Engineer shares how to build an electric vehicle from the ground up: Lead-acid vs Lithium-ion batteries
Lead-acid vs lithium-ion batteries
The original batteries were lead acid,
weighing in at 800 lbs. However, over
the three-year span of the project, the cost of Li-ion batteries dropped in
half and their cycle life doubled. The
new 350-lb Li-ion batteries are from Thunder Sky. Thirty 200AH cells form a 100V,
200Ah pack (20 kWh), which gives around 90 miles range!
Santini does not have a battery balancing circuit right now, but the cells stay in balance pretty well when new. Stay tuned for the next steps for further improvements. See Figure 5.
Lead-acid batteries pros and cons
- One of the lowest energy-to-weight and energy-to-volume battery designs in existence, making them very big and heavy for the total amount of power they can put out.
- Very high surge-to-weight ratio, meaning they can deliver a big jolt of electricity all at once. This makes them perfect for applications that need a big, sudden surge of power, such as car starters.
- Inexpensive to produce.
- Not very good in roles that require a steady, low, or middling supply of electricity over a long period of time.
- Long recharging times.
Lithium-ion batteries pros and cons
- High power-to-weight and power-to-volume ratio, so are light and small as compared to lead-acid.
- Special types have high surge capacity, but those are more expensive. Regardless, an EV does not need "cranking" power to start the car like a gas engine. The AC motor only draws higher currents during acceleration.
- Do not have frequent maintenance needs like lead-acid.
See Figure 6 for a summary of Li-ion's advantages.
A lead-acid discharge curve is shown in Figure 7 and a lithium ion in Figure 8.
Also see :
- Video: John Santini describes internals of self-built electric vehicle
- Video: Just who is John Santini and why did he design his own EV?
- Engineer shares how to build an electric vehicle from the ground up -- Part 2: Specs, challenges, and future design
- Drive For Innovation: The ultimate electronics roadtrip
- Automobile sensors may usher in self-driving cars
Stephen Taranovich has 40 years of experience in
the electronics industry. He received his MSEE from Polytechnic University,
Brooklyn, NY, and his BEEE from New York University, Bronx, NY. Steve is also
chairman of the Educational Activities Committee for IEEE Long Island.