Sunday, June 13, 2010

The Electric Car Resurrection IV: Plug-in Prius Conversion

As the the Deepwater Horizon sinking slowly destroys the Gulf of Mexico and the consequences of our addiction to carbon-based energy go from being diffuse and hard to see to painful and in our faces, I though I would continue the Electric Car Resurrection series with a post about our plug-in hybrid Prius conversion.

If you've been following the series, you'll remember from this post, admittedly some time ago now,  that after studying electric cars for 3 years, I was really ready to go electric. At the time, we had a 2002 Prius that was averaging around 42 mpg and a 1996 Corolla that was averaging around 30 mpg. I was really motivated to replace our 1996 Corolla with something that I could plug in to reduce our carbon footprint. Also, I figured we could get some of the power free from our solar PV since we regularly gave back around $80-$120 per year to PG&E in unused credit (though we did use around 1000 kwh from the grid so we were not 100% carbon  free). Despite all my investigation, I hadn't found an electric car option that would really work.

In the spring of 2008, A123 announced their plug-in hybrid conversion package for the 2004-2008 Prius, the L5 plug-in hybrid conversion module. The details of the package looked pretty good. The conversion removes the spare tire and installs a 5 kwh booster battery in the spare tire well, along with a traction battery charger, and a 12v battery charger to handle the increased load on the 12v battery from the electronics in the booster battery. The booster battery uses a technology which A123 calls "lithium nanophosphate", in reality, it is their proprietary development of the lithium iron phosphate technology. This technology is reported to  be exceptionally stable and  long lasting, unlike the lithium cobalt technology used in laptops. A123 had pictures on their Web site of crash tests in which the batteries simply crushed along with the rest of the car, instead of exploding or anything like that.

The 5 kwh battery is connected in parallel across the 1 kwh OEM battery, and it trickle charges the OEM battery, which means that the 5 kwh battery does not recharge from the regenerative braking. Because the basic drivetrain power equipment is untouched, the warranty for the drivetrain is not voided. In fact, several Toyota dealers in the mid-West offered the A123 plug-in conversion as an option. The battery management system in the booster battery interfaces with the CAN bus, and the state of charge for the booster battery is smoothly integrated into the Energy screen on the car's flat panel display. The booster battery appears as an overlay second battery on top of the OEM battery and the display flashes between the two so you can see the state of charge in both.

While the car ends up not having a spare tire, it isn't a practical problem because the tires are all equipped with slow leak detectors, so as long as you stay on top of any reported  leaks, the only problem could occur with a blowout. With that, you of course need to call a tow truck. Alternatively, you could take  along a can of the inflator goo that re-inflates the tires and seals the leak, but that also destroys the leak detector, which is somewhat expensive to replace. Other than that,  there didn't seem to be any drawbacks or negative  impact on the car.

So we decided to do a conversion. The first step was to locate and buy a 2008 Prius. I wanted a model with everything but nav system (I can get that from Google maps on my phone or a paper map), silver in color. If you recall, spring 2008 was the peak of gas prices,  where gas was going for $4.00 a gallon here in California, and Priuses were selling like hotcakes. I had a hard time locating a car, most dealers were sold out with 6 weeks  to 3 months waiting time. However, I did find one,  but unfortunately it had been used by a salesman and had 3,000 miles on it. I tried to argue the sales guy down (it was really used car) but he would have none of it. Priuses were hot items and he knew he could sell it elsewhere for full list price.

I bought the car in May 2008, then we waited. A123 was having some problems with CARB getting the license for the conversion. One little known fact about converting cars to use something other than the fuel they originally come equipped with is that it is illegal  without an EPA and, in California, CARB license. The licenses are difficult to obtain, cost upwards of $24,000, and only apply to a specific make and model of car. This is one reason why you don't see many conversions to E85 (in addition of course to the lack of stations selling it). There are very few companies that are licensed to do legal E85 conversions (and most of those do ancient Dodges and such), any others - including those done by hobbyists - are illegal. The ostensible reason is because EPA wants to make sure that the converted car doesn't pollute any more than the original, and that in fact was the holdup with the A123 conversion. EPA was afraid that the catalytic converter wouldn't get hot enough because the engine doesn't go on much and so therefore the car would pollute more. A123 was finally able to satisfy them, and in October 2008, A123  started notifying people who had signed up and paid their deposit when their installation date was.

In November we got a notice saying that our L5 conversion package would be shipped to Pat's Garage in San Francisco shortly. I took the car up to San Francisco when it arrived and they had the L5 conversion installed in about 4 hours. Pat recommended to me that I get a set of sports car shocks installed in addition, because the original squishy shocks that come with the Prius tended to wear out under the additional 200 lbs of battery. I took his advice and, I must say, I am perhaps even more pleased with the shocks than with the electric conversion. Toyota's shocks are almost uniformly squishy, but these shocks make the car feel like a BMW. The shocks cost an extra $1K but they were really worth it. If I ever buy a Toyota again, I'll probably have them replace the shocks. In addition, a few weeks after the conversion, Pat told me about the need for an extra 12v battery charger. If the 12v battery goes out in the Prius, you can't simply jump it like in any other car. You must tow it to the dealer and have them replace it. Since the L5 electronics about double the load on the 12v battery, I thought it prudent to have the 12v battery installed.

Below you can see the back of the car with the electric socket and an extension cord plugged in in our garage.

We had the car decked out with decals on the back bumper and side.

Here's an overview of the booster battery pack:

And this shows more details of the battery pack, including the ventilator that keeps the battery cool:

The ventilator is the black plastic box across the middle of the picture. Normally we also carry a 25 ft. extension cord for "opportunity" charging. Many places will let you plug in for a couple hours, or even overnight if you are traveling longer distances.

The installation also includes a switch on the dashboard for switching the booster battery on and off, and a red light that glows when the booster battery is on and charging the OEM battery:

When the car is plugged in, the back tail lights go on for about a minute, then switch off.  Originally, the lights stayed on while the car charged but about a year after the battery was installed, the car got a software upgrade that fixed that and another  problem, involving the inability to go into electric mode. If you try to push the acceleration sometimes below 33 mph, the car starts beeping and the display says that it can't go into EV mode. This problem occurred frequently on the original software, especially on steep hills, now it has been improved to where it almost never occurs.

The original specs for the battery pack promised 30 mi. all electric range after maybe 5 min. of standard hybrid drive in order to burn off any evaporated gas vapors and heat up the catalytic converter. A standard 110v 15 amp house current socket is sufficient for charging, so no need to install a specialized 220v recharging station. Recharging takes about 5 hours. While the booster battery still has charge, the car remains in EV mode up to 33 mph (60 kph). In EV mode, the car only switches on the engine if the amount of acceleration needed is large, much larger than causes the motor to cut in in hybrid mode. But above 33 mph, you really need to work to keep the car in EV mode even if there is still sufficient charge in the booster battery because the engine cuts in more often (though not as often as if only the OEM battery is providing power). In practice, the car really only gets around 20-25 mi in all electric range before the booster battery is exhausted but that is enough to get me to work and back with a side trip to the gym for a workout.

You'll also notice the decal for the PulseStar spark plugs on the back of the car. If you read my previous posts (here , here, and here) you'll remember that I had the PulseStar plugs put into my 2002 Prius and that they shorted, destroying the ignition coil. But the company paid for the work on the car and gave me a discount on new plugs, so I bought a new improved set for the 2002 Prius. I also  installed them in the 2008 Prius around the time I put the first set in the 2002 Prius. So far, I've not had any problem with them. With no booster battery, the plugs increase the gas mileage around 2 mpg or so.

With mostly around town driving and an occasional trip to San Francisco, Yosemite, or Monterey, the car gets a long term average of around 80 mpg, 30 mpg more than the EPA combined rating. The first six months we had the car, we tried to push the  mileage as high as we could, with hypermileing maneuvers like driving slowly to keep it in electric mode, and we never took it out of town. We were able to get the mileage up above 100 mpg (actually, it was around 110 mpg as measured from gas consumption, the in-built meter won't measure higher than 99), but as soon as we took a trip to Yosemite it dropped.

Despite the fact that the car doesn't get the advertised range, I am still more than pleased with it. We don't fill up more than once every month and a half if we just drive it around town, and most of our driving is around town. Assuming we keep the car 10 years and drive about 8,000 miles  per year (lower than average, but about what we usually do), the cost of the eliminated carbon is around $1.36 per kg of carbon eliminated. The initial upfront cost of the system is somewhat steep, but during the same 10 year period we end up saving around $8000 in avoided gasoline cost if gasoline is $3.00 per gallon (about what it is now). Since we get the electricity for free from our solar PV system, we don't have to pay for electricity either. This will not pay back the cost of the conversion, but, on the other hand, it will not break our bank account either. We could have chosen to buy a luxury car like a Lexus that cost about the same as the plug-in Prius, but then we would have had to pay for gas on top of the carbon pollution, and we would be contributing to the kind of consumption that leads to incidents like the Deepwater Horizon.

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