Hoovie's Garage: Bought a Prius with a dead battery

[kevm14]

I forgot an important one: total energy capacity of this generation Prius battery is 1.31 kWh. Say you'd access 85-90% of that. So 1.179 kWh. With ~100 lbs of battery.

E10 gasoline stores 32.78 kWh per gallon. With 7 lbs of gas plus some portion of tank weight to store 1 gallon. You can see where this is going.

Put another way, a 100lb Prius battery holds 1.2 kWh of electricity. To reach the same energy storage as a gallon of gas, you would need 27 battery packs. That is 2,700 lbs of battery to hold what 7 lbs of gas can hold (1 gallon). Now, that gas is only useful for 25% of its actual energy storage so that drops the battery pack down to 700 lbs assuming a nearly 100% efficiency. Still, that is 2 orders of magnitude worse in energy density.

[kevm14]

Let me look at that 25% efficiency thing more.

I can use EPA MPG and eMPG ratings to look at how much more energy efficient EV propulsion is than gas.

And I can use plug-in hybrids to do it as they have both an EPA gas rating and an eMPG rating.

2011 Chevy Volt: 37 mpg combined gas, 93 eMPG combined. Gas is 40% as efficient as electricity.

2018 Chevy Volt: 42 mpg combined gas, 106 eMPG combined. Gas is 40% as efficient as electricity.

2017 Toyota Prius Prime: 54 mpg combined gas, 133 eMPG combined. Gas is 40.6% as efficient as electricity.

So that means when comparing energy efficiency, I will use 40% rather than 25%. This makes it even worse for batteries.

Put another way, a 100lb Prius battery holds 1.2 kWh of electricity. To reach the same energy storage as a gallon of gas, you would need 27 battery packs. That is 2,700 lbs of battery to hold what 7 lbs of gas can hold (1 gallon). Now, that gas is only useful for 25% of its actual energy storage so that drops the battery pack down to 700 lbs assuming a nearly 100% efficiency. Still, that is 2 orders of magnitude worse in energy density.

Redoing this with my new numbers, that would take 1,100 lbs of Prius battery pack (the 04-09 one) to equal 1 gallon or 7 lbs of gasoline. So even more than 2 orders of magnitude.

[kevm14]

A 2011 Chevy Volt battery pack holds 16 kWh and weighs 435 lbs.

Assuming the same 90% usable energy storage as the Prius, it looks like this compared to gasoline: it would take 2.25 Volt battery packs to equal one gallon of gasoline, which is 990 lbs, but multiplied by that 40% figure means 396 lbs. Much better than the Prius (2.5-3x better). But still way, way worse than gasoline.

The penalty for that energy density, while maintaining a 100,000 mile warranty is this:

For the 2011/2012 model years, the battery pack stores 16 kWh of energy but it is controlled or buffered via the energy management system to use only 10.3 kWh of this capacity to maximize the life of the pack. For this reason the battery pack never fully charges or depletes, as the software only allows the battery to operate within a state of charge (SOC) window of 65%, after which the engine kicks in and maintains the charge near the lower level. The minimum SOC varies depending on operating conditions. When more power is required, such as mountain mode, the lower limit of the SOC will rise to 45% to ensure there is enough power available.[71][79] The battery capacity was increased to 16.5 kWh for the 2013 model year, the SOC window will be increased to use 10.8 kWh of the total battery energy, and the buffer to ensure battery life will not be reduced. These changes will increase the Volt's all-electric range but charging will take slightly longer. The improved battery performance and durability were achieved through minor changes to the material composition of the battery cell chemistry.[4][84]

Because batteries are sensitive to temperature changes, the Volt has a thermal management system to monitor and maintain the battery cell temperature for optimum performance and durability. The Volt's battery pack provides reliable operation, when plugged in, at cell temperatures as low as −13 °F (−25 °C) and as high as 122 °F (50 °C).[71][88][89] The Volt features a battery pack that can be both warmed or cooled. In cold weather the battery coolant is electrically heated during charging or operation in order to provide full power capability; in hot weather the battery coolant can be chilled utilizing the vehicle's air-conditioning system preventing over-temperature damage.[71][88][90]

The Volt's battery is guaranteed by General Motors for eight years or 100,000 miles (160,000 km), and will cover all 161 battery components.[88][91] GM estimates that the Volt batteries will degrade by 10 to 30% after 8 years or 100,000 miles.[92] GM has applied for a patent that may allow technicians to quickly and cheaply recover some of the performance of degraded battery packs.[93] The Volt’s battery management system runs more than 500 diagnostics at 10 times per second, allowing it to keep track of the Volt’s battery pack in real-time, 85% of which ensure the battery pack is operating safely and 15% monitor battery performance and life.[88]

Condensed:
- They use 65% SOC of the battery
- Heavy thermal management (using A/C compressor as heat pump as necessary)
- Heavy state monitoring for safety, performance and longevity

[kevm14]

Chevrolet Bolt uses a 60 kWh battery pack that weighs 960 lbs. It is a structural member of the car so that helps with weight. It is likely that some of that structure can be removed if you were repurposing the battery pack. You wouldn't stick it in a motorcycle but from a proportional standpoint, let's say the pack weighs 900 lbs.

So now we're in the big leagues. This battery pack holds nearly 2 gasoline gallons worth of energy!

Assuming 90% SOC range can be used:
- 54 kWh usable
- Contains equivalent energy as 1.65 gallons of gas
- Given the 40% efficiency for gasoline, this would give the battery pack a "1 gallon of gas range" weight of 218.5 lbs

You can see huge differences as we compare old Prius NiMH packs with 7 year old Volt packs to brand new Bolt packs. You can also see that 218.5 lbs to store what gasoline can store in 7 lbs is still way, way off. It turns out that you don't need to actually get there, though, as you can do clever stuff with packaging and structural engineering.

Still, the Bolt is only a 3,563 lb car and 960 lbs of that is battery pack.

Tesla is going to be in this same ballpark. Haven't done the research yet.

Let's test my math.

218.5 lbs of battery per gallon of gas in equivalent range.

960 lbs of battery energy at this density. Let's call that 4.4 gallons.

This car gets 119 eMPG combined. Remember that as a gas car it would get about 47.6 mpg combined (remember it would operate like a hybrid with regen). So with 4.4 supposed gallons onboard and 47.6 mpg supposed gas mpg, it would have a range of 209 miles.

Advertised range is 238 so I'm in the ballpark here. A big factor that I hadn't realized before is that a gas HYBRID is 40% as efficient as EV, per energy unit. But the hybrid itself was already some percentage more efficient than a regular gas car. So gas would take an even bigger hit in efficiency. Said differently, that 40% is even less if you are comparing a straight up gas car, to that same car converted to electric propulsion. I'll say a hybrid buys 50% extra fuel efficiency based on a cursory look at a 2015 Accord hybrid vs the 4 cylinder. Point is, you don't need 20 gallons worth of battery pack when the vehicle has an eMPG of over 100.

So, I guess if you wanted to look at any gas car, here's the algorithm that I will try to put into a spreadsheet:
- Determine EPA combined mpg
- Multiply that by 1.5 to get hybrid combined MPG (or use that if it exists)
- Multiply that result by another 2.5 to get to eMPG if it were an EV
- Subtract the weight of the engine, transmission, gas/gas tank, exhaust
- Add the weight of motors, controllers, cooling stuff
- Add the weight of a battery pack, figuring 218.5 lbs per gallon equivalent

At the end you'll find out how much that vehicle weighs. I guess this would work for a motorcycle.

[bill25]

Also subtract the weight of the exhaust, not a lot but everything adds up.

[bill25]

Tried finding some prices. Looked at A123 which I thought produced Tesla's batteries. No prices...

This site has some pricing:

http://www.electriccarpartscompany.com/ ... V-AC-Motor

This would be crazy. It also comes with some monitoring and control. This setup is really for a small car. - $4,150...

Shaft torque has been measured at 173 lbs.-ft at zero RPM. Peak RPM is 8000 with a maximum continuous RPM of 3300. Dimensionally, it is 13.98” long with a sealed frame diameter of 8.66” and a weight of 120 lbs.

Still would need all the battery stuff including charger, regulator.

[Bob]

A123 does not produce batteries for Tesla, Panasonic does. A123's cells seem to be pretty available in the aftermarket and even secondary markets like craigslist, whereas it would probably be pretty hard to get your hands on a Tesla version 18650 or 21700 from Panasonic in the general market. Historically, A123 used iron phosphate technology which is known for being safer, but also having lower energy density than some of the nickel-based chemistries. Their cells are still going to be light years beyond a NiMH cell from a Prius though.

A123 seems to have shifted away from making EV batteries, at least for western OEMs, though their parent company Wanxiang makes a lot of EV batteries for Chinese OEMs. A123's major EV program "wins" include the Fisker Karma and early model year Chevy Spark (before GM switched to LG).

[bill25]

http://www.msn.com/en-us/autos/motorcyc ... ocid=ientp

Well guys, we have less than 18 months to get this together...

[Bob]

Interesting. I got to ride the Harley Livewire prototype in 2014. It was actually a lot of fun, but quite different than other motorcycle rides because there's no shifting and instant torque.

[kevm14]

Time will tell if their brand can sustain a complete 180. A Harley without the sound kind of seems like they should just close up and open a new company under a different name.