By Purkeys | Sep 15, 2014



A fleet installed GPS units on their reefer trailers, which created a parasitic draw on the reefer battery. Shortly after the fleet began having problems with reefer units not starting after they sat for extended periods of time. This increased the fleet’s costs in jumpstarts and service calls, which created operations issues because the reefers would not start and pre-cool. Purkeys was brought in to find a solution.


Purkeys used their Mobile Data Acquisition units, or MODAC, to develop an electrical profile of this fleet. The MODAC is placed near the battery and can record ten readings per second for up to a month. It provides the necessary information to locate problem areas by looking at:

  • Battery and alternator voltages
  • Start events
  • The operating electrical profile of the vehicle

The data was then collected and analyzed by Purkeys and developed into an electrical profile for the fleet.


As Purkeys examined the data they noticed the charging systems were working properly but some of the trailers were left on customers lots for up to three weeks at a time. When the trailers sat without running the reefer for weeks at a time the parasitic loads from the GPS devices drained the batteries until it required a jump-start. Since the system was operating correctly, Purkeys advised the fleet use a low voltage disconnect, or LVD, on their reefer trailers. This would disconnect the parasitic draws from the batteries when the voltage drops to a predetermined level, which reduced jump-starts and costs.

Are you experiencing problems with batteries? Do you have more questions about Purkeys’ electrical profile service? We welcome your comments and questions below.

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