Back in the 1970s, AM General—American Motors Corporation’s renaming of Kaiser Jeep’s “Defense and Government Products Division”—built an electric mail carrier Jeep called the DJ-5E “Electruck.” It was so advanced, NASA conducted a bunch of research on it, even referring to the Jeep as “state-of-the-art.”
In October 1977, researchers at NASA submitted a research paper to the Department of Energy describing the inner workings of one of the most advanced EVs on the road at the time: the AM General DJ-5E postal carrier.
That paper was part of a project that required the Energy Research and Development Administration to “develop data characterizing the state-of-the-art of electric and hybrid vehicles.” NASA describes what that data would be used for, saying:
The data so developed are to serve as a baseline (1) to compare improvements in electric and hybrid vehicle technologies, (2) to assist in establishing performance standards for electric and hybrid vehicles, and (3) to help guide future research and development activities.
In the 1970s, NASA and other government agencies conducted track testing on 17 electric vehicles (here’s the report on the “The C. H. Waterman Renault 5"—that’s a story unto itself) to understand the vehicles’ performance characteristics, taking the DJ-5E to the Dynamic Science Test Track in Phoenix in March of 1977. Here’s the data NASA was looking to understand through this testing:
The characteristics of interest for the DJ-5E Electruck are range at constant speed, range over stop-and-go driving schedules, maximum acceleration, maximum speed, gradeabilty, gradeability limit, road energy consumption, road power, indicated energy consumption, braking capability, and charger efficiency.
The DJ-5E (one of less than 400 produced), provided by the USPS for testing, came with a 20 horsepower DC compound-wound motor mated directly to the rear axle, which had an extremely short 5.89:1 gear ratio. The photo below shows how that 263-pound motor mounted up to the Jeep’s frame: it’s in the center, approximately where the transmission would normally sit .
The battery module, which came from supplier “Gould, Inc.,” was a 27-cell, 54-volt lead-acid semi-industrial unit with a total capacity of 330 Ah.
Unsurprisingly, all those cells were heavy, weighing down the front of the Jeep with 1,305 pounds—heavier than any gas engine that had been used in a traditional DJ.
In addition to the heavy battery pack, under the hood sat a 150 pound “silicon-controlled rectifier (SCR) continuously adjustable controller,” which controlled motor speed and direction, sensed the battery’s state of charge, and managed auxiliary power. The controller even allowed for the Jeep to have regenerative braking at certain speeds.
Driving the Jeep involved simply releasing the hand brake, putting the “directional control lever” (which looked just like the floor-mounted transmission lever on the standard DJ) into either forward or reverse, and applying pressure to the “gas” pedal.
To gather the research they wanted, NASA needed to measure the Jeep’s speed, distance traveled, and ampere-hours going to and from the traction battery. To do this, the scientists rigged the Jeep up with the following extremely nerdy instrumentation:
(1) A Honeywell 195 Electronik two-channel, strip-chart recorder: ...Vehicle distance and speed were recorded continuously during each test.
(2) A Curtiss Model SHR-3 current integrator: This instrument measured integrated current into and out of the traction battery during each test by means of a 500-ampere-per-100-millivolt current shunt.
(3) A Tripp Lite 500-watt DC/AC inverter: The E inverter provided 120-volt, alternating current (AC) power to the strip-chart recorder and current integrator.
(4) A Nucleus Corporation Model NC-7 precision speedometer (fifth wheel) with a Model ERP-X1 electronic pulser for distance measurements, a Model NC-PTE pulse totalizer, and a Model ESS/E expanded-scale speedometer, and a programmable digital attenuator: The accuracy of the distance and velocity readings was within ±0.5 percent of reading.
(5) A 12-volt starting, lighting, and ignition (SLI) instrumentation battery that supplied power to the inverter and the required 12-volt supply to the fifth-wheel components.
With the Jeep rigged up, researchers did range tests at 25 mph and 30 mph on level ground, concluding the test as soon as the DJ-5E couldn’t maintain 95 percent of the test speeds. They even did a range test for a dynamic drive cycle shown below, which were done once the Jeep couldn’t accelerate quickly enough to match the speed trace.
In addition to range, NASA also tested acceleration. They did four runs (two in each direction) at 100 percent, 80 percent and 40 percent states of charge on flat ground. In addition, the team conducted straight-line braking tests (with wet and dry brakes), charger efficiency studies (by using clever methods to observe the charger’s input and output power), and tractive force testing.
NASA did its tractive force testing through a very strange–and rather primitive—method in which the Jeep had to tow a second car that was hard on its brakes. Here’s how NASA describes the test:
The driver of the towed vehicle, by applying the footbrake, maintained a speed of about 3 kilometers per hour (2 mph) while the test vehicle was being driven with wide-open throttle. The force was measured by a 13 000-newton (3000-lbf) load cell attached to the tow chain between the vehicles.
Using the forces from the load cell at 2 mph, NASA figured out how steep a grade the Jeep can crawl up while still moving forward (albeit, barely). The paper even goes through the calculations of how to determine this gradeability limit using the tractive force measurements (the Jeep provided a maximum of 615 pounds of pulling force, corresponding to a max grade of 14.4 percent).
On top of this, NASA conducted coast down tests, wherein they sped the car up to its maximum speed of 35 mph, and let the car coast to a stop to determine the vehicle’s coast down coefficients (since the motor couldn’t be detached during coasts, NASA corrected for “motor friction and windage losses”). The point, here, was to come up with what’s called “road energy,” which is just the energy needed to overcome air drag, rolling resistance, and mechanical losses.
The researchers also used those numbers to determine the road power that’s needed at various speeds to overcome air drag, rolling resistance, and mechanical losses via these equations:
Finally, NASA measured energy consumption, which it defined as: “the energy required to recharge the battery after a test divided by the vehicle range achieved during the test, where the energy is the input to the battery charger.” In other words, this figure represented the energy consumed over a certain distance while traveling a certain speed.
NASA’s final results—showing acceleration, range, maximum grade, road power, road energy, and energy consumption—are summarized in the image below:
You can read NASA’s entire nerdy research paper here. The study of a boxy old Jeep with lead acid batteries is great example of just how far EV technology has come.
And if the pathetic results in that study somehow inspire you to want an AM General DJ-5E, there’s one for sale on Ebay right now.