Introduction:
The original objective of the SunDragon data acquisition team was to design and
implement a data acquisition for SunDragon V and VI. However, due to the bleak
outlook of Drexel University’s solar car team, our team decided to redefine the goal of
our Senior Design project. The new objectives is to first correctly re-wiring the electrical
systems of the schools Electric Vehicle and second to incorporate a small data acquisition
system including the use of Cruising Equipments e-meter to gather battery pack; voltage,
current, and current-hours and dump the data onto a laptop in the car.
Someone outside the University acquired the electric vehicle, a converted 1984
Honda CRX, as an incomplete project car donated to the Drexel electric Vehicle team.
The car was about ninety percent complete with the low voltage electrical system
requiring the most work, along with some mechanical re-design. Our primary goal is to
make sure that all the wiring in the high and low voltage systems are correctly wired with
the proper documentation of schematics and manuals. When the wiring is correct we will
be able to attempt to charge the batteries and test drive the car to make sure everything if
functioning properly. We also need to test the batteries to ensure they will hold a charge.
After the car is working we will mount the e-meter in the center of the dash to display
battery status.
The changing goal of the team defines a logical overall financial decision and the
ever-changing world on engineering. After reassessment of the initial problem it was
found that this would be a reasonable change with the time remaining in the term. Thus
making it feasible to complete the re-wiring and implementation of a small data
acquisition system.
Work on the Electric Vehicle
After obtaining working space in the basement of the Hess labs we were able to
bring the car to Drexel to begin our assessment of the Electrical systems. Both the High
and the Low voltage system were already installed from the original conversion project.
However, these systems were not finished and not correctly installed in the car. As a
result we needed to document and trace all wiring previously installed. Using this
information we were able to decide the best approach fixing the electrical systems. We
first started the high voltage system.
The High Voltage Electrical System
The High Voltage system contains the following parts:
o 10 12-Volt batteries; 4 up front and 6 behind the drivers seat.
o DC-Motor with Curtis PWM Motor Controller
o Potbox to control speed via the original gas pedal.
o 30A Breaker Box
o K&W B-20 Charger for 120-volt, 20-amp line
o Contactor
o E-meter for voltage, amp and current readings
o Shunt to measure current across the battery pack.
The first objective of our work on the EV car was to ensure the proper setup of
the high voltage system. Tracing each of the high voltage cables throughout the car we
were able to determine that the system with the motor, motor controller, contactor, and
battery pack was properly setup. A Honda CRX requires the motor run in a clockwise
direction and from the motor documentation we determined that the motor was correctly
wired (See Appendix?). Another issue that needs to be resolved with the system is the
placement of the two batteries, which are currently located directly behind the front
bumper. The current location for these batteries is not safe and poses a great safety risk if
there was a collision involving the front end. There for a good position would be in the
trunk with the six other batteries once the heavy duty springs are installed. However, the
battery placement will be left to the to the mechanical design team, who will determine
the best battery positions based on weight distribution throughout the car to ensure a safe
vehicle.
The battery charger is also not hooked up to the batteries, but the wiring in place
in the engine compartment. There are four wires that need to be attached to the battery
pack once the low voltage system is complete. The final issue is the ten batteries in the
car have been sitting outside without having maintained a charge for several years. As a
result many of the batteries individual voltages are around 6-8 volts each, which might
result in not being able to be re-charged. If that is the case we are going to have to either
purchase new batteries or use the batteries donate by Lockheed Martin.
Low Voltage Electrical System
The low voltage electrical system contains:
o DC-to-DC converter
o 12-Volt auxiliary battery
o Vacuum pump
o Vacuum pump switch
o Original electrical system (Lights, horn, turn signals, stereo, etc…)
o Ignition Switch
o 2 relays to control the contactor and potbox
o Light indicators
One look at the low voltage system and one can see that there were many
components improperly wired. Initially, we did not have a good low voltage-wiring
diagram to use as a reference, so we decided to trace the existing system starting at the
dc-to-dc converter. Tracing wires off the converter we quickly released that the inputs
from the battery pack to the converter were improperly wired, both going to the positive
terminal of the contactor. Next we moved to the contactor, which was only wired to a
switch located on the center console, not the key switch and no power source. At this
point in the tracing process we decided that we should just rewire the entire low voltage
system using a wiring diagram from Michael Brown’s Convert It for reference.
We started rewiring the low voltage system in the 7th week of classes by start with
the key switch relay and the poxbox relay as seen in the diagram in appendix? The
potbox relay controls the contactor by allowing the contactor to close only when the gas
pedal is pushed down. The use of this relay is a safety measure that allows the flow of
current to the motor only when the pedal is used and not just by turning the key. The key
switch relay activates the low voltage system when turned to either position one or two
allowing for the potbox relay be triggered when the gas pedal is pressed. We mounted
the two relays on the firewall close to the divider panel for easy access to all the
components. We were able to test out the key switch and the potbox relays by attaching a
12-volt battery to the low current system and a 12-volt battery to the high voltage
terminals of the contactor. We turned the key causing only the low voltage system to
work, but not closing the contactor. Next, stepping on the gas pedal caused the micro
switch in the potbox to close causing contactor to close, thus completing the circuit.
The original person to do the conversion removed the connection in to the original
12-volt system in the engine compartment. Therefore we need to figure out the correct
lines off the OEM fuse box, which will allow us to supply power to the headlights, turn
signals, brake lights, horn, etc… Once the OEM 12-volt system is working we will be
able to connect it into the low voltage system through the dc-to-dc converter outputs and
a chassis ground.
E-meter
The E-meter is being used to take measurements of the High Voltage system in
the electric car. With the use of a 500-volt prescaler we will be able to monitor the
voltage, amp, and amp-hours via a LCD panel mounted in the center of the car’s
dashboard. We are going to use an existing hole in the center of the dashboard, which is
wide and deep enough to mount the e-meter in a smoked Plexiglas top to cover the hole.
Also, there is a serial port located on the back that can be used to download data to a
computer or other storage devices.
Currently we have the E-meter running with the 100V prescaler on a test bed with
a 12-volt battery is being used to power the E-meter. It is measuring a total of 50V from
a battery pack wired in series and with a shunt to measure the current. The output of the
prescaler is 10-volts on the e-meter without setting up the e-meter to multiply by a factor
of two. We do not have enough batteries currently at a high enough charge to measure
something that the e-meter without the prescaler cannot handle. The 500-volt prescaler
was tested to ensure that it is functioning as designed.
The e-meter measures the total voltage across the entire battery pack by hooking
it up in series with the High Voltage circuit. It also measures the current using a shunt,
which installed on the firewall and attached in series to the high voltage circuit. Since the
e-meter is going to be installed in the dash we will need to run a serial line cable from the
back of the e-meter to a port on the dash in order to hook up a laptop at anytime.
Budget
The following is the budget from last years EV senior design team with the
addition of the costs incurred this year.
Item
1984 Honda CRX chassis
9” Advanced DC Motor
CurtisPMC Motor Controller
CurtisPMC Potbox
Albright Contactor
Current Shunt
Cruising Equipment E-meter w/ 500V prescaler
Sevcon DC/DC Converter
K&W Battery Charger
K&W Battery Charger Booster
Power Brake Vacuum Pump
50mV Shunt
10-12 Volt Batteries
Car relocation
Miscellaneous
Total Cost
Cost
$1150.00
$1623.00
$906.00
$77.00
$165.00
$22.75
$300.00
$580.00
$675.00
$195.00
$285.00
$30.00
$1500.00
$155.00
$300.00