i3 as emergency generator?

[WoodlandHills]

I have read that Prius cars are able to send battery and generator power back into a home in case of power failure. Living in earthquake country I have a small 2.4kw genset for essential loads such as lights and refrigerator, but would like to have the option of also using our REx as an alternate power source. Is this theorethically possible without hardware changes? Given how much sense having such a capability makes, I would not be surprised to see this become a mandated feature on plug-in hybrids and EV's just like rear cameras are today.

 

[tiburonh]

I have read that Prius cars are able to send battery and generator power back into a home in case of power failure. Living in earthquake country I have a small 2.4kw genset for essential loads such as lights and refrigerator, but would like to have the option of also using our REx as an alternate power source. Is this theorethically possible without hardware changes? Given how much sense having such a capability makes, I would not be surprised to see this become a mandated feature on plug-in hybrids and EV's just like rear cameras are today.

Excellent idea!!

 

[ultraturtle]

Check with these guys: http://www.converdant.biz/plug-out/

Given enough interest, they're likely to come up with a BMW i3 REx version of what they now offer for the Prius and Prius Plug-In (PiP).

You can assemble the same basic components for a DIY system, but will probably not save any significant bucks.

A caveat - unlike other brands' REx implementations, BMW schedules the REx's power output based on speed in order to have road noise mask the sound of the gas engine kicking on, so power will likely not be delivered with efficiency comparable to the PiP.

Note that in the USA implementation of the REx, your house would be powered by the i3's battery pack until its depletion before the REx kicks in. A rather desirable design point, in my opinion.

The biggest advantage to this idea is that your i3 based gasoline generator backup will spew a tiny fraction of CO2 and particulate emissions of a portable gen-set for the same power generated.

 

[WoodlandHills]

Which wheel has the speed sensor? I could put the car on jack stands and set the cruise to 56 and then climb out the open window if it was a driven wheel. Even easier would be to have an OEM Hurricane/Earthquake setting for plug-out operation.

 

[ultraturtle]

Which wheel has the speed sensor? I could put the car on jack stands and set the cruise to 56 and then climb out the open window if it was a driven wheel. Even easier would be to have an OEM Hurricane/Earthquake setting for plug-out operation.

Not necessary. The battery pack itself can power any reasonably sized inverter all the way to 6.5% SOC point, at which the REx engine will spring to life even if the vehicle is stopped. At zero vehicle speed, it is programmed to operate at ~2200 RPM, outputting 12.2 kW of kinetic energy, or approximately 11.5 kW of electrical power. The only advantage to be gained by tricking the car into thinking it is going faster is higher output. 11.5 kW of energy is sufficient for any reasonable residential emergency power scenario.

It is a very simple process of specifying the proper inverter and safely tapping power from the main battery leads. The car handles all of the complicated stuff.

 

[Boatguy]

We'd have to check the tech manuals, but I suspect there is a diode to stop the flow of current out through the charge port.

Can you confirm that this actually works on a Prius, or is it urban lore?

 

[ultraturtle]

Can you confirm that this actually works on a Prius, or is it urban lore?

Lots of folks:
http://priusgen.sandbox.org/
http://www.peakprosperity.com/wsidblog/79974/running-inverter-prius-backup-power
http://www.fperkins.com/me/prius-home-generator.php
https://www.youtube.com/watch?v=Uh02JLAP3lo
http://cleantechnica.com/2012/11/10/man-lights-house-with-toyota-prius/
http://green.autoblog.com/2013/01/30/these-kits-turn-your-prius-into-an-emergency-generator/
http://priuschat.com/threads/using-pip-as-a-generator.117378/#axzz3FCJ23oyY

 

[Boatguy]

I read two of those articles. Both were pulling from the 12v cig socket to drive 1,000w inverters. This is nothing unique to EVs and a painful path for getting very little power; 1,000 watts won't even run your wife's hair dryer. Any vehicle with a cig socket would work. For that matter many vehicles (e.g., my 2011 MB) have 110v outlets so you could skip the inverter and plug straight into the car.

 

[ultraturtle]

I read two of those articles..

Read on and report back.

Neither pulled from the 12v cig socket by the way - it's only fused to 180 watts.

Check your facts.

 

[jadnashuanh]

FWIW, the 12vdc battery in the i3 which feeds those 12v sockets is quite small, and no way you could power much of anything for any time. To supply anything useful other than to recharge your phone, you'd need access to the main EV battery pack, and with the voltage and current available from those, you better know what you're doing! ANd, you better have some logic on the device you attach to so you don't damage them by discharging too far, REx or not. The 12vdc battery is only recharged while either you have the EVSE attached, or the vehicle is in the READY state, otherwise, it's essentially disconnected from the main battery pack.

 

[ultraturtle]

..To supply anything useful other than to recharge your phone, you'd need access to the main EV battery pack, and with the voltage and current available from those, you better know what you're doing!

These guys have been providing this capability for years, supplying up to 4 kW of electricity directly from the Prius and PiP traction battery/gasoline engine system: http://www.converdant.biz/images/custom/Plug-Out_Brochure.pdf. Others have done the same with a home brew solution at similar cost.

Analyze your power needs for an extended power outage. If you need to operate more than 3 hair dryers simultaneously at any point during such an outage, this may not be an optimal solution for you, but you do have my pity.

 

[mindmachine]

I personally think using my car for a back up power supply is pure folly. Apparently many who like this idea do not realize how much load their house can and will produce. Starting current for electric motors for example is 50% more than continuous running current draw levels. Refrigerators and furnaces draw a lot of power and if several appliances try starting at once that is a bigger problem. Also you need to figure out how to fuse the power supplied and then there is the problem of isolating loads that you can't supply enough power for and can't risk their requiring more load than your supply can handle.

 

[ultraturtle]

I personally think using my car for a back up power supply is pure folly. Apparently many who like this idea do not realize how much load their house can and will produce. Starting current for electric motors for example is 50% more than continuous running current draw levels. Refrigerators and furnaces draw a lot of power and if several appliances try starting at once that is a bigger problem. Also you need to figure out how to fuse the power supplied and then there is the problem of isolating loads that you can't supply enough power for and can't risk their requiring more load than your supply can handle.

Using a PHEV as a backup power supply has many advantages over a dedicated gasoline powered gen-set. A couple, off the top of my head:

• - Starting current for electric motors is far more capably handled, as inverters are typically rated at 50% higher than continuous load for a longer time period than gasoline gen-sets which can typically only handle 25% higher surge loads for a very short time. Compare the 4 kW Converdant inverter, which can provide 6 kW for 20 seconds, wheras a 4 kW Honda gen-set can provide only 5 kW for 10 seconds
  - Fuel is utilized far more efficiently with a PHEV/inverter system. Consider that gasoline gen-sets operate continuously at a fraction of their rated output, which far from their most efficient operating speed and load (which is typically just shy of max continuous output). The PHEV/inverter cycles the gasoline engine on only as needed to restore energy to the traction battery while powering loads, thereby operating at a higher, more efficient loading, for much less time. Folks with a system like this report the engine kicking on typically less than 50% of the time.
  - Because PHEVs must adhere to very strict emissions standards that gasoline gen-sets do not, and because they operate for far less time, the PHEV/Inverter system emits far fewer harmful gasses and particulates per kWh generated.
  - The cost, maintenance, and storage space requirements of a PHEV/inverter based system are less than a similar capacity, inverter based (clean power) gen-set.
  - Reliability. An inverter is a solid state device that requires nearly zero maintenance and pretty much always works. Getting a generator that has been improperly stored for a couple of years to crank is an iffy proposition.
  - Gasoline in the PHEV/inverter system is always fresh. There is no need to deal with fuel preservatives, draining the generator tank for storage, or constantly cycling fuel cans to maintain a fresh fuel supply.
  - Gasoline storage in the PHEV fuel tank is inherently safer than any other option.
  - The PHEV/Inverter system gives you the option for power provided nearly silently during the night, assuming you have the means to plug in and charge during the day. Any of you with a SMA Sunny Boy TL-US inverter integrated into your PV solar system can charge your PHEV at 120 volts, 12 amps while the sun shines, storing plenty of power to run a refrigerator and a TV all night long.

What to back up is a completely different topic, with individual needs varying tremendously. I have all of my critical circuits on a separate 60 amp sub-panel. Refrigerator, microwave, computers, TVs, garage door openers, furnace blowers, and selected lighting, that typically draw a total of less than 10 amps at 120 volts, and never more than 20. I could probably get by with a 2.5 kW inverter if this were a backup system only, but have a 6 kW inverter/charger because of the PV panels. Mind you, I manually shut off all but a couple of amps worth of power draw during power outages.

 

[WoodlandHills]

That's how I power manage too. Emergency use is very rare here as in never used it yet...... Given that, I plan to simply switch off all unneeded loads before connecting and starting the genset if we ever need it for real. A live test a few years ago allowed me to mark the appropriate breakers, no reason I couldn't do the same with an inverter system and an EV too.

 

[Chrisn]

I think the point is that the car's DC-DC converter pulls power from the High Voltage battery to power 12V systems in the car AND to charge the modest 12V battery. So long as the car is "on," you pull 12V from the small battery/DC-DC converter (using, for example, a 2000W inverter). If the car is "on," it will happily discharge the big battery and then, presumably, fire up the REX periodically to maintain 6.5% level of charge.

Key questions are:

1. Can you keep to car "on" indefinitely while stationary (seems to turn itself pretty quickly)? Maybe if you leave it in "D" with e-brake on?

2. What is the rating of the DC-DC converter, and will sustained heavy loads break something? I have to believe that a 1000W inverted would be a piece of cake, but much above 2000W would be WAY above any normal design load.

 

[jadnashuanh]

A 170hp electric motor is equivalent to over 133Kw, but it probably won't supply that output for very long.

 

[ultraturtle]

The are two ways to accomplish what we are talking about here:

• 1. Tap off the 12 volt circuit to a 10 volt inverter.
  2. Tap off the 360 volt circuit to a 360 volt inverter.

Of the two, the second option can power a substantial load (4 kW typical for the Prius.) I would not mess with anything but the smallest inverter on the 12 volt circuit without thoroughly researching specs of the buck inverter, wiring, and shared loads.

 

[jadnashuanh]

As I understand it, the 12vdc battery in the i3 does NOT get any power from the main batteries unless you are either in the ready state or you're charging via the EVSE, so to tap off that for any inverter, especially since it's more like a motorcycle sized battery than a typical car, would be somewhat folly. If it can be done safely, you'd want to power from the main 360vdc battery pack, and doing it might just void your BMW battery warranty. You'd definitely want a low-voltage cutout circuit on the inverter to prevent dropping the battery charge below where the vehicle normally would cut things off, and building one of those specifically tuned to the i3's battery pack may be tricky. While many inverters do have a low-voltage cutout, it likely would try to draw the i3's batteries down further than the car normally would, and that could be a big problem.

 

[ultraturtle]

Successful implementations of the concept on the Prius and Prius Plug-In have these characteristics, and there is no good reason to believe an i3 would be any different:

• - Warranty is not a concern. It is protected by the Magnuson-Moss Warranty Act. Since no modification to the car other than the addition of a high voltage connector takes place, the manufacturer would find it impossible to prove doing so would in any way damage the car.
  - Operation takes place with the car in the ready state.
  - The car does not know, and couldn't care less whether the draw from the traction battery powers the motor or an inverter. That's the beauty of the system. It draws down battery power until automatic activation of the REx, then cycles on and off to maintain battery charge state until fuel depletion, then it stops outputting current. The key is locating the proper tap point from the high voltage system output (i.e. at the electric motor input), and combobulating a quality disconnect. Inverter low voltage cutout would be a nice failsafe.

 

[WoodlandHills]

All it takes is one populous state to mandate this, like the way CA emission rules have become a de facto US standard. If Florida (hurricanes) and California (earthquakes) made these systems mandatory on all NEW EV's and hybrids sold in state they would be OEM available to the whole world. Just like the rear view camera mandate that comes into effect soon.