U.S. Xpress Test Results: 10+ Hour Rest Period HVAC & 300 Watt Solar Battery Charger

Test and System Design Overview

eNow installed our 300 Watt Solar Battery Charger to power HVAC and other auxiliary loads on a Peterbilt 579 tractor operated by U.S. Xpress.

In order to monitor the effectiveness of the system with the addition of solar, eNow installed an Onset HOBO data collector, which records current, voltage, and temperature data from the truck’s main (crank or starter) battery and the auxiliary battery banks.

The data is sampled from various sensors every 10 seconds, averaged, and logged in 5 minute increments.

Thus, the reading at the time stamp is the average reading for the previous 5 minutes.

The data is uploaded to the cloud every hour via the cellular network. If the tractor is not in an area with sufficient cellular coverage, the data is stored until the next good cellular service area is entered.

The data may be downloaded into a CSV file format which can be directly opened in Excel.

The data can be further analyzed and graphed. Although driver logs were not available during this period, it is our understanding that the tractor was being operated by a team of two drivers in long-haul operations in the southern U.S.

Summary Results

Over the past several years, eNow, Inc. collected data from a U.S. Xpress Class 8 Sleeper Truck equipped with a battery-powered Air Conditioning (A/C) system and 300 W Solar Battery Charging system during an extended rest period.

Based on the data collected during this period, we can conclude:

• A/C with the 300 Watt solar system kept the cabin temperature below 75°F, and usually below 70°F throughout a 10-hour rest period despite outside tractor cabin temperatures that reached well over 100°F. Based on the slope of the discharge, we estimate the A/C could have been run for an additional 1.5 hours.
• Solar connected to the truck battery did effectively charge both the truck battery and auxiliary battery, even during this period of heavy auxiliary load use.
• Solar charge current to the auxiliary battery during the 10-hour rest period was 47 amp-hours, which we estimate to be approximately one additional hour of A/C operation.
• In addition, solar charged the truck battery over the same 10-hour period, keeping the truck battery fully charged at well over 12.8 volts, instead of being depleted by truck parasitic loads.
• Total solar charge current to both batteries could not be quantified, but it was clearly greater than the 47 amp-hours that was transferred to the auxiliary battery.