Power Gen

Generator Testing Locations-Use Extreme Caution!!
Generator Testing Locations-Use Extreme Caution!!

Troubleshooting Generators, A Three Part Series

Part 1-SER Generators

(Note:See more articles on the PMG and MAC generators below this piece. Click on photos and drawings to enlarge or print.)

We handle three main types of AC electrical power generators at MER that cover any fishing application, including motor starting for marine refrigeration systems. We are finding that our new LED marine lights require only one eighth the power of conventional sodium ar quartz lights. If you use lights for night fishing, our LEDs will put more light in the water and require less power doing it. 

We are also seeing a change in the power generation market as many decide to take their homes and businesses off-grid, and not only generate their own electrical power, but also take advantage of heat recovery options.

Our plan is to help you identify the machine on your boat and then get you lined up to go as far as checking the various parts of the system with a multimeter.

Successfully working through these few easy checks and a cell phone call are all it takes to keep your fishing operation up and running.

Review: In vol. 6 of the MER Newsletter we dissected the Anatomy of a Generator and compared power and efficiency in these 3 types: Synchronous Exciter-Regulated (SER) Generators—very good at minimizing voltage fluctuations, often used on commercial fish boats for AC (Alternating Current) hotel power. SERs have a component that no MAC style generator has—an automatic voltage regulator (AVR).

Just like new cars, you can order generators with a range of increasing voltage control with optional regulators.

MAC Generators—a transformer controlled machine that excels in applications where large electric motor-starting is a higher priority than weight or ultra-precise voltage control. Per unit of electrical power, these machines are heavier & more costly than more closely regulated sets. Commercial fish boats use MACs for motor starting such as in refrigeration systems, large electro-hydraulics, and pump loads.

Permanent Magnet-Excited Generators—offer the best capabilities of both MACs and SERs, often used on vessels with large motor-starting loads and finicky electronics in the wheelhouse.

SER Generator Troubleshooting–For slightly low or high frequency just reset the engine speed until the cycles are at 60 Hertz for engines with electronic governors, 61.5 for mechanical governors.

Likewise, if slightly low voltage is the problem, locate the AVR and increase voltage as needed with the small voltage adjusting screw. The AVR controls voltage by increasing or decreasing the strength of the exciter’s magnetic field.

When all is well the minimum voltage to the exciter windings (no load) is close to 6.7 volts, increasing to 21 volts under load. Regulators, though, are capable of a 63-volt maximum for starting heavy loads. Brownouts and engine-speed variations can be a result of starting very high loads, & for this reason you may need to use the strategy of manually starting the largest loads first before adding the smaller loads. If, however, brownouts or engine speed surges continue, it’s time to suspect dirty air & dirty fuel filters or air in the fuel.

Track down air in the fuel by installing a transparent sight glass downstream of the engine’s fuel transfer pump. After you get the engine fuel system bled of air and warmed up, put a load on the engine and watch for steady air bubbles in the sight glass. Just one bubble of air means there is 5% air in the fuel—5% is a substantial power loss and will cause brownouts and low power. Beginning with the engine, check and reseal every connection between the engine and the fuel supply.

The Visual Check–Now do a visual check of the generator looking for burned wires or components.

Run your fingers along the wiring, prodding & pulling gently to find anything loose or or disconnected. Check continuity of both the sensing & control circuits for the AVR. Take notice how the unit smells—a burnt smell most likely indicates burned wiring or insulation.

Check the appearance of the voltage regulator (1, Fig. 2) followed by the regulator fuse (1a)–the only fuse most generators have. In older units the fuse is often inside the cabinet on top of the generator, newer units include the fuse on the AVR. Note that the fuse holder can also cause trouble if one of the internal contacts is burned or broken. Use your multimeter to verify continuity through the fuse and fuse holder.

Beginning The Electrical Testing–This part of the procedure will show us one of three conditions: Low voltage, No voltage, or, finally, we’ll test for the presence of Residual voltage.

Visualizing SER Generator Internals

Visualizing SER Generator Internals

Note: Like a magnetized screwdriver tip, generators depend on their iron content to hold magnetism. A generator’s residual magnetism creates residual voltage when the generator rotor spins, even if the regulator is not doing its part to increase the magnetism of the rotating member.

Carefully!! start the generator & check the voltage line-to-line (Fig.1). In most fishing boats it’s 208 V. Your system could be 240 or 480; you may want to verify. If voltage is low, proceed to check AVR function. For a generator configured at 208 volts, if the actual generator voltage is only 50-60 volts line-to-line (L) or 25-30 volts line-to-neutral (N), you are seeing residual voltage. What this means is the voltage regulator, fuse, or wires to & from are faulty.

By checking voltage line-to-line & line-to-neutral, your voltages should be equal if the stator assembly and its individual coils (L1, L2, L3) are O.K. Therefore, replacing the AVR should set the system right.

However, if there is no voltage, it usually means severe damage, such as stator wires (4, Fig. 2) burned open. Check stator windings by disconnecting the 12 leads, 2 for each of the 6 coils around the barrel of the generator housing.

Lastly, to check the generator windings (Lines 1, 2, 3, & Neutral), check voltage between three legs first, then from each leg to neutral. Should be 120 V line-to-neutral. If one leg has low voltage, suspect generator windings. If readings are equal, proceed to check the stator windings (2). To get a quick idea of diode function (3) note that the generator may have full voltage with no load when a diode is faulty, but the voltage on the leg with the bad diode will not reach full rated voltage under load. The diodes are located on or near the exciter rotor and the cluster of diodes make up the rectifier assembly (3).

When beginning to check a generator, before starting it perform a voltage check of the generator leads (L1, L2, L3, & N, Fig.1) to verify they are indeed electrically dead, and that the unit is safe to touch. This protects you from shore-power current or the possibility that another generator is running.

The PMG Automatic Voltage RegulatorPart 2-PMG Generator Troubleshooting

Permanent Magnet-Excited Generators offer increased motor-starting capabilities of 10-15% with the close voltage control of the regulated-style units like the SER style. Often used on vessels with large motor-starting loads and finicky electronics in the wheelhouse, PMG equipment [Fig.1, and (1) in Fig. 2] can be retrofitted on many existing generators should larger motors be installed in the boat. The PMG bolts on outside the rear bearing (2), and requires a new Automatic Voltage Regulator (AVR). Simple AVRs come with a basic generator, but more elaborate digital AVRs are available, for example, for paralleling generators.

Inside The PMG Generator

Inside The PMG Generator

For low or high frequency problems just reset the no-load engine speed until the cycles are at 60 Hertz for engines with electronic governors, 61.5 Hz for mechanical governors. Likewise, if slightly low voltage is the problem, increase voltage as needed with the small voltage-adjusting screw on the AVR (3). The AVR controls voltage by increasing or decreasing the strength of the exciter’s magnetic field. At no-load the minimum voltage to exciter windings should be close to 6.7 volts and increase to 21 volts under load–although AVRs are capable of 63 volts maximum for starting heavy loads. Check the PMG AVR for these three things:

  1. power to the AVR from the PMG must be present;

  2. power to energize the field must be present; and,

  3. the AVR’s sensing circuit must be working.

If all circuits work with correct voltages but brownouts continue, suspect either dirty air or fuel filters, or air in the fuel.

Th  The PMG can be tested as an independent generator. Disconnect the AVR power-supply leads from the AVR terminals. Run the generator at rated speed (the speed must be correct for accurate results). Check the PMG output voltage with a multimeter, set to the AC volts range.

For 60Hz generators, voltage should be approximately 200VAC.

Important Safety Note: When checking a generator, and before starting it, perform a voltage check of the generator leads (L1, L2, L3, & N) to verify they are indeed electrically dead & the unit is safe to touch. This protects you f r o m s h o r e – power current or the possibility that another generator is running and energizing the circuit.

The Visual Check–Now look for burned wires or components. Running your fingers along the wiring, prod and pull gently to find anything that’s loose or disconnected. Check continuity of the AVR’s sensing, power, and control circuits–a burnt smell likely means burned wiring or insulation. Check the appearance of the voltage regulator (3), followed by the regulator fuse (4)–the only fuse most generators have. Older units often have the fuse inside the cabinet on top of the generator, newer ones include it on the AVR. Note that the fuse holder can also cause trouble if one of the internal contacts is burned or broken–use your multimeter to verify continuity through the fuse & fuse holder.

Beginning The Electrical Testing–This will show us 1 of 3 conditions: Low Voltage, No Voltage, or Residual Voltage. PMG generators depend on 4 If your voltage is low on one or two legs it’s probably an unbalanced load. Check the current (Amps), & on each leg you should find the leg with highest current will have lowest voltage & the leg with lowest current will have highest voltage.

PMG generators depend on their iron content to hold magnetism. All generators have some residual magnetism, which results in Residual Voltage when the generator rotor spins, even if the regulator is not doing its part to deliver voltage to the magnetic field. The PMG system, however, creates voltage to excite the field with the use of permanent magnets.

Caution: Start the generator & check voltage line-to-line (Fig.1). Most fishing boats are 208 V but your system could be 240 or 480. Be sure to check.

If low voltage is the case, proceed to check AVR function. For a generator configured at 208 V, if the actual generator voltage is only 50-60 V line-to-line (L) or 25-30 V line-to-neutral (N), you are seeing Residual Voltage–this means the voltage regulator, fuse, or wires to-&-from are faulty. Voltages line-to-line & line-to-neutral should be equal if the stator assembly and its individual coils (L1, L2, L3) are O.K. If not, replacing the AVR should set the system right. If one leg has low voltage suspect the generator stator windings (5). No Voltage usually means severe damage such as stator (5) or rotor winding burned open. Check stator windings by disconnecting the 12 leads, two for each of the six coils around the barrel of the generator housing. Check continuity on each coil, i.e., T1 to T4, T2 to T5, T3 to T6, and so on. You should have continuity on each coil but not to ground or another coil.

Diodes are located on or near the exciter rotor & the cluster of diodes make up the rectifier assembly (7). To get a quick idea of diode function (6) note that the generator may have full voltage with no load when a diode is faulty; however, the voltage will drop as load is applied–greater the load, lower the voltage dip.  If your voltage is low on one or two legs it’s probably an unbalanced load. Check the current (Amps), & on each leg you should find the leg with highest current will have lowest voltage & the leg with lowest current will have highest voltage.

Inside The MAC Generator (Coutesy of Marathon Electric)

(Courtesy of Marathon Electric)

Part 3-MAC Troubleshooting

What Makes It Tick?-How then does the MAC generator control voltage without a voltage regulator or a rheostat? An electrical engineer might say, “The MAC generator is a transformer controlled machine.” What this means to the rest of us is that a very carefully calibrated, partial amount of the current to the load is wired to run through the exciter stator windings. When operating with no load the unit’s residual magnetism creates the basic system voltage. When the load increases, however, the added current flowing to the load increases the strength of the stator’s magnetic field–it is this feature of the MAC that increases or decreases the excitation voltage to the generator’s revolving field, depending on the load.

The MAC excels in applications where large electric motor-starting is a higher priority than weight or ultra-precise voltage control. Per unit of electrical power, these machines are heavier & more costly than more closely regulated sets. For instance, commercial fishing boats use MACs for motor-starting refrigeration systems, large electro-hydraulics, & pump loads.

MAC Generator Troubleshooting–For slightly low or high frequency just reset the engine speed until cycles are at 60-61 HZ for engines with electronic governors, 61.5-62.5 HZ for mechanical governors. Likewise, if slightly low voltage is the problem check the engine speed carefully. Also check for possible problems that limit engine speed under heavier loads. This would include a partially plugged air or fuel filter, air entering the fuel, or even a poorly adjusted shutdown solenoid linkage. As with all g e n e r a t o r engines, track down the source of air in the fuel by installing a transparent sight glass downstream of the engine’s fuel-transfer pump. After you get the engine fuel system bled of air & warmed up, put a load on the engine and watch for steady air bubbles in the sight glass–the fewest bubbles means you have at least 5% air in the fuel, which will cause brownouts and low power.

Beginning with the engine, proceed to check and reseal every connection between the engine and the fuel supply. Brownouts & engine-speed variations can also be a result of starting very high loads, & you may need to manually start the largest loads first before adding the smaller loads.

Important Safety Note: When checking a generator before starting it, perform a voltage check of the generator leads (L1, L2, L3, & Neutral) to verify they are indeed electrically dead & the unit is safe to touch. This protects you from shore-power current or the possibility that another generator is running.

The Visual Check–Now do a visual check of the generator looking for burned wires or components. Notice how the unit smells–a burnt plastic smell most likely indicates burned wiring or insulation. Run your fingers along the wiring, prodding and pulling gently to find anything loose or disconnected.

Note: Of course no water must ever enter the air intake of a generator. But smaller MACs are constructed so that any water that does splash into the generator’s air intake can become trapped–resulting in severe corrosion of the conductors connecting to the exciter stator!

Beginning The Electrical Testing–This shows us 1 of 3 conditions: Correct voltage, Low voltage, or No voltage. First verify the unit’s voltage. Guesswork at this point is not to your advantage! Start the generator & check voltage line-to-line; in most fishing boats it’s 208 V but your system could also be 240 or 480.

Low Voltage: If voltage is normal with no load but low under load, proceed to check the diodes by disconnecting them and doing a continuity check on each one. A good diode will allow continuity in only one direction. Note: The MAC has 6 diodes on the rectifier assembly–3 classified as forward (also called normal), and 3 classified as reverse. The difference is that they allow flow in opposite directions to each other. For a generator configured at 208 V, if the actual generator voltage is only 50-60 V line-to-line or 25-30 V line-to-neutral, you are seeing residual voltage and the exciter is not working, probably due to faulty wiring or diodes.

By checking voltage line-to-line and line-to- neutral, your voltages will be equal if the stator assembly and its individual coils (L1, L2, & L3) are O.K.

No Voltage: A generator’s residual magnetism creates residual voltage when the generator rotor spins. If there’s no voltage at all the unit may have lost its residual magnetism over time, either from proximity to another source of magnetism or even from dropping during shipment. When there is no voltage, flash the unit to see if this restores residual magnetism (and residual voltage).

Flashing uses outside current to restore residual magnetism so make sure the generator’s off or at rest. Prepare two 14-gauge wires, one with an in-line 30-amp fuse to protect the circuit.

Voltage used to flash the circuit may be 20 V either AC or DC. Flash any two generator leads using a quick glancing movement to temporarily touch the leads, then run and check the unit. If flashing the unit does not restore the voltage it usually means severe damage such as stator wires burned open.

Check the stator windings by disconnecting the 12 leads, 2 for each of the 6 coils around the barrel of the generator housing. Check continuity of the 12 leads for the 6 generator stator coils & that there is no continuity between the coils & the frame of the machine (ground). If one leg has low voltage, suspect the generator windings.

Finally, monitor the temperature of the generator’s rear housing that contains the bearing. If the rear plate seems to warm up before the rest of the generator housing, follow up by replacing the bearing. More troubleshooting resources: http://www.marathonelectric.com/generators/index.

This article continues our troubleshooting series with the Permanent Magnet Generator (PMG), much of our troubleshooting is very similar to that of the Stamford Series 3 or Marathon Magnaplus (SER) generator. Hang onto this for the day you have to confront your generator and need a little help making heads or tails of it.

 

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