Archive for electric power

car powered inverter

Posted in house tech, technology with tags , on May 4, 2010 by marksun

If you have a source of 12 V DC power you can run an inverter to power up refrigeration in the house if you lose power.

Costco recently had a nice 1000 watt Xantrex inverter in the store for $30. I had purchased this for use with my Escape hybrid at $65 and thought I got a deal.

Because the DC-DC inverter (replaces the alternator of a regular car) is so expensive on hybrids, I made an adapter that limits the inverter to contributing 100 amps when the inverter is attached to the 12 v battery.  (He used a 100A Fuse assembly on the 12V side  which will blow at about 1200 Watts)

When the power is out , I can run lights, computer, etc off the hybrid. It starts itself as needed to recharge it’s batteries, then shuts off. It is much quieter than my 4000 watt generator, but will not run my furnace motor.

John Sweeny:
“One of the components in the Prius is a specialized DC-DC converter that uses energy out of the drive battery at roughly 200 volts DC to create 12-volt DC. Twelve volts is the “nominal” voltage of a 12-volt power system in the Prius as well as other standard cars; in actual usage the 12-volt system runs from 13.7 volts to 14.4 volts. In the Prius, the DC-DC converter (which is equivalent to the alternator in a normal car) is limited to 100 amps. Power = volts × amps, so in the Prius, we can get a total of 13.7 × 100 = 1,370 watts out of the 12-volt system. From the online forums, it turns out that the internal Prius electronics take about 300 watts, which leaves about 1,000 watts available for external use, and I had a 1,000-watt inverter in my basement.”


Here are some safety tips for readers tempted to try something similar:

1. Do not use an inverter larger than 1,000 watts because this can overload and damage the Prius 12-volt system. Keep in mind that running the inverter close to the 1,000-watt limit could also overload it because the startup power to many appliances greatly exceeds the steady-state power.

2. Follow normal safety procedures when dealing with the Prius 12-volt system. You should feel completely comfortable changing the 12-volt battery in the Prius by yourself before you attempt to make any changes to that system.

3. The Prius is a super low-emissions vehicle with a very efficient catalytic converter. In contrast, a standalone generator lacks a catalytic converter. Although the Prius is less risky than a standalone generator, the exhaust should be routed outside to eliminate the possibility of carbon monoxide poisoning. Carbon monoxide is extremely dangerous and has no odor.

With the Prius running in the Ready mode, he used this hookup for 4 days to power up a few appliances in the house including refridge and freezer and used about five gallons of gas.  This makes the Prius an efficient emergency power source.

Interview with Sweeney

One of the original articles