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Marathon Generator SE350 Voltage Regulator Instruction Manual

Aug. 06, 2018

INTRODUCTION of Marathon Generator SE350 Voltage Regulator

The SE350E voltage regulator is an encapsulated electronic voltage regulator which controls the output of a brushless AC generator by regulating the current into the exciter field.




Sensing (Average) & Power Input

190-240 Vac


500 VA

Output Power - Continuous

73 Vdc at 3.5 Adc (255w)

Output Power – Forcing (240 Vac Input Power)

105 Vdc at 5 Adc (525w)



Exciter Field Resistance

15 ohms minimum

Remote Voltage

±10% with 2000 ohm rheostat

Adjustment Range

±5% with 1000 ohm rheostat

Frequency Compensation


Roll Off Frequency

54-61Hz for 60Hz Operation

45-51Hz for 50Hz Operation


7.4 oz

Operating Temperature

-40°C to 60°C

Storage Temperature

-65°C to +85°C

Power Dissipation

8 watts maximum



Voltage Build up

Internal provisions for automatic voltage build up from generator residual voltage as low as 10 Vac.

EMI Suppression

Internal electromagnetic interference filter (EMI Filter)



Caution: DO NOT megger or high-pot the generator with the regulator connected. DO NOT high-pot the regulator.



The SE350E voltage regulator can be mounted in any plane. See Figure 1 for mounting dimensions.

SE350 Voltage Regulator.jpg



Connect the regulator wire F+ to the generator F+ or F1 field terminal. Connect the regulator wire F- to the generator F- or F2 field terminal. See Figure 2 for typical connection diagram.

exciter power circuit.jpg



Input power and sensing is achieved through terminals 3 and 4. The voltage input requirement of the SE350E is 190 to 240 vac.

See Figure 2 for typical connection diagram.


A 4 Amp 250V - 5 X 20 mm fuse is supplied with the regulator (Part A-527066).


The screwdriver adjustable potentiometer adjusts the generator output voltage. Adjustment clockwise increases the generator output voltage.

When using a remote voltage adjust rheostat, remove the jumper wire across terminals 6 and 7 and install a 2000 ohm 1/2 watt (minimum) rheostat. (See Figure 2). This will give ±10% voltage variation from the nominal. (For ±5% voltage variation use a 1000 ohm 1/2 watt rheostat).


System stability is the ability of the generator to respond to load transients. Decreasing the stability makes the generator less slug-gish and faster to respond to load transients. If the stability of the regulator is decreased too much, the generator will tend to hunt under steady state conditions.

The screwdriver adjustable potentiometer adjusts the system stability. Adjustment clockwise increases the stability. In-creasing the stability increases the response time of the generator. Conversely, decreasing the stability decreases the response time of the generator.

Stability Selection (On applicable regualtor models)

When excitation under voltage, it can result in insufficient adjust-ment range for stability adjustment and when excitation over voltage, the response from the AVR becomes sluggish. The AVR is equipped with 2 bridging wires J1 and J2 to help improve this problem. See Figure 2.

• If the unloaded excitation voltage is less than 7 VDC, please cut open the J2 red bridging wires.

• If the unloaded excitation voltage is greater than 25 VDC, please cut open the J1 white bridging wires.


The roll-off point is the frequency where the generator voltage starts to decrease. This reduces the Kilowatt load to the engine, which allows the engine to recover in speed under any load tran-sient condition.

Use jumper to select 50 Hz or 60 Hz. The screwdriver adjustable potentiometer sets the roll-off frequency from 54-61 Hz in the 60 Hz setting or from 45-51 Hz in the 50 Hz setting.

The SE350E has the roll-off point preset to 58 Hz in the 60 Hz mode and 48 Hz in the 50 Hz mode. To change the roll-off point, adjust engine speed to the desired rated speed. (50 or 60 Hz). Set the voltage to the desired setting at rated speed. Adjust en-gine speed to the desired roll-off point. Turn the potentiometer clockwise until the voltage starts to drop off. Then adjust the po-tentiometer counter-clockwise until the voltage returns to rated. Re-adjust engine speed to rated speed.



Ensure the voltage regulator is correctly connected to the generator. Refer to the specific connection diagram supplied with the generator.

Set the regulator voltage adjust to full counter-clockwise (minimum voltage level).

Set the remote voltage adjust (if used) to the center position. Set the stability control full clockwise (maximum stability level).

Connect the positive lead of a 100V D.C. voltmeter to F1 and the negative lead of the voltmeter to F2 or use an appropri-ate AC voltmeter on the generator output leads.



Start and run the generator at no load and rated speed. The generator voltage should build up to a minimum level. (Actual level is dependent upon connection). If it does not build up, refer to field flashing section in generator manual.

Slowly adjust the voltage control until the alternator voltage reaches the nominal value. If used, adjust the remote voltage rheostat to set the generator voltage to the exact value desired.

Turn the stability adjust counter-clockwise until instability is shown on either of the voltmeters mentioned in the “PRE-LIMINARY SET-UP” section. With the system operating in an unstable condition, slowly adjust the stability control clock-wise until generator stability is reached.

Interrupt regulator power for a short time (approximately 1-2 seconds).

If the alternator remains stable, no further adjustment is nec-essary. If the generator does not remain stable, increase the stability slightly and interrupt regulator power again.

This procedure should be repeated until system stability is reached and maintained.



1. Connect the test setup as shown in Figure 1. Do not apply power. Insure that the light bulbs are 120 volt, and less than 100 Watts.

Marathon generator AVR.jpg

2. Adjust the regulator VAR and/or remote VAR and the STABILITY ADJUST to maximum CCW.

3. Apply 240 volts AC, 50/60 Hz power to the regulator. The light bulbs should remain off.

4. Slowly adjust the regulator VAR clockwise. At the regulation point, the light bulbs should illuminate. Small adjustments above and below this level should cause the light bulbs to go on and off. Note that the light bulbs go on and off rapidly.

5. Rotate the STABILITY ADJUST FULLY clockwise. Now adjust the regulator VAR above and below the regulation point. The light bulbs should still go on and off, but the transition from off to on (and vice versa) should be much slower than in step 4 above.




Residual Voltage - No Output

Residual voltage at regulator power input wires 3 & 4 below 10Vac

Check wiring diagram for proper connections

Flash generator field. Refer to field flashing section in generator manual.

Acceleration time to rated speed too long

Reduce acceleration time.

Interrupt power input to regulator after achieving rated speed.

Field leads F1, F2 not connected

Connect field leads F1, F2.

Power input leads not connected

Connect power input leads 3, 4.

Blown or missing fuse

Replace fuse

Defective regulator

Replace regulator.

Defective generator

Consult generator manual

Output Voltage Low

Incorrect connections

Check wiring diagram for proper connections.

Voltage adjust turned down

Rotate voltage adjust CW until desired voltage is reached.

Remote voltage adjust is turned down

Rotate remote voltage adjust CW until desired voltage is reached.

Defective regulator

Replace regulator.

Output Voltage High

Voltage adjust turned too high

Rotate voltage adjust CCW until desired voltage is reached.

Remote voltage adjust is turned too high.

Rotate remote voltage adjust CCW until desired voltage is reached.

Output Voltage High - No Adjustment

Defective regulator

Replace regulator.

Remote Voltage Adjust Voltage Operates Backwards

Voltage adjust wire backwards.

Reverse the wiring of the remote voltage adjust.

Generator Output Voltage Hunting

Stability adjust not set properly.

Rotate the stability adjust in a CW direction until hunting stops.

Poor Regulation

Defective regulator

Replace regulator


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