Onan RS 12000

I am the product manager for Cummins Onan residential products. We have sold thousands of the Honda powered RS 12000 generators with excellent results. Our new Subaru powered RS 12000 is an upgraded version of our previous design. The new feature set is superior to any product on the market. Below are a couple of the key features. The Subaru engine coupled with a Cummins Onan designed fuel system boosts the power to 12kW on propane and 10.5kw on natural gas. This new design is the quietest on the market with a sound level of 64 Db(A) at 12kW and 61 Db(A) at no load. We have also improved the aesthetics of this product so it blends into a residential environment. Our product is the only residential generator that can send you an email when maintenance or service is due and allow you to check on your generator via a web page from anywhere in the world.

We live off the grid and have both solar and wind generating equipment as well as an inverter and a bank of batteries. After much research and careful consideration, we purchased a RS12000 Onan generator in early 2006 because of its control system and power capacity. This sizeable investment (more than $7000) was expected to give us reliable back up power generation when needed and the ability to leave the house for a few days.

The RS12000 has come short of our expectations and of the claims made in your corporate documentation. The following repairs and service calls have been done to our unit since its installation:

- Feb 26, 2006: oil seal blown, hrs on unit: 58
- Oct 26, 2006: governor problems, hrs on unit: 486
- Dec 12, 2007: control board, hrs on unit: 875
- Dec 27, 2007: oil seal blown, hrs on unit: 900
- ongoing problem: very sensitive oil level

We do not have reliable performance from this unit.

The first time the oil seal failed, we were told by Onan that this had never happened to any other unit. It has now happened twice within 900 hours of running. This problem is catastrophic for us since we cannot repair it ourselves and it leaves us without any power to the house whatsoever; no lights, no water, no boiler.

It has been two years now and we do not feel that we have a reliable generator in this RS12000. We need a generator that we can depend on and this is not it.

Anned have you tried asking the Honda engine people about that oil seal? From your description it sounds like the oil seal is located on the engine, not the electrical generator. Typically seals blow from excess pressure due to high viscosity in colder weather, too much oil volume in sump or excess loading on engine.

Is this the shaft seal between the engine and electrical generator part. Normally an oil seal is not hard to replace. What feature makes it not possible for you to repair it yourself?

I understand your frustration and it is our commitment at Cummins Onan to ensure you have a reliable product. Please contact your local Cummins Onan distributor so we can help rectify this situation. Ask them to directly contact the Cummins Onan factory service department before servicing for our recommendation to resolve this issue.

I have a RS12000 on my home running with natural gas. It has been an ok generator for us. THere was a grounding issue that took me 4 hours to hunt down and finally screw down a loose screw. But also, i have a real problem with the PCV system clogging the air filter after about 8 hours of operation. DOes anyone else have this issue?

What is the model number of the RS12000?

Hello Kles0015

Its the start of another cloudy and cold season. I am beginning to hear comments from our customers with the same issue as Anne posted last winter. The issue is not just with Onan or any other specific brand; it has to do with the fact that even big inverters able to power an entire houlehold only impose a certain size load on the genset when in charging mode. A 10kW 12 or 15kW genset is running very light loaded when the maximum charging load is only 3kW. In the marine industry we call it wet stacking. Maybe land based users have another term for it. Off-grid solar houses seldom use the entire throughput from a big genset since they are designed to not have any big electrical loads. Therefore it is NOT possible to load the generator properly. What do you suggest in such cases?

In my opinion spec'ing a 12kw genset for a solar house doesn't make sense. Especially when that same solar house only uses and needs a 3 or 4kW inverter. The genset is intended as emergency back up when the solar panels cannot provide enough power. This usually happens in the depth of winter during prolonged overcasts. Now you have a stone cold engine trying to build up heat, but running with very light load. It simply ain't gonna happen. Being cold, the rings will not seal properly. This produces blow by and that pressurizes the crankcase. Result, lube oil being blown out the seals and any available opening like the PCV hose. And since by design the solar house cannot fully load the genset engine, it will never get really warmed up on a -20 F winter day.

It would be far better to have a smaller engine sized to match the charger load since it would be worked fully and thus warm up. For even faster charging a DC genset would actually prove to be a more economical and fuel efficient configuration. Depending on battery bank voltage such DC gensets can be built from off the shelf conponents for around $1000. Less, if you salvage used parts. I built one for $400.

GHAB purchased in 2001-2002. I've checked the compression on the cylinder and they are good. Just too much oil getting into the air filter after about 8-10 hours of run time. Im guessing the PCV is working just as it should, letting pressure pass, but the placement of the outlet directly into the air filter chamber is not the best. Is there a kit to modify this?

I'm not aware of any kits. This is also the first time I heard of this issue on the GHAB. How long have you had this issue?

It happened Last November when we were out of power for 4 days. Family at home all day and the generator ran 24/7. It worked like a champ for the first 24-36 hours, i changed oil using 10w-40 then it started oiling up the filter every 6-12 hours. Basically choking air flow. I changed the filter twice. It still ran very well running around 50-70% load during the day and around 30% at night. I run the generator for about 1-2 hours every 2 weeks for exercise, but have not seen any substantial oil buildup on the filter, just a little in the bottom of the air pan. Since the storm season is upon us again I wanted to fix the issue. At this point im thinking of fabricating a branch over pipe that will flow directly to the throat of the "carb". It seems everything is working as it should, but just needs to be closer to the throat (hopefully wont affect the airflow). Most all other PCV's on other engines are at the bottom end of the carbs, not the top end. And they do push oil.

Most all other PCV's on other engines are at the bottom end of the carbs, not the top end. And they do push oil.

Some marine engines are infamous for dribbling oil. A lot of operators fitted "slobber cans" on the PCV hose to trap the oil before it clogged the air filters.

Its essentiall a labyrinth trap with a baffle and gravity drain to trap out the oil befoer it blows into the air filter element. Maybe you can fit something similar.

Thank you. I appreciate your input and helping me move forward with a fix. Just wanted to make sure there was or was not an "easy fix".

Just a long awaited folloup. I fabricated a flow tube that directly points down to the throat of the carb from the breather tube. Though i have not had a "loaded-generator" time since the last post, the exercist runs have not produced any oil in the filter. Hopefully this fixed the issue, though it should have never been on in the first place had the engine been designed correctly with the pvc at the base of the carb, not into the filter area.

Hello Kles0015, I wonder if you can tell me what service issues arise from light load running of your RS12000 when on propane fuel. I am familiar with gasoline and diesel genset service issues but lack familiarity with propane. By light load I mean someting under 3kW on a RS12000 possibly aas litte as 1kW.

Thanks in advance.

Elnav

In extreme cases (ie. low ambient temps, extreme moisture conditions) it is important run the product for an extended period of time (30 minutes or so) at around half load to ensure you the engine oil reaches a high enough temperature to boil off any moisture or condensation in the oil. The only other concern is unbalanced loading of the generator. For example, if one leg of the generator is loaded to 3kW and the other at 0kW this can impact alternator life. Otherwise, low load levels do not hurt the generator. With proper application, maintenance, and care these products can last a long time.

Kles 0015 wrote: In extreme cases (ie. low ambient temps, extreme moisture conditions) it is important run the product for an extended period of time (30 minutes or so) at around half load to ensure you the engine oil reaches a high enough temperature to boil off any moisture or condensation in the oil.

REPLY

And therin lies the problem. How do you load a 12kW generator to 50% when you haven't got anything to connect that is larger than one 3kW charger feeding from the 120V supply.

Anne told me Onan replaced the air cooled honda powered 12kW with a 15kW liquid cooled engine. BUT . . nothing changed in the solar house. They still have only one 3kW charger. And yes you are probably correct it is a 120V load thus creating unbalanced loading on the windings. That just makes the situation worse.

The 15kW genset is going to run even lighter load than the 12kW genset on the same charger. Which means it wil be even harder to get the engine up to proper temperature. So you end up with blow by and a pressurized crankcase. It's gonna blow oil.

The Onan emergency power pack makes good sense as a back-up to a conventional home wired 120/240 with center tapped neutral configuration. The home owner is not accustomed to managing loads and their electrical panel is not configured with split busses to prioritize loads in the way a solar powered home is. And it has electric hot water, washer and dryer, and so many extra loads its easy to load the genset to at least 50%.

BTW early winter is also the worst time for solar houses. There is still lots of moisture in the air, but ambient temps have dropped - ideal conditions for cloudy, snowy weather. Later on in the winter, as the air dries, you get more sunny, but cold weather. That the solar panels can cope with. And thus there is less reliance on back-up gensets since the panels are now providing more charging power. Late Dec and early Jan is the worst months in Ontario for a solar house. I lived in Ontario for a quarter century so I know. I was involved in alternative energy even than.

> I am the product manager for Cummins Onan residential products.

Well, I admire your willingness to reach out and engage those who might have had less-than-positive experiences with their Onan products. In that vein, I have a situation for you and/or anyone wlese who might want to weigh in:

My family and I live in an off-the-grid home with a battery bank and inverter (currently Xantrex XW series 120/240 inverter/charger) that powers all house loads via AC. We have had a few generators as back-up power and, with a relatively small PV system, they get a fair amount of use (200 hrs/yr?).

After using a cheap, portable, gas generator for several years, I wanted to get something more reliable that had auto-start capabilities and for which field service was available. So in 2002, I bought an Onan RS12000 new from the local distributor. Not long after it went into service, it developed a surging under load with the AC Hz swinging from 63 to 57 Hz on a roughly 1Hz surge frequency. The surging is clearly audible and the oscillating is visably evident at the throttle actuator. Our local Cummins/Onan distributor has tried, unsuccessfully, to solve the problem and it has cost me much time and money. The following have been replaced (some under warranty, some on their dime, some on mine, some on homeowners): plugs, wires, coil, governor control board, and, most recently, the main control board.

Nothing has really made a difference. The surging limits the load I can put on it to approx 6A/leg, though sometimes I can get away with 20+A/leg. I can dial the load to whatever I want via the battery charging controls of the inverter/charger. Often, the surging swings enough to generate an 'over/under frequency alarm' on either the generator or the inverter. As you would expect, the volts and amps also fluctuate. I end up using much more fuel than necessary while generating relatively little power.

None of the other generators I have used with this inverter/charger equipment have had this issue and I would consider them all to be much less sophisticated than the RS12000. It will also continue surging if I electrically disconnect the charger load once the surging starts. I am at the point where I need to get rid of the RS12000 and go with something else.

I have been listening to the pulsing drone while writing this (cloudy lately) and just noticed that it must have over/under frequency alarmed again, as I now have zero amps coming in. ARGH!

Help!

Tim

I have the same generator. 699 hrs. Tons of issues. 4 control boards.

The surging is caused by a weak actuator/solenoid. I dealt with your same problem for two years before just replacing it after watching it hunt around and audibling hearing the frequency drop. You can buy one from Onan or buy it through distributors for much cheaper. It took about 15 minutes to replace it.

After spending three years and over $1,000 trying to eliminate the surging, including several visits by Cummins/Onan techs, it turns out that, yes, it was the governor actuator. This was the same actuator that had tested out fine per the factory diagnostics. I replaced it today and it ran rock solid. Many thanks.

I had a failure of the automatic transfer switch Model#: 12GHAB-102A that was bought, together with an RS12000 generator,from Costco. I was told by the local service dealer that this ATS had a design issue, and had been discontinued for that reason. I'm trying to understand what the true situation is with this switch, and what my options are for repair or replacement. I described the situation in an email to ask.powergen@cummins.com last April, but never got a response. What would you suggest?

More information is needed to determine precisely what is behind the 'design issue' causing a discontinuance. Has UL or CSA issued a consumer warning? such a warning would contain details. Having seen too many dealers dissing competitors products in an effort to sell a new product to unsuspecting consumers I am inclined to go for a second opinion.

I have a RS 12000 Genset purchased in late 1999. Can you tell me the sparkplug and gap to use for this equipment. Thanks.

I think you have got your answer straight from the horse's mouth - so to speak

John.

well.. .I could have gotten that exact reply from their website. I am looking for a more hands-on, un-corporate view. Anyone out there have any other opinions?

Yeah, I have an opinion backed up by experience, although I don't have your specific generator. The Honda is a great engine. Well built and doesn't require a lot of maintenance. Mine (several) always start. The trick, if you can call it that, is to run the carb dry every time you put the unit away for any more than a week. Use fuel stabilizer in the tank. And if you're not using the generator often it will pay to drain the tank of fuel and only add gas when you're going to use it.

I suspect you have a gummed up carb. It shouldn't be a difficult DIY project to take it apart and clean it. I bet it would be fine after that.

if you're not using the generator often it will pay to drain the tank of fuel and only add gas when you're going to use it.

Good advice! but . . . what about gensets specifically intended for emergency (back-up) use. The whole concept relies on having the generator fuelled and ready to run on a moments notice. The description of these units being residential and "blending in" with a residential landscape suggest they are intended for placement outdoors next to a house. I wondered why the recent shift to natural gas or propane fuel. Now I begin to see some possible reasons. We have the same problem in the marine world. Fuels destabilize when stored in tanks on board.

I have been told that most fuels are burned witin 30 days of leaving the refinery. Therefore refiners no longer add long term stabilizers to the end product. Its a cost reduction practice.

Some of the emergency gensets run on the natural gas piped to the house. If that's not possible then fuel stabilizer in the tank and a water seperator in the line has to be used. The reason for the latter is that, no matter how full the tank is kept, condensation will form after enough temperature changes.

The best way to take care of the problem is to drain the fuel regularly and use it in a machine that gets a lot of use, preferably something that has a much larger tank than the genset.

Unless you have health critical equipment or a really large server farm then UPCs will do for a few things and the food in the fridge isn't going to spoil in the time it takes to get the generator fueled and running.

I think people are being sold a pig in a poke with the automatic systems because they don't need instant power and they probably won't follow the maintenance required, so when the do need the thing to run the fuel will probably be stale, the starting battery flat and the piston siezed.

Oh well!

While I agree with comment about a pig in a poke when you are talking suburban homes, there are many applications where unattended automatic start would be required. Nor is the usual UPS adequate for the task of back up power. Evidently you assume there will always be someone there to automatically handle starting up the genset. If that start up includes refuelling the genset, initiating the manual transfer switch operation, and possibly also manual load management, I submit that this is often considered too complicated by many householders, especially their wives..

Nor does this manual system which involves draining the fuel tank after every use make sense in areas with random or selective power cuts. These power cuts are not always scheduled like clock work. The duration may be indeterminate. Homes in cold climates where freezing is a strong possibility are not candidates for such an approach. Most heating systems depend on fans and pumps powered from AC mains. Propane is not an option since propane wil not volatize at such low temps.

Homes with two working parents are often left unattended 12 hours at a time.

You wrote: "The best way to take care of the problem is to drain the fuel regularly and use it in a machine that gets a lot of use, preferably something that has a much larger tank than the genset."

REPLY: That raises some interesting problems. What other machine? Hereabouts generators are typically run on farm fuel which is colored. The only other machine using fuel is the road vehicle. Its illegal to use colored farm fuel in on the road vehicles and incurs a large fine when you are caught!. On the other hand the road tax saving buying farm fuel makes it hard to justify buying road taxed fuel for generator use. Not to mention which you normally don't buy farm fuel in little dinky 2 gallon tote cans.

Our well serves three families. No power and suddenly three families can't use the toilet, can't wash their hands or do any number of normal household activities.

The sad reality is that we are likely to see more outages, more controlled brownouts or rolling black outs. The EPA proponents don't want to allow building more power plants period. The Environmentalist crowd don't like nuclear, coal, or fossil fuel power. The Sierra Club advocates are dead set against any further hydro electric dams. And the NIMBY crowds don't want wind power or visible transmission lines that spoils their own view.

Our ageing power distribution grid is wearing out. Without new construction to meet growing power demand, we will see much more outages, and they will last longer. Herabouts a short outage can last 8 hours. It might take a day or more if the damage is storm related. Standby generators is definitely a coming thing and represents a growing market. Fuelling these will involve a lot more than having a few piddly little 2 Gal. tote cans in the garage..

"I submit that this is often considered too complicated by many householders, especially their wives.."

Harumph! <stomps around>

We wives know a lot more than you might think...

Oh yes I know. My wife will chop wood, run the saw mill and mix formula for new born livestock. She is an absolute wiz cooking over an open fire. But no way will she mix 2 cycle fuel for the chain saw or replace a blown head gasket on a tractor.

Mind you she's also pretty dang good on the 'puter. Specially since she didn't even know how to turn it on seven years ago when I first met her.

She comes from 3 generations of saw mill operators & loggers. There ain't no job on the saw mill she or her mother won't tackle. But don't ask 'em to do nuttin' with dem new fangled infernal combustion engines.

It's them citified young fillies I'm talking 'bout! Scairt ta do anyting lest they break a well manicured finger nail. And heavens! dey mite achully git dirt under dem purty finger nails.

Mind you, I've had a couple of girl friends who could turn a wrench with the best of 'em at the racetrack. Could drive too! Some even blow my doors off at times. But dey be de excepshun rather than the rule. He he he!

Ann, I have sent you another letter in regards to your issues. I have yet to here back from you in regards to your service intervals. As discussed the service as outlined in my letter must be followed in order to insure product reliabilty.

Dennis McIntyre

If this is off topic I apologize but I am interested in an opinion. I had a natural gas Pow'r Gard AE12 unit installed about nine years ago. Aside from some minor problems, it has functioned well. When it did not kick in last week during a power outage, I had the installer check it out. I was told the entire unit is rusted out, the company is no longer in business and that I should replace this with a Cummins 20Kw unit along with redoing the transfer switch and having to make some modifications at the outside site. His price for everything is about 15K. Does this sound reasonable? Could I get away with the smaller and less expensive 12K model? Any additional advice would be appreciated as well. Thanks in advance.

Two issues emerge from this post. Apparently the 12kW unit was sufficient for the load when it ran so why would you go for a much larger unit except to line to pocket of your dealer with your cash. Secondly motors do not 'rust' out for no good reason. I work around boats and except when a water cooled manifold perferates after many years of service in salt water you do not get water inside the motor . I have seen engines with valves left in open position allow moist air into some cylinders that created surface rust on the cylinder. Any competent mechanic can fix that. Had to do it myself on a few occasion. If the motor is water cooled and the head gasket blew and allowed coolant into one cylinder it might require an cylinder rebuild. Sounds very much like the installer figured he could make a quick sale of new and more expensive equipment.

I appreciate your comments. I have addressed this with my installer, who is an electrical contractor. I told him that $15K to replace the unit is excessive and he is allegedly "seeing what he can do". I'm not sure if I can get someone else to come out and check on the unit but based on your comments, I will make a better effort. The 12kW unit did not run everything and we have had house renovations since then so a slightly larger unit would not be unreasonable, though probably not mandatory. I was told the residential units were not as reliable as the larger, more commercial units. Thanks again.

Since there seems to be an abundance of offgrid understanding here I have a RS1200 that is 4 years old and will not run.

I changed the plugs, since it didn't sound like it was getting any spark, but that didn't help. Also checked all the settings on the inverter system and it doesn't seem to be sending any signal to shut down, so doesn't appear to be that either (plus it always worked before when switched to "on", regardless of the inverter). I also thought it might not be getting fuel, but the propane tank is full and the hot water, gas fireplace and gas stove are working fine and they all feed off the same line.

The generator turns over fine but just doesn't "catch" and power up like it used to. It sounds like the starter is continuing in the background, then it shuts down after about 5-10 seconds and the readout says it overcranked.

Any ideas?

Your last paragraph gives a significant clue. If the circuit of something like the low oil pressure is not over ridden the low oil alarm willl inhibit the ignition and no start happens after a time-out period, the cranking limiter kicks in and stops the cranking.

First check the oil level and be sure it is right on the mark, not low or overfilled.

Verify you get spark right at the spark plug.

Can you get or download a service manual? Follow the trouble shooting guide.

Even if the propane tank is full, the fuel solonoid may not be opening on the genset. This would also cause the cranking limiter to trip eventually.

I'm most suspicious of the oil pressure circuit. Cranking for 5 - 10 seconds should bring up enough pressure to cause the crank circuit to switch off. The most common way to detect the generator has begun running on its own is if the pressure comes up. Since the starter runs for the full duration of the time out period. either you are not getting pressure or the wire fell off the sensor.

Thanks for that. The solutions for Fault Code 4 for Overcranking is very limited and has been done. The fuel solenoid is a good option as it sounds like it is just not getting fuel. The oil pressure may explain things too. The worst part is that it is a couple hundred miles from the nearest assistance. I am a renewable guy acting like a mechanic to try to help a customer/friend to avoid having to have a mechanic come all the way out or having to pull the gen.

I can sympathize. We only live 50 miles from a town but the genset dealer there has to check back with their main office 600 miles away. Sometimes those automatic controls are more trouble than they are worth. However unless you have some understanding of electrical circuits it might be difficult to bypass all that stuff and reduce the engine to basics. as in manual start/stop, no controller etc. I would be inclined to tee in a manual oil pressure gauge and maybe a check lite to verify the fuel valve is activated and open. The advantage of growing up in farm country is you get lots of practice in fixing machinery and recalcitrant engines.

I once had difficulty with some propane fuelled equipment because the vapor pressure was too low. Running off a fresh full 20 lb propane bottle solved that issue.

Still trying to figure this thing out. Now got rid of the overcrank message and am getting "needs service" (three flashes). Generator now runs for about 2 minutes (starter kicks out after about 10 seconds) then shuts itself down. Actually ran for about 5 minutes at one point, generated lots of amps, had the inverter blinking "bulk" and was running the house, but then shut down again. Never did really kick up to the high rpm it used to when it would run the house. Changed the oil, oil filter, air filter and plugs, but no luck. Seems to be a control kicking in as you said. Waiting to hear back from Cummins on it. Any further advice would be appreciated. Rob

Home | Mechanical Engineering | Mechanical Engineering | Onan RS 12000

Home | Mechanical Engineering | Mechanical Engineering | Onan RS 12000

The GHAB and RS12000 units both use AC voltage to disconnect the starter. As soon as the controller senses the voltage it disconnects the starter. The slip rings on the back end of the generator get dirty and it no longer makes enough voltage in the 6 sec time delay, therefore causing the "overcrank" fault. Either use slip ring stones or very light (220 grit+) sandpaper on a stick and clean the slip rings while cranking unit until it makes proper voltage.

-Onan Tech

Sorry to revive an old thread, but I could use some help.

I have a 2004 Onan Generator RS 12000 Model 12GRCA-422A running on propane. I'm getting an error code, 4 flashing red lights, so I would like to perform regular maintenance such as replacing air cleaner and oil filter. However, I was a bit shocked to discover the price of the replacement parts from Onan: Air Filter Part #184-0142 for $173 and Oil Filter Part #184-0141 for $55.35.

Onan customer service could not explain the exorbitant price and suggested I contact a Honda dealer or even an RV maintenance site. I can't locate a Honda engine number to even know what to ask Honda for. It's very annoying of Onan to charge such outrageous prices for basic parts when they go from Honda to Subaru engines. I don't think I would purchase their products again. Can anyone suggest another less-costly option for the air cleaner and oil filter?

Thanks