Onan genset question

[Paladin]

I occasionally run across used gensets and have thought of getting a 6.5kw gas Onan to replace the Kohler 10kw that I have that is quite loud and not very practical. Yes, I would prefer a diesel unit but.....
How loud is an older model 6.5 kw Onan by it's self and then in a decently built box?
What have people used to maybe further muffle without excessive back pressure? How much mechanical noise is there beyond the exhaust noise?

I know there have been many, many discussions on how to build a box and many differing views but when it's all said and done how loud can one expect it to be? Has anyone ever used a db meter to measure it before and after a box or other mods?
This isn't really a project that I'm considering tackling real soon since I'm inundated with other projects but I like to keep a smart eye open in case a good deal falls into my lap.

Does anyone have anything positive or negative to say on the various 6.5kw units?

[gumpy]

I can't speak in terms of db, but my 7.5Kw Quiet Diesel is quiet enough that you can carry on a normal conversation standing next to it. You can still hear it, but it's not obnoxious. More
like a low hum.

The unit is self contained, and relatively new, not an older unit, so I didn't build any other type of enclosure. I still have to route the exhaust toward the back of the bus, and hope that
will quiet it even more, but I'm very happy with the unit. I'm currently working on completing the installation and sealing it around the floor, and then will be connecting the autostart
to the inverter and building a remote panel for inside.

craig

[JackConrad]

   One of the things we did when we made our sound compartment that our diesel generator is installed in was to separate the sound sources. The generator is installed in the OEM AC condenser bay (driver's side behind front wheel), the exhaust is plumbed to exit just in front of drive axle, driver's side and radiator (and electric fan) is remoted to rear of OEM spare tire compartment. It can be heard but you can carry on a conversation in a normal voice anyplace outside the bus.
   This generator replaced an older Onan 6.5 air cooled gasolene version. That one required a larger opening for cooling air supply and the air fan on the generator exhaust was directly below the generator through the floor. It was louder than the new one, but you could carry on a conversation, lthough it required raising your voice slightly.  Sorry, no dB ratings.  Jack

[WEC4104]

I have an Onan gas unit similar in size to the one you mention.  It is installed in the bay on my 4104 that used to house the coach's original A/C engine.  This bay's door is covered with a heavy mesh screen, instead of being solid.  I have not added sound deadening insulation, an enclosure, or extra mufflers.

As far as the noise level is concerned, I find it pretty satisfactory.  From inside the bus, you can hear it running, but it is rather non-intrusive.  Outside, you can stand next to it and carry on a conversation easily, but even 150 feet away you can tell that it is running.   The sound coming from it is also a low mechanical rumble which is not the type of noise I find unpleasant, either.

Parked closed to other campers, I would never run the generator all night long, especially if they are in a tent.   But if I was boondocking somewhere, and for some reason I needed electricity all night, it would be no problem to sleep with it running.  From the inside, it makes no more noise than the roof A/C unit.

As far as reliability goes, I have had my share of issues with it. I have performed surgery on the controls and wiring several times. Once, I found a blown rectifier and was able to replace it for $7.  Another time I found it had stopped sending power to the fuel pump and my only solution was to replace the main control board ($175?).  Overall, it hasn't been one of the bus' more reliable systems, and I cross my fingers everytime I go to start it. Hopefully though, I have worked the kinks out of it. It was installed by the bus' previous owner, and if I can trust the hour meter, it currently has about 850 hours on it. I can pretty much figure on .6 gallons of fuel per hour under my typical usage.

Like anything else, I think it comes down to what you can get for the $.  If the right deal comes along for a used Onan, it might be an acceptable option for you. Personally, I think from my past experiences, if I had the option to choose something else (Honda EV6010?) or a diesel, that would be my dream.  

 

[TomC]

I have a Powertech 10kw Diesel genset that I made my own sound box for out of 3/4" plywood and 1" leaded insulation.  It is quiet enough on the outside that if a "Quiet" Onan is running across from where I'm parked, you have to be within 10ft of my bus before you'll hear the low hum of mine.  Inside, it is not as quiet as I like, but I'm more concerned with my neighbors.
Air cooled anything is harder to quiet since air flow is a big consideration.  I had a Onan 6.5kw Emerald Commercial on my truck and I can say without a shadow of a doubt-spare your self the agony and frustration of trying to keep a gasoline unit running.  They require spark plug cleanings and periodic spark plug replacement, decarboning (and I always had at least a 1500 watt load on it [my block heater] at all times), carbuerator problems (have to adjust for altitude), replace the brushes in the alternator-and this with me getting 12,000 hours out of it before it gave up.  As compared to what I have to do with my Diesel genset-change oil and filters at 150hour intervals-period-no comparison.  Good Luck, TomC

[gus]

I had an Onan gas, air cooled gen. It was originally 7.5KW, three phase. After it was converted to single phase it became 5.5.

Even though it was mounted on two huge rubber cushions it was noisy and shook the whole bus. It got so hot, mostly the exhaust system, that I finally had to use a lot of insulation on the exh system to be able to use it while stopped.

It drove me nuts so I finally gave it away and bought a Honda liquid cooled 6KW which is quiet and doesn't shake the bus at all.

The Onan weighed twice as much as the Honda.

In fairness, the Onan was originally a stationary standby gen so was never meant to be mounted in a bus.

I won't ever own another air cooled gen for a bus.

[JimGnitecki]

The 1979 Eagle conversion I bought just recently came with an Onan 7.5 kw diesel liquid cooled generator.

It is NOT enclosed, and was installed in the screened area on my Eagle, beside the bus engine, where the bus air conditioning system used to be.

Here is the surprise: When I drove it in the first time to an RV park where two of my friends keep their motorhomes, BOTH of them separately remarked how QUIET my generator is compared to most!

Now I myself do not consider it "quiet" when I am anywhere NEAR it. I consider it annoyingly loud. However, I do have to admit that if you are not literally right beside it, it does seem fairly quiet. If you are near the bus, you know there is a generator running, but it is not objectionable.

VIBRATION though is notable. My generator sets up a resonance in the upper cabinets in the bedroom, which I will likely only be able to subdue by putting some weight in the cabinetry. (It's empty right now)

As for electrical power performance, I'm not that thrilled so far. The good news is that it appears to use no oil at all. The bad news is that it takes at least 3 ten second cranks to get it running, and despite its 7.5 kw rating, it is NOT able to handle the peak load if BOTH basement air conditioning units try to start up their compressors at the same time. It stumbles a bit, and one of the air conditioners flashes a "power issue" light and shuts down its compressor to protect it.

The inability to handle a dual compressor startup might be expected, as a 7.5 kw generator will produce at best maybe 60 amps theoretically. Each air conditioning compressor requires about 14 amps to stay running, but probably requires 3 times that when STARTING UP. Hence, the 7.5kw is probably not enough for dual basement air conditioners.

Jim Gnitecki

[Barn Owl]

I see old 6.5 Onans for under $500 all of the time. My bus came with one and I find it acceptable and not unpleasant. If I had a magic wand I would get something else but until that happens I will keep it.

[Len Silva]

The 1979 Eagle conversion I bought just recently came with an Onan 7.5 kw diesel liquid cooled generator.
(snip)
As for electrical power performance, I'm not that thrilled so far. The good news is that it appears to use no oil at all. The bad news is that it takes at least 3 ten second cranks to get it running, and despite its 7.5 kw rating, it is NOT able to handle the peak load if BOTH basement air conditioning units try to start up their compressors at the same time. It stumbles a bit, and one of the air conditioners flashes a "power issue" light and shuts down its compressor to protect it.

The inability to handle a dual compressor startup might be expected, as a 7.5 kw generator will produce at best maybe 60 amps theoretically. Each air conditioning compressor requires about 14 amps to stay running, but probably requires 3 times that when STARTING UP. Hence, the 7.5kw is probably not enough for dual basement air conditioners.

Jim Gnitecki

Don't know what basement unit you have but chances are there is (or should be) a time delay after ac power is available.  It should be fairly simple to change the delay on one of the compressors so that they don't start at the same time.  It only needs to be a few seconds difference.  Trying to start both at the same time, on generator or shore power is hard on everything including the compressors.
If it's the thermostat that's calling for both to come on at the same time, then a two stage stat might be in order.

[JohnEd]

I have had a 6.5 for 19 years and full timed with the coach for more than a year.  It has a squ. cage blower that moves a lot of air in keeping it cool and it moves the same amt of air whether the gen is hot or cold and without regard to load.  It isn't silent in that regar but it isn't something I would want to "fix".  The gen "head" seems to make a low pitch hum....not all that bad.  Even taken together my 6.5 isn't bad at all.  I have slept with it running the roof AC on many occasions but sleeping is my long suit.

The exhaust is a slight bit more intrusive.  That sys needs to be constructed from heavy gage "water pipe".    Get a spendy muffler off of a high line Jap road bike.  They are over engineered to be quiet and last an eternity.  If you have enuf space to mount a car muffler that may be a solution to consider or try.


John

[Paso One]

I have the 6.5 onan and it is fine for noise. I don't notice any excess vibration . FWIW