[Nut-upsuser] Bluetti as a UPS?

[Bill Gee]

I don't have a way to do a controlled discharge at 25 amps.  The best I 
can do on my test jig is about 6 amps.  This is mainly due to a limit on 
the relay contacts which have a max rating of 10 amps DC.

When I bought the current batteries back in February, I ran them through 
my test jig using a 4 ohm load resistor and 11.0 volt cutoff.  With that 
they ran for a bit over 9 hours and delivered around 31 amp-hours.  I 
figured with a rating of 35ah that they were at least in the ball park. 
Those ratings are not an exact science ...

How do I change the shutdown to trigger at 22volts?  That has to be a 
NUT setting.  The display on the UPS says it has 15 minutes of runtime. 
A query from NUT shows variable runtime numbers in the range of about 
950 to 1100 seconds.  Here is a partial dump from NUT:

battery.charge: 100
  battery.charge.low: 10
  battery.charge.warning: 50
  battery.date: 2001/09/25
  battery.mfr.date: 2026/02/13
  battery.runtime: 1107
  battery.runtime.low: 120
  battery.type: PbAc
  battery.voltage: 26.9
  battery.voltage.nominal: 24.0
  ups.beeper.status: disabled
  ups.delay.shutdown: 20
  ups.firmware: 865.L5 .D
  ups.firmware.aux: L5
  ups.load: 37
  ups.mfr: American Power Conversion
  ups.mfr.date: 2015/06/18
  ups.model: Back-UPS RS 1500G
  ups.productid: 0002
  ups.realpower.nominal: 865
  ups.serial: 3B1525X12484
  ups.status: OL
  ups.test.result: No test initiated
  ups.timer.reboot: 0
  ups.timer.shutdown: -1
  ups.vendorid: 051d

Even if I can figure out a way to get these batteries to really run, the 
  runtime will still only be in the range of 45 minutes.  An 
improvement, but nothing like what a 2kwh power bank might offer.  My 
calculation shows that two 35ah 12 volt lead-acid batteries will store 
around 400 watt-hours of energy, and might deliver only a bit more than 
half of that.

Your point about BlueTooth Disease is well taken!  I agree completely. 
I have an Android tablet but not a smartphone, so running that app might 
not work for me anyway.  Another person commented that his EcoFlow works 
with recent versions of usbhid.

==========
Bill Gee

On 9/8/26 8:13 AM, Greg Troxel wrote:
> Bill Gee <bgee at campercaver.net> writes:
> 
>> I have been getting very frustrated by the short runtime of my main
>> UPS.   It is an APC BR1500G.  I have a pair of 35ah batteries on it,
>> but even so it runs for only 10 minutes.  The batteries are good
>> (independent testing) and the load is only 350 watts.  I think the UPS
>> runtime calibration just does not work.
> 
> Did the testing do a controlled discharge at 25A and measure the
> capacity to 10.5V?
> 
> Change your shutdown to trigger at 22V, instead of remaining lifetime.
> I suggest logging battery voltage and claimed remaining runtime, and
> doing a test with a simulated failure, graphing that, and posting it for
> comment.
> 
>> Recently I noticed that some models of Bluetti power bank, such as
>> AC200L and Fridge, have a "UPS" feature.  They boast of switching time
>> under 10ms in event of a power failure on the AC mains.  The energy
>> capacity is around 2kwh which should run my load for three to four
>> hours.  Expansion batteries can be added.  And the price is not much
>> different from a brand new 1500 VA traditional UPS.
> 
> That's interesting.  The first thing I checked was the battery
> technology.  Units like this used to have Lithium ion and that would
> seem dangerous.  This says it is LiFePO4.  It claims listing to UL2743.
> 
>> Has anyone used one of these as a computer UPS?
> 
> not me :-)
> 
>> Is there a way to have NUT monitor it?
> 
> It looks like bluetooth/app, the modern disease.  I would suggest
> contacting bluetti, exlaining NUT, and asking for protocol details.
> I suspect if you asked a lot the manufacturers of UL listed LiFePO4
> power banks, one of them might end up being reasonable.