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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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Originally Posted by DirtRoadLife View Post
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.

https://www.walmart.com/ip/Camco-444...IaAvuLEALw_wcB
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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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