[drquine]

The story of John Sweeney's use of a Toyota Prius to power his house in Harvard MA after the ice storms in December 2008 has been widely reported. The ability of the car to autostart as the traction battery became depleted through the intermediary 12 volt battery and a 1,000 watt 12 volt DC boat inverter made this a "seamless solution". The engine averaged about 5 minutes of use per half hour to keep the battery recharged and it consumed only 5 gallons in 4 days.

Last week Hurricane Irene knocked out power for more than half of Connecticut. We were down for 3 days. I managed to keep our cell phones and laptop computers charged with periodic use of a 400 watt inverter off the conventional starter battery of my Honda Civic Hybrid (as one could from any car). I started the car manually from time to time to keep the battery charged. My understanding is that the traction battery is high voltage and that the auto-restart function only works when one releases the foot brakes. Therefore neither the voltage nor the auto-restart function are available to enable more robust continuous power.

While the Honda Civic Hybrid is extremely quiet, efficient, and non-polluting compared with the neighbors' generators, is there an economical way to utilize the my car for more substantial emergency power until the smart grid and PHEV cars are readily available? My current plan is to attach a 1,500 watt inverter (only $100) directly to the starter battery. I'll leave the engine running (outdoors obviously) while it is providing power and use my Kill-A-Watt power meter to monitor the power use.

[bwilson4web]

drquine said:

. . .
While the Honda Civic Hybrid is extremely quiet, efficient, and non-polluting compared with the neighbors' generators, is there an economical way to utilize the my car for more substantial emergency power until the smart grid and PHEV cars are readily available? My current plan is to attach a 1,500 watt inverter (only $100) directly to the starter battery. I'll leave the engine running (outdoors obviously) while it is providing power and use my Kill-A-Watt power meter to monitor the power use.

The maximum, sustained power load is limited by whatever charges the 12V battery. I just don't know enough about the Honda Civic Hybrid electrical system to say how much power can be provided from the 12V system.

Do you have the electrical schematic for the car? That is where I would start to find out. In particular, I would look at any fusible-links or fuses that connect the battery to the car as these are the ultimate limit.

This is how I modified my Prius but I had the electrical diagram and used a careful test program . . . while it was nice.

Bob Wilson

[drquine]

Bob - Thanks for your quick response. You've done an extraordinary piece of work - and analysis. Clearly the Prius has great potential as an emergency power source. It will be nice when a factory installed vehicle to grid (V2G) version is available. Can the mix of devices (inductive motors or light / heat resistance) help mitigate the problems on an ongoing basis or at startup? In addition to the inrush issue, do you see any cost effective way of further enhancing / conditioning the waveform quality of the inverter output to avoid the undesirable ongoing effects with digital power supplies that now supply our TV, computers, CFL / LED lighting, and system controllers? Meanwhile, it looks like I have my work cut out for me getting a basic emergency power system. - Doug

[bwilson4web]

drquine said:

Bob - Thanks for your quick response. You've done an extraordinary piece of work - and analysis. Clearly the Prius has great potential as an emergency power source. It will be nice when a factory installed vehicle to grid (V2G) version is available.

Amen!

It is a d*mn shame it took a Tsunami disaster to finally strike some of the Toyota engineers with a 'clue by four!'

drquine said:

Can the mix of devices (inductive motors or light / heat resistance) help mitigate the problems on an ongoing basis or at startup?

Not really. In a perfect world, all loads would be resistors or perfect "P factors." The real world is quite a bit different but now we are seeing options not available as recently as 2-3 years ago.

MODIFIED SINE WAVE

These used to be the highest efficiency, 92-95%, least expensive inverters that typically have a two-step, waveform. They work on many things but some sensitive electronics with marginal power supplies like our house thermostat 'lose their mind.' Normal motors (aka., induction) have problems and can run hotter than normal. The rule is every load that will be used must be tested "in nice weather" to make sure they will work in bad weather.

One subtle problem is extension cords look like lossy capacitors. The sharp dV/dt of the step functions 'leaks' through the adjacent wires of an extension cord and you can measure a couple of volt drop depending upon quality of length. My typical configuration is a 25 ft contractor cord with 3-sockets. This feeds the TV and living room lights. Then a 50 ft. cable goes down the hallway to light the bathroom and/or run the 800W gas furnace fan motor.

SINE WAVE INVERTER

In the past couple of years, we've seen their efficiency increase up to the 92-94% range and price come down somewhat. They still are about 2x the price of modified sine wave inverters but they work so much better on all loads, this is the way to go if you can afford it.This is what I'm putting in my wife's 1.8L Prius.

drquine said:

In addition to the inrush issue, do you see any cost effective way of further enhancing / conditioning the waveform quality of the inverter output to avoid the undesirable ongoing effects with digital power supplies that now supply our TV, computers, CFL / LED lighting, and system controllers?

I don't think there is much that can be done about 'inrush' except to test when it is nice and plug-in the worst, inrush loads first. Many times these load run less than 100 W but that inrush is a killer. In our house, the TV/cable box and my laptop power supplies are the worst offenders. Then add the others.

drquine said:

Meanwhile, it looks like I have my work cut out for me getting a basic emergency power system.

Getting the car electrical diagram is the first step. Once you see where the 12V battery system gets its power and the fusing, you can make informed decisions. Then there is the radical approach.

Some folks have 'tapped' the main traction battery. I've thought about it but could not justify it for just emergency house power. If I tap my traction battery it will be for bi-directional purposes. <GRINS> It is called 'co-generation' and potentially could be a game-changer:

• engine waste heat -> house hot water, space heating, and cooling
• natural gas fueled -> only when parked and plugged in. May use propane instead for electro-political reasons.
• electrical output -> house power, offloading from the grid

What this does is the car starts each day fully warmed up and the house goes 'on the grid' for the rest of day. When I return, the car plugs in and my utilities are reduced. <wink>

Bob Wilson

[drquine]

Bob,

Thanks again for the insightful updates and information. I see that the 2005 Honda Civic Hybrid does not have an alternator but instead uses the IMA to recharge the high voltage traction battery and the 12 volt starter battery. There is an 80 amp fuse between them (which neither local Honda dealer has on hand so getting a spare in advance might be prudent to prevent getting stranded if the fuse blew from an unexpected power surge when inverter power was in use).

I see hints of movement towards vehicle / house two way connections from Toyota. There was a recent news report that "Toyota Fits Prius with Emergency Power Systems" (Jul 21, 2011 ... http://www.evworld.com/news.cfm?rssid=26138). It said that 40 Priuses outfitted with energy storage and generation systems were being donated to Japanese prefectures devastated by earthquake.

I also saw a couple of articles on Google last week mentioning (as I recall) a forthcoming 1,500 watt 120 volt power cord option for emergency power for $200 in future models. I believe that would be a great feature.

[bwilson4web]

drquine said:

. . . I see that the 2005 Honda Civic Hybrid does not have an alternator but instead uses the IMA to recharge the high voltage traction battery and the 12 volt starter battery. There is an 80 amp fuse between them (which neither local Honda dealer has on hand so getting a spare in advance might be prudent to prevent getting stranded if the fuse blew from an unexpected power surge when inverter power was in use).

It may not be so dire. A fuse exists to protect the wiring but as I increased the load, I found the output voltage dropped so the total output limited itself to 1 kW. BUT I was testing the Toyota designed part and there is no guarantee with the Honda part.

What I am going to suggest is the maximum power out of a 12V, 80A fused circuit will be:

12*80 = 960 W

Yes, you could put in an oversized inverter and hope the 12V battery makes up the difference. But it might be wiser to go with say an 800 W inverter with a 1,000 W surge for a simple, car based approach. There is an alternative approach to increase the surge power but it is more complex.

If you had a large, deep-discharge battery in the garage on a 'trickle charger' the heavier inverter could make sense for AC power. During a power outage, the Civic becomes the sustaining charger for the battery-inverter. Use a 50A circuit breaker (see RV supply companies) to protect the Civic. Alternatively, a MOSFET/IBGT configured as a current limiter could protect the Civic during periods of deep discharge when the battery is making up the difference.

Of course the best power option would tap the traction battery but I'm not ready to go that way with my car. But others have with success.

LATE THOUGHT:
http://picasaweb.google.com/threewhe...ickleCharging#

In this case, a trickle charger is used to add power to a Honda traction battery. However, using heavier gauge wire would allow power to be drawn for a power inverter. Power can flow both-ways if the wiring is heavy enough and attention paid to the electronics.

drquine said:

. . . I also saw a couple of articles on Google last week mentioning (as I recall) a forthcoming 1,500 watt 120 volt power cord option for emergency power for $200 in future models. I believe that would be a great feature.

I'm ready . . . but then I did my 1 kW inverter in 2005 and already have a 1.5 kW inverter ready to integrate with my wife's car. I've never been one to 'curse the darkness.' <grins>

Bob Wilson