UPS charging past safe voltage need advice

[ThepowerboX]

I've set up a little backup system for my workshop that includes a 24V hybrid UPS and two 12V 100Ah batteries. So far, I've only been using it with mains power. Recently, it's started to hum loudly and the charging voltage is creeping way past full, it's hitting over 29V. I don't have any solar connected at the moment. I've also tried doing a full reset, but that didn't help. Do you think it could be an issue with the controller?

 

[the detective 🔍]

Have you checked the charge controller? Could've failed or is malfunctioning.

 

[Even_Vexan]

First things first: verify that each 12 V battery is healthy (no shorted cell). A bad battery/cell can confuse the controller and push the voltage higher as it fights to charge it. After that, trace the controller’s voltage feedback circuit (sense wires) possible a loose wire or bad solder causing the controller to “see” a lower voltage and thus overcharge.

 

[Greg0riee3]

I've set up a little backup system for my workshop that includes a 24V hybrid UPS and two 12V 100Ah batteries. So far, I've only been using it with mains power. Recently, it's started to hum loudly and the charging voltage is creeping way past full, it's hitting over 29V. I don't have any solar connected at the moment. I've also tried doing a full reset, but that didn't help. Do you think it could be an issue with the controller?

I'd also suspect an issue with the controller inside your hybrid UPS. The correct float voltage should be around 27.0V to 27.6V for a 24V lead-acid system. Hitting 29V means the unit has lost control of its charging algorithm and is now severely overcharging your batteries, which will quickly kill them by cooking the electrolyte. The loud humming suggests a potential hardware failure, possibly a transformer or power stage, which aligns with the erratic voltage. Since a reset didn't help, the fix is beyond a simple setting change. I think it's crucial to immediately disconnect your batteries from the UPS to prevent permanent damage, and contact the manufacturer's technical support right away. Do not use the UPS or connect solar until you get this charging fault resolve!