Generac Troubles Fixed

[scdiver]

We have a 1995 Generac np66g in our mh that has needed a few repairs. In hopes of helping others I want to report the two problems and the fixes that I employed to keep this running.

The first problem sowed up on our 2015 trip to the Grand Canyon and Las Vegas. In the heat we drove with the genny running so we could run the air conditioners. I would shut the genny down at least every 24 hour to check the oil. After getting hot running in the desert the genny would not start, click or do anything when I hit ether start switch. As part of my diagnoses I took off the cover on the electronics, connected a jumper cable to the plus side of the coach batteries, the other side of the jumper cable to a large screw driver, then touched the screw driver to the starter side of the starter relay. This not only started the genny but caused the relay to loosen up and work correctly till the next hot time. A simple change of the relay fixed this problem.

The second problem was much harder and from some of the threads on the forums a common problem with these Generacs.
I would start the genny and it would start right up, but would produce no electricity. I was advised to hold the starter switch down a few seconds longer when starting and this seemed to help. Then it started to get worse. It seemed if the genny was cool, from rainy weather or just from cold weather, I had to run the genny for up to half an hour, stopping it then starting it about every ten minutes till it would produce electricity. This did not go over well when DW wanted to fix a meal. It was also a sign to me that something was going to fail permanently. I googled and found the service manual and the owners manual for this np66g Generac. I studied the service manual and since the temperature here in St. Louis was on the cold side and the genny would not produce power when cold I was able to follow the diagnostics and determined that the voltage regulator was probably at fault. Looking up the part number in the owners manual gave me a number of 74074. That number is not available any more but, there is a new number that is available. That number is 0830480SRV.
It was easy to install but there is a catch. To install this I took off the cover and turned off the circuit breakers. I then unbolted the old regulator and bolted the new one loosely with just the top bolt. Then since the wire connecting to this regulator are ether black or blue, yes all of them, I moved them one by one to the new regulator. I then finished up bolting it in the genny. Now came the catch. Leaving the breakers off I clipped a cheap volt-ohm meter to the input side of the breaker and the other line to ground. I then started the genny and got excited when the led on the regulator showing a high voltage output came on. The meter showed 89 volt output. I set the output by turning the pot next to the led to get 122 volts with no lode. I shut down the genny unclipped the meter and put the cover on the genny. Turned on the breakers and started the genny and got the proper voltage right away. This morning it was 38 degrees out and that genny started right up and produced electricity of the proper voltage so that I could run both air conditioners and a 1500 watt heater. I consider this genny fixed.
I know this is a long story but I hope it can help someone that is having these same problems with there Generac generator. Remember that new part number is 0830480SRV. I found several on Ebay and they are not cheap but I hope I have avoided having the genny fail me when I relly need it and my doing the repairs was a lot cheaper than having a shop do it. One last thing, the np52, np66, and np72 are basically the same gennys. I do not know about other Generac models.

 

[Charlie 5320]

You need to set the regulator to the correct hrz not voltage, unloaded per the manual. I set my 6600 to 61 hrz and 127 volts unloaded. Loaded it runs 121 volts @ 60 hrz.

 

[scdiver]

According to what I read in the service manual, the hertz is set by the engine speed that is controlled by the engine controller circuit board. The voltage regulator controls the voltage out. since I did not mess with the engine controller the hertz was not changed.

 

[Charlie 5320]

The generator speed needs to be 3600 not the engine. If you don't have the means to check engine speed, it can be done with knowing what the voltage and hrz is. All Generacs I have seen are 2 pole generators that have to run at 3600 rpm.

This right out of the repair manual. I tried to copy paste but couldn't.
Note: AC output frequency at 3720 RPM will be about 62 hrz. The NO LOAD speed is set slightly high to prevent excessive RPM, frequency and voltage droop under heavy electrical loading.

 

[scdiver]

Your correct that the generator speed on all Generacs need to be set at 3600 rpm. This is done by controlling the engine speed. On a NP66 the engine speed needs to be set at 2700 rpm. On a NP52 the engine speed is set to 2300 rpm. On a NP72 the engine speed is set to 2900 rpm. This is still done through the Engine Control Board not the voltage regulator. All the voltage regulator controls is the voltage out and that is set by the only thing you can change on the voltage regulator, the pot next to the diode.

 

[scdiver]

When I received my new voltage regulator the control pot was set counter clock wise as far is it would go. The hertz was correct as the engine, thus the generator speed was not changed. My meters showed 62 Hertz at no load yet the voltage at the factory setting on the regulator was 89 volts. When I adjusted the pot clock wise I was able to get 122 volts at no load and the Hertz never changed.

 

[scdiver]

Further update, the engine speed is not controlled by the engine control board, but is controlled by the governor and must be set up as shown on page 28 and 29 of service manual 94468. This controls the engine speed, thus controls the generator speed, thus controls the Hertz output. If the problem is intermittent as stated in my first post, and the only thing needing a change is the voltage regulator, then I stand by my first post.

 

[Russ+Chris]

The generator speed needs to be 3600 not the engine. If you don't have the means to check engine speed, it can be done with knowing what the voltage and hrz is. All Generacs I have seen are 2 pole generators that have to run at 3600 rpm.

This right out of the repair manual. I tried to copy paste but couldn't.
Note: AC output frequency at 3720 RPM will be about 62 hrz. The NO LOAD speed is set slightly high to prevent excessive RPM, frequency and voltage droop under heavy electrical loading.

A 2 pole generator at 3,000 rpm will give you 50 Hz. That's what they use in Europe. What is stated above is correct. 2 pole generator at 3,600 rpm will give you 60 Hz. Think small generators and combine cycle power plant.  A 4 pole generator at 1,800 rpms will be 60 Hz. diesel power generators, coal burning power plant, some nukes. 8 pole generator at 900 rpms, 60 Hz, nuke plant, some hydro. 16 pole generator at 450 rpms, 60Hz, hydro. 32 pole generator at 225 rpms, 60Hz, LARGE hydro.

On some large diesel back-up generators. There is an adjustment knob for Hz. It's used for fine tuning. +or- about 3 Hz.

 

[GA_Boy]

For the lesser Electronic proficiency knowledgeable folks like me I check my Generator Frequency  with a stopwatch and a 120 volt analog clock that has a sweep second hand. Plug clock into running gen.
Wait until the second hand is a 12 and simultaneously start the stopwatch.  When the sweep second hand again reaches 12 stop the stopwatch.  If the stopwatch reads 61 seconds the Freq. is 59 htz.
Stopwatch reading 60 seconds and your htz is 60. Stopwatch= 54 then the htz is 66.  etc,etc,etc.
Marvin
Marvin

 

[Charlie 5320]

For the lesser Electronic proficiency knowledgeable folks like me I check my Generator Frequency  with a stopwatch and a 120 volt analog clock that has a sweep second hand. Plug clock into running gen.
Wait until the second hand is a 12 and simultaneously start the stopwatch.  When the sweep second hand again reaches 12 stop the stopwatch.  If the stopwatch reads 61 seconds the Freq. is 59 htz.
Stopwatch reading 60 seconds and your htz is 60. Stopwatch= 54 then the htz is 66.  etc,etc,etc.
Marvin
Marvin

Much easier to just use a meter.