Calculating UPS Backup Runtime?

[PinkFloydEffect]

I am trying to calculate the run time of a UPS for a mini aquarium. If the power fails the pump stops, which supplies water to the rear wall that is covered in plants now. Without water they dry up quickly and die, all aquatic species so they rely on constant water. The filter clogged and the rear wall dried up, which made me think about a power failure.

I have two APC Back-UPS units laying around I could use but they will need new batteries. The first is a model BE550G rated for 550VA / 330W.

I also have what they are calling the BE550Gs successor, model BN650M1 rated for 650VA / 360W.

I do not understand how it is a successor, it may have a higher output capability @ 650VA and 360W but the battery is only 2/3 the size of the BE550G...likely 7AH tops. Seems like a dumb idea to increase the power handling of the inverter while decreasing the battery size. On the other hand I just bought a new 9AH upgrade battery for the BE550 which is typically 7-8AH. I am not sure if there is something wrong with it though, when testing with a drill it actually speeds up when I unplug the AC...yet the voltage drops from 120V to 85V when you unplug the AC with no load so I do not understand why it speeds up or if 85V is a failing inverter.

With my 9AH battery in mind, I have two things I want to run on the UPS...the pump and light (not my main light shown here). The pump is rated 6W @ 110-120V (0.05A?) and the secondary accent light is rated 0.30A @ 110-120V (36W?) so how long will this run on a 9AH battery?

 

[System Error Message]

they could change battery type, to lithium polymer. find the voltage of the battery, multiply by the AH rating and you get your watts, then divide by half (inefficiencies) and the rated wattages of your appliances.

 

[PinkFloydEffect]

It came with a 7AH battery and I upgraded it to 9AH since I work at a battery store and was able to get it for $18. This is also a high-discharge approved battery, better than the OEM so I believe it is deep cycle but I would assume the APC would cut it off before the voltage drops too low.

After some testing with a Dremel I think this APC has some failing circuitry. When you unplug it from the wall the voltage drops from 120V to 80V yet the Dremel speeds up if it is on max setting! If I add more to the load the voltage on the APC goes from 80V to 95V but the Dremel does not speed up any further. I played with this for a while even using a 1500W heat gun but it only works on the lowest settings since it draws way too much. After playing with it the battery voltage dropped from 13.6V to 12.5V which is not bad for 10min using a Dremel and a heat gun...the APC never cut out power with a low battery warning (not sure where the threshhold is set). Therefor I figure the tiny aquarium pump should run a while.

 

[ColinTaylor]

How are you measuring the voltage? Apparently you will get the kind of readings you're seeing with a "normal" volt meter. That's because UPS's don't output a true sine wave but a modified squarewave, so you'd need to use a True RMS meter to get an accurate reading.

 

[PinkFloydEffect]

How are you measuring the voltage? Apparently you will get the kind of readings you're seeing with a "normal" volt meter. That's because UPS's don't output a true sine wave but a modified squarewave, so you'd need to use a True RMS meter to get an accurate reading.

Oh really!? I did not know that, I am just using a cheap multimeter but I have a Fluke I can see if it has an RMS setting. Thank you

 

[System Error Message]

cheap multimeters are ok, but you may want a more expensive one that has proper fuses to deal with the amps.
And yes you do need a true RMS meter to measure the AC voltage, and also the AC amps. it doesnt have to be fluke, but any decent meter with a true RMS setting is needed to measure AC voltage.

Actually the UPS does output close to a sine wave, however its not quite as a curve because it is switched, so the squares are based on the switching speed, and cant really be seen unless you zoom in very near on an oscilloscope. To output a real sine wave means using a motor but thats highly inefficient but can work both ways converting DC to AC and vice versa. Whats important is that the output of the UPS AC voltage is stable, with little to no noise keeping as close as possible to a sine wave, only can be seen with an oscilloscope, but different UPSes have different customers they aim at. Many switching based PSUs that PCs and PC equipment will take in those square waves but AC motors may not run as smoothly. Honestly it will be far more efficient to use DC to DC converters and just connect things directly in DC, this will give you a far far better run time on better while also lowering the power use when on mains because those switching PSUs do have internal losses too.

 

[sfx2000]

I am trying to calculate the run time of a UPS for a mini aquarium.

1.6 * Wattage Load = Minimum Volt-Amperes (VA)​

Size it accordingly.... most UPS are sold as VA capacity

Watts = Volts * Current

(P = I * E)

 

[PinkFloydEffect]

cheap multimeters are ok, but you may want a more expensive one that has proper fuses to deal with the amps.
And yes you do need a true RMS meter to measure the AC voltage, and also the AC amps. it doesnt have to be fluke, but any decent meter with a true RMS setting is needed to measure AC voltage.

Actually the UPS does output close to a sine wave, however its not quite as a curve because it is switched, so the squares are based on the switching speed, and cant really be seen unless you zoom in very near on an oscilloscope. To output a real sine wave means using a motor but thats highly inefficient but can work both ways converting DC to AC and vice versa. Whats important is that the output of the UPS AC voltage is stable, with little to no noise keeping as close as possible to a sine wave, only can be seen with an oscilloscope, but different UPSes have different customers they aim at. Many switching based PSUs that PCs and PC equipment will take in those square waves but AC motors may not run as smoothly. Honestly it will be far more efficient to use DC to DC converters and just connect things directly in DC, this will give you a far far better run time on better while also lowering the power use when on mains because those switching PSUs do have internal losses too.

Very interesting! So that explains why the Dremel was acting funny when I was applying different additional loads, may have been the way the AC motor was handling the "squares".

While it may be possible to wire my light in DC the AC pump motor still requires AC.

Even with a non-RMS meter shouldn't the output voltage be near stable without 40V swings from 120 to 80?

 

[System Error Message]

Very interesting! So that explains why the Dremel was acting funny when I was applying different additional loads, may have been the way the AC motor was handling the "squares".

While it may be possible to wire my light in DC the AC pump motor still requires AC.

Even with a non-RMS meter shouldn't the output voltage be near stable without 40V swings from 120 to 80?

the amps and volts are against each other in an AC circuit. https://electronics.stackexchange.c...cal-difference-between-watts-and-va-volt-amps

All meters take measurement at a certain frequency, that frequency is not in phase with AC frequency, so you get different voltage measurements each time. What RMS means is root mean square which is exactly what it says, take the voltage, square it, get the mean, than root that, essentially that is where your 120V or 240V mains mean, not that the peak is 120V or 240V, but the average is. Basically if you took the voltage line, and flattened it (averaged) in volume rather than line, that is your actual voltage. This is why you need a true RMS meter to measure AC as it does some maths to get the actual voltage of a sine wave.

A non RMS voltage/amp meter gets the measurements, about some amounts, averages them and displays it. It will be getting voltages at different points along the graph so giving you inaccurate readings. If you average the voltage readings you will get a different value compared to the voltage volume.

 

[PinkFloydEffect]

the amps and volts are against each other in an AC circuit. https://electronics.stackexchange.c...cal-difference-between-watts-and-va-volt-amps

All meters take measurement at a certain frequency, that frequency is not in phase with AC frequency, so you get different voltage measurements each time. What RMS means is root mean square which is exactly what it says, take the voltage, square it, get the mean, than root that, essentially that is where your 120V or 240V mains mean, not that the peak is 120V or 240V, but the average is. Basically if you took the voltage line, and flattened it (averaged) in volume rather than line, that is your actual voltage. This is why you need a true RMS meter to measure AC as it does some maths to get the actual voltage of a sine wave.

A non RMS voltage/amp meter gets the measurements, about some amounts, averages them and displays it. It will be getting voltages at different points along the graph so giving you inaccurate readings. If you average the voltage readings you will get a different value compared to the voltage volume.

Thanks for the breakdown!

Still not sure if there is something wrong with my UPS hardware...I tested it today with the tank. My LED accent lights did not flinch when I unplugged the AC but the small pump ran very slow and choppy. It is rated for much more capacity than I am using but it doesn't make sense to me, I could run a Dremel at full speed off of it if I wanted.

 

[ColinTaylor]

The type of load (inductive) that electric motors put on UPS's can cause problems. Looks like that's your problem?

http://www.apc.com/us/en/faqs/FA158851/

Cause:

APC's Back-UPS and Smart-UPS SC product lines are designed for use with computer type loads only. They are not designed to be used with motor loads such as fish filters, air conditioning units, space heaters, vacuum cleaners or any other machinery.

Resolution:

One potential issue is the inrush current draw for a motor. It can easily overload a Back-UPS UPS model. Secondly, these models of UPSs output a stepped approximated sine wave when on battery. This waveshape, while ideal for computer type equipment, is not particularly compatible with most motor loads. The result may be that motors run very slowly, erratically, or not at all when the UPS is on battery.

To protect this type of equipment, APC recommends first determining the appropriate size UPS for the motor load in question. Ensure that the Volt Amp rating of the UPS is sufficient to handle the start-up inrush current draw of the motor. Secondly, select a UPS which outputs a pure sine wave when on battery, such as a Smart-UPS (minimum of a 750VA model), Smart-UPS Online, or Symmetra LX/RM.

 

[PinkFloydEffect]

The type of load (inductive) that electric motors put on UPS's can cause problems. Looks like that's your problem?

http://www.apc.com/us/en/faqs/FA158851/

Yes that is exactly my problem