Lucas Regulator

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Page created by T June 30th 2011:

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Regulator for a Lucas 12 Volt 30 Amp Generator on an EH Holden. Click to Enlargen. Photo by Daves59.

==Lucas Regulator:==

===Operation:===Because the Engine's RPM and the Car's Electrical Load can change continuously, an automatic system of maintaining the Generator's Output Voltage is used. Early Car's left this to the Driver with a Lever that controlled the 3rd Brush. The 3rd Brush required the Driver to adjust the Generator's Output Voltage by moving the Lever. 12 Volt Lucas Generators do not have a Driver controlled 3rd Brush.

A Generator's Output Voltage increases proportionately to Engine RPM and reduces with the increase in Load. To automate all this, some means of making the Generator maintain a constant Output Voltage is need.

Lucas 12 Volt 30 Amp Generator on an EH Holden. The Earth, Field and D Terminals are shown.  Click to Enlargen. Photo by Daves59.

===Internal Devices:=== The 12 Volt Lucas Regulator contains 3 Relays.

1. Voltage Regulator Relay.

2. Current Regulator Relay.

3. Cut Out Relay.

===Voltage Regulator Relay:===This Relay performs Voltage Regulation by making or breaking the Power Connection to the Generator Field. It's Contacts remain connected until the Generator's Output Voltage reaches a Peak. The Contacts are closed when the Engine is stopped.

===Voltage Regulator Resistance:===Once the Generator's Output Voltage reaches a Peak, the Voltage Relay opens preventing Current from directly powering the Field but providing Field Current through a Resistance. Should the Output Voltage increase further, the Field Contact is connected to Earth. 

Grey 132 cu in Holden Six Cylinder Engine. The Earth Wire is missing from the Generator. Click to enlargen. Photo by ReaperHR.

===Current Regulator Relay:===This Relay allows Current to flow out the Generator +ve Terminal until the Current reaches a Peak. At that point the Relay opens the Field Circuit preventing Current from being Generated. By continuously opening and closing, this Relay limits the amount of Current flowing out of the Generator preventing the Generator from burning out. Below the Peak Current, this Relay remains closed. The purpose of this Relay is to protect the Generator from burning out due to excessive Electrical Load. The Current Regulator Relay is closed when the Engine is stopped.

===Cut Out Relay:===If the Generator's Output Votage falls below the Battery Voltage, Current tries to flow from the Battery back through the Generator to Earth. The Cut Out Relay detects the presence of any Current flowing into the Generator and opens its Contacts preventing this. Reverse Current Flow would burn out the GEnerator and flatten the Battery if the Engine was shutdown.

The Cut Out Relay's Contacts are open when the Engine is stopped.

===Compatibility:===Each Generator needs a matching Regulator. While it's possible to adapt one from another Generator, caution must be observesd in the Adjustments. Adapting a 6 Volt Regulator to a 12 Volt Generator or a 12 Volt Regulator to a 6 Volt Generator is not  advised.

===Adjustments:===Each Relay has an adjustment.

The Voltage Regulator Relay can be adjusted to increase or decrease the Generator's Output Voltage. Caution: Excessive Output Voltage will destroy the Battery.

The Current Regulator Relay can be adjusted to increase or decrease the output Current. Caution: Excessive Output Current will destroy the Generator. The Output Current should not exceed the Generator's Output Current Rating.

The Cut Out Relay can be adjusted to disconnect the Generator's Output +ve Terminal earlier or later.


1.A typical failure is caused by the Voltage Regulator Resistor burning out. This is a large Resistor or pair of Resistors mounted in the base of the Regulator. These Resistors can burn out and will need to be replaced. Recheck all the Relays and adjust as necessary before putting the Regulator back into service.

2. Loose Connections. Make sure all Electrical Connections are tight and clean and the the Regulator's Mounting Screws are tightened firmly.

3. Make sure the Earth wire is clean and secure at each End.

===Generator Failures:===Naturally the Regulator can only function properly with a working Generator. If the Generator's Brushes are worn out the Charge Light will not Glow.

If the Generator's Bearings fail the Generator will not produce Output Voltage. The Charge Light may stay on when  the Ignition Switch is on.

===Regulator Connections:===

====The B Terminal:====The B Terminal connects to the Battery +ve. This Wire must be thick enough to carry the Generator's full output Current which in this case is 30 Amps.

====The D Terminal:====The D Terminal connects to the largest Terminal on the Generator which is the Generator's Output Terminal. This Wire must be thick enough to carry the Generator's full output Current which in this case is 30 Amps.

====The F Terminal:====The F Terminal connects to the Field Terminal on the Generator and controls the amount of Voltage the Generator produces.

====The Indicator Wire :====The Indicator Wire connects to the D Terminal. Whenever the Cut Out Relay Contacts open, the Charge Light grounds through the Generator's +ve Brushes. When the same Contacts are closed, the Charge Light goes out because the Voltage becomes the same on each of its sides.

====Ground Connection:====A Ground Connection is connected between the Generator and the Regulator to provide reliable operation. This Wire keeps the Generator and Regulator at the same level of Potential. Without this Wire the Output Voltage would become excessive. 


12 Volt Generator


===Terms:=== Terms

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