What type of UPS: pure sine wave or modified sine wave?
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I have have at least 2 dozen 12v power bricks connected to a APC UPS that produce a "simulated" sine wave output without any issues.
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@Gertjan said in What type of UPS: pure sine wave or modified sine wave?:
Enter both shown power lines (tension) into the 1100 and it will die right away.
So one can't directly plug 120V AC into something wanting 12VDC? (yes I'm kidding)
Simulated sine wave vs true analog sign wave is the same argument as music from vinyl or from CD: it's all about the sampling rate.
Sample fast enough, you get small steps and it may be close enough. -
@mer: The assumption is that the sampling rate is rather low, especially compared to a CD sampling rate of 44 kHz. The images shown in this thread imply that the sampling rate may be in the 2 kHz range. The specs for the UPS I was thinking of using doesn’t specify it.
I wish I had an oscilloscope. I would post real-world measurements here. I have used only APC UPSs in the past, including a few Smart-UPSs, which output sine waves. Maybe with an oscilloscope I would still be able to detect steps, albeit much closer together. Perhaps, though, that output is low-pass filters to eliminate those. Unfortunately, APC documentation is silent on those details.
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@elvisimprsntr: Looking at the troubleshooting section of the UPS I am looking to use I found this:
It was the only occurrence of the word “sine.” It makes sense that a power brick or computer power supply can handle the more “steppy” waveform.
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@Gertjan: As you can see from my posts above, it seems like APC considers their BackUPSs sufficient for electronics and computer equipment. It is understandable that there could be issues with electric motors, where I am sure rotation frequencies corresponding to sampling harmonics could wreak havoc. Reminds me of what the Stuxnet cyber attack on the Iranian uranium enrichment centrifuges did to them.
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I wouldn't expect a problem, though I haven't tested it specifically.
However every computer PSU I have ever come across, including external power bricks, are switched mode. The first thing it does is rectify the incoming AC power and smooth that with some large capacitors. Then it chops that up at some much higher frequency and filters it to get the required output voltage(s). That means it doesn't really care much about what goes into it. They usually have a very wide input voltage range for example, 90-250V perhaps. There are limits to that though, some PSUs are better at filtering garbage than others.
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This post on Stack Exchange Super User did the analysis of various UPSs with an oscilloscope. It’s very insightful. Bottom line is, however, that the quality of the AC output wave form does not matter for the vast majority of digital electronics.
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@DominikHoffmann I have been running 1100’s and 2100’s and 6100’s of the “cheap” APC and Eaton modified sine wave UPS’s for years without issue.
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The (bridge)diodes and big 350v capacitors in your PSU will be thankful if you use SINE wave.
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The answer to the question pure sine wave or modified is more technical and outside the scope of these forums.
The advise to use APC is a good one, they are a good solid brand, many rebadge APC but the design is sound have used them for decades.
To get more technical, if the load is transformer inductive then sine wave is very important becuase of how the energy tranfers from one winding to the other to step up or down the voltage.
For example your fridge , AC or simular.
However switch mode powersupplies firstly rectify the incoming voltage into DC, in the UK we're nomally 220-252vAC that becomes 310-355vDC (being the RMS of the peak usable voltage figures are all 'ish' becuase the vary)
That is then fed into a transisitor and turned on/off at high frequency, the switch mode part and the resultant output then smoothed and fed to the device. This is the basics of how a SMPSU works.
The bottom line is, whilst pure sine wave is desirable, most well designed SMPSU's inside quality electronics will quite easly cope with a modified sine wave.
In fact if you look at the incoming AC on an scope, its pretty awful, full of noise and spikes and varies over time. So even a modified sine wave is an improvement.
Last comment on AC. We're seeing more and more failures of PSU's , we've identified that becuase the UK mains voltage has begun to creap up and holds nearer to the top limit of 253 rather then the lower limit of 215 its placing more strain on the PSU's and often the smoothing caps are out of spec. for the hgher voltage. Here is our incoming voltage over the last 12 hours.
