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I am setting up an experiment that will need to run for 15 days straight and I am using a Raspberry Pi as a data logger. In my place power outages occurs from time to time. I am searching for cheap options to power my Rasp.Pi for at least 24 hour power interruption. I found this cheap UPS

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with this following specifications:

Max Wattage: 600V watts
Input Voltage: 220V AC
Voltage Range: 165~275V AC
Frequency: 60Hz
Output Voltage regulation (Batt: Model) 220VAC ± 10%
Frequency: 60Hz ± 1Hz
Waveform; simulated sine-wave
Battery Transfer Time <6Ms (Typical)
Battery Type: 12V DC
Recharge Time: 5hrs to 90% after discharge
Battery Protection; Over discharge protection & Short circuit Protection by Fuse
Function With advantage battery management
Display: LED status indicators for AC normal (Green), Back-up (Yellow), UPS cut-off (Red)
Alarm: Buzzer on for Back-up mode, battery low, overload
Output Short Protection: AC fuse and Electronic circuit (Back-up mode)
AVR (Auto Voltage Regulation)
DC star Function Auto-Restart UPS Over/Under Voltage Protection
Environment Operating Temperature: 0-40ºC
Relative Humidity: 0~95%, non-condensing
Audible Noise: <40dB at 1M
Physical Dimension: 356mm x 130mm x 232mm
Fuse: 4A 250v
Output socket: NEMA type 4 Socket
Materials: ABS Plastic
Net Weight: 3529 g
Gross Weight: 3622 g

Is this set-up possible for me? I don't have any knowledge on electrical aspects but I really need the pi to log my data continuously for 15 days please help me.

  • Like @Edward_178118 said, a UPS isn't really intended to power a device for a prolonged period of time. A power bank with overcharging protection like this one should supply enough power to run your Pi for at least 24 hours (see this). – tjohnson Mar 10 '16 at 17:04
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So, you choose this ups here: http://www.cdrking.com/index.php?mod=products&type=view&sid=16847&main=140
Which sadly won't give any information on how large the Power Storage is (Mostly in Ampere (A) ). But in the title it gives us a maximum of 30 minutes and says it can output up to 600 W per hour at 220 V.
That makes a storage of 300 W at 220V.

Let's take the peak wattage they take. (Watts is measured per hour w/h, so it's an easy calculation.) It depends on the Pi and Power Supply, since every Pi takes another peak wattage from the supply.

Every Pi compared:

Raspberry Pi 1: 1.5 W (model A), 1.0 W (model A+), 3.5 W (model B), 3.0 W (model B+) or 0.8 W (model Zero)

Raspberry Pi 2: 4.0 W

Raspberry Pi 3: 4.0 W

Let's take the Pi 3, which takes 4 Watts/hour peak.
Your supply is 300w/h. Let's do the math here:

(300w/h) / (4 w/h) = 75 hours of service.

But we have to take in account that the power supply for the pi itself wastes some energy (that's normal and you can feel this as the heat coming up from it). So it's a few hours less than 75, let's say 70 or even 60. that's nearly two days then, if you're going with the Raspberry Pi 3.

PS. This isn't the fully correct way to get the perfect time it will run.

Source for the Pi Wattage: https://en.wikipedia.org/wiki/Raspberry_Pi

  • Might want to be a wee bit cautious with that projection. It looks like you're using a peak current draw of 800mA for the Pi 3. While that's true as long as you're running it completely bare of peripherals, adding things like storage devices may impact the run time significantly. I've at least one well festooned Pi here that's none too happy about being run on less than a 2.1A power supply - that would take your wattage to 10W and reduce your run time to closer to 30 hours. – goobering Mar 10 '16 at 16:02
  • Your units are way off here. Amps and Watts are a measure of flow. (Watts is Joules per Second.) Capacity is Amp-Hours (That's Amps times hours, not Amps per hour) or Watt-Hours. When you pay your electricity bill each month, you pay based on how much capacity you used, in Kilowatt-Hours (KWh). Watts and Amps are a measure of flow: a particular device might draw 50 Watts for 2 seconds, or for 2 hours, but it's still drawing 50 Watts. There's no such thing as "Watts per hour" unless a device draws more and more power the longer it's left on. – David Yaw Mar 10 '16 at 17:34
  • You're right David. I just always assume watt hours since it comes down to that when I comapre the Watts ans watts they draw over time when i measure this stuff at home. And Watts with DC current is Amps times Volts. Your comparison takes all the stuff better into account. :) – alsternerd Mar 11 '16 at 8:15
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The UPS you chose doesn't list their exact times, so there's no way to calculate how long it will last under a given load. I'll run through the calculation for a couple different UPSs, so you can repeat it on one of your choice.

I'm going to use this UPS, which has a similar wattage rating as the one you chose: CyberPower EC650LCD ECO 650VA/390W.

The specs on that page list the following:

  • VA Rating: 650 VA.
  • Watts: 390 Watts.
  • Battery Run Time:
    • 10.7 minutes (160 W)
    • 2.8 minutes (325 W)
    • At Half Load (min.): 8
    • At Full Load (min.): 2

OK, so it can run for 10.7 minutes at 160 Watts. That means it has a capacity of (10.7 / 60) * 160 = 28.53 Watt-Hours. (High draw applications will decrease the amount of time it'll last faster, because of how batteries work. Note that the "at full load" number isn't half the value of "at half load". Therefore, pick the statistic that's closest to our target draw, which is very small for the Pi.)

Let's say the Pi draws 1 Amp at 5 Volts. That's 5 Watts draw. (Your Pi is probably a bit lower than that, but there's some inefficiencies in the various conversions, so this'll work for now.)

OK, 28.53 Watt-Hours, 5 Watts. 28.53 Wh / 5 W = 5.7 Hours. The UPS I linked above should be able to power your Pi for around 5.7 hours.

Now, let's approach this math from the other side: The Pi draws 5 Watts. If you want a full day, that's 24 * 5 = 120 Watt-Hours. We need to find a UPS that has at least 120 Wh of capacity.

Here's a larger UPS: CyberPower Intelligent LCD Series CP1500AVRLCD 1500VA 900W.

  • VA Rating: 1500 VA
  • Watts: 900 W
  • Battery Run Time:
    • At Half Load (min): 11
    • At Full Load (min): 3

11 minutes at half load. Full load is 900 Watts, so that's 11 minutes at 450 Watts. (11 / 60) * 450 = 82.5 Wh. Still not large enough.

OK, let's try this one: CyberPower TAA Compliant Smart App Sinewave PR1000LCDRT2UTAA 1000VA

  • VA Rating: 1000 VA
  • Watts: 700 W
  • Battery Run Time:
    • Runtime at Half Load (min): 32
    • Runtime at Full Load (min): 11

32 minutes at half load. Full load is 700 Watts, so that's 32 minutes at 350 Watts. (32 / 60) * 350 = 186.67 Wh. OK, that'll keep you running for a full day!

As you search for UPSs, watch out for ones that claim a run time, but don't specify how much power is being drawn for that time. There's no way to tell how they came up with that number, and there's no way to do the math to figure out what the capacity is. With the one you linked, the front of the box says "10-30 minutes", but there's no way to tell what the wattage of that is, so we can't use that number in our calculations.

Also, one thing to keep in mind is that most UPSs are designed to keep a system running for a few minutes, not a full day. 5 Watts for the Pi is almost nothing, the internal circuitry of the UPS is probably taking that much as well, and we didn't account for that in our calculations, and as our runtimes get longer and longer, it'll throw our math off more and more, but this'll get you close.

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You should contact the maker of the UPS you are using and discuss the power requirements of the Raspberry Pi and whatever else might be connected to it. I would discuss this with them in detail saying you want to have it provide power for 15 days, because they might recommend another model for you. Or additional batteries. I don't believe most UPSes are made to handle supplying power for that long a period of time. A UPS also has a built-in fan, which is likely to draw even more power the longer it is on.

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