60Hz UPS on 50Hz mains

Logician

Joined Jul 20, 2019
3
As title says, I’m trying to run a 60Hz UPS (specifically a CP1500AVRLCD) on a 50Hz supply via a step-down transformer. The unit pretty much refuses to turn on, which I suspect is because a) it must be connected to AC power to turn on for the first time, and b) a 60Hz detector is telling it that mains power is not present.

Anyone know how I can modify the timing circuit to detect 50Hz instead? I’m pretty sure the lower frequency won’t hurt anything (and I’m willing to risk losing magic smoke if it does). I assume I can probably add or swap a resistor, but I can’t find a service manual or schematics anywhere online, and I’m not great at figuring out a circuit board visually. Any help is appreciated!

SamR

Joined Mar 19, 2019
2,260
According to its tech specs it requires 60Hz +-3% on its input when means a minimum 58.5Hz.

Logician

Joined Jul 20, 2019
3
According to its tech specs it requires 60Hz +-3% on its input when means a minimum 58.5Hz.
Thanks SamR. I’m hoping to modify to tune the frequency detector to 50Hz instead of 60Hz, but I’m not really skilled enough to identify the frequency detecting circuit on the PCB without a schematic. Hoping someone either has the schematic or can point me in the right direction for finding the relevant components on the PCB.

nsaspook

Joined Aug 27, 2009
7,356
A modern UPS typically uses a microcontroller for the frequency detector duties with the help of a zero-cross detector. It's most likely a firmware function instead of a discrete circuit on a PCB.

Joined Feb 20, 2016
3,572
You may get away with changing the processor crystal. For example, if it is 10Mhz, use 10 * (50/60) = 8.3Mhz.
Then the UPS still "thinks" it is running at 60Hz.

Logician

Joined Jul 20, 2019
3
You may get away with changing the processor crystal. For example, if it is 10Mhz, use 10 * (50/60) = 8.3Mhz.
Then the UPS still "thinks" it is running at 60Hz.
That’s brilliant. I’ll give that a try.

Ramussons

Joined May 3, 2013
828
As title says, I’m trying to run a 60Hz UPS (specifically a CP1500AVRLCD) on a 50Hz supply via a step-down transformer. ......
Any help is appreciated!
The same unit CP1500AVRLCD is available from Amazon India. Its 50 Hz here, so I guess that there must be a simple change to convert these between 50 and 60 Hz.

Look for a strapping option on the board. I recall quite a few mains operated clocks working on 60 Hz that could be operated on 50 Hz by a strap change.