>     How long can a UPS be left disconnected from the mains.
How long can a UPS be left disconnected from the mains.
 General questions - what UPS fits best for your use?   Started by NB-23   2024-05-01 15:40:15 +01:00   Comments: 2    Viewed: 257

  1. NB-23
    NB-23 Member Warrington
    APC UPS have been designed to be left connected to the mains even when they are turned off.
    They absorb energy to trim charge the cells even if they appear inert.

    This does not suit some peoples use profile, either wanting to save energy, reduce noise, or just have everything turned off at the end of the day.

    The worry is that if you cannot isolate the cells when you unplug the UPS from mains power, you could still be discharging the cells, which could be destroyed by this if left too long. 

    Some UPS have a battery isolator that you can pull out so that you can disconnect the cell pack for long term storage. 


    We have a customer with SUA2200i (Tower) UPS who was experimenting. They discovered that once you disconnect the UPS from the wall, provided you press the off button twice (hearing a clunk of a relay opening on the second press) the draw from the cells is very low.

    This might not apply to all UPS, but I hazzard a guess will apply to all UPS in the SUA range, with 2 buttons, and LED indicators (no LCD panel). 


    Thanks to Dr D. K. for sharing this information.
    NB-23, 2024-05-01 15:40:15 +01:00
    #50
  2. NB-23
    NB-23 Member Warrington
    The tests and measurements: 

    I have not got the other battery yet, but I did a test on the old battery in the UPS by disconnecting one of the battery leads and putting a good quality multimeter in series to measure current flow. The batteries were charged fully. 
     
    I connected an AC load of around 70 W so something was connected. After powering off the UPS by pressing 0, turning off AC mains, the fan runs and the meter shows a current of 130 mA. However, when the 0 button is pressed for a second time the fan stops and the current drops to 27 μA. I think for all practical purposes a current of 27 uA is insignificant.  That must be less than the self discharge rate of the batteries - it’s equivalent to 0.22 Ah over a year! 
     
    So I believe pushing 0 twice turns that off so much that there’s no point disconnecting a battery. Would you agree? 
    NB-23, 2024-05-01 15:41:06 +01:00
    #51

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