
So as you say, we can use it in a different way like you suggest, keep it turned off until necessary when power outage occurs, but that implies being always present on site, or use it outdoor during picnics. In this case BLUETTI should remove the advertised UPS function from the product features until this thing is fixed, otherwise I would call it scam or fraud. I’m giving them another chance. I’m very upset.

It is not pleasant to connect computer equipment to a UPS to protect them and discover that they have suddenly turned off because the unit that was supposed to ensure the power supply at some point suddenly turned off, shutting down all the equipment that you wanted to protect. Ironic if it weren’t tragic.

It’s like buying an expensive life preserver to find that instead of keeping you afloat it drowns you.

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@TheQuickFox Thanks for the info, that’s interesting.
In short: I’m located in Ukraine, and as they say - beggars can’t be pickers :slight_smile:
Poking support for a firmware update with “smart silent” mode that is only active above 95-98% sounds more realistic than getting something better over here.

I’m considering using a RPi or similar SBC that will connect via Bluetooth and enable silent mode when appropriate.
But ideally, there should be “smart silent” mode in the firmware


Lots of people from Ukraine here. I wonder why… :thinking:

Welcome. In your case I would certainly keep my unit yes. It’s quite a challenge to get it transported there in the first place. And you will very much need it thanks to the actions of our Russian military friends and their great leader in the Kremlin.

Side note: Be careful with firmware updates. When you dig in the forums there have been some users with a different Bluetti system that had a failed firmware update last month. Perhaps as long as your solar generator is of critical need for you, consider waiting with a firmware update until the war/“special military operation” is over. Most of these units needed to be returned to Bluetti which is not easy when you have a war situation around you.

Bless you. I hope your Bluetti system will bring you light in dark places, when all other lights go out.

Hi. I hope youre well.

It is totally normal to have this 100-99-100… behavior. There is a video on YouTube called “Bluetti UPS Modes Explained” where he explains why does it behave this way.

I recently bought AC500 with one B300s.

Sometimes it discharges to 98 percent while working in UPS mode (most of the times 99%).

As for having noise when charging, I do not have it charging on maximum speed (I mean, when it works in same conditions). IOT v9041.06, ARM v4048.02, DSP v4057.03, HMI 6052.07, BMS 1022.09
When changing above 98 percent, it gets about 600w from grid, no matter if silent mode is on or off.

So I guess they fixed this issue. Thx for that :)

Btw, it would be great to see schedule for turning on/off silent charging in the Bluetti app.

I’m not complaining about 100-99-100 cycles, I just don’t see why it has to be charging from 99 to 100 in UPS mode with fans blaring at full speed.

As for firmware updates - I recon my unit is a bit older with latest DSP being v4047 and it doesn’t even show HMI in the UI.
Also, I’m running 2xB300s, so perhaps that’s also adding to charge rate and thus noise.