05 May 2006
SETI League
PriUPS Project


We Interrupt This Blog...

With important news!  I had a power failure on Tuesday of this very week!  Normally not a situation to be greeted with glee, but this was the first actual, true, genuine, utility-related power failure since I completed the PriUPS system earlier this year.  Heralded by almost unnoticeable beepage from the 230V supply that is not connected to the main PriUPS system, and with the continuous announcement of "AC Power Failure" in my own voice, the AC power to my house was interrupted.

The good news:  Power Failure!  Whoopie!
The bad news:  It only lasted for about an hour.  Because the UPS batteries alone will run all my emergency circuits for as much as three hours, no power was actually drawn from the Prius.  But was it ever ready!

This first display shows the onset of the power failure:

Onset of power failure, PriUPS connected at 45 minutes

At 26 minutes into the graph the blue line, which represents the AC power voltage from the utility, dropped out.  Immediately, the yellow line, which is the UPS battery voltage, dropped by about 15 volts from its normal charging voltage to the voltage expected under a light load while the batteries are still fully charged.  At this point, the UPS is supplying power to the house.  The fluctuations in the yellow line are a combination of the battery slowly discharging and a reflection of the household load, represented by the green line at the bottom.  Because many power failures are brief, I didn't instantly run out to connect the Prius.  After about 20 minutes, I drove the Prius into the garage and connected it, as indicated by the red line.  Looking at the graph, I noticed that there was a problem.  The Prius battery was charging and discharging much more rapidly than it should have, given that there was no load on it.  Sure enough, I had left the heat on, which requires a lot of power.  When I turned it off (at 53 minutes), the discharge curve flattened.

Here is the remainder of the event:

Balance of power failure, PriUPS disconnected at 35 minutes

Continuing from the previous graph, you can see that the Prius battery voltage is still slowly discharging under the minor load that the car was presenting, and the UPS battery was also slowly discharging.  Unfortunately, long before the UPS battery discharged, the AC Power (Blue) came back on.  At this point, the UPS battery resumed charging and the "emergency" was over.  If power had remained off, within a couple of hours the yellow line would have converged with the red line and the Prius would have been supplying power to the house. 

Nerd Heaven!

Richard Factor