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Old 11-14-2020, 12:04 AM   #1
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Has anyone quieted the NPS 5500 generator?

Hello just got a new XLR Boost and it came with the NPS 5500 generator. Wondered if anyone has tried to put a muffler on are move the exhaust at all to quiet this model down?

Thanks
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Old 11-14-2020, 07:53 AM   #2
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welcome to the forum its a great place to get your questions answered. I suspect it has a muffler installed. You might consider getting one of those exhaust extensions kits to reduce the noise or build one yourself. Are you sure the noise if from exhaust and not vibration of the unit?
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Old 11-14-2020, 10:42 AM   #3
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I am getting ready to put some dampening material in the box and seal the area. I was just wondering if anyone had any luck with the exhaust. I am debating on trying a gensilencer.
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Old 11-14-2020, 11:07 AM   #4
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Don’t forget to consider the impact on cooling also.
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Old 11-14-2020, 11:59 AM   #5
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I am getting ready to put some dampening material in the box and seal the area. I was just wondering if anyone had any luck with the exhaust. I am debating on trying a gensilencer.
Like eye95 said you need to be very careful of not blocking the cooling of the gen . . as far as routing the exhaust they do make extension kits and parts for general locating of the exhaust
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Old 11-14-2020, 01:52 PM   #6
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Yeah I have been trying to find a relocation pipe kit for it. But since it is new I might just use a flexible exhaust hose and route it differently. I will be making sure I don't overheat the generator. Was just hoping someone might have already taken on this venture and have and idea I can use.
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Old 11-14-2020, 04:42 PM   #7
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I put some Kilmat sound deadening material on the door, helped a little. I bought a 6 ft piece of flexible exhaust pipe, it has a larger diameter than exhaust pipe so it will not create any back pressure, it made a little difference in the noise level, also kept the exhaust away. On my FR3 the door to the generator has vents on it and ducting to the generator cooling intake, a lot of noise comes from there so I made a box out of plywood open at the bottom so the sound is directed downward, it hangs from the top of the door and I put felt around edge to prevent chaffing the paint on door. I covered inside of box with Kilmat and that really helped with noise level. It is larger than vent opening so it will not restrict air flow.
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Old 11-14-2020, 07:22 PM   #8
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Helps a bit.

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Old 12-01-2020, 11:04 PM   #9
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I just got a new Nitro XLR with this "Yamaha" generator and ran it for 50 hours straight while at the track (stopping at 20 hours to perform the break-in oil change, of course) and I can certainly say that this is MUCH louder than Onan units I hear in other toy haulers at the track.

Fortunately, it's already somewhat loud at the track so, unlike a campground, I'm not getting any complaints. That said, it is still much louder than the portable inverter generators I've used on my other toy haulers in the past...

Given the nature of the sound, I'm actually thinking the noise is primarily a high speed cooling fan and not actually the engine itself. The consistent, loud, almost jet engine/turbo prop sound, makes me think it is simply a single speed cooling fan that is generating the bulk of the noise. What is particularly annoying is that this noise is the same across all load levels.

If the generator is indeed an inverter type it should adjust its engine speed in concert with load since there is no need to match engine speed to AC frequency. So, again, I think that the issue is actually the cooling fan.

I'm planning to place a temperature probe in the casing of the unit to measure temperature while under load and under various ambient temperature conditions. Once I have an idea of what its running temperature ranges are then I might look to see if it is feasible to modify the generator's cooling fan to adjust speed with temperature--assuming that I do confirm the primary source of the loud noise is the cooling fan.

Anyway, I'm curious to hear what others think regarding the source of the noise?
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Old 12-02-2020, 07:03 AM   #10
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I was running mine and also trying to figure out where the bulk of the noise comes from. I don't think its exhaust noise but actual engine noise. In my Wolf Pack it seems like its really loud under the generator compartment where its mounted. I also pulled the engine access cover to find the source. Its still seemed like the engine was making the bulk of the noise.
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Old 12-02-2020, 12:35 PM   #11
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I completely agree that the bulk of the noise seems to not be from the exhaust but, rather, from within the cabinet. The nature of the noise, particularly its frequency, leaves me thinking it isn't the engine itself but the cooling fan.

I'm going to get a multimeter to measure the spark pulse frequency to determine engine RPM to first verify that the engine changes speed with load. If it does, then this should be very detectable in the signature of the noise generated by the engine. I will also see if I can momentarily disable the cooling fan--I'm sure it is electric as I doubt very much a small engine like this would have a shaft-driven fan--as this would most certainly prove if the source of the noise is the fan itself.
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Old 12-02-2020, 02:25 PM   #12
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Let us know what you find out. I know audibly the engine sounds the same with everything off as it does with both A/C units running. Its certainly isn't the same technology as a portable Honda that you can hear rev up and down based on load.

I think there is some false advertising with this genset but that's a whole different discussion.
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Old 12-02-2020, 02:56 PM   #13
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Given the nature of the sound, I'm actually thinking the noise is primarily a high speed cooling fan and not actually the engine itself. The consistent, loud, almost jet engine/turbo prop sound, makes me think it is simply a single speed cooling fan that is generating the bulk of the noise. What is particularly annoying is that this noise is the same across all load levels.
I read the literature for this generator and the "Jet Engine Sound" was mentioned. They purposely engineered the cooling system to create massive air flow so the generator wouldn't shut down due to extreme hear and to overcome air restrictions due to their extra sound controls built into the enclosure.

From an engineering standpoint it may only be possible to deflect sound or place some acoustical damping medium in the air exhaust path that "sucks up the noise".

The problem is sort of like removing the air cleaner on an engine and the amount of noise it produces. The air filter diminishes the noise but still has to let enough air flow to let the engine "breathe". Now one has to figure out how to put a device on the air discharge to diminish the noise without impeding the air flow.
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Old 12-02-2020, 03:15 PM   #14
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You might consider getting one of those exhaust extensions kits to reduce the noise or build one yourself.
If it's a new rig, I'll caution the owner to check the owner's manual and find out if these are spoken about in them. I know we are talking about a different generator but my Onan specifically talked about the Genturi and related devices and threatened warranty claim issues if you used one.

I'll also say, with the Onan at least, it doesn't make any difference in sound to me. Just the direction of the exhaust.
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Old 12-29-2020, 08:13 PM   #15
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I had an opportunity to look into this a little more and I have some findings...

First, the centrifugal fan appears to be shaft driven which would make any electrical PWM or VFD approach to adjust fan speed by housing temperature impossible...

Second, I installed an inductive RPM meter along the spark wire and it is measuring around 3800 RPM the engine speed does not appear to change with load when I tested by running both ACs at full. This is further reinforced by what I believe to be the engine throttle which seems to be locked into a constant position with a screw....

I hope I'm wrong about the fixed throttle position, however, as this would mean that the only advantage of this being an "inverter" generator is that it is simply converting the initial multi-phase AC 60hz signal into a DC signal and back into a single-phase but very smooth 60hz AC signal. It would also mean that this generator is leaving on the table any fuel efficiency gains by reducing throttle when under light load thus avoiding additional friction losses, etc...

Given what I have come across thus far I can say the following about this generator--please feel free to correct me where I may be wrong:
1. Engine cooling is direct drive and constant speed; since
2. Engine speed does not vary with load; which comes as little surprise since
3. Engine throttle is locked at one setting

As far as sound dampening goes, I'm going to install some acoustic foam panels in the generator compartment while keeping an eye on the change in temperature in the compartment. This will not really resolve the primary issue I have with the generator which is simply the noise it produces when outside the rig. I suppose the only solution at this point would be to build a collapsible wall that is lined with acoustic foam panels that I would have to place roughly around the engine and cooling exhausts....

So, in summary: get the Onan!
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Old 08-24-2021, 09:42 AM   #16
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I know this is somewhat of an old thread. We have been dealing with this issue since our first trip using the generator. If you have never experienced how loud this thing is let me elaborate. I used to work in aircraft maintenance and we had generators on the flightline that were quieter than this thing.

What I found was the bulk of the noise is generated by the highspeed flywheel fan. This noise echoes off the ground and is trapped by the bottom of the RV amplifying the sound kinda like pointing the speaker of your cell phone into a cup to play music.

My approach to this problem was to make a sheet metal duct lined with heat resistant sound absorbing material to duct the airflow and the sound horizontally away from the generator and at a more gradual slope to the ground. This deadens the initial noise while not limiting air flow and also prevents the bounce back effect of the sound reflecting off the ground under the RV. This was a major success but did not cure the problem 100% because I still needed to deal with the intake side of the generator. I used the same material to make an airbox of sorts with overlapping passages that would still allow the air to freely flow to the generator while still redirecting and absorbing the sound. This probably deadens 85% of the sound from the generator, now you can actually hear the exhaust, before you couldn't even hear it over the whine.

It is no where near as quite as my super quite inverter generator but I think it is about as good as it will get unless I can tackle the load sensing throttle so the generator isn't running at 85% all the time.
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Old 08-24-2021, 09:57 AM   #17
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I know this is somewhat of an old thread. We have been dealing with this issue since our first trip using the generator. If you have never experienced how loud this thing is let me elaborate. I used to work in aircraft maintenance and we had generators on the flightline that were quieter than this thing.

What I found was the bulk of the noise is generated by the highspeed flywheel fan. This noise echoes off the ground and is trapped by the bottom of the RV amplifying the sound kinda like pointing the speaker of your cell phone into a cup to play music.

My approach to this problem was to make a sheet metal duct lined with heat resistant sound absorbing material to duct the airflow and the sound horizontally away from the generator and at a more gradual slope to the ground. This deadens the initial noise while not limiting air flow and also prevents the bounce back effect of the sound reflecting off the ground under the RV. This was a major success but did not cure the problem 100% because I still needed to deal with the intake side of the generator. I used the same material to make an airbox of sorts with overlapping passages that would still allow the air to freely flow to the generator while still redirecting and absorbing the sound. This probably deadens 85% of the sound from the generator, now you can actually hear the exhaust, before you couldn't even hear it over the whine.

It is no where near as quite as my super quite inverter generator but I think it is about as good as it will get unless I can tackle the load sensing throttle so the generator isn't running at 85% all the time.
Allow me to save you a lot of time...

Someone posted elsewhere that NPS has an ECO conversion kit with a sound box. The eco kit allows the genset to idle down with no load. I gambled and bought the kit (520 shipped with sound box for free) and installed it within an hour
It is literally a night and day difference. The genset was idled down with no load, one 15k A/C slightly bumped the RPM's. The 2nd 15k A/C raised it slightly more. Then I added the microwave which even with all this load the genset was still quieter than before.
The sound box might not make much difference but sounds like what you created already.

https://www.npsrvpower.com/product/eco-kits/
https://www.npsrvpower.com/product/sound-box/

YouTube video that convinced me to give the kit a try...
https://youtu.be/as-j05pEneE
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Old 08-24-2021, 10:21 AM   #18
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Allow me to save you a lot of time...

Someone posted elsewhere that NPS has an ECO conversion kit with a sound box. The eco kit allows the genset to idle down with no load. I gambled and bought the kit (520 shipped with sound box for free) and installed it within an hour
It is literally a night and day difference. The genset was idled down with no load, one 15k A/C slightly bumped the RPM's. The 2nd 15k A/C raised it slightly more. Then I added the microwave which even with all this load the genset was still quieter than before.
The sound box might not make much difference but sounds like what you created already.

https://www.npsrvpower.com/product/eco-kits/
https://www.npsrvpower.com/product/sound-box/

YouTube video that convinced me to give the kit a try...
https://youtu.be/as-j05pEneE
Ok two things. One the sound box is pretty much what I made except mine is a little longer. Two how in the hell in 2021 is that "eco-kit" not standard on a generator in an RV? Not only do I have to dismantle the entire generator to install not difficult but time consuming but I have to remove the f___ing generator from the RV to do it.... That looks to be a huge PITA.
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Old 08-24-2021, 11:08 AM   #19
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Ok two things. One the sound box is pretty much what I made except mine is a little longer. Two how in the hell in 2021 is that "eco-kit" not standard on a generator in an RV? Not only do I have to dismantle the entire generator to install not difficult but time consuming but I have to remove the f___ing generator from the RV to do it.... That looks to be a huge PITA.
Fully agree! It looks like their new models are all standard with the Eco set up.

From starting to remove genset to firing it up back in the RV was roughly a little over 2hrs start to finish. Maybe our 5th wheel has easier access?

6 bolts hold the genset to the RV plus the exhaust clamp had to be removed to take the exhaust pipe off from the underside.
By far the biggest pain was the fuel line clamps (x2)
A wire connector had to be unplugged, ground strap un bolted, and the "line feed" disconnected from the circuit breakers.
After this we were able to pull the genset out and work on it in the garage and follow the NPS video of the kit install. Then reassemble.

It looks like a PITA but it really wasn't. Really just need a helper to get it out. NPS claims its about 120lbs.
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Old 08-24-2021, 11:27 AM   #20
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Fully agree! It looks like their new models are all standard with the Eco set up.

From starting to remove genset to firing it up back in the RV was roughly a little over 2hrs start to finish. Maybe our 5th wheel has easier access?

6 bolts hold the genset to the RV plus the exhaust clamp had to be removed to take the exhaust pipe off from the underside.
By far the biggest pain was the fuel line clamps (x2)
A wire connector had to be unplugged, ground strap un bolted, and the "line feed" disconnected from the circuit breakers.
After this we were able to pull the genset out and work on it in the garage and follow the NPS video of the kit install. Then reassemble.

It looks like a PITA but it really wasn't. Really just need a helper to get it out. NPS claims its about 120lbs.
Looking at pictures online I think our generators have similar placement though the bay where yours is looks a little bigger. Funny thing, before I posted anything I went to NPS "site" and there is no mention of this update or upgrade. I emailed them so we will see what happens.
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