This page provides information on my Prius generator project, which is a system to utilize the battery and charging system of the Toyota Prius to provide power for the home during emergencies.
First off, this isn't my idea, just my particular implementation. Full credit for the idea and research for this project goes to Richard Factor (www.priups.com). Please visit his site if you are interested in all the details.
Disclaimer: This project involves high voltage and other potentially dangerous activities and should not be attempted by anyone unless they know what they are doing!
Well, in order to get power from the Prius, the first thing that is required is access to the high voltage traction battery. This is achieved by connecting to the high voltage battery leads in the trunk. I did what other people have done, and that is to bring it out to the driver side storage bin in the trunk.
The UPS consumes about 200W in idle mode, so leaving it on standby continously wasn't an option for me. However, since the unit would not start up without 240V input power, I needed an alternate means of starting it. I settled on using my gas generator to start it. You can see an existing generator transfer switch on the right side of the panel that is normally connected to the generator. When I first loose power, the idea is to first fire up the gas generator until the Prius makes it home, and/or then use the generator to start the UPS. The UPS 240V power outlet on the left of the load center is wired to two cutover switches above it that can switch it from it's normal circuit breaker to the 240V from the generator. Once the UPS is started and connected to the Prius battery, input power can be disconnected and it will now be running on battery. At that point, the input to the transfer switch is switched over to the UPS output (manually via L14R20 plugs), and the gas generator can then be shut down.
So, that's it. That's the whole system. It works well. Although I have a 6KVA UPS, my regular loads are less than 3KVA, so it's running very much below it's limits. The battery voltage at the UPS varies between 210V and 245V when connected to the Prius, which equates to 2 and 3 bars respectively on the Prius display. I had some concerns that the high voltage might cause the UPS batteries to overcharge and start to gas, but it is at that high voltage for less than 30 seconds before the engine shuts off and the voltage starts to drop. At my normal consumption, which is mostly computers, furnaces, entertainment system, lights, etc, the Prius runs a 23-33% duty cycle. Charging seems to take about 2 1/2 minutes and discharge times vary from 8 to 5 minutes, depending on the load.
I look forward to the next power outage :)
Constructive comments or questions are welcomed at priusgen (at) sandbox.org
** Update - Nov 2011
On October 29th, 2011, an early winter storm took out power for almost 2 full days. The Prius generator performed flawlessly, and consumed about 5 gallons per day, which was a lot less than a normal generator, but still a lot more than the grid.