1977 Jeep Electric Mail Truck

1. The DJ-5E Electruck

In the late 1970s, American Motor Corporation’s AM General division built an electric mail carrier called the DJ-5E "Electruck." The vehicle was so advanced that it attracted the attention of NASA who, in turn, conducted research on it, going so far as to conclude the truck was “state-of-the-art.” The DJ-5E came with a 20HP DC compound-would motor mated directly to the rear axle. The following are some of the more interesting notes the NASA team put together on the AM General DJ-5E postal carrier. 

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2. A different motor mount

The Jeep Electruck had an extremely short 5.89:1 gear ration. In the photo above, you can see that the 260-pound motor was mounted in the center of the Jeep’s frame, essentially where the transmission would normally sit.

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3. The battery was enormous

The battery module came from supplier Gould, Inc. It was a 27-cell, 54-volt lead-acid, semi-industrial unit. Its total capacity was measured to be 330 Ah. All told, the battery weighed just over 1,300 lbs, which weighed down the front of the truck considerably and made it heavier than any gas engine used in a traditional DJ.

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4. Silicon-controlled rectifier

Speed and direction were controlled by a silicon-controlled rectifier (SCR) that featured a continuously adjustable controller. The SCR weighed 150 lbs. In addition to controlling speed and direction, it also sensed the battery’s state of charge, managed its auxiliary power, and allowed the Jeep to have regenerative braking at certain speeds.

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5. NASA testing

NASA used a lot of instruments to test the Jeep as evidenced by the list below: 

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 were 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.

6. More NASA testing

Researchers conducted range tests at 25 mph and 30 mph on level ground. They concluded that it could not maintain 95% of test speeds. They also performed a series of acceleration tests — four runs at 100%, 80%, and 40% states of charge, twice per state of charge in each direction. Additionally, they did a tractive force test, though in a rather primitive way. They had the Jeep tow a second car that was hard on its brakes. Here’s how they described their findings:

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 (3,000-lbf) load cell attached to the tow chain between the vehicles.

There were a series of other tests. All the final results—showing acceleration, range, maximum grade, road power, road energy, and energy consumption—are summarized in the image above.

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