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GENERATOR AND ALTERNATOR TESTING

MAGNETS

There are three basic types of magnets: natural magnets, permanent magnets, and electromagnets. The magnetic fields set up by these magnets are alike, that is, they each have a north pole and a south pole. They differ only in the way in which the magnetic field is produced and retained. Since unlike magnetic poles attract, the south pole of a permanent magnet is attracted to the north pole of a D.C. electromagnet just as it would be to the north pole of another permanent magnet.

NATURAL MAGNETS

The Earth is itself a natural magnet because it has a definite north and south magnetic pole. Some ores are also natural magnets. Since they are not strong enough or durable enough for use on small gasoline engines, natural magnets will not be discussed further.

PERMANENT MAGNETS

Permanent magnets are no more or less permanent than a lady's permanent wave. Permanent magnets are man-made and can be destroyed at any time. Hardened steel can be magnetized and will retain its magnetism for a long period if it is handled properly. Special alloy magnets now available have extremely long lives.

A screwdriver is a good example. The hardened blade of a screwdriver may become magnetized and will remain magnetized for many years. Some screwdrivers are purposely magnetized to help hold screws or to pick up objects, A screwdriver so magnetized is a permanent magnet.

Good permanent magnets are usually in the form of a bar or horseshoe. Like natural magnets, they have a definite north and south magnetic pole. A strong attraction exists between the north and south magnetic poles which causes lines of force to be set up between the poles. Study the diagrams on lines of force on the opposite page.

DESTROYING THE PERMANENT MAGNET

Magnetism in a hardened steel permanent magnet is a result of moleculer alignment. The molecules may be returned to their normal random arrangement and thus destroy the magnetism. Permanent magnets such as flywheel magnets may be destroyed by a sharp blow, for example, by dropping, heating, or by exposing them to alternating current magnetic fields such as large electric motors.

ELECTROMAGNETS

When electric current is passed through a wire, a magnetic field surrounds the wir«. The illustration at the left shows how soft iron filings will be attracted in a circular pattern to a wire carrying current. A coil of wire made up of several turns wound closely and continuously will produce a strong magnetic field.

The magnetic field produced by each turn of wire adds to the magnetic field produced by all the other turns of wire to form a single strong field around the coil. As with the natural magnet and the permanent magnet, the electromagnet will have a north and south pole. Reversing the battery terminals will reverse the current flow through the coil and wilt reverse the north and south poles.

If the coil is wound on a soft iron core, the magnetic field will become concentrated and much stronger. Most electromagnetic devices used on engines (the ignition coil, generator, and alternator) have coils of wire wound on laminated steel to improve the magnetic strength. The laminated layers of sseel are insulated from each other to prevent currents through the core which would decrease the magnetic strength and produce heat. Sometimes rust will bridge across these laminations and will seriously cut the efficiency of the electromagnet,

The strength of the magnetic field surrounding a wire is dependent on the amount of current flowing through it. The strength of the magnetic field around a coil of wire depends on:

1. The size of wire used. The larger the wire size, the easier it is for the current to flow. Thus, rriore current flow and a stronger magnet are produced.

2. The number of turns of wire. Since the magnetic field of each turn of wire adds to that of the adjacent turns, more turns of wire will produce a stronger magnet.

3. Increase of the voltage to the coil. Increasing the electrical pressure (voltage) will cause more current to flow. If the voltage is increased to the poini that the current flow exceeds the wire size, the coil will heat up causing damage to the coil.

RESIDUAL MAGNETISM

Note that in making an electromagnet a soft iron core was used. A soft iron core will act to concentrate the magnetic fields satisfactorily, but it will lose its magnetic characteristics as soon as the current stops flowing. It is usually desirable to have an electromagnet that will shut off completely when the current fHnv is stopped, for example, one used to load scrap iron. If the coil is wound on a core that has been hardened, the hardened core will retain some of the magnetic strength of the electromagnet. This remaining magnetism is referred to as residual magnetism.

If the core is sufficiently hardened, it will become a permanent magnet, that is, it will retain considerable magnetic strength after the current flow in the winding has been stopped. If not destroyed, this remaining magnetism could remain for several years.

The pole shoes of a D.C. generator retain some of the magnetic strength of the field coils around them. This makes the generator self-exciting and makes it possible for the generator to generate when it is not connected to a battery. An automotive alternator usually does not have this characteristic. It will not charge if the battery is completely dead because it relies on the battery to supply the excitation or magnetic field. If the battery is too weak to create a magnetic field in the alternator, the alternator will not charge.

THE CHARGING CIRCUIT

The purpose of the charging circuit is to replace the charge used from the battery while the engine is not running and to supply current flow to electrical units while the engine is running. The battery is an electrical storage unit that supplies current when the engine is not running or if the load becomes greater than the generator output.

The GENERATOR is a device that changes mechanical energy (rotary motion) into electrical energy. The generator may be either a D.C. generator or an A.C. generator (alternator) which uses diodes to change the A.C. to D.C. if a battery is in the circuit. Some lawn and garden tractors and motorcycles operate the headlights directly front the A.C. output of an alternator. In this case the engine must be running before the lights will operate. D.C. generators and alternators will bf- discussed in detail in the following pages,

The REGULATOR UNIT may consist of a voltage regulator coil, current regulator coil, and a cutout relay, depending on the design of the unit.

The VOLTAGE REGULATOR COIL limits the voltage output of the generator. The generator must be capable of charging at less than maximum engine rpm. If the generator can create from 13 to 14 volts at 2,000 rpm, the voltage could be excessive when the engine is operated at 3,000 rpm or higher. Some charging systems require a voltage regulating unit.

The CURRENT REGULATING COIL limits the amount of current flow that the generator is allowed to produce. When the battery is quite low and/or the accessory load is heavy, the D.C. generator will try to supply more current than it was designed to produce. This would result in overheating and burning out of the generator and wiring. Some charging systems have a current regulating coil in the regulator unit or some current limiting device in the circuit. The A.C. system is self-current regulating and does not need & current regulating coil in the regulator.

The CUTOUT RELAY is necessary on D.C. generators to prevent the battery charge from discharging back to the generator when the generator is not charging. It disconnects the battery from the charging system when the charging system is not charging.

An AMMETER may be placed in the wire connecting the charging circuit to the battery. Since an ammeter measures the amount or current flow, the current must be made to flow through the meter. Note in the diagram on the opposite page how the ammeter is connected in the circuit so that current flow is through the meter. The meter shown in a ZERO CENTER type.

The meter will read the D.C. current flow in either direction. If the current flow is charging the battery, the meter will indicate the current on the charge side of zero; if the battery is being discharged, the ammeter will show the rate of discharge. Normally, the ammeter will not show the starter current draw.

CREATING CURRENT FLOW

Current flow was induced in the primary winding of the ignition coil by a moving magnet. The same principle is utilized in the charging system whether it is the D.C. or A.C. type. As you recall, moving a magnet rapidly past a conductor will induce current flow in the upper illustration on the opposite page, the magnet is moved rapidly past the conductor and the current flow will be indicated on the ammeter.

If the magnet is moved back past the conductor in the opposite direction, the current will flow back the other way as indicated by the direction of deflection of the ammeter.

Moving a south pole past the wire will create current flow in one direction. Moving a north pole past the wire will cause current How in the opposite direction.

PRODUCING ALTERNATING CURRENT

If the magnet were attached to a shaft and rotated, current flow would be induced in the wire first in one direction when the north pole moves past and would be induced in the other direction as the south pole movos past. This back and forth movement of current would cause the ammeter to deflect both directions from the center zero point.

If the magnet is turned fast, the meter would not be able to deflect fast enough and would not accurately read the amount of current flow. Damage to the meter could result. This continuous back and forth movement of current is called ALTERNATING CURRENT (A.C.). The current produced by a battery that is always flowing the same direction is called DIRECT CURRENT (D.C.).

PRODUCING A STRONGER CURRENT

The current produced by moving the magnet past one wire would be very small. Increasing the wire area being passed by the magnet will increase the current flow. If the wire is wrapped into a coil, the current will be induced in each turn of the coil. The current induced in each turn of the wire adds to the current of all the turns producing a strong current flow. Winding the coil of wire on a laminated iron core will help the passing magnet set up the magnetic lines of force through the winding which will increase the current flow in the winding.

Typical small gas engine alternators use a series of coils (stator winding) mounted on a laminated ring (stator) under the flywheel using the flywheel magnet to induce the current flow in the stator winding. The ignition coil may or may not be integrated into the same set of coils.

Keep in mind that this is alternating current at this point and is not suitable for charging the battery because the current flow is equal in each direction and no charging of the battery would occur.

DIODES

A diode is a one-way electrical check valve. It permits the electrical current to flow easily in one direction, but it stops the current flow in the other direction. Just as a check valve will permit water to flow in one direction and will block flow in the opposite direction, a diode performs this function in an electrical circuit

One use for the diode as seen in the electronic ignition system is to allow current to flow freely from the charging coil to the capacitor, charging the capacitor. The diode prevents the current from flowing back through the coil trapping the charge on the capacitor. This is a typical use for a diode.

The diode might also be compared to an electrical switch that is quickly closed so that the current can flow in one direction, but it is quickly opened to prevent current flow in the opposite direction.

Diodes are available in a number of shapes and sizes, depending on the job they are performing. Diodes are rated by current capacity and maximum voltage.

The CURRENT rating is the maximum amperes the diode can pass in the forward direction. Current flow in excess of this amount will blow the diode.

The VOLTAGE rating determines the maximum voltage that can be applied to the diode in the reverse direction when no current is flowing without forcing its way across or bridging the diode. Remember that voltage is electrical pressure and that high voltage is capable of jumping distance. High-voltage diodes are very different from those used in Iqw-yoltage circuits. High-voltage diodes usually look like illustration B oh the opposite page.

A HEAT SINK is necessary for high-current diodes such as shown in illustrations A and D on the opposite page. The type shown in A is used on larger alternators. It is pressed into the alternator frame or isolated heat sink. The type shown in D is bolted to a heat conducting surface, in both cases the heat sink becomes part of the circuit because there is only one connecting terminal on the diode.

Most diodes used with alternators on small gas engines are like C and E on the opposite page. They do not carry enough current to need a heat sink and they usually tit into a clip: connection for easy removal.

DIODE TESTING

Diodes may be tested with an ohmmeter. Connecting the lead to the diode one way should show Low resistance. Connecting the lead the other way should show high resistance. If the diode shows either high or low resistance both ways, it is defective.

The circuit showing the dry cell and light bulb connector through a diode may be used as an effective diode tester. Place the diode in the circuit both ways. The bulb should light with the diode connected one direction and should not light at all if connected the other way. If the bulb lights both ways, the diode is shorted. If the bulb will not light either way but will light when connected without the diode, the diode is open. If the light glows dimly during the reverse CONNECTION, the diode is leaking and should be replaced.

THE BASIC ALTERNATOR

Study the diagrams on the opposite page carefully. In the upper diagram we have the basic alternator, a stationary (stator) coil and a rotating magnet (rotor). Remember that as the rotor turns, the alternating north and south poles will cause current to flow back and forth in the circuit (alternating current). The light bulb does not care that this is alternating current (A.C.) because the A.C. will heat the filament and produce light just as will direct current (D.C.).

DIODE RECTIFIED OUTPUT

In the next diagram a diode has been placed in series with the circuit so that all current must flow through the diode. As one magnetic pole passes the stator winding, it will produce current flow in the circuit if the current flow is in the forward direction of the diode. As the other magnetic pole passes the stator, it will try to induce current flow in the reverse direction to which the diode acts as an open switch allowing no current flow. The circuit is shut off by the diode.

Now the bulb will be lighted by pulses of current all moving in the same direction. When the current flow is all in one direction, it is called direct current (D.C.). The bulb is now operated on pulses of D.C. In this circuit A.C. has been changed to pulsating D.C.; this is called rectifying. The diode is one type of rectifier that will change A.C. to D.C.

CHARGING THE BATTERY

When this circuit is connected to a battery, the pulses of D.C. can be used to charge the battery. Notice that the diode is placed in the circuit in reverse to battery polarity. The battery cannot discharge through the diode and coil. The diode is placed so that the current can flow in the direction that charges the battery but cannot flow in the direction that will discharge the battery.

Compare the illustration of the tire pump with the simple alternator above. When the pump pressure becomes greater than the tire pressure, the air moves through the check valve into the tire. As the pump moves back up, the air is prevented from coming back out of the tire by the check valve (enlarged). The back and forth movement of the pump is changed into a one-way movement of air by the check valve.

When the voltage in the stator becomes greater than the voltage of the battery, the current will flow, charging the battery. When the current tries to flow the other direction in the stator, which would discharge the battery, the diode acts as an open switch and prevents the current flow.

LOW CURRENT ALTERNATORS

Typical charging systems use the engine lis one side of the electrical circuit. This is called the grounded side. Compare the two circuit diagrams. On both diagrams, a complete circuit exists from the battery negative (-) terminal to the stator coil, to the diode, and to the battery positive ( + ) terminal. Using the engine as one side of the circuit eliminates some of the wiring and reduces confusion for there are fewer wires to keep straight and less danger of hooking something up backward as the engine block is always the same as the battery negative terminal.

On some older cars and tractors, the battery was reversed and the engine (entire chassis) became the same as the battery positive terminal. They were referred to as positive ground systems, it is important to check this out before removing the battery cables or attempting any tests on the circuit.

The low current alternator diagram shows two charging coils mounted under the flywheel. The flywheel magnet, or magnets, induces current flow in each of the coils as it passes. Note that each coil has one lead connected to the engine ground which in turn is connected to the battery negative terminal. The other lead from each coi! is connected through its diode to a common fuse and to the battery positive terminal.

As the flywheel magnet passes charging coil No. 1, the current flow induced one direction in the coil is passed through diode No. 1 to charge the battery. The current flow induced in the opposite direction is blocked by the diode. The magnet continues on, inducing A.C. current in coil No. 2. Diode No. 2 allows current flow to charge the battery and blocks the reverse flow,

This is an alternator typically used on lawn and garden tractors. It is simple, inexpensive, and trouble free if it is not abused.

Since charging coils are quite small, they limit the output of the system. Since the output is limited, it is not likely that the battery will become overcharged during use; thus, no vottage regulator is supplied with this system. If the engine is operated for long periods of time without restarting, the battery will be overcharged by the system.

The first symptoms of overcharging will usually be excessive water consumption by the battery. Removing one of the diodes will cut the charging system output and will prevent overcharging during extended engine operation. If the engine is used only for short periods calling for frequent starter use, an additonal battery charge may be necessary occasionally.

Since the alternator is an A.C. current device, it is self-current regulating and no current regulating device is needed as with D.C. generators. Ik. u-ise the diodes prevent the return of the battery current to the alternator when the alternator is not is use, a cutout relay is not needed.

FLYWHEEL ALTERNATOR SYSTEM TESTING

Although flywheel alternator systems vary somewhat, they are similar in operation and tend themselves to some common tests. Many of the components have been molded into modules which if found defective by simple tests must be replaced.

OUTPUT VOLTAGE TEST

Before starting the engine, connect a D.C. voltmeter that will read at least 16 volts to the battery terminals. Read the battery voltage carefully and record. Battery volts with engine stopped (should be 12.6 volts)

Crank the engine briefly. Recheck the battery volts.

Battery volts after short load (should be 12.6 volts)

Start the engine. Allow the engine to run at 3,000-3,600 rpm near wide open for one minute, CAUTION: Do not rev an unloaded engine. Read the battery voltage while the engine is still running 3,000 3.600 rpm. Battery voltage, engine running rated rpm

TEST RESULTS	PROBLEM
Battery volts before running are 12.6 volts or higher. If higher, probably the battery has recently been charged.	OK.
Battery volts are less than 12.6.	Check battery. See Battery Test section.
White the engirt is running, the battery volts are higher than before running.	Charging circuit OK.
Battery volts do not increase after engine has been run 3,600 rpm for one minute.	Possible charging circuit problem.
Battery volts during running are 15 volts or higher.	Overcharging. If it is an unregulated unit, remove one diode during extended operation.
Battery volts increase, but battery becomes discharged periodically.	Reduced output. Check diodes and perform ammeter test. Possibly the unit is being started frequently. Boost charge battery periodically.

AMMETER OUTPUT TEST

An ammeter can be used to determine the amount of charge being placed on the battery. Connect a D.C. AMMETER (available at automotive stores) in series with the charging lead. Remove the charging lead from the rectifier. Clip one lead from the ammeter to the rectifier output and the other lead to the battery charged lead. The output current will now flow through the ammeter. Bring the engine speed to 3,600 rpm and observe the ammeter reading. Look carefully. A very low output may be difficult to detect on a 30-ampere meter.

If little or no output is observed, use an automotive headlamp (GE No. 4001) as a battery load. Connect the lamp directly to the battery terminals with test leads. Again, bring the engine to 3,600 rpm and read the ammeter carefully. Failure to produce output indicates charging circuit problem. Continue the charging circuit tests.

As you have seen on the diagrams of the simple flywheel alternator, there are no friction causing, moving parts and unless abused, they usually cause no trouble. Components such as the fuse and the diodes will take very little abuse. A loose wire or terminal can make momentary opens or shorts in the circuit which could blow the fuse or diodes. A visual check of leads, plugs, terminals, and the clip-in mountings may reveal such a problem.

To check the fuse, remove it from the fuse holder and test for continuity with an ohmmeter. If an ohmmeter is not available, a small light bulb and battery can be used. A good continuity tester can be made by soldering test leads to a bulb. Placing the fuse in question in series with the bulb and battery so that the current must flow through the fuse to light the bu"> will determine if the fuse is still good (continuous). Clean the fuse and fuse holder terminals before replacing the fuse. Use emery paper or fine sandpaper if necessary to assure good contact.

Check the diodes with an ohmmeter or battery and test light as shown. In one direction, the diode should read ZERO ohms. Reverse the diode and the meter should read infinity or high resistance. If the diode is connected in series with a test lamp and battery, the lamp should light when connected one direction and should not light when reversed. If the diode symbol is printed on the diode, or if the polarity is marked, the lamp should work as shown in the bottom two illustrations.

DIODE TEST RESULTS	CAUSE
Continuity one direction. No continuity when reversed.	Good diode.
Continuity both directions.	Shorted diode. Replace.
No continuity either direction.	Open diode. Replace.
Continuity one direction. Some continuity when reversed. Low meter reading or lamp glow.	Leaking diode. Replace

•

Clean the diode contacts the same way as the fuse contacts. Check all wires and connections. When replacing covers make sure that wires are not pinched causing a short circuit.

To check the stator winding, use the ohmmeter or test lamp and battery to check continuity through the coil winding, A break in a wire or a bad connection will be detected by this test. Disconnect the alternator leads from the diodes before testing. Test each coil.

REGULATED FLYWHEEL ALTERNATOR

SCR

The unregulated flywheel alternator will do an acceptable job of charging the battery on lawn and garden equipment that is normally run for a predictable time between each start. As pointed out earlier, if an unregulated unit is operated for short periods or at low speeds, external recharging may be necessary occasionally to supplement the small output of the flywheel alternator.

If the unregulated unit is operated for long periods at high rpm, the battery will be overcharged. The REGULATED flywheel alternator overcomes these disadvantages with increased output to recharge the battery faster and a voitage regulator to prevent overcharging.

The REGULATOR COIL is added to the charging coils. One lead from the regulator coil is connected to the battery (+) plus lead of one of the A.C. coils. The other lead goes to ground through the SCR. The SCR, when electrically switched ON, allows current flow in the regulator coil. The current flow in the regulator coil sets up a magnetic field that opposes the A.C. coils reducing their output. When the SCR is not ON, there is no current flow in the regulator coil and it has no effect on the charging coils, permitting full output.

The SILICON CONTROLLED RECTIFIER (SCR) is an electronic switch that has no moving parts. When a small voltage is applied to the gate connection, the SCR is turned ON. Until voltage appears at the gate, the SCR remains OFF to current flow through the SCR from the regulator coil to ground.

A ZENER DIODE is a very sensitive electronic device that allows a small amount of current flow only when the applied voltage exceeds a certain level (breakdown voltage). Zener diodes are available in a wide range of voltages. When the voltage reaches the firing voltage of the Zener diode, the diode turns ON (fires) allowing current flow. In this circuit the Zener diode is connected to battery positive. As the battery becomes charged, the voltage begins to rise above the normal battery voltage (12.6 volts). The Zener diode is usually set to fire at about 14.5 volts. When the battery voltage reaches 14.5 volts, the Zener diode fires applying voltage to the gate of the SCR. The SCR is turned ON permitting current flow through the regulator coil which opposes the A,C. coils and thus reduces output.

The VARIABLE RESISTOR may be used to permit an adjustment in regulator output. Changing the resistor would change the firing voltage of the Zener.

The CAPACITOR is quickly charged by the current flow through the Zener diode to build up the voltage to cause the gate to fire the SCR.

The SCR, Zener diode, resistor, and capacitor are all molded in a compact MODULE and are not accessible for testing. If an overcharging or undercharging condition exists, check the battery condition (see Battery Tests), check the fuse and diodes (see Component Tests), and check physically all wires and connections. If these are not at fault, replace the regulator module or check the manufacturer's literature for specific checks.

A.C. LIGHTING CIRCUIT

Some lawn and garden tractors are equipped with a headlamp that is powered directly from A.C. charging coils. The lights are not connected to the battery in any way. Some of these systems appear on units without battery or electric start or they may be used with a flywheel alternator and electronic ignition. The A.C. lighting system is completely independent of the battery charging circuit. The charging coils are sometimes contained in the same molded module.

The A.C. lighting circuit is similar to the low output flywheel alternator except that it does not require the rectifying diodes. The lights are operated with the alternating current created in the charging coils. The brightness of the headlamp depends on engine speed. This circuit has been common on motorcycles for several years.

To test the circuit, use a 12-volt test light with lead attached as for diode testing. Operate the engine at about one-half throttle with the light switch ON and make these tests.

1. Test the switch. Connect the test lamp to the switch terminals. If the lamp lights, the switch is defective.

2. Test the bulb. Connect the test lamp to the bulb connections. If the test lamp lights, the bulb is defective.

3. Test for headlamp ground. Connect the test lamp to the headlamp ground connections and to a good engine ground. If the test lamp lights, the headlamp is not making a good ground. Inspect carefully for bad connections and rust. Clean all connections.

4. Test for stator output. Turn the light switch OFF. Connect the test lamp to the charging coil lead at the light switch. Touch the other test lamp lead to a good engine ground. If test lamp lights, the stator is producing current and the problem is one of the above. Check wiring carefully for bad connections, frayed insulation, loose connections or rust.

THE GENERATOR

Until inexpensive and dependable diodes were available, the D.C. generator was used to create current flow for accessories and for recharging the battery. The generator is somewhat the reverse of the alternator in that it has a stationary magnetic field, referred to as the field, and a rotating coil (armature) that turns within the magnetic lines of force set up by the field windings. Instead of moving the magnet past the coil of wire, the coil of wire (armature) is turned in the magnetic field.

The FIELD is two electromagnets wound in series. When voltage is applied to the field windings, they become strong magnets creating lines of force through the space between them. When power to the field windings is shut off, the field pole shoes on which the windings are wound retain some of the magnetism (residual magnetism).

The ARMATURE consists of several turns of heavy wire that moves through the magnetic lines set up by the field magnets. The generator output current is induced in these windings. Since this is the output current, the wire in the armature must be large enough to carry the output current.

The COMMUTATOR is a number of copper segments insulated from each other and fastened to an insulated hub on the armature shaft. The armature windings are connected to the commutator segments. The output current flows through the commutator to the brushes.

The BRUSHES are stationary and ride against the commutator providing a path for the output current. The brushes are fixed in their relationship to the field coils so that the brushes are always connected to the armature winding that has the maximum current flow.

The RECTIFYING action of the commutator and brushes keeps the current flow going in the same direction in the brushes at all times. The output of the generator is D.C. The armature passes both a north pole and a south pole as it makes one revolution; thus A.C. current is produced in the winding.

Study the diagram. Note that the side of the winding passing a magnetic pole is always connected to the same brush. The direction of current flow induced in that winding will always be the direction of current flow in that brush. The action of the commutator and brushes changes A.C. to D.C.

THE GENERATOR CHARGING CIRCUIT

Tlie strength of the magnetic field created by the field windings determines the amount of current that will be induced in the armature windings at any speed. Turning the generator faster also increases output. In order to produce a strong magnetic field, the field windings must be connected to the battery.

Trace the field winding circuit. One wire from the windings goes to the generator "F" terminal which is connected to the "F" terminal on the regulator unit. Inside the regulator unit the circuit passes through two sets of contacts to the engine ground. These contacts are spring held in the closed position so that the field is now connected to the battery negative terminal through the engine ground.

The other winding lead is connected to the positive brush which in turn is connected to the generator "A" terminal. The generator "A" terminal is connected to the "ARM" terminal of the regulator unit where it is connected through the cutout relay to the battery positive terminal. Note that the cutout relay prevents the current from flowing through the field windings while the engine is not running.

1. If the cutout relay is open, the entire generator is disconnected from battery positive.

2. If either the current regulator contact points or the voltage regulator contact points open, the Held windings will be disconnected from battery negative. Opening either of these contacts would turn the field OFF which would reduce the output of the generator.

The voltage regulator coil is cor.,iected to the generator output. The coil is magnetized by the generator output. When the output voltage becomes excessive, it pulls the contacts open and cuts down the field strength. Thus the generator output is reduced and the battery is protected from overcharge.

Output current passes through the current regulator coil. If the current flow becomes excessive, the contacts will be pulled open. Again, the field will be turned off and the generator output will be reduced, thus protecting the generator from overheating or burning out.

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The cutout relay is held open by the spring and is normally open when the engine is OFF. The shunt winding of the cutout relay is connected to sense generator voltage. When the generator voltage is equal to the battery voltage (12.6), the cutout relay contacts are pulled closed by the shunt winding to connect the generator annature to the battery. Generator output current flow through the series winding adds to the magnetic pull of the shunt winding to help hold the cutout relay contacts closed.

When the engine is stopped and generator voltage drops below the battery voltage, the current will momentarily flow backwards from the battery to the armature. This reverse flow through the series winding will create a magnetic field which will oppose the magnetic field of the shunt winding. This will open the cutout relay so that the battery will not continue to discharge through the armature winding while the engine is not running.

GENERATOR CIRCUIT VARIATIONS

Although the end result is the same, some manufacturers connect the field to the positive brush and go to ground through the regulator. This circuit is referred to as the EXTERNAL GROUND or TYPE "A" circuit. Note that the field windings are not connected to battery positive and negative. Either the voltage regulator contacts or the current regulator contacts can disconnect the field winding from ground.

Some manufacturers connect the field to the grounded brush and connect the field to positive in the regulator. This circuit has an INTERNAL GROUND for the field and is a type "B" circuit. The regulator controls the field on the positive side of the circuit.

Whether the generator has a type "A" or type "B" circuit must be determined before tests are made. If a label on the generator or regulator does not specify this, consult the owner's manual or if the manual is not available, remove the generator end frame and determine whether a wire from the field windings is connected to the positive or grounded brush.

Some equipment manufacturers connect the batteries' POSITIVE terminal to the engine ground instead of to the negative tenninal. Be sure to check this before removing the battery or making any tests on the charging circuit.

POLARIZING

Whenever leads have been disconnected from a generator for any reason, the generator should be polarized. This means briefly running the current flow through the field windings to make sure that the pole shoes are correctly magnetized. Reversed polarity may result in arcing and burning of the regulator contacts. On a type "A" circuit momentarily connect a jumper wire from the "'B" or battery terminal of the regulator unit to the "A" or armature terminal. A quick touch is all that is needed. A small spark may be visible.

On a type "B" circuit it is necessary to remove the "F" or field wire from the regulator terminal and momentarily touch it to the "B" or battery terminal.

Polarise the generator after the leads are reconnected and before the engine is started. Do not attempt to polarize alternators.

THE GENERATOR AND ALTERNATOR COMPARED

	GENERATOR CIRCUIT	ALTERNATOR CIRCUIT
Output	From the turning armature through the commutator and b rustles. Limited by the amount of current the brushes can carry. Brushes must be replaced periodically.	From nonmoving statoi windings. No limit to wire size or amount of current the statur could produce. Output travels through solid-state diodes. No moving par" in the output circuit.
Field	Two coils wound in series on pole shoes which retain residual magnetism. Tire generator can charge a dead battery.	On flywheel alternator systems a permanent magnet or magnets embedded in the flywheel. Liiv?Sed output because of limited magnetic field. On externally mounted alternators the rotor is an electromagnet powered by the battery.
Voltage regulation	Must have a voltage regulator.	On low output units, not needed because of limited output. Output can be reduced manually if overcharging occurs. Larger models need voltage regulation to prevent overcharging. Usually in solid-state module.
Current regulation	Must have current regulator to prevent generator overheating or burning out.	Self-regulating.
Cutout	Must have cutout relay to prevent battery from discharging through field when engine not running.	Diodes prevent return flow of current.
Dependability	Commutator must be turned occasionally. Brushes must be replaced occasionally. Contacts in the regulator burn out, Bearings fail.	Diodes are damaged by misuse. Flywheel magnets destroyed by misuse. On extern-ilty mounted types bearings may fail.
Polarity	May be type "A" or type "B" field circuit. May be negative ground or positive ground.	Flywheel alternator has no field circuit. Always negative ground.

BASIC GENERATOR TESTS

Without going into a great deal of detail, basic generator tests can be made that will usually determine whether it is the generator or regulator unit that is defective.

POSITIVE OR NEGATIVE GROUND

Determine the ground polarity of the unit by checking the battery ground cable. On some equipment the positive battery post is connected to ground; on others the battery negative is connected to ground. If the battery has been removed, look for decals on the equipment which might tell ground polarity. If there are no decals, the manufacturer's manual should be consulted.

Ground polarity_____________

INTERNALLY OR EXTERNALLY GROUNDED FIELD Look for a decal on the generator or regulator which might give this information or consult the owner's manual or service manual if one is available. If these are not available, the type ground can be determined by removing the end from the generator and by checking the field wire connection.

Type ground circuit _____________

BYPASS THE REGULATOR

Adjust the engine speed to a fast idle. DO NOT accelerate the engine during these tests! Connect a jumper wire from the field terminal to a good engine ground if the generator has an externally grounded field. This eliminates the regulator from the circuit. If the generator is good, it should charge now. Internally grounded generators are bypassed by connecting the jumper to the positive battery terminal and to the field terminal.

If the equipment being tested does not have an ammeter, either a voltmeter or ammeter may be connected as shown at left to determine if the generator is charging. Connect the voltmeter to the generator output terminal and engine ground. Observe polarity when connecting voltmeter. If the generator is charging, the voltage will rise when the engine is speeded up from slow idle to fast idle.

If an ammeter is used, remove the cable from the regulator's BATTERY terminal and connect the ammeter between the regulator terminal and the cable that just has been disconnected so that the current will flow through the ammeter.

TEST RESULTS

If a charge is indicated when the jumper wire is connected at fast idle, the generator is good and the problem is the regulator unit or wiring. Check the wiring for bad connections.

No charge at fast idle with the jumper connected indicates that the generator will not charge and must be repaired or replaced.

Adapted from:

SMALL GAS ENGINES

James A. Gray and Richard W. Barrow

School of Technology Indiana State Univetsitv

Prentice-Hall, Inc., Englewood Cliffs, New Jersey

Drawings by Robert F. MacFarlane

Retrieved from the CD3WD project.
Rebuilt and re-compiled to be useable by Autonopedia

Autonopedia