Design and Conversion for an
Electric Plug-in Vehicle
330:174 Senior Design I, Fall 2007
Faculty Advisor: Dr. R. Pecen UNI EIET Program [email protected]
My objective is to design and build an electric plug-in vehicle by converting an internal combustion engine (ICE) driven vehicle. The electric plug-in vehicles replacement drive train will consist of a bank of batteries (traction pack), an electric DC motor, and a motor controller. The traction pack will consist of 12 series connected deep cycle absorbed glass mat (AGM) batteries, and be recharged by an on-board battery charger that plugs into a normal 120 volt AC outlet. The motor controller will then convert the 144 volt DC traction pack voltage into an output variable DC voltage to vary the speed of the electric motor. The motor will still be coupled to a manual transmission with a clutch and drive nearly the same as any other vehicle on the road, only that to run efficient, the electric motors revolutions per minute will be much higher than an ICEs revolutions per minute while running at cruise speed.
It is my goal to create an alternative fueled vehicle that will be comparable or less expensive to drive than my internal combustion powered vehicle that I currently drive. The plug-in must be reliable and be able to handle my average daily commute, while being a cleaner source of transportation than an ICE vehicle. This all must also be done within a reasonable budget that average households would be able to afford.
With the cost of fuel rising, many people have begun looking for different means of transportation that is within their budget. The most widely used current form of transportation is driven by the internal combustion engine, which is only has a maximum theoretical efficiency of 40%. The internal combustion engine also is a large polluter in todays world, which is something that many people would like to see changed. One alternative means of transportation that many are looking at is an electrical plug-in vehicle. Currently in the United States no major car manufacturers offer a fully stand alone plug-in vehicle, but in the recent past there were a few, like the GM EV1, Toyota RAV4 EV, and Ford Ranger EV. Electric vehicles offer the possibilities of greater efficiency and less emissions. The electric motors are capable of running above 90% efficient, but the efficiency of lead acid traction packs can be below 50% and up to around 90% efficient. The higher the state of charge the traction pack is put into, the lower the efficiency while charging, with below 50% efficiency being reached while charging above 90% state of charge. The technology of batteries is increasing at a rapid pace, and the advances in lithium ion technologies offer very promising outlooks. Lithium Ion packs are much lighter, more efficient, and have a very large power capacity compared to traditional lead acid batteries.
Since no major U.S. car manufacturers offer a plug-in vehicle, many do it yourselfers are converting their ICE vehicle to an electric plug-in. There are many sites dedicated to the converting of vehicles and offer large amounts of information. Some sites that I have visited are: http://en.wikibooks.org/wiki/Electric_vehicle_conversion, http://www.evparts.com/, http://www.electroauto.com/, and http://www.diyelectriccar.com/forums/.
Many people take great care in assuring that their cars are safe, but if the conversion is not done with safety in mind, the car could be a hazard in an accident. Since DC traction packs are almost always above 50 volts DC, they should be isolated or floating from the main vehicle chassis ground. The traction pack also needs to have fuses or circuit breakers within them, and the holding tray needs to be able to hold them securely if the vehicle is in an accident or rollover.
My design and conversion to an electric plug-in will address all of these issues. The vehicles operating costs will be comparable or cheaper to a normal ICE vehicle, be able to handle my daily commute, be safe to drive, and pollute the atmosphere less than ICE vehicles.
The vehicle I have chosen to convert is a 1991 Dodge Stealth R/T. This particular stealth is front wheel drive (FWD) with a V6 motor and an automatic transmission. Some models of the Stealth were offered with an all wheel drive option. My FWD Stealth has a drive shaft hump along the center of the passenger compartment floor, and areas on the rear frame rails for mounting an independent rear suspension (IRS) setup. I will remove the current motor and FWD transmission and install a rear suspension to convert it to rear wheel drive (RWD).
The traction pack will have a motor circuit breaker in it for safety along with a shunt to monitor the overall current output from the pack. A shunt will also be located in the motor circuit, so the current efficiency can be figured and viewed while driving. A general wiring flow diagram is displayed to the left.
The current drive shaft hump will be modified to fit an electric motor that is coupled to a manual transmission inside of it, and a drive shaft will be used to connect the transmission to the rear differential. I will try to keep weight balance in mind while converting the vehicle, so depending on how much weight is removed from the ICE and automatic transmission, the batteries, electric motor, and transmission may be placed in different places in the car. If more weight is needed in the back, I can either put part of the battery pack where the gas tank was, put the motor and transmission where the rear seats are, or both. If more weight is needed in the front, the motor and transmission can be located closer to the front of the vehicle, like most other RWD vehicles. The two possible layouts are displayed in Figure 2:
The majority if not all of the traction pack will be located in the old engine compartment and reinforced so it will not bend easily if in an accident. I would rather have it move as a motor would if it is in an accident, so I will likely mount the traction pack at the same locations and motor mounts as the factory motor did. I will also take an extra step to keep outside debris, and water off of the motor and batteries. The whole area under the hood will be totally enclosed with a floor pan. I will need to address cooling issues with especially the motor, but believe I can use an intercooler in the front of the vehicle and circulate the inside hot air through it. If driving the vehicle in the winter, I could also use the motor heat to keep the batteries and driver warmer if enough heat is created by it.
An electrical heater will replace the heater core in the conversion so the driver can have a heated cabin and be able to defrost the windshield if needed. All factory electrical components on the vehicle will use the factory wiring. The Stealth has a few features that will need to be researched by dismantling the car, like the electronically adjusted ride control, and the antilock brakes (ABS). The ride control uses a separate computer, but I am not sure if the ABS is run by an external computer or not. The ABS can either be disabled, or run by a stand alone ABS computer if needed, and the ride control should be able to use the factory computer, but maybe not if it relies on data from the factory engine computer.
The weight that I will loose by removing parts is hard to calculate because I cannot find figures for the parts that will be the bulk of the weight. The parts that will be removed are the engine, transmission, radiator, exhaust, fuel tank and system, and rear suspension. The parts that will be added are 750 lbs of batteries, a 150 lb motor, 100 lb transmission, and an independent rear suspension. I believe the weight exchange will be close, but could also be off by 500 lbs easily.
The budget I will be working with is around $10,000, I have a line of credit that I will draw upon when needed. I am not looking at it as an outlay of cash, but as an investment. I believe that with 50,000 miles of travel on the vehicle, I can recoup the initial $10,000 by driving it instead of my current vehicle. I will explain how
this is possible by comparing the cost to operate my current vehicle compared to an electric vehicle. I do understand that there are other vehicles out there that get better gas mileage and that are cheaper to operate, but I am doing a comparison of my transportation costs.
I have a 1994 GMC Yukon, that gets around 13 mpg if I am lucky. Most of my driving is back and forth from work, which is a 2 mile drive each way, and all city driving. An average fill of gas will cost me about $80.00 and last me about 300 miles. $80 / 300 = $0.27 per mile cost to travel.
The electric vehicle will have a traction pack that is 75Ah and 144 volts. Which equates out to be 75 * 144 = 10800Wh, or 10.8KWh. Figuring a 50% efficiency in charging, which will be low considering charge efficiency can be up to 90% at lower states of charge, the maximum power used to charge the batteries will be 10.8 * 2 = 21.6KWh. My electric companies highest current electricity rate is just below $0.07 per KWh, so 21.6 * 0.07 = $1.512 for each charge. The part that is hard to figure is the distance I will be able to travel per charge. I believe that if the discharge (DOD) is 20%, I can get about 15 miles out of my vehicle, but at 80% DOD I think 50 miles could be achieved. traction pack depth of Some data I calculated using Uves Electric Vehicle Calculator , is listed below in Figures 3, 4, and 5 to support my claims. This calculator also takes into account the weight, and the specific components I will be using in the project. From calculations I made, and information I have heard throughout experience in the automotive field, I believe this calculator is the most accurate. Even though some of the mileage ranges seem high, the rest seems to be accurate. Other people using the same components as I will seem to average my assumed ranges listed above. Although the initial cost of batteries will be figured into the build of the vehicle, to be fair, I will figure the batteries as a consumable like gasoline, to figure the real cost of transportation. My price for the 12 optima batteries will be about $2300 total. At 20% DOD, I have heard claims that you can get around 4000 charge cycles, but with 80% DOD, you can get around 250 cycles. If that is the case, I would be better off by discharging to 20% DOD, which would yield 4000 * 15 = 60,000 miles. 2,300 / 60,000 = $0.038 per mile. So if a full charge, or a $1.512 charge would get you 50 miles, that is 1.512 / 50 = $0.03 per mile. So a total cost of $0.07 per mile.
Over driving my truck, that is a $0.20 per mile savings. $10,000 / $0.20 = 50,000 miles until initial payback. If I go to 80% DOD, 2300 / (250 * 50) = $0.184 per mile for batteries or about $0.214 per mile overall cost, still a $0.07 savings per mile.
Proof of Concept
The only proof that I have that this project will work, is that others are doing it. Web sites like http://www.austinev.org/evalbum/ display electric vehicles that others have converted, with various bits of information like what they used for components and the ranges they are getting out of them. An average range of travel with like weight vehicles is around 50 miles, which also corresponds with my calculations. A 3500 lb vehicle should not use more than 15 horse power driving down the road at 55 miles an hour. 15HP corresponds to 11.2kW, and with a 144 volt battery pack, that is 77 amps. With efficiency losses, 85 amps would roughly be the power used. 75 Ah batteries would let you drive for about [1 hour * (75A/85A)] = 50 minutes. 50 minutes at 55 miles per hour is about 46 miles it will travel.
The components I have decided on, and that are the most costly parts of my project are listed below:
Currently the project is on schedule and a very large portion of the research and design ideas are completed. There will be modifications to designs depending on how things look after the car is dismantled. I may find that some things are not going to work the way that I want them to, so my design will need to change with that. I have ordered the motor controller, which has a 4 month lead time, and I will be ordering the rest of the parts soon. I want to have all parts by the time I am ready to start fabricating. The schedule may seem packed and people may wonder how I can get this done in one semester, but I have years of experience in automotive repair. I also have taken enough vehicles apart and put them back together to understand how the vehicles are constructed, and how my modifications should be made.
Created by Brian Sellers
Created by Brian Sellers
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Created by Brian Sellers
 Sandia National Laboratories, John W. Stevens and Garth P. Corey. A Study of Lead-Acid Battery Efficiency Near Top-of-Charge and the Impact on PV System Design. Accessed: December 3, 2007. http://photovoltaics.sandia.gov/docs/PDF/batpapsteve.pdf
 Wikipedia Electronic Encyclopedia. Battery Electric Vehicle. Accessed: December 3, 2007. http://en.wikipedia.org/wiki/Battery_electric_vehicle
 Uves Electric Vehicle Calculator. Accessed December 5, 2007. http://www.geocities.com/CapeCanaveral/lab/8679/evcalc.html
 Zilla Controller Package Specifications. http://cafeelectric.com/products/zilla/index.html