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The alternator on a 2018 mitsubishi outlander along with many other vehicles has a 4 wire connector going to it. They are labelled as follows:

  • G-Ground
  • S-Sense
  • L-Lamp
  • FR-Field

Ground - is self explanatory.

Sense - is the input that the alternator is suppose to use to regulate its output voltage with.

Lamp - is suppose to allow the alternator to tell the car to turn on the red battery lamp on the dashboard when it has a problem.

Field - I do not understand what does. I'm not sure which way the communication on this wire occurs or what its purpose is?

charging system system diagram

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The functions of the four pins on the Mitsubishi Outlander alternator connector are as follows:

G - Ground

S - Voltage regulator pin that senses the battery voltage.

L - 'No charge' control signal, from the voltage regulator to the ECU, to turn on the warning light.

FR - 'Field regulation' voltage signal, from the voltage regulator to the ECU, when the alternator is charging. During engine idle, with headlights, blower etc. on and the alternator voltage not high enough to charge the battery, the dropping FR signal voltage triggers the ECU to accordingly raise engine idling speed to enable charging.

Here's a reference:

'Alternator FR Terminal System' (Credit : Mitsubishi Automotive)

Operation

The energised state of the alternator field coil is inputted from the alternator (terminal No. 4) to the engine-A/T-ECU (terminal No. 86).

Function

A signal of the power supply duty ratio for the alternator field coil is inputted to the engine-A/T-ECU.

In response to the signal, the engine-A/T-ECU detects the alternator output current and controls the idling speed according to the output current (electric load).

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So for the first 3 so far so good.

Edit: The sense wire is the battery voltage, usually controlled by the ignition switch.

The last one "Field" is the excitation signal or voltage which is controlled by the regulator or ecu on the car.

Given that most cars now have built-in regulators (there were some manufacturers later to this party than others...) and you don't show the circuit diagram then I assume that the "Field" is the ecu control to switch off the alternator during periods of high acceleration or for similar reasons. However, if the regulator is still external or controlled by the ecu then it will be the field excitation current to control the alternator output.

Edit: Yes, as explained above, the ecu can turn the alternator on and off. Whether this is a binary (on/off) signal or some value between 0V and Max V will depend on the system. If the regulator controls the alternator output, then the ecu may only need to send on/off, but the ecu could be designed to modulate the output more precisely - but then an internal regulator would not be needed.

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  • \$\begingroup\$ Hello Mike. Ive attached diagram photos to my original question. I am still unclear about if the field wire controls alternator output what is the purpose of the sense wire? Are you saying that the Field wire can use a boolean value to turn the alternator on and off? Im interested in what the waveform looks like but i don't own an oscilloscope and couldn't find an explanation online. \$\endgroup\$ Jun 23, 2022 at 2:53
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    \$\begingroup\$ So buy or borrow an oscilloscope and check out exactly how that particular system works. \$\endgroup\$
    – Solar Mike
    Jun 23, 2022 at 7:55

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