by Anura Guruge
Dick, who had owned a Toyota Prius for many years, just upgraded to a Prius Prime. I (very ignorant when it comes to electrified cars) had no idea what the difference was and why Dick was so excited about the Prime. When I asked for clarification, Dick, as is his wont, came up with this brilliant and pithy tutorial. It was too good NOT to publish and share. So, for your edification.
I’ll give you a short course in “Electrified Cars.” There are now three types of “Electrified” vehicles now for sale:
Hybrid Electric Vehicles (HEV): These have a small battery, which traditionally have been Nickel-Metal-Hydride (NiMH) chemistry, typically about 2 KwHr capacity. and you have no ability to externally recharge the battery. As the car is driven, the traction electric motors draw energy from the battery when appropriate, and then they put energy back into the battery when appropriate. This has been the design of the classic Toyota Prius since its inception in the U.S. in 1999. These cars are medium size cars, carry five passengers and luggage and get over 50 mpg.
The great efficiency of this configuration comes mainly from three factors:
(a) The Internal Combustion Engine (ICE) never has to be idling. The car can startup under electric-only power and then bring the ICE into play when appropriate depending on throttle opening, temperature, speed, battery reserve energy, as well as other factors. So, sitting at a traffic light everything is dead off. – No idling.
(b) The hybrid car uses dynamic braking, so when you press on the brakes, the computer slows the car by turning the electric motor into a generator and this both slows the car and charges the battery. This efficiently transfers the kinetic energy of the moving car into potential energy stored in the battery. In non-electrified cars this energy is dissipated as heat by the brake disks.
(c) This one is more complicated, but very important. The computer uses the ICE to charge the battery only when the ICE is being used also to propel the car, which greatly improves the efficiency of generating electricity. If I want to put 10 horsepower (Hp) of electricity (aprx. 8 Kw) into the battery and I started up the ICE to do that, I would be running the ICE, with all of its horrible internal losses, just to produce that 10 Hp. – Very inefficient. BUT, if the ICE is already running at say 50 Hp driving the car, then I can draw off the additional 10 Hp much more efficiently since all of the ICE’s internal losses are already being expended in driving the car. I hope that makes sense to you.
Plug-In Electric Vehicle (PHEV): These include my Prius Prime, the Chevy Volt and several others. The battery is externally chargeable, and gives 25 – 50 miles of electric range, and then the vehicle operates like any hybrid, combining the ICE and battery for the best results. Since the majority of working folks have a commute drive of less than 25-50 miles, this means that for most of their use of the car, they will only need electric power. However, unlike a pure electric car, the PHEV can easily do a cross-country trip with no electric charging needed. My Prius Prime uses an 8.7 KwHr Li Ion battery which is about four times the size of the battery in our old 2006 Prius we enjoyed for 12 years.
Battery Electric Vehicle (BEV):
the Chevy Bolt, and the Nissan Leaf are the best selling of these pure electric vehicles. They have no ICE and are powered only by a Li Ion battery supplying electric motors. The battery capacity in now-available BEVs varies greatly, and therefore the driving range of the vehicles varies greatly. Early BEVs had only 50 – 80 miles of range, but that was not very popular. Remember, when a BEV its out of charge, you are struck at the side of the road! Tesla upped the game a lot with around 200 miles of range in their cars. The Chevy Bolt has 238 miles of range and the Leaf is moving up to 210 miles with their upcoming 2019 model. Batteries in these cars are all Li Ion, and energy capacity is in the 60 -80 KwHr range. Currently, these Li Ion batteries cost about $180 per KwHr, making a 80 KwHr battery account for about $14,000 of the cost of building a BEV! Remember, though, there are great savings in manufacturing costs by eliminating the ICE and transmission.
The electric motors in BEVs are typically permanent magnet, three-phase, AC synchronous motors. Since the speed of a synchronous motor varies with the input frequency, the car’s D.C. battery voltage is fed to an inverter that supplies the variable frequency power to the motor. These motors work at voltages in the 500 – 800 volt range. This high voltage is necessary so as to reduce the current loads. The Tesla electric motor can produce a whopping 700 Hp! – This requires about 500 Kw of electric input. If the operating voltage is 500 volts, then you have about 1,000 amperes flowing into that motor. The total capacity of the service entrance in your whole house is only 200 amperes, so this car at max power requires the current equivalent of five US households, drawing the maximum energy their service entrance panels can put out. Wow!
Ok now go out and buy a Prius Prime. So far, for the 200 miles I have driven, my average fuel mileage is over 66 mpg.
Dick’s brand new 2018 Prius Prime.
Check Category ‘New Hampshire’.
by Anura Guruge