110 VAC inverter installation

This is my second, 12V inverter install in a Prius, the first is in our 2003 Prius. Since this is our second Prius, a 2010 ZVW30, I'm going for the upper limit and my sine-wave, inverter 1.5kW/3kW, is oversized. But for more conservative owners, I would recommend:

• 1kW/1.2kW surge - I've already seen 30-45 seconds at 1.2kW with the existing battery. Although I don't have a 1kW, sustained load test, our 2003 Prius worked OK so I think it is a fair risk.
• permanently mount inverter - I really don't like the Anderson connector losses and clamp-on cords are risky and as lossy as the Anderson. I would mount to the battery cover but to the side would work provided the battery cover can still be removed.
• directly connect 4 awg to battery post clamps - don't fiddle around as there are going to be losses BUT compared to a gas generator, the improved hybrid cycle, absence of toxic carbon-monoxide, quiet, and large tank is a big winner.
• sine-wave inverters are nearly as efficient as modified sine-wave - if you're not into load testing, go with a sine-wave and be happy. Just make sure you test the output voltage with a true RMS meter as my inverter shows 110VAC, not 120VAC. A lower voltage increases the current draw and that is undesirable.

Yes but I've only studied one and it was designed for fixed operation in a home. Personally, I think the right answer is to modify the Prius inverter, MG2 circuit, to provide AC power. The technical aspects are simple to outline but not trivial to implement:

• serious switch between MG2 and AC outlets - it needs to be mounted in the engine bay which is already pretty tight. It also has to be weather proof and pretty robust.
• switch inverter interface from HV ECU to microcontroller - less risky than the high power side, this is still tricky since these are shielded leads from the HV ECU.
• reverse engineer the inverter drive circuits - Toyota has not provided open source for how the inverter signals works. Good Prius Friend Hobbit has done some initial work and I've some ideas. But this is where it gets really tricky. My understanding is a modulated, 10kHz signal operates the inverter but we don't know if there are special setup or undocumented digital communication between the inverter and HV ECU. This really is 'black box' magic.

In theory, we should be able to draw about as much power as MG1 can provide, 18kW in the 2001-03 Prius. This is three times the nominal 6kW power of ordinary houses. Since we already know one house-sized solution provided 3kW, the true number is somewhere between 3kW and 18kW.

Bob Wilson

 

One last update before rebuilding. I added a variable 0-250W load and found:

• 900W AC, 84A @13.2 V - this is about the limit for this configuration
• 840W AC, 79A @13.3V - stable operation for over 10 minutes

The B+ output of the 120A, circuit breaker got hot, 110-115F. So we're losing major power here. The ambient was 57F and I measured 70-75F on the Anderson connectors.

My goal is stable operation at 1kW AC with a surge capability to operate a portable air conditioner in the event of a power outage. I believe when I rework it to directly connect to the 12V battery, this can be achieved. I will be using the rear mount, accepting the (I**2)*R losses from the front to the rear. The operational advantage of having the inverter permanently mounted and available for cross country use out weights the additional 150W lost.

Bob Wilson

 

All of my testing is with the car in "READY" and the original, 12V battery.

I have no brand preference but would recommend:

• 1kW maximum - anything more won't be supported for long and risks overloading vehicle systems
• sine wave - avoids a lot of issues with modified sine-wave or less expensive inverters
• direct connect - minimize loss for maximum emergency power but installation takes more care and planning
• kill-a-watt instrument - great for load measurement and balancing

Bob Wilson

 

I used a portable space heater to put ~730W load. Then yesterday, I bought a dimmer rated to 600W, hardware, and a 250W heat lamp for the variable load. With both plugged in, I used the dimmer to add the extra load and monitored the battery voltage. After 5 minutes, the battery voltage stabalized but I let it run for an additional 5 minutes, car always in READY, to make sure. Then I took my first set of measurements.

Since my goal is 1kW, I increased the load and again took measurements. Since i knew the 120A, cirrcuit breaker and Anderson connectors were wasting power, I didn't feel the need to go any higher in this configuration.

My next test will be after I reconfigure the inverter to power it directly from the 12V battery. I expect to get a sustained, 1kW with enough surge to power our portable air conditioner (steady state load 930W.) At this point, I will be done . . . no further development of the 12V solution.

There have been suggestions to power the inverter from the front, possibly using the jumper post in the forward fuse box. I think this has merit BUT it also has risks. There is a 125A fusible link from the DC-to-DC converter and now the battery is on the wrong side of the cables needed to provide surge current. Worse, it is unavailable while driving down the road. So it would not work for us.

All of my load testing is with the car in READY and the gas engine cycles as needed to refresh the traction battery charge. Normally I would measure the fuel burn at different power settings but I do not plan to keep this configuration. Once the circuit breaker and Anderson connectors are gone and it is directly connected to the 12V battery, I'll run a complete set of tests including fuel burn at different power levels.

Bob Wilson

 

Not much to report.

I bought an Odyssey PC930 to replace the original 12V battery. Unfortunately, other events had precluded my work on the new configuration.

Bob Wilson

 

Hi Dave,

The biggest problem is the high currents needed at 12V. My testing showed I was losing about 10-15% of my total energy just in the Anderson connector and the 120A, 12v circuit breaker. My new plan:

• minimize 12V connectors - eliminate the Anderson connector and 12V circuit breaker
• 12V circuit breaker backup to 140A fusible link - on the theory that loss of the 140A fusible link renders the car unusable, the backup circuit breaker is kept 'OPEN' unless needed.

I am replacing the stock battery with one designed to have both deep discharge and surge capability. For now, I'm assuming the stock fusible links will protect the DC-to-DC converter but . . . I don't feel good about it. The existing DC-to-DC converter has a 125A fusible link.

Once the voltage steps up to 110-120 VAC, longer distances become practical.

Bob Wilson

 

I've been a little busy too.

Bob Wilson