Kohler 20RESL Trouble

[Kohlertech76]

The 20RESL means that it was bought through a big box store (HD or Lowes). Did you have a Kohler Factry Start up? It could be that the fuel changeover was not done properly. You sometimes have to change the piping over and there is a jumper that needs to be connected or disconnected.

[Daverepair]

I worked as a generator tech for ten years in SE. ma. I found that UPS's, Low Voltage Lighting and even some larger HVAC controls caused many problems just as you have described. If this is a new purchase/installation by a generator company then they should make it right or should not have installed that machine. Kraft in woburn had some good techs at one time or South Shore Generator in Wareham. Ask for Malcomb, if he can't fix it it aint broke.

[LWB250]

Dave,

Is Harry still at South Shore? I remember working with him some years ago - great guy, a real character.

Dan

[bec98x]

Just wondering if you solved the problem. I would have had the tech bring out a load bank and test the generator that way. This would eliminate any feedback from devices inside house.

[tommax]

Hi jclaf19. I have the exact same symptoms you describe, exactly. I have 66.3 hours on my 20RES. The 59 to 61Hz, makes my Cyberpower UPS’s flip out almost constantly but not my Belkin UPS’s. Lights flicker that are CF’s or dimmable, I’ve been seeing everything you described. I installed my 20RES in 11/11. I noticed when I was home after it was about 6 months old in the spring to listen to the weekly self-test that the RPMs were fluctuating around 3600, not at low speed as much. I’ve only had a couple of PF’s not more than a couple hours tops until Sandy came thru here a couple of weeks ago. I ran about 50hrs with some shutdowns at night to save gas, and during that 3-day outage it shut itself off with a High Engine Speed error 3 different times. It was cycling around 3600 and on the way up it kept going and over revved so it shut itself down. Error code was OS. I have my Kohler dealer coming next Friday to take a look. My money is on it being a vacuum leak, at initial installation the tech took off the carb and scraped out the gasket to keep the butterfly from hitting it with his pocketknife. I was saying to myself I hope I don’t develop intake leaks from that sloppy backyard fix that Kohler instructed him to do. I couldn’t believe he didn’t come with a new gasket; he had to take that one off and enlarge the center, OMG! I also saw that under 500 watts load I was cycling more and over 2K watts load, things ran smoother, but are still not right. Did you ever find out what the root cause was? I will let you know what happens with the Kohler tech next week.

[len k]

Originally Posted by jclaf19

One other thing to point out is that the genset hunts even with the breaker on the generator off. I also thought that my dimming modules could be causing this to happen however when I hit the main breaker on the genset and the hunting continued I didn't know what to think. Even if I shut the genset down, kill the breaker, then hit run it still hunts.

If the speed is still oscilating while all loads are disconnected, that pretty much nails it as a governer problem. Funny electrical loads (scr) might make the problem worse, but sounds like the under laying problem is a governer issue. Possiably a design defect with all gens they made with that model governer and governer software settings. Esepecially if other people are having the same problem.

[LWB250]

A 3600 rpm generator with an isochronous governor is going to be less stable at lighter loads as you describe. As the load increases it will become more stable as the higher load tends to "dampen" the response of the governor and fuel system.

The fuel system, governor and engine all have a "sweet spot" where they are designed for the best combination of response to load changes. If you are outside of this band, such as having very light or heavy loads, the stability of the system will be somewhat less than when it's in the "sweet spot."

Dan

[tommax]

When it was new it was very stable and any fluctuations in RPM were about +/- 15 RPMs, not noticeable at all. Over time it has gotten worse, more and more noticeable, even during the variable speed test at the low RPM I can hear it oscillating back and forth to try and hold a steady RPM. Now the RPMs at 3600 are +/- 50-80 which doesn't effect the voltage much but the frequency drifts to as high as 61.7hz and into the high 58's on the low side.

[len k]

lwb250.....Assuming it's not other issues like play in the carb linkages, I think it's still an issue with the governer design (as engineered when it left the factory). IT seems a better governer design might be one that senses the load and adjusts the governer closed-loop control settings with load so genset will have better stability.

Either way it's not an acceptable design to have the voltage/rpm hunting. It's interesting that when governer was replaced it ran good for ~~10 hours. Wonder if it's a learning type that adjusts it's settings to the way you run it, like a car computer. (but not learning well)

[LWB250]

It is probably a proprietary design, as Kohler has been designing their own governors in-house since the early 1990s.

Since you indicate that it's something that has grown worse with time, it could be a matter of an adjustment of the speed pickup or throttle body (mixer).

The only definitive way to really check and adjust it properly is with a load bank.

Dan

It is a closed loop design. It uses feedback from the engine speed (magnetic pickup) to monitor and adjust as necessary.

[tommax]

I had a good tech come out on Friday, we tried many things and had many observations but when all was said and done almost 6 hours later we left the generator basically as it was. Here are some observations to share since we didn’t determine the root cause of the hunting. He told me he has been seeing most 20RES having hunting problems, no 14RES has had hunting problems, only difference is the engine. Hunting occurs unloaded and loaded. It is more noticeable when unloaded or lightly loaded, increasing the load helps smooth things out but hunting still occurs to some degree when loaded. When running with the hood open and the side off we struggled to make the generator hunt. Normally closed up we could hear it hunt within seconds. We messed with a parameter in site tech to adjust the governors sensitivity we ended up leaving it at 40, tried as low as 20 and as high as 80 with little to no effect so we left it where it was. My internal regulator already had vent tubes installed from the initial install last year, venting into the battery compartment. We tried plugging 1 up and venting the other inside the engine compartment which made hunting worse, and outside which made little difference if any from inside where they were so we left the tubes as they were, both in the battery compartment. I have no vacuum leaks anywhere. He watched his manometer while we ran for a while the pressure was at 11 I believe, and he said normal is 7 to 11 so he decreased it to 10 but that made no difference. We noticed that the voltage across the battery was as low as 11.1 and as high as 14.7 from his Fluke on min/max for about 20 minutes runtime. Some of the time the voltage remained relatively constant in the 13’s but at other times we saw a large swing in the voltage across the battery. The tech told me I should call Kohler and see if I can pressure them into helping to resolve this problem since he led me to believe that this problem with hunting on a 20RES is very common. I think a lot of people might never know, in my case I am a electronics guy and have UPS’s which complain, if I didn’t have UPS’s I might not know my frequency is drifting a little too much.

[Kevin K]

Originally Posted by tommax

We noticed that the voltage across the battery was as low as 11.1 and as high as 14.7 from his Fluke on min/max for about 20 minutes runtime. Some of the time the voltage remained relatively constant in the 13’s but at other times we saw a large swing in the voltage across the battery.

How can the voltage on the BATTERY vary from 11.1 to 14.7? That just doesn't make any sense. If the battery was weak it wouldn't start the generator.

I would put a scope on the battery and look for any kind of AC ripple or noise. A lot of noise on the 12 volt system could confuse the computer and cause all kind of problems, including the hunting.

It would also be a good idea to scope the entire 12 volt system looking for noise and voltage fluctuations. Also check all the grounds to make sure they are solid.

[tommax]

The generator and battery are just 1 year old, the battery is like new. When the generator is not running, i.e. it's in off or auto, the voltage across the battery is rock solid for the year I've had this rig at about 13.1v in oncue. When the engine is running either unloaded or loaded it seems that the battery charging system that is charging the battery acts different than when not running? I think this is what we are effectively looking at when we measure the voltage across the battery? I've noticed that during self tests when watching in oncue the battery voltage ramps up to the high 14's and then jumps back down to the low 12's in just a couple of seconds. I've also observed that the battery voltage is rock solid at about 13v but more than not it seems that the battery voltage is hunting as well. The Fluke showed slightly different numbers than oncue but side by side they were close. We did try unplugging the charger and let the battery voltage drain down to about 12.0v with little effect, below 12 it started to run rough and we plugged the charger back in and it was steady in the 13's for a few seconds and started to fluctuate from 12 to 14v like usual. We were thinking if the charging system was throwing dirty power at the battery it might mess up the computer but the fluctuating battery voltage is not aligned to the hunting in RPM problem that this is all about. They appear to happen unrelated to each other, I can't see the pattern. This is getting fun, I have to go dig up and dust off my scope!

[Joe Batts]

Don't know if you ever had this problem fixed. Tell your service company to install regulator vent tubing to vent the Garretson demand regulator to an area that has no vacuum w/ the machine running. The junction box is perfect. Also, tweak the gain to 40 or 35, tweak the Transient integral gain from 1.0 to .75, slow correction integral gain from 1.0 to .4, diagnostic derivative gain to 3 and diagnostic transient intergal gain to 2. You will need a dealer / distributor to do this as they will need the latest version of site tech to do this. You may be able to do this through the OnCue server but may likely have to be done through usb. If all else fails, tell them to call Kohler and ask for the patch version of firmware that seems to help this issue. If all else fails, Kohler will be releasing a final firmware version that may help this issue but no release date yet. Good Luck!!

[Scott Scherbon]

Have your generator guy ask for the updated Kohler sb722 update to correct your exact problem. It was issued to dealers on 1/13/2013.

[Ken68]

Scott, can you tell me how I could get a copy of sb722?