APC SMT1500i problem

[nnemanja]

Every few days, and consistently at night when it is at minimum load, a problem arises with the UPS, marked by a clicking noise (resembling an abnormal and rapid relay clicking, as captured on camera). After about a minute, it draws so much power from the wall that the fuse in the fuse box turns off. Following this, it operates on battery for the next 5-6 hours until the battery is depleted. In the morning, after manually resetting the fuse in the fuse box, the UPS charges the battery and continues to work normally. This has happened multiple times, always at night and under minimal load. I disassembled it, but I am unable to diagnose the issue. The only thing I noticed on the table is that a few hours after powering on, relay RY900 shuts off, and transformer T900 on charger board (module located on a separate charge behind the battery compartment) starts abnormal whining. Has anyone experienced a similar problem or does anyone know what steps to take next?

[Teken]

What is the production year of the UPS? You can find this via the LCD under About. This can also be identified by looking at the serial number at the rear of the unit. Has the UPS ever declared a relay weld error? What errors has the UPS declared in the past? 

You can do a search on YouTube where they show similar behaviour where the relays click back and forth quickly. If the unit is out of warranty and you believe your electrical and soldering skills are sound.

You can replace all the relays inside the unit as a starting point. They are pretty cheap and would suggest if you go this route upgrade the same with higher quality and specifications. While you’re in there consider replacing the capacitors with low ESR and high operating temperature components.

A couple last suggestions for you to review and try. Set the UPS to less sensitive value from good to poor. Increase the high and low transfer voltage to something higher. If you no longer experience this problem it indicates dirty power. If however this does not resolve the issue it does narrow down the problem to being an internal hardware fault inside the UPS.

Rock On . . . 🤟

[nnemanja]

Hello Teken,

To cut a long story short, I ended up with 2 broken SMT1500 units. I described the problem with the first one, and the second was reporting a relay fault. However, both experienced the same issue with the spark extinguishing circuit for the SMPS relay. Both SMT1500 units are now working fine.

[Teken]

The two UPS were replaced under warranty? 

[nnemanja · Accepted solution]

No, they are from 2013 and out of warranty. I repaired their spark extinguishing circuit.