Re: Output Voltage Incorrect at High Idle

output voltage incorrect  at high Idle


I think you have to adjust you generator idle speed .If the idle speed goes up then your generator will goes up to 50 Hz frequency repidly and and at high speed it will respond incorrect voltage at display due to incorrect frequency . so I will advise you to do setting to work for adjustment of idle spee and your problem will be solved defenetly.

Best regard




Re: Output Voltage Incorrect at High Idle

Mr Charis which AVR (automatic voltage regulator) is mounted on this Generator ? I agree with Mr Ahmed If you are getting 145v then need to adjust the knee frequency or bypass its external potentiometer and adjust its voltage from AVR if there is no output voltage or only blow 50v then you need to follow Mr Mikel advise means you need to proper diagnose may be AVR faulty or problem with alternator.







Re: Output Voltage Incorrect at High Idle

What type of voltage regulator is used?.


Please try to adjust the Knee frequency on the regulator it should be -2Hz of rated frequency.

Checked the wiring of the remote potentiometer for loosing/or potentiometer may faulty.




Regular Contributor

Re: Output Voltage Incorrect at High Idle

Probably need to do a little basic troubleshooting for this, do you have someone electrically competent to make some measurements on your unit while running?


If so, at the voltage regulator, you need to measure the following, the voltage at the regulator sensing inputs, will be half the value of the voltage at the generator terminals on most units, a unit this size should be set up for  3 phase sensing, so between all phases you should get a similar reading, likely about 205-210 withg things working normally.  Next measure the voltage coming from the permanent magnet generator, usually terminals 26, 28 and 30 on most CAT regulators, should be 85-100 VAC at rated speed.  Next find terminals F1 and F2, this is the output of the regulator, and at no load is usually 12-20 VDC depending on your generator arrangement.


If you have sensing and power to the regulator it should output votlage on the field to control terminal voltage.  If you have no output on F1 and F2, you may have a faulty regulator.  If you have an output, and it's higher than I mentioned before, you likely have a generator problem, could be a rotating rectifier problem, a problem in the main rotor or in the stator.


Hope that helps, Mike L.


Output Voltage Incorrect at High Idle

We have the following Cat generator:


Gen Set Number: 3508

Model Number: SR-4 7C-1621

Serial Number: 69A03300

Main Circuit Breaker: 1500 A

Generator Rating: 820 kVA

Generator Full Load Amps: 1232 A


When going to high idle, the specified voltage (in this case 415/50Hz) does not come up.  Display shows 145VAC.  The frequency does go to 50Hz as it should.  This problem has existed for years.  Everytime a Cat technician comes out, it works properly.  Usually we can power down and it will work after a couple of trys.  Today, is the worst I've seen.  Over 25 attempts to no avail.  Any ideas what the problem could be?