Constructing the electric7

What's new for 2008?

To better track the battery state of charge, we started installing an Amp*Hour (Ah) Meter in 2007.  This involved wiring in and mounting a sensor unit to measure Battery Assembly current and voltage, as well as connecting a display unit.

This device measures battery pack current, and determines the amount of Ah capacity discharged from the Battery Assemblies when the vehicle is being driven, or charged into the Battery Assemblies when the vehicle is plugged in.  The displayed Ah value allows the driver to assess the state of charge and determine when recharging is required.

This Ah Meter also digitally displays total Battery Assembly voltage, current, and multiple battery module temperatures.

Ah counter.
Ah Meter temporarily installed in testing configuration.

Now that the Ah Meter has been tested, the next step is to mount the display with its neighboring switches. 


When you can't buy it, build it yourself!


The continuing mission to build a light weight, high performance battery powered car.

The main ingredients:

Note:  working with high voltage and batteries is dangerous and can be lethal.  Those involved with this project are trained in high voltage safety and battery safety, and the depth of their involvement depends on their level of engineering expertise.  Do not involve yourself in a similar project unless you are qualified and are aware of the safety precautions that must be taken.  Always take appropriate precautions:  even training and expertise does not eliminate the possibility of injury or death.

Here we go!

The chassis comes from a Birkin S-3 car kit.

<>Chassis in crate.
Crated Chassis

The kit comes with most of the parts needed to assemble the car. 
It is designed to be powered by a four cylinder gasoline engine, one of the main items not included with the kit.

Kit Parts

The car will instead be propelled by an electric Motor powered by rechargeable Batteries.

The motor is a 3-phase AC induction Motor, which can convert over 100 horsepower of electrical power into wheel turning mechanical power.

Picture of motor.

The torque and speed of the Motor is controlled by the Motor Controller, which converts DC Battery electricity into 3-phase AC electricity to power the Motor.

The Motor Controller constantly adjusts the way this electrical power is delivered to the Motor,
based on the position of the Accelerator Pedal.

Additionally, the Motor Controller has a built-in DC-to-DC Converter for charging the car's
on-board 12 Volt car battery.  This 12 Volt car battery powers the lights,
windshield wipers, and other traditional automotive electrical accessories.

Picture of motor controller.
Motor Controller

152 NiMH battery modules provide power to the Motor Controller.  These battery modules were removed from hybrid-electric cars found in salvage yards.

Picture of battery modules.
NiMH Battery Modules

The hybrid-electric car battery packs were combined and re-engineered to provide four times the original capacity and power.  The original battery module enclosures were modified and re-used in the creation of the Battery Assemblies.

Picture of battery module assembly.
Battery Assembly

A total of five custom Battery Assemblies will power the vehicle.

Picture of five battery assemblies.
The five Battery Assemblies.

The original Birkin S-3 kit requires assembly and modification to make the electric7 a reality.
The Chassis is seen here with Suspension and Wheels installed.

Picture of chasses.
Chassis with Suspension, Steering, Wheels, and Tires.

Special low rolling resistance Tires have been selected, a type designed for GM's EV1 electric car.

Their design extends driving range, and their self-sealing capability
allows the spare tire to be left behind, saving weight.

Picture of tires.
Low rolling resistance, self-sealing Tires.

Light-weight aluminum Wheels were chosen to complement the Tires.  Is the "E" for Electric?

Picture of wheel.
Aluminum wheel with tire mounted.

The Motor fits into the Chassis's transmission tunnel.

Picture of motor end.
Motor in transmission tunnel.

This leaves engine compartment space available to mount Battery Assemblies and the Motor Controller.

Picture of engine bay.
Engine compartment space with Motor in transmission tunnel.

In the engine compartment area, three Battery Assemblies are installed, along with the Motor Controller.  The top two Battery Assemblies (shown incomplete) are in their design intent locations.  The Motor Controller is visible beneath these Battery Assemblies, and a third Battery Assembly is located below the Motor Controller.

Front of car
Front Battery Assemblies and Motor Controller.

The other two Battery Assemblies are located in the rear of the car, along with the Battery Charger.

Rear Battery Assemblies and Charger.
Rear Battery Assemblies and Battery Charger.

The mounting of the Battery Assemblies and Motor Controller require a number of custom-made Mounting Brackets.

Picture of brackets.
Custom-made Mounting Brackets.

The Motor requires a custom Adapter Plate and Motor-to-Chassis Mount.

Picture of DE motor mount.Piture of motor mount.
Motor Adapter Plate and Motor-to-Chassis Mount.

A custom-splined Intermediate Shaft bridges the gap between the Motor and the Drive Shaft.

Intermediate Shaft with Bearing

The Adapter Plate and Motor-to-Chassis Mount attach directly to the Motor, and allow the Motor to be connected to the Drive Shaft Carrier.  The Drive Shaft Carrier also attaches to the vehicle Chassis, but its main purpose is to couple to Motor to the Drive Shaft, which turns the wheels through the rear Live Axle.

Picture of powertrain.
Powertrain assembly.

It is congested, but the Motor is shown installed with the Motor-to-Chassis Mount.

mounted motor
Mounted Motor.

With the Powertrain fully installed, the Driveshaft can be seen connecting the Live Axle to the Intermediate Shaft, which gets turned by the Motor.

installed drivetrain
Assembled Drivetrain.

With the the Motor installed, the front lower Battery Assembly gets bolted into position.  The 12V Lead Acid Battery and the Contactor Box are also attached on their welded-in Bracketry.

lower front pack in place
Lower Battery Assembly with Contactor Box and 12V Lead Acid Battery.

A custom-made cooling manifold connects the radiator to the Motor Controller.  Both the Motor Controller and the Motor are cooled by regular antifreeze.

hose to inverter
Cooling manifold connects radiator to Motor Controller.

The other end of the cooling manifold connects to the Motor.  Antifreeze gets circulated through the Motor and the Motor Controller by an electric pump.

motor hoses
Two cooling hoses connect to the top of the Motor.

With some modifications made to the instrument panel to accommodate their size, a Speedometer and a 10,000 RPM Tachometer are installed.  Also shown is the headlight switch, hazard switch, and heated windshield switch.  The windshield wiper switch is ready to be installed.

dashboard instruments
Instrument panel coming together.

All of the Instruments are now installed into the Dashboard!
From left to right:  Speedometer, State of Charge Gage, Tachometer, 12V Battery Voltmeter, Propulsion Battery Ammeter (-100 to +300 amps), Propulsion Battery Voltmeter (200 to 400 Volts).

Also, from left to right, Horn Button, Turning Signal Switch, Low Brake Fluid Light (red), Turning Signal Indicator Light (green), High Beam Switch Button, TBD Light (orange), and High Beam Indicator Light (blue).

All instruments.
Dashboard complete with Instruments.

 The next goal is to get the car ready for an initial test drive.  The center console, seats, and seatbelts are bolted in and are ready for the drive.  Carpeting and other upholstery can be installed later.  The steering wheel will be installed once the tachometer tests out OK.

Cockpit with seats, shoulder belts, and center console bolted in.

Here is another view of the cockpit seating.  Note that the rollbar is installed behind the headrests.

Seating area.

The rear compartment is ready for the first test drive.  Wiring is protected by convoluted tubing and is restrained.  Screens have been installed on battery pack air inlets to limit debris entry.  The 12V fan power supply has been tested to power the battery fans when the 220V AC plug is connected.

rear compartment
Rear compartment, viewed from the top rear.

Most of the pre-test drive work remaining is in the front section.  Wiring has been put in convoluted tubing for protection and is being routed.  Above the front lower battery pack, the inverter can be installed.

front lower layer
Front compartment, viewed from the top right.

With wires routed, the inverter is bolted in place to brackets above the front lower battery pack.  Coolant fittings are mated.  Both power and signal electrical connections have been made. 

Inverter installed.
Inverter installed above front lower battery pack.

With specific modifications to allow its battery cooling fan to fit under the hood of the car, the front left battery pack is installed on its bracketry.  It sits above the inverter, which sits above the front lower battery pack, resulting in three layers of hardware in the front section.

Left front battery pack.
Left front battery pack installed above inverter.

The front right battery pack sits on its mounting points, awaiting installation of its cover.  Once its cover is installed, the fan control and temperature sensor wiring will be connected and the battery system installation will be tested.

Right front pack partially installed.
Right front pack partially installed without its cover.

The front right battery pack's cover is now installed with its fan and temperature sensor wiring hooked up.  The next step will be to retest the battery system by powering the inverter and performing a wheel spin test.

Both front packs installed.
Both front top battery packs installed.


Charger monitor screenshot.
First charge monitor data.

With the help of an old laptop computer,  the charger was programmed and has now charged the batteries with 3.3 kW of electrical power!  Check out the photograph of the charger monitor screen.

First Driving Test

On January 8, 2005, we drove the car down and back up the driveway on its own power six times!  Click on the image below to download and watch the video of Steve driving the car!  The hood, windshield, and nosecone were not installed for this test.

Driveway test image.
Steve drives the car up the driveway!  (Click on image to watch the Quicktime movie.)

Portions copyright 2001 - 2008 by Carlton Brown