Hi all. I've been trying to fix a CyberPower UPS that isn't charging the batteries. The initial symptoms were that on applying mains power, the unit would come on for a couple of seconds, turn off again, and keep repeating this cycle.
Initially I thought it was just bad batteries as they'd been fitted for a while, so I fitted a new set. After a couple of weeks these flat and the UPS stopped working, so clearly an issue with the charger.
With no batteries connected, the UPS exhibits the same power cycling behavior, so it seemed like an issue with the switch mode charger. After reading After finding this thread I decided to treat the UPS to a complete new set of electrolytic caps. I also replaced the Viper22A switcher and feedback opto for good measure, as from the state of the PCB, it looked like the Viper had been running quite hot.
The UPS now powers on properly with no batteries connected and I'm seeing about 27V open circuit at the battery terminals, which sound reasonable for a 24V string. However, with batteries connected and an ammeter in series, the batteries still aren't charging properly. I'm seeing about 500mA into the batteries for a couple of seconds, followed by 200mA out for a couple of seconds, and this just repeats. On feeling the Viper, it is *extremely* hot and so I suspect what I'm seeing is it going into thermal protect and shutting down, then cooling off a little and coming back on. This is supported by the fact that I get a few more seconds of charging current from a cold start.
I'm struggling to find a service manual for this UPS, so I'm unsure as to how the charger circuit should work. There's a 0.68R power resistor immediately after the smoothing cap on the low voltage side, so I wonder if this might be a sense resistor. There's also a TL431K adjustable regulator that looks like it might be involved, but it can't be the primary means of controlling the charging current as it's only rated to 100mA.
If anyone has a service manual they could share and/or some tips on where to look next, it would be much appreciated.
Initially I thought it was just bad batteries as they'd been fitted for a while, so I fitted a new set. After a couple of weeks these flat and the UPS stopped working, so clearly an issue with the charger.
With no batteries connected, the UPS exhibits the same power cycling behavior, so it seemed like an issue with the switch mode charger. After reading After finding this thread I decided to treat the UPS to a complete new set of electrolytic caps. I also replaced the Viper22A switcher and feedback opto for good measure, as from the state of the PCB, it looked like the Viper had been running quite hot.
The UPS now powers on properly with no batteries connected and I'm seeing about 27V open circuit at the battery terminals, which sound reasonable for a 24V string. However, with batteries connected and an ammeter in series, the batteries still aren't charging properly. I'm seeing about 500mA into the batteries for a couple of seconds, followed by 200mA out for a couple of seconds, and this just repeats. On feeling the Viper, it is *extremely* hot and so I suspect what I'm seeing is it going into thermal protect and shutting down, then cooling off a little and coming back on. This is supported by the fact that I get a few more seconds of charging current from a cold start.
I'm struggling to find a service manual for this UPS, so I'm unsure as to how the charger circuit should work. There's a 0.68R power resistor immediately after the smoothing cap on the low voltage side, so I wonder if this might be a sense resistor. There's also a TL431K adjustable regulator that looks like it might be involved, but it can't be the primary means of controlling the charging current as it's only rated to 100mA.
If anyone has a service manual they could share and/or some tips on where to look next, it would be much appreciated.
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