Mains frequency is too low


This is Engineer Majid , from Iraq .

I own an APC 1500 ups , the problem is that the utility power is always at 45Hz , causing my ups to work on backup mode all the time

Is there any way or modification to reduce this frequency sensitivity feature ?


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Hi, Have you asked the Utility why their supply frequency is low? It must be affecting everybody, e.g. electric clocks would run slow, electric timers would be inaccurate etc. Surely they must be aware of this.



Thank you for your reply , I called it (utility) because it is a diesel generators that supply each tens of houses , and we rely on them , because the REAL utility power is a disaster ! , and yes , I've asked him many times ! it's a way of cheating as well ! so I decided to modify my APC electronically , and I've all schematic diagrams since I'm an engineer , I don't know the way of frequency sensing , either by (Averager) circuit or directly by microprocessor .


Hi, Not sure if this is the manual for your UPS or not. if it is, have you tried adjusting the "local power setting " to 'poor' as shown on p.8 to see if this makes a difference? Apologies if you have tried this already.


Thank you Sir , I tried this many years ago ,the APC won't accept less than 47Hz , so I need an electronic interference !.


Hi, Your problem is above my competency level but have you tried contacting the manufacturer of your UPS and asking them what you would have to modify so as to get your UPS to accept 45Hz if the 'local power setting' is set to 'poor'? See the manual in the above link for the contact details for support.


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Zamolxe , Sir

Every notes you've mentioned is correct , I know roughly that the efficiency will drop by 20% since using 45Hz frequency , but they're long hours of using diesel generators , all I wanted from APC , is passing this 45 Hz as it is to my loads , but APC refuses this , since it's out of (clean power) criteria !.

But finally I succeeded to (Trick) the processor to deal with such low frequency by using external standard 50Hz function generator , you could watch my youtube channel to find how !.

My youtube channel : majid khafaji

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Well, this is also above my competency level, but this ups has a "line-interactive" topology (the term is outdated and nowadays it's officially called something else, but the standby/offline; line interactive; online definitions still stick) and thus has the following basic schematic:

As such, isn't it the job of the AC/DC Converter of the device to "accept" your 45 Hz or not? If so, could it just be that you have to modify that?...of course i don't know what effects this will have. Presumably these have been designed to work in a specific way at a specific efficiency - it will probably decrease efficiency? (or maybe you will be limited to power up less load in the manner that an online UPS will work as a step up transformer that will accept 110V instead of 230V but limits the load power draw to 50% of the rated VA)

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majidsarah will be eternally grateful.
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