Heavy Duty Alternator

Tech Tip: Voltage Drop Test

The electrical problems related to excessive voltage drops are more common than you may realize. Think of your starting and charging cables as a two-way street. The battery needs to deliver its available power to the starter through the cables and connections for cranking the engine. In turn, the alternator needs to replenish the battery and provide the power for the vehicle loads through the charging cables and connections. If the street is too narrow to carry the current, it shows up in measurable “voltage drop” or loss. This is often manifested in short battery life, frequent jump-starts or perceived alternator and starter problems.

It’s not uncommon for an alternator or starter to be replaced because it’s believed to be faulty or run its normal life cycle, only to later discover that the root cause of the problem doesn’t reside with the alternator or starter.

High or unwanted resistance is one contributing factor that leads to cranking and charging system problems. High resistance is often caused by one of these four main issues:
  • Loose connections
  • Corrosion in the cables and wiring
  • Improperly sized wiring or cables
  • Improperly crimped connectors
While a technician may regularly do a visual inspection of cables and connections it doesn’t show what is going on inside the cables or the connections. This is why the concept of voltage drop testing is the only sure method of determining if there is an adequate current delivery path for optimum starting, charging, battery performance and life.

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