The purpose of this test is to evaluate a Ford-type alternator command signal, feedback signal, and the output current under no load and loaded conditions.
Connection for diagnostic work will vary dependent on application.
Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.
General connection advice
PicoScope offers a range of options within the test kits.
Dependent on difficulty of access, choose from:
Testing sensors and actuators (to include relevant circuit/connectors):
Repeat the test from step 5 but with as many electrical consumers as possible switched on and engine speed around 2000 to 3000 rpm to increase alternator load.
These known good waveforms have the following characteristics:
At low loads the alternator output current (channel A) is approximately 14 A. With additional electrical loads, such as those from the heated screen, main beam headlights, and heater blower, the output current increases to 70 A.
The alternator feedback signal (channel B) is a pulse-width-modulated voltage waveform dependent on the alternator current output: with a low load, the waveform is around 0 V for approximately 60% of its cycle duration; at high loads it is around 12 V for approximately 100% of its cycle duration.
The alternator command signal from the ECM (channel C) is a positive-switched pulse-width-modulated voltage waveform. With no load, it remains off, at 0 V. With moderate electrical loads, it is around 13 V for approximately 63% of its cycle duration.
The function of a smart alternator is to provide the energy required to power the vehicle’s on-board electrical systems and to replace the charge consumed during cranking and start-up of the engine. This system also balances the needs of the driver, the requirement for maximum torque on hard acceleration or less engine drag during normal operation, for better fuel economy.
The system will also closely manage the battery needs, for example providing the ability to produce a higher charging rate at cold ambient temperatures.
Very nearly all vehicle manufacturers now use smart charging systems but Ford were the first to add the feature to mass market vehicles.
The alternator works at maximum capacity only when absolutely necessary and the battery is kept in a constant and healthy state of charge.
Battery temperature is estimated from the intake air temperature sensor, which is a good indication of the temperature under the hood.
as the ECM is able to better monitor electrical loads and battery temperature, the alternator output can be increased to 18 V in the right conditions. Therefore, it is essential that only silver calcium batteries are used in these systems.
Conventional lead-acid batteries are not suitable.
If the smart alternator controller detects a system fault, the smart charging functionality will be disabled. DTCs set and the engine management and battery warning lights illuminated. Provided the fault is not within the alternator, it will still function conventionally with its output regulated to 14.75 V.
Smart charge systems can be highly intolerant to any alternator that is not manufactured to the original specifications.
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.
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