Home > Are ECU Controlled and Temperature Compensating Alternators Causing Problems?

Are ECU Controlled and Temperature Compensating Alternators Causing Problems?

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article image BCDC 1220 Vehicle Battery Charger in a Pajero Engine

Redarc Electronics  has fielded several inquiries from customers over recent months relating to the problems experienced by them with the charging of dual or auxiliary batteries in late model vehicles.  

Put simply, the vehicle alternator was never designed to fully (100%) charge the main vehicle battery. It was however designed to maintain the charge of the main vehicle battery and run electrical loads such as lights and air-conditioner once the vehicle was operational.  

By introducing extra batteries into the vehicle charging system with the expectation that the alternator will recharge them from a partially or fully discharged state is not realistic.   

These problems have been exacerbated with the introduction of ECU controlled and temperature compensating alternators.  

These alternators can be found in late model vehicles such as the Toyota Prado with the D4D engine. They reduce the alternator output voltage to approximately 13.5 volts when the temperature under the bonnet reaches its predetermined level.  

So the charging of dual or auxiliary batteries regardless of where they are located has now become more difficult.   

New battery types (gel, AGM or calcium) also play their part in the ever-increasing challenge for the vehicle’s alternator to fully charge dual or auxiliary batteries.  

Redarc Electronics has successfully provided a solution to this problem with the release of the BCDC1220, a Smart Start microprocessor controlled, in-vehicle, DC/DC 20 amp 12 volt battery charging system.   

The BCDC1220 vehicle battery charger with its in-built smart battery isolator will recharge and maintain the dual/auxiliary batteries to 100% by using one of its three charging algorithms (selectable on installation).   

The BCDC1220 includes special charging programs for gel/AGM, standard lead acid as well as the popular calcium type batteries and is designed to step up the voltages to the required levels (from as little as a 9-volt DC input).  

The BCDC1220 simply waits for the vehicle to start sensing the charge from the alternator and will then commence the charging of the dual/auxiliary battery.  

The first smart charging process is the ‘Boost’ stage. The BCDC1220 will then seamlessly switch to its second stage ‘Absorption’. Once the battery has reached a fully charged state the BCDC1220 will maintain the dual or auxiliary battery at 100% with its third stage ‘Float’.  

The BCDC1220 was fully designed and manufactured in Australia by Redarc to overcome all the problems associated with the charging of dual or auxiliary battery systems including:

  • Alternator charging systems
  • Paralleled dissimilar battery types
  • Voltage drop over long cable runs
  • Over-current battery intake
  • 24 volt DC vehicles charging 12 volt DC batteries


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