Generac 11Kw Generator – A tale of woe, abandoned by customer support, and why I’ll never recommend this brand

This story details my life with a Generac 11KW propane-powered stationary generator and my tale of misery keeping it running.

The generator was bought new in 2014. The size and capacity of this generator was calculated to be more than enough for the loads I need to power and my battery charging needs. The purchase included the optional remote start option. This option comes with two foot-long wires, each with a Molex connector on one end, and instructions on how to install the wires and configure the controller to start with an external control signal (contact closure). This will tie into my inverter’s Automatic Generator Start (AGS) module.
I installed the generator at my off-grid campsite. It is plumbed in to the camp’s propane distribution system and fed by a 250 gallon tank. We are entirely off grid for electricity, and have 2200 watts of photovoltaic modules to charge a bank of 12 530Ah flooded lead acid batteries. The batteries power some low voltage loads and an inverter system.
We’re not hardcore campers, so we shut down and winterize at (US) Thanksgiving, and do not return till springtime, when the weather starts to warm up, usually in April or May. The AGS and generator remain off during this winter hibernation period, and the solar modules continue to keep the batteries at full charge.

The generator provides backup power when there isn’t enough sunshine, or when power consumption exceeds solar generation to maintain a proper battery state of charge. If the battery voltage drops to a certain threshold, the AGS starts the generator automatically and runs for a pre-configured 30 minutes. The AGS also provides for quiet time from late night to morning.

Oil and filter changes and other routine maintenance was done at each of the recommended intervals.

In October 2018, the generator began having a hard starting issue. Once started, typically after 2 attempts, it ran fine. It had 1508 hours by then. It got an oil and filter change and new spark plugs. The valve lash was adjusted according to recommended procedures. Valve cover gaskets were also replaced.
It started first time, every time after that.

Fast forward to August 2019 – it starts and runs, then shuts down with one of two under voltage error codes.

This is when things start to get serious.

Following research I did online, I performed some basic diagnostics to determine the cause. One diagnostic step was to test the rotor resistance and examine the brushes. Resistance was ok, indicating continuity from the controller wires through the brushes and slip rings and the rotor.

The brushes, however, were a concern. The outboard (rear-most) brush was long and looked almost unused. The inner brush was worn down to about a quarter of the length of the outer brush. The inner slip ring also showed some wear compared to the outer.
I replaced the brushes. The generator had 1806 runtime hours at this point.
After reassembly, the throttle speed control problem was still there. If a large load kicked in such as my water pump, the engine would slow down, sometimes enough for the output voltage to drop, causing either an under speed or under voltage error. Whichever was detected first would cause the generator to shutdown and display an error code on the controller display.

Further troubleshooting found that the stepper motor controlling the throttle was not moving to make the necessary speed adjustments. I tested the windings of the stepper motor – it is a 5-wire unipolar stepper, so test procedures are well known and well documented online. One winding was found to be open-circuit.
Generally, stepper motors are not that expensive and are easy to replace. Or so I thought. This one appears to be a private label stepper, so only available from Generac. Ok, I thought, it’ll cost way more than it should, but I don’t have a choice.
I discovered that the stepper is not sold separately, but as a ‘mixer assembly’ worth $220USD. That’s awfully pricey when you only need a 20 dollar stepper motor…

September 2019 and the new mixer assembly arrives. I measured the stepper windings to verify and confirm the earlier diagnostic of the open winding. The mixer assembly gets installed. After starting the engine, I notice the throttle control issue is still there, with the controller not adjusting the engine speed as loads vary, and then shutting down with an error code if RPMs are too high or too low.
Now it appears the Evolution controller board has a fault.

By then, it was winter hibernation time again, so this would wait until spring…

Actually, fast forward to April 2022…
I ordered a new Evolution controller, and this one has a newer revision number than my original. $475 later, I installed the new controller, and the first thing I observed at startup is that the stepper now ‘sweeps’ bottom to top before settling near the center of travel. That look promising. Then the starter engages and the engine starts and runs as it should. As loads come and go, the throttle adjusts to keep RPMs and output voltage at the correct levels.

Problem solved.

Wait. Until…

A few weeks later, the generator starts and runs for a few minutes before shutting down with error code 1902 on the controller’s display. Online research provided less than helpful answers – ‘contact dealer for service.’ Some more detailed explanations talk about both zero-crossing failure, but none suggesting what to look at or what to fix or replace.

As a troubleshooting step, I reinstalled the defective (no throttle control) controller to determine if this new fault was within the controller or external to it. This error condition persisted, indicating it was not a new controller fault.

I found a dealer offering a detailed troubleshooting manual, so I bought and downloaded this manual. Walking through various troubleshooting steps, I tested for continuity through to the rotor – NO continuity. The manual says to test each wire segment, the brushes, and the rotor. After disassembly to get access to the brushes, I once again observed that the inside brush was worn down to almost nothing. It was worse than the first time I changed them. This explains the no continuity test result observed earlier.

The outboard brush (right) shows almost no sign of wear. The inboard brush is so worn it no longer touches the slip ring.

The outboard slip ring (left side below) shows virtually no wear.
The inboard slip ring has a deep scalloped groove and is discoloured (burnt?) in the middle. It is obvious that it destroys its brush.

The significant question here is what would cause this condition to develop? Is there some operating scenario that would cause this? Before exploring this further, let’s document the rings.

Here are a few observations and measurements:
The outboard ring is <.002″ out of round. This is possibly within factory tolerance.
The inboard ring is >.014″ out of round. This appears to be a serious manufacturing flaw. Is this within factory specification? Did this actually pass quality control?
The inboard ring diameter is 0.18mm thinner than the outboard ring. Is this with factory specification?

At this point, it seems the repair path calls for a replacement rotor assembly, along with the long retaining bolt, which you need to cut up to make the necessary removal tool. Prices for the rotor assembly from the various resellers vary between around the $475 to almost $800.

This really appears to be a manufacturing defect or a quality control failure, the more I think about this…
When I reached out to Generac customer service, their response said that the unit “too far outside of warranty for us to offer any concession on the repair” and “If yore (sic) current dealer is unable to solve your issue, we recommend working with another dealer.”

Meanwhile, I start to explore machining the slip rings to get them back round. But the groove is very deep, so there may not be enough material left on the rings after machining it back into round.
Or can the rings be replaced? Slip rings are replaceable on large motors and generators, so what about on this generator? Either way, mine are shot, so I have little to lose by trying to remove the rings. I further disassemble the generator and remove the back end housing to expose the bearing and slip rings. With a bearing puller, I remove the bearing.

Then, being careful because the slip ring base is plastic, I use the puller to remove the slip ring assembly. It slides off quite well. Here’s another view of the rings.

After more searching, I found a dealer that lists an available slip ring assembly for less than $30USD. Order placed, along with another set of brushes.

May 27 2022: Waiting for parts…

May 28 2022: Parts arrive. Earlier than expected.
A quick look and comparison shows these are right, and confirm the rings are the same diameter on this assembly.

Here I want to give a shout out to They responded quickly to my inquiry, and most importantly, they has the parts in stock.

I installed the ring assembly, wired up the rotor windings to the rings with crimp sleeves, and testing for continuity and the correct 5.2 ohm resistance at the rings at every step. A little bit of lubrication and some moderate tapping with a PVC pipe fitting and hammer drove the ring assembly in place.
Then I reinstalled the bearing using the same PVC pipe, then the rear bracket. Finally, I installed the new brushes. One final resistance measurement confirms everything is good after the reinstallation.

At this point I’m pretty eager to verify that the 1902 error is gone and that I get proper AC voltage output. So I slip on the muffler, set up my voltmeter, and set it to manual run. Moments later, we have success.

No error code, 238.5VAC output, plus or minus, and a big smile on this owner’s face.
Now it is time to reassemble the enclosure and button this job up.


So what was learned from this adventure?

First of all, generators are not so complex as to requiring a rocket scientist to figure out and understand.
A proper technical manual is very helpful for troubleshooting and performing some repairs. My manual included part numbers, but to my surprise, was incomplete: the slip ring assembly was not shown or listed. I am grateful to this dealer who offered the part number and said they had stock.
Generac’s customer support organization seems to exist for the primary purpose of steering business to their dealers, only some of whom can service their products. These dealers, at least the ones I’ve dealt with, are independent businesses. The customer support folks insisted I have a dealer come out to have a look.
Generac does not sell parts directly to their customers; you must go through a dealer, many of whom take your order and your money, and then Generac drop-ships your parts to you. I also found prices can vary between dealers. This is their prerogative, of course, as independent businesses. Some dealers actually stock parts, I found, so it pays to shop around.

Regarding my manufacturing defect theory, I am still convinced this is the case.
Prior to buying this generator, I had an older Kohler stationary generator that I bought used from someone I knew. It had nearly 3000 hours and had never had an issue with the generator portion, including still running on the original factory brushes.

Do many people have these issues with their Generac, probably not. The typical use case for the generators is backup home power. In many cases, the normal exercise cycles probably rack up more hours than power outages do, so they may never have so many hours that this problem would ever manifest itself. So this speaks to the expected duty cycle of these machines: they are best suited where they are seldom used. They are best for making their customers feel good that they have protection.

Don’t ask what possessed me to buy a Generac instead of another Kohler, because I don’t know.

Would I buy another Generac? At this point, after all these issues, I definitely would not, nor would I recommend them to anyone.