UPS Power Supply Not working off Batteries, 240V mains OK.

[NicholasD]

Nikko / Powercom 1500VA 900W Line-Interactive UPS
MODEL: BNT-1500AP

I have / had this UPS in my Studio and every night at around 11pm it would switch over to generator power, thus engaging the UPS batteries briefly while it switched over. Now my computer goes off as the UPS does not seem to provide any power off the batteries under load. It just dies... WHY I really wonder?

The 2 Batteries have been load tested and pass all OK. IT IS NOT THE BATTERIES. I have also tried new ones. The 2 x Orange 40A fuses on the Board also tested fine.

I suspect that there is a short or an open circuit in the battery or DC side of the circuit but I do not know where to start... There is perhaps some capacitor leakage seen on the board near the relays / switches...

Could it be the transformer and if so, can I test this easily? Where would you look / Test? What is most likely?

Thanks very much... Some photos here: Any tips or ideas appreciated!

 

[SpruceMoose]

Check the voltage at the batteries while the system is on AC power and when it switches over to battery power. This will show if the battery charging system is working ( higher voltage than when the battery pack is disconnected) and if the batteries are actually under load when they should be (lower voltage than when the batteries are disconnected).