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3 Pole Regulators and How Regulators Operate

In this article, if you have any questions regarding the meaning of the terminology of items in the section please refer to previous sections as they provide the background for this one.

This article will deal specifically with 3 pole regulators.  This is the regulator that is used on the long frame generators, usually on the horizontal shaft engines.  There are three units that control the charging.  On the left are the Cut-out contacts. They connect and disconnect the armature from the battery.  When the generator output voltage reaches 11.8 or more, the contacts are pulled together.  When they pull together, the armature A terminal is connected through the heavy wires [bold black] through the heavy black wires on the current limit [center] section.  Note the cutout section has a fine winding also.  This winding is connected to ground [also called shunt connected] and provides the magnetic energy to pull the contacts together.  In the real regulator, the contacts have a specific air gap and there is a spring pulling the contacts open.  The spring tension is adjusted to allow the contacts to come together from 11.8 to 13 volts.  The heavy winding around the outside provides additional pull on the contacts when current is flowing to the battery to prevent arcing when the voltage out of the armature is very close to pull in voltage.  At the point when the voltage at the armature is less than the battery voltage current starts to flow from the battery to the armature.  This reverse flow of current reverses the polarity of the magnetic field produced by the heavy current winding. This magnetic field opposes the field created by the small wire shunt winding. This cancellation of magnetic fields provides a clean release of the contacts.

Remember that on these starter generators the output is controlled by grounding the field terminal and are known as an [A] circuit type.  Higher output automotive generators may need voltage applied to the field to energize the field.  These are known as [B] circuit generators. The voltage regulators are built different. Instead of controlling the ground they have the control contacts arranged to put voltage on the field terminals.  If you are using this information to work on a farm tractor or automotive application be sure to determine the type of generator you have, as they are NOT interchangeable

The center pole is the current regulator.  This section regulates the maximum current the generator is allowed to put out so it does not destroy itself.  It has a pair of contacts that are normally closed [NC]. When the generator voltage starts to flow through the cut-out section all of the current flows through the heavy winding in this coil. Since this is a series winding, the more current the stronger the magnetic field and the greater pull on the contact arm.  When the current exceeds a predetermined level, [10 amps normally on the long frame starter generators] the spring tension on the contacts allows the contacts to break.  Note that the current section contacts are in series with the voltage section contacts and the two provide the ground path for the field winding of the generator. When this contact opens it removes the hard ground on the generator field [F] terminal. Note: There is a resistor connected to the [F] and ground. This provides a reduced current ground path for the field winding in the generator. This reduces the output of the generator. When the generator output drops the spring pulls the current contacts back together and bypasses the resistor to ground. The generator is again running full output.  If the current exceeds the set level the contacts again break and the cycle repeats.  If the load is too high the contacts will be continuously vibrating to limit the current to the preset level. This allows the charging current to be limited to the maximum safe output of the generator preventing damage to the unit.

On the right is the third unit. The voltage control section. It consists of a pair of normally closed [NC] contacts connected in series with the current control contacts to ground and to the field [F] terminal.  Under these contacts is a coil wound of very fine wire wound around a metal pole piece, as the coils on the other two units are.  The air gap and the spring tension on these terminals are adjusted to control the voltage coming from the armature.  This is normally set from 14 to 14.5 volts.  Since this coil is connected [parallel] across the armature terminal to ground its magnetic field is created relative to the voltage applied to it. When the voltage reaches the preset level the contacts break opening the direct ground path through the current contacts and leaving the resistor across the [F] terminal to ground. The generator armature output drops the contacts snap shut and the generator is full output [also called full fielded] again.  It works exactly like the current section only it responds only to voltage output. There is commonly one more resistor that goes from the [F] terminal the armature contact of the cut-out.  I didnít include it because its purpose is to provide a damping effect when the control contacts open and reduce the arcing of the contacts. It plays no part in the "controlling" operation of the regulator.  When the unit is running the contacts are constantly vibrating.  They seldom open more than a couple of thousandths of an inch. The contacts are made of Tungsten and are designed to do this for years. Actually when you look at how long they last, it is almost unbelievable.

This is a picture of a 3 unit or 3 pole regulator.  Note that the Voltage control coil is wound of many turns of very fine wire.  The Current unit is wound with few turns of VERY large wire and the cut-out unit is wound like the voltage coil on the inside and has a very heavy series winding wound over the inner shunt winding. The heavy wires are in series and ALL of the charging current flows through them.  They create their magnetic flux from all of the current they carry and the flux is relative to the amount of current. The fine wires are shunt wound, meaning that they are across the voltage source to ground and the magnetic flux they create is proportional to the voltage across the coil. All are wound around an iron rod or pole piece. In all three, the contacts are operated by the magnetic flux pulling on the arm that the contacts are mounted on, causing the contacts to make contact or break contact. The contacts are held in their static positions by a spring on the rear of the contact arm.  Note the little tab at the back of the arms.  Below it is a tab that adjusts the spring tension for calibration.




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