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 <[email protected]> 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.
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