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Toyota Alternators

Page history last edited by wilbo666 6 months ago


 

Introduction

This page provides information in regards to Toyota alternators basic operation and wiring.

 

This page will focus on the Toyota alternator with inbuilt regulator, however some information maybe valid for generic alternators.

 

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Alternator Function

The function of the alternator is to supply electrical energy to support the electrical loads in the vehicle's electrical system.  These loads include the electronic fuel injection system, radio, lights, defogger and more.  As a number of these loads are critical (i.e. fuel injection system) it is important that the system functions well.

 

It is worth noting that under normal operating conditions the alternator is responsible for supplying all of the electrical energy required for the vehicle systems, the battery is only used to help in filtering out voltage spikes and supplying small amounts of extra current during short duration events such as when heavy electrical loads are turned on (e.g electric engine cooling fans turning on).

 

Of course the alternator is also responsible for charging the battery after the engine has been started, to replace the electrical energy that is used to start the engine.

 

Alternator Operation

In general terms the alternator is driven by the engine to turn mechanical energy into electrical energy.  I won't explore the details in regards to how the alternator generates electrical energy from mechanical energy in this article, however I will briefly explore how and why the output of the alternator is regulated.

 

As the alternator is required to (ideally) output a fixed voltage regardless of the electrical load (current) of the vehicle system and the engine RPM it makes sense that there needs to be a system that controls the alternator to ensure that the alternator voltage output remains stable and consistent across the wide range of operating conditions that are likely to be experienced. 

 

The alternator 'regulator' is the component that is  responsible for controlling the alternator to achieve the desired operation.

 

Alternator with Inbuilt Regulator

This section will discuss the Toyota alternator with inbuilt regulator and the wiring associated with the alternator and regulator.

 

Since the early 1980's (~1983) Toyota have used an alternator with an inbuilt regulator, prior to this the regulator was a module that was mounted external to the alternator.  As mentioned previously this page will focus on the alternator with inbuilt regulator.

 

Alternator with Inbuilt Regulator Pinouts

There are a number of different pinouts for Toyota alternators with inbuilt regulators. 

 

The following pinouts are viewed looking at the open end of the female pins, or another way to look at is is that the wires connected to the female plugs pictured would exit the rear of your computer screen.

 

 

Alternator Regulator 'S' Terminal

The alternator regulator 'S' terminal is used to 'Sense' the battery voltage at the battery, hence the abbreviation 'S'.

 

Symbol Definition Input/Output What Why How
S Battery Voltage Sense
Input This pin is used to sense the voltage at the battery
The voltage at the battery is the main parameter that the regulator uses to control / regulate the alternator output.
This pin is connected to the positive terminal of the battery at all times, in most wiring arrangements via a 7.5A fuse marked ALT-S (Alternator Sense).

 

Importance of 'S' Terminal

The 'S' input is a very important input to the regulator as it serves as the basis for the control of the alternator output.  In normal operation the alternator regulator will try and keep the positive terminal of the battery at ~14.5V.  It is this voltage that is measured by the 'S' input of the alternator.

 

To understand why the 'S' pin is important and why the alternator regulator doesn't simply just measure the voltage that the output terminal of the alternator it is worthwhile to spend some time to think of the current flow and voltages in the charging system when it is under load.  There is a very good reason that an extra wire all the way back to the positive terminal of the battery should be installed, and this make sense as Toyota were unlikely to add an extra wire (and hence extra) cost unless it was needed!

 

So onto the reason...when the alternator is generating a large amount of current for the electrical system the voltage at the power terminal of the alternator is higher than that at the positive terminal of the battery.  The reason for this difference in voltage is due to the 'voltage drop' across the main power cable that connects the output of the alternator to the positive terminal of the battery. 

 

As the main power cable connecting the alternator and the positive terminal of the battery has a small amount of electrical resistance a voltage drop that is proportional to the current and the resistance of the cable is generated according to Ohms law that says the Voltage is equal to the Current times the Resistance, or V=IR (where V=Voltage [Volt], I=Current [Amps], R=Resistance[Ω]). 

 

We can use some numbers to make this concept into something that will hopefully make a bit more real world sense.

     Say the alternator is outputting 50A of current

     Say the resistance of the power cable connecting the alternator to the positive terminal of the battery is 0.01Ω

 

Using Ohms Law, V=IR, we can calculate the voltage drop across the power cable connecting the alternator to the positive terminal of the battery.

     V = I*R

     V = 50A * 0.01Ω

     V = 0.5 Volts

 

As we said before most alternators will try and keep the voltage at somewhere close to 14.5V at the positive terminal of the battery, so using this example if we want to have 14.5V at the positive terminal of the battery we need to have 15V (14.5V + 0.5V) at the alternator output.  We need to have a higher voltage at the alternator output as we will have an 0.5 Volt voltage drop across the main power cable that connects the alternator output to the positive terminal of the battery.

 

If the regulator was to get its sense voltage from the output terminal of the alternator we would only end up with 14V at the battery when in fact we wanted 14.5V, if the resistance of the cable that connects the alternator output to the positive terminal of the battery is high, or the current being drawn is very high you can see that this can start to present an issue!

 

The solution to this issue is the 'S' wire that connects directly to the positive terminal of the battery and hence allows the alternator regulator to measure the true voltage at the positive terminal of the battery.  It is worth noting that the 'S' terminal on the voltage regulator has a very high resistance so there is very little current flow and hence a very small V=IR voltage drop across this 'S' sense wire.

 

The below image summarize the above.

 

 

Alternator Regulator 'L' Terminal

The alternator 'L' terminal is used to turn the alternator charge warning light located in the dash on when the regulator has detected that the alternator is not charging.

 

Symbol Definition Input/Output What Why How
L Alternator Charge Warning Light
Output This pin is used to turn the alternator charge warning light ON / OFF
If the alternator regulator detects that the alternator has failed it can indicate this to the driver so action can be taken.
This pin is Grounded by the regulator as required to turn the alternator charge warning light ON.  The alternator charge warning light should be wired with one side of the light connected to battery voltage (Ignition Switched) and one side of the light connected to this regulator pin.  Light ON = Error Condition, light OFF = Normal.

 

 

Alternator Regulator 'IG' Terminal

The alternator 'IG' terminal is used to turn the alternator on when the engine is on.  If the regulator didn't have a signal to turn on / off it would drain the battery.

 

Symbol Definition Input/Output What Why How
IG Ignition Switch Input This pin is used to determine if the ignition is ON. The alternator regulator is turned on by this signal. This pin is connected to battery voltage when the ignition switch is in RUN and CRANK positions.

 

 

Alternator with Inbuilt Regulator General Wiring

The below wiring diagram taken from the JZA80 TSRM shows the general wiring arrangement for alternators with inbuilt regulators.

 

 

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