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I have a UPS that was powering my Monitor and CPU unit whenever main power was failing. I also have a modem that provides internet connection to the entire house. Now, the modem gets power from mains, so whenever main power goes off, there is no internet connection. I wanted to prevent this from happening because I am having online exams and a power failure(hence no internet) is a disaster for me.

So, I stopped using the UPS for Monitor and CPU unit and I tried to use it for my modem. But UPS is not able to provide power to it. UPS is working fine and so is the modem. Let me provide some more information-

The UPS model is not listed on it's official site(MicroTek) anymore, however it can be found in an Indian E-Commerce site named Flipkart-Here. In case the link goes down, here is the picture of the specs:

UPS Specs UPS Battery Specs

  1. The UPS(say X) has input specs- 230VAC, 50/60 Hz, 4.5A and output specs- 230VAC, 50/60 Hz, 2.9A(Also DC Voltage 12V is mentioned which I do not know why since output is AC). It has one plug that goes into mains for charging itself and 3 output sockets giving AC output.
  2. The adapter(say Y) or plug that gives power to modem from mains has input specs- 100V-265V Max, 0.3A, 50 Hz and output specs- DC 12V, 1A
  3. An adapter(say Z) that charges my phone has following input specs-100-240V, 50-60 Hz, 0.35A and output specs- 5V(DC presumably as output cable is micro USB), 2A

So, what is astonishing is that Z works perfectly with X and mains(hence my phone gets charged), Y works only with mains, when Y is plugged into X, modem doesn't power up. And you can notice that the specifications of Y and Z are very similar. So, I'm not able to understand why UPS can't power up the modem.

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  • Some UPS models have different ports for battery and surge protection. Make sure you are plugging the modem into a battery + surge port and not just a surge port, as it won't be powered in a power failure.
    – Sam Forbis
    Oct 11, 2020 at 17:01
  • Also , does your UPS produce decent Sine Wave output? Some do not and the resulting hash (average out to the RMS voltage) may not be compatible with your modem. Something to check. My own UPS produces proper Sine Wave and powers my ISP's Modem, and all network gear.
    – John
    Oct 11, 2020 at 17:06
  • @SamForbis Indeed it is mentioned in my model that there is battery+surge protection. However, I have tried all 3 output ports but is doesn't power up the modem. One observation I made was whenever I was plugging in modem to UPS and switching on UPS(with UPS plug not attached to mains-to simulate a 'no-mains' scenario), the modem was not powering up, but when I switched off the UPS then the modem powered on just for a second. It's as if the sudden fall in voltage powered up the modem(but this is unnatural behaviour, right?) Oct 11, 2020 at 17:17
  • @John checking Sine Wave requires an oscilloscope, right? Because I don't have one and I have to find an alternative to check the Sine Wave output. Oct 11, 2020 at 17:18
  • Yes. I do not know another way to check the output except to contact the UPS manufacturer and ask them for advice.
    – John
    Oct 11, 2020 at 17:22

2 Answers 2

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Some devices have a problem connecting to a UPS with a modified sine wave.

You will find a treaty of the technical aspects of the subject in the post
When do I need a pure sine wave UPS?

One important remark over there is that the use of a modified sine wave UPS with a PFC PSU does not cause physical damage to either the UPS or the PSU, so no harm will occur to your devices. However, when incompatible, the UPS will just fail to keep the device powered on, which is just what is happening in your case.

It might be worthwhile investing in a pure sine wave UPS, although they are usually costlier.

As another remark, if power is inconstant in your area, I strongly recommend not to run your computer without a protecting UPS or at least a surge protector. Otherwise, worse things than lost internet connection may occur.

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Indeed the specification for the UPS on a site(as mentioned above in the now edited question) says the output is 'modified sine wave'. I think that might the issue.

Here is a good discussions of the differences

https://blog.tripplite.com/pure-sine-wave-vs-modified-sine-wave-explained

The main difference between pure sine wave and simulated sine wave UPS systems is that a pure sine wave system in battery backup mode is guaranteed to produce a cleaner output for any piece of equipment connected to it, whether it’s a desktop computer, lab equipment or a server in a data center. The same cannot be said of a modified system, which produces a stepped approximation to a sine wave

I hope this helps you make a decision.

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