UPS cycles when on generator

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tshea

tshea

Senior Member
Location
Wisconsin
10kw Generac 120/240v measured output 124,125, 248 (no load)
Loaded voltage 118, 118, 236 (at panel) Amperage 12-20.
Biggest load is a 1 HP water pump for a well.

300 watt APC UPS input voltage 115, output 117 (at unit 75' away)
Unit is clicking every 20-30 seconds (battery is discharging to bump voltage to 117)
Smart UPS does not have the problem It is 115 input, 115 output.

Have you experienced this? Is the small UPS defective?

POCO power is 112, 113, 225. This business is at the end of the line on poco grid. UPS does not do this while on POCO power only generator.

Thanks!
 
ceb58

ceb58

Senior Member
Location
Raeford, NC
tshea said:
10kw Generac 120/240v measured output 124,125, 248 (no load)
Loaded voltage 118, 118, 236 (at panel) Amperage 12-20.
Biggest load is a 1 HP water pump for a well.

300 watt APC UPS input voltage 115, output 117 (at unit 75' away)
Unit is clicking every 20-30 seconds (battery is discharging to bump voltage to 117)
Smart UPS does not have the problem It is 115 input, 115 output.

Have you experienced this? Is the small UPS defective?

POCO power is 112, 113, 225. This business is at the end of the line on poco grid. UPS does not do this while on POCO power only generator.

Thanks!
Click to expand...

The UPS doesn't like the frequency from the generator or there is not enough load on the generator to settle the AVR in to a steady voltage. Try adding some restive load and see if the UPS will stay locked on.
 
Electric-Light

Electric-Light

Senior Member
zbang said:
The one with a problem is a BackUPS (not a SmartUPS)? If so, use it as a doorstop and get a better one.
Click to expand...

There's not much difference between Smart and Back UPS when its on utility power.

SmartUPS has sine wave output on battery and more networked control capabilities. BackUPS puts out modified square wave on battery.

They are both stand-by UPS which means the load is connected directly to power line and switches to battery with relays. There is a transfer time of 15mS or so.

They're picky about incoming power. If they don't like it, they switch over to battery. For repetitive dips, they hunt back and forth.

If you want to use it on a generator, you should consider a double conversion UPS which is available in size as small as 750VA from TrippLite all the way up to 100s of kVA.
 
weressl

weressl

Esteemed Member
Location
Texas by the Gulf, geat crab, great shrimp
tshea said:
10kw Generac 120/240v measured output 124,125, 248 (no load)
Loaded voltage 118, 118, 236 (at panel) Amperage 12-20.
Biggest load is a 1 HP water pump for a well.

300 watt APC UPS input voltage 115, output 117 (at unit 75' away)
Unit is clicking every 20-30 seconds (battery is discharging to bump voltage to 117)
Smart UPS does not have the problem It is 115 input, 115 output.

Have you experienced this? Is the small UPS defective?

POCO power is 112, 113, 225. This business is at the end of the line on poco grid. UPS does not do this while on POCO power only generator.

Thanks!
Click to expand...

Neither of those designed to work with each other. The UPS is designed to work from stable utility frequency, and the generators are designed to supply approximately 60Hz+/-X%.

Larger UPS's have a frequency tolerance window that is selelctable and/or adjustable, and the bypass is much tighter than the main input. Some generators don't like the non-linear load that a UPS front end represents and their voltage regulator goes crazy, so your generator needs to be specifically selected for the UPS load. Size also matters, if the UPS is a magnitude smaller than the generaotr your chances are better.
 
kwired

kwired

Electron manager
Location
NE Nebraska
The smaller the generator is the less stable voltage and frequency will be. Does not take as big of a load to switch on or off to make significant voltage and frequency changes as it takes with a larger generator. The generator may be able to handle loads but the engine driving it is also a factor. It takes time for it to respond for additional load or decreased load resulting in over or under voltage and frequency for what is a long time for the monitoring components in the UPS.
 
Electric-Light

Electric-Light

Senior Member
You can change the steady state transfer voltage on many UPSs. SmartUPS allow the dv/dt response to be changed by sensitivity button, however, frequency swing is not configurable.

No matter what you do, small generators do not have large enough mechanical inertia to avoid frequency swings.
 
Electric-Light

Electric-Light

Senior Member
zbang said:
Technically correct (not configurable) I guess, but on the newer units "Input Frequency 50/60 Hz +/- 3 Hz (auto sensing)". Older units may or may not accept this.
Click to expand...

This means that the UPS is capable of operating at 50 or 60Hz. If you run it on 50Hz 120v and unplug, the on-battery power will be 50Hz.

dV/dt is an adjustable factor, but the frequency itself or the rate of change df/dt is factory set.

On grid, frequency swing in excess of 1/2 Hz is almost never there, and there rate of change is always very slow as it is controlled by millions of pounds of flywheel inertia at power plants.
I guess APC forecasts fast frequency swing as imminent power loss and switch over to battery.
 
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Electric-Light

Electric-Light

Senior Member
zbang said:
Just for fun, I check the WECC Pullman monitor point- freq went from 59.991 to 60.004 over about 30 seconds, then started down again. Pretty accurate over time.
Click to expand...

Long term cycle counts is very accurate over long run on power line. Barring power outages, alarm clocks hold time just as good as radio synchronizing watches.

The reason for such a close tolerance over time is just that.
 
tshea

tshea

Senior Member
Location
Wisconsin
Thanks everyone for the help. I'll post what we decide to do. I'm the 4th or 5th person to come into this situation and I don't have a real good feeling....
 
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