[Nut-upsuser] Questions about FSD (Fast Discharge)

[excelsius at free.fr]

Hi :)

I use NUT on Home Assistant, the version of the add-on is 0.6.2. Home 
Assistant is installed on a Raspberry Pi 4b.
A have a APC 1400, the UPS is connected with USB to the Rasp.

I'm working to built an automation, to receive notifications when there 
is a power cut.
So I used OB DISCHRG (On battery discharge) to detect the power cut and 
trigger the automation.
Then I use OB CHRG to detect that the power is coming back and the 
battery is charging.
Then OL the normal operation, with a full battery.

In the same time I send notification to follow the % of battery (97 > 93 
 > 90 etc). It's working.

During my real test, the load was to light (3%, only a rasp pi), so it 
was slow to empty the battery. So I connected and started my main PC, 
than the load was 18%.

Then the battery fell to 48%, and instead to have OB DISCHRG, I had FSD 
OB DISCHRG (Fast Shutdown On Battery Discharge).

Then I re-plugged the UPS to charge it.
And I was surprised to see FSD OL CHRG until the 100%.
Then, I had FSD OL, even everything was back and normal, and the battery 
fully charged.


I saw today, few days later, than now it's only OL (Online). I imagine 
that FSD disappeared after a reboot or when I disconnected some USB cables.


So, I have some questions. I didn't find this kind of information on 
internet.

  - please, could you explain why FSD is coming ? Is it depending of the 
load, or the % of battery?
  - Why FSD didn't disappear when the current was back and the UPS was 
charging the battery or full?
- Is there a list of all "modes" that NUT can show? (because my 
automation didn't work any more when FSD appeared, so I would like to 
know all modes).

In advance, thanks a lot for your help :)
Jey