Prius owner uses car to power home during power outage...

I had understood that in this mode, Prius is providing 12V from the DC-DC converter powered by the traction battery, not from the 12V battery.

The article I remember was for a past winter, therefore a GenII, with 1500cc exhaust displacement. Intake displacement is variable, the numbers that come to mind are 550-1050cc. We also need to account for RPM. If the same as my GenIII, the Prius will be probably be spinning at 1280 RPM. What is the Eu1000 RPM?

I also notice the Eu1000 efficiency drops off considerably at 1/4 load. The Eu2000 holds up much better, as would the Prius.

I don't see the specs from which you derived 8kWh/gal for the Eu1000. I'm getting 5.7kWh/gal at full load, 3.1 at 1/4 load. For the Eu2000, I'm getting 5.8 and 5.45, respectively.

It seems that Prius should be getting about 13 kWh/gal at the ICE shaft. After multiple conversions (MG1-HVbattery-Inverter-cable-Inverter), I'm not sure how much of that actually reaches the AC socket.

 

My measurements are:

• 0.25 gal per kWhr at 1 kW at 0C/32F
• 0.06 gal per hr at no load at 0C/32F

With a full tank, I would expect ~40-44 hours of operation at full power before the tank runs dry. But power consumption goes down when the lights, TV and internet access loads are taken down.

Bob Wilson

 

Bob do you have a schematic and parts list for your Pigtail Outlet, I am trying to visualize this, also how did you come up with the spec for the Thermistor you used : NF08AA0330M (33 ohm/2.2W)
thanks

 

I went to a hardware store and bought a plastic utility box sized for a dual, 110 VAC receptical; a 3 prong plug; and used a 6" length of three conductor 15A rated house wiring cord (the pig tail.) I then cut the link between the first and second outlet and put a 0.01 ohm resistor between the first and second plugs. I then measure the steady state, current draw.

Using the steady state current, I looked up the thermistor data table for the part rated at that current. I put it in the bridge, replacing the 0.01 current sense resistor and it worked first time.

The thermistor gets warm, uncomfortable to touch, but that is how they are supposed to work. I just have it inside the plastic utility box and there is plenty of air flow to keep things from getting hinky.

Bob Wilson

 

Peirhead, I'm curious how you've wired your inverter. Have you connected the positive input directly to the positive 12v battery terminal and the negative input directly to the negative battery terminal?

I don't know if it matters, but in my inverter setup, I've attached a 4 gauge wire to the positive battery terminal and another 4 gauge wire to the body of the Prius rather than to the battery. In my original setup, I connected these wires to a deep cell battery, and, using the deep cell's second set of terminals, I connected my 1,500/3,000 watt inverter to the deep cell. I figured I'd wire around the Pruis mini-battery, and the deep cell battery would provide the necessary surge protection. This worked fine, until my son borrowed the deep cell battery. I even inadvertantly ran a 12.0 amp leaf blower on the inverter without the deep cell battery in the circuit. (Prius didn't like it, but hasn't had any repercussions. It did, however, give me that "hot transformer" smell but no blown fuses.)

I have several SU3000 UPS, and while I don't know the surge load when starting up, the "no load" current draw is only about 160 watts. Did you, by chance, have a substantial load being run on your 1400UPS' internal batteries when you plugged it in? Might you have been transfering a substantial load directly to the inverter?

 

So the Honda Eu at 1/2 load works out to be 8 kwh/gallon, or 1kwh/.125gallon.

The Prius .25gal/kwh would be double the fuel consumption.

Like I said, except for some small 120vac convenience outlet, I wouldn't bother. (or risk the Prius)

 

Of course buying a Honda generator would be more fuel efficient than using a Prius. For lighter electric loads, like a lightbulb or two and an LCD TV, taking the inverter type generator is a definite winner in fuel efficiency over the Prius.

On other hand, you already have the Prius.

 

Yes, for a light bulb or two or even a LCD TV, but the origin of the idea was to use the Prius as a large UPS for emergency power to power fridges/freezer/furnaces etc, which is a horse of a different color.

 

Ouch!

Based on past BSFC figures of 220grams/kwh, I'll revise my Prius efficiency at the ICE shaft down to 12 kwh/gal. You are getting 4 kwh/gal at the 120VAC outlet. That is a miserable 33% efficiency for the chain of conversions in between. No wonder some folks want to skip the 12V conversions and try to run directly from the HV battery.

Where are you getting this? From the Honda brochure, I'm getting--
Full load: 0.9kw * 3.8 hrs / 0.6 gal = 5.7 kwh/gal
1/4 load: 0.9kw * 0.25 * 8.3 hrs / 0.6 gal = 3.1 kwh/gal

 

Truth be told, I'm getting it from memory of personal experience that is mostly anecdotal. I live off grid for ~6 months a year with a Battery based solar system. In the rare event when we don't have enough sun I run a Eu 1000 into a 20 amp charger which draws ~400 watts, that plus a few watts of other load = ~60% load. A full fueling will run better than 6 hours. So in point of fact, I haven't done a real test with measured load and measured fuel. Perhaps sometime I will, but I am away from home for a while. Sorry for any confusion.

If memory serves the honda while listed at 1000 watts, it really will only produce ~800 continuously. So running full out at .9 kw might be more than the little gennie likes over time.

 

One significant energy loss from the Prius-UPS is heat from the engine. Consider this, a 400 W block heater will reach a steady state of +35C (others have reported +40C) relative to ambient temperature. But we are typically running the Prius in cold weather and the engine control laws do everything to keep the engine block at 60 to 70C. The heat loss rate increases the temperature difference. Roughly:

400 Whr / 40 C ~= x Whr / 70 C :: linear relationship, assumes 0 C ambient
70 C * (400 Whr / 40 C) = x Whr
(70 C / 40 C) * 400 Whr = x Whr
1.75 * 400 Whr = x Whr
700 Whr :: thermal losses while generating 1000 Whr
​

The engine works efficiently when it runs BUT when it is off, it loses heat. Now a perfect, cogeneration setup would be an insulated garage with a heat-exchanger, exhaust pipe to the outside. The heat collected at the top of the garage would be piped into the house for space heating.

To complete the system, a second set of injectors for natural gas would be added to the intake manifold (may be able to get away with a single injector at the throttle body.) Once the car was warmed to operating temperature, after the first 'auto-off,' the natural gas injection system would take over for the gas injection system.

Bob Wilson

 

One other issue that hasn't been mentioned. It takes approximately 20% more energy to charge a battery than it gives you net/net. So for example if you draw out 100wh it will take at least 120wh to restore the battery to the same state of charge. This number is quite variable due to certain battery chemistries, and states of charge, but 20% is a pretty good average number.

A lowered state of charge battery will absorb power (amp/hours) faster than one near full. Battery charging is an imprecise art, more than science. Car and Deep Cycle Battery FAQ, Battery Manufacturers and Brand Names List, and
Deep Cycle Battery FAQ

 

At 1 kW, we're drawing 1000 W / 270 V ~= 4 A. For the 6.5 Ahr battery this is ~4/6.5 C (charge level) or ~.62 C. This is well within the 90% efficiency range when the engine is off. While the engine is running, the power comes directly from the generator/inverter. Only the excess charge is going to the traction battery.

Bob Wilson

 

Bob, I am quite sure I don't understand what you are trying to say here. A little clarification please?

As to my point, regardless of how you cut it, it takes more energy to recharge any battery, than that power gives you.

Icarus

 

The charge-discharge efficiency is a function of the charge rate. What happens is at higher currents, the efficiency drops off. But generally speaking, if you are under "1 C" (where "C" is the amp-hour rating of the battery,) you'll be at fairly efficient point. Depending upon the Ahr rating and chemistry, it seems to be pretty good up until above "2C":

Any rates below 1C can usually be treated as near unity, well above 90% efficiency. Your example showed an 80% efficiency that is way too low at the rates we are dealing with. I'm trying to suggest this is not a biggie. It exists but not quite that much.

Bob Wilson

 

Bob,

I think I got it. In the solar business we are not used to looking at charge rates anywhere near C1. We tend, with FLA (flooded lead acid) batteries to see charge rates in the C/5-C/15 range. Higher charge rates result in heating the cells too much and boiling the water away. Seal LA and gel cells also have suggested rate limits.

I certainly don't argue that the HV battery can deliver 1 kw. My argument is that getting it through the 12v battery is pretty risky. 1000 watts delivered through 12.0 volts is ~83 amps! To draw 80+ amps from the cigarette lighter/aux plug is going to do nothing but blow the fuse!

Even if you wire an inverter hard wired to the 12v battery, the 80 amp draw requires a wire size of AWG #1 or so. What are the battery cable sizes?

 

Less than a foot in length, I'm using AWG 4, 135 A (chassis) / 60 A (power.) During the integration and test, I monitored the temperature at 1 kW ... no hot spots. FYI, the 12 VDC system is really running closer to 13.75 V @71-74A with a 1 kW load. As the load increases the voltage ramps down and the current up but it hovers at 1 kW, 11.48 V, 89-90 A.

Bob Wilson

 

good to know that i have a backup power and heat supply with the prius that is fully automated.. now only to find a 1kw dc-ac inverter before the cO2 ice age's hits..

i would connect the radiator form the prius to the house CH ( central heating ) system.
and use the heat produced from the prius ice to warm the house and the dc-ac is used to run the CH pump and some lights,radio/tv and a water heater for some nice warm cup of the.

 

For the charger/inverter on my boat, I used 00 AWG wire. With 12V wiring, usually safety isn't the limiting factor. At low voltages and high currents, usually the I*R voltage drop gets you first.

Tom

 

I've moved away from that approach to a sealed garage approach with a heat-exchanger, exhaust pipe that leads outside. This allows efficient capture of the low-quality heat for house and/or cold-water, preheating.

Think of a one car garage that is heavily insulated ... say 5 cm thick, beaded polystyrene foam blocks assembled so there are no air leaks. The roof of the structure is angled and that is where insulated air ducting is located. The duct work passes by a loop of 'cold water' feed to the hot water tank. It is in the duct to avoid risk of freezing. The Prius is left in "READY" and ideally, a 'docking system' makes the bulk of the connections.

The engine heat and heat recovered from the exhaust will rise to the top where it will 'pre-heat' cold water that feeds the hot water tank. The collected warm-air is forced into the house by an electric fan for space heating. Ideally, house, cold air feeds back to the insulated garage to minimize 'cold air' infusion.

To really work, a low cost fuel needs to substitute for gasoline, natural gas comes to mind. Since the Prius and engine will be running at low power settings, this won't need a big piping and pressure setup. So the natural gas that formerly just heated water and the house now keeps the Prius at operating temperature and the waste is used to keep the house comfortable.

In the morning, the car is already warmed up so the morning commute will be very efficient. In the evening, the car will arrive already warmed up and once in the insulated garage, it should soon produce enough heat to sustain the house. No net change in natural gas usage but a significant savings in gasoline costs from the morning commute.

Bob Wilson