Quiet Generators

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mkgrady

Senior Member
Location
Massachusetts
I have installed several 10-20KW standby generators over the last couple of years. Generacs and Briggs and Stratton. I think they are both made by Generac. They are not very quiet. A couple of customers said they want a generator that is much quieter than these units. They likely will want a 10-20KW unit

Who makes quieter generators and are any of them anywhere near the price of a Generac?
 

eHunter

Senior Member
I have installed several 10-20KW standby generators over the last couple of years. Generacs and Briggs and Stratton. I think they are both made by Generac. They are not very quiet. A couple of customers said they want a generator that is much quieter than these units. They likely will want a 10-20KW unit

Who makes quieter generators and are any of them anywhere near the price of a Generac?

Cummins/Onan can deliver quiet, reliable and long life, but they are not as "cheap" as Generac.
 

mkgrady

Senior Member
Location
Massachusetts
Cummins/Onan can deliver quiet, reliable and long life, but they are not as "cheap" as Generac.

Yes they look to be about $1-2k more. The 13KW Cummins is on the higher end of that spread

Just found a site that lists decibels for several 20KW units
Cummins 62db
B&S 69.1db
Generac 66db
Kohler 69db

Looks like Cummins is what I will propose. Is there anything different about how they are wired as compared to Generac?
 

GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Just found a site that lists decibels for several 20KW units
Cummins 62db
B&S 69.1db
Generac 66db
Kohler 69db

Looks like Cummins is what I will propose. Is there anything different about how they are wired as compared to Generac?
The noise level will also vary more than that between models for the same manufacturer.

A difference in sound level of only 4db is not very significant, and you can make much larger differences in noise level by adding additional soundproofing and by placing the generator where there is earth, buildings or vegetation between it and the house.
To some extent the problem is not that the generator is so noisy but that the location is so quiet. :)

Normal conversation heard from 3' away is roughly 60-65db.
 

hurk27

Senior Member
Generac sells quieter generators, most generators have two pole alternators which require the engine to run at 3600 RPM to produce 60hz, the Generac Quietsource series are 4 pole generators that require the engine to run at 1800 RPM and are much quieter as well as they come with more sound deadening material in the cabinets and a much quieter muffler.

Heres a link to them: Generac Quietsource

The problem with running a gas engine at lower RPM's is that most gas engines develop their max HP at much higher RPM's so these generators will also come with a much larger engine that will produce the required amount of HP at this lower RPM, older versions used to have gear drives to run a two pole alternator at 3600 RPM while allowing the engine to run much slower but this just gave it another failure point to wear out, but these newer designs went with 4 pole alternators the engines had to be much larger to provide the HP at the slower RPM's, the 15kw through 20kw full speed (3600 RPM) Generac had a 1 liter 2 cylinder air cooled engine, the Quietsource series will have a water cooled 4 cylinder and all cast iron block and heads its the GM industrial version of the 2.4 but carb aspirated (no injection) it is called a industrial vortex, from the 22kw to the 36kw, the 36kw adds turbo charging, and a 5.7 V-8 GM carb aspirated industrial engine for the 48kw. some of the industrial versions ran the 4.3 GM V-6 industrial vortex again because your running NG or propane gas theres no injection which was one of the problems with the GM 4.3 because of the popits going bad on the end of the injection spider in the intake, again these are industrial versions of the same GM engines we see in many of GM vehicles but these are all cast iron both heads and blocks.

But as the engines get bigger so does the cost, which might bring sticker shock to your customers.
 
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renosteinke

Senior Member
Location
NE Arkansas
Generators seem to be trendy things these days, with everyone nodding sagely as they say 'whole house generator.' As if that were a good thing.

Just to stay on point, folks ALWAYS overlook the noise factor. I've installed generators so loud that one would think a dragon was roaring at start-up.

Is noise important? Well, I've had the gentle hum of an air handler become an issue in residential areas.

Let's look back at one basic: decibels. Did someone say 4 db wasn't much? WRONG. 72db is more than twice as loud than 68db- it's a logarithmic scale. 68 db is TEN times as loud as 58db.

For nearly every generator, the basic price has only minimal noise control. Nearly everyone offers a 'sound package' that cuts the sound dramatically - but it doubles the price.

Fences, shrubbery, and out-buildings area poor second choice. Do them wrong, and you'll make the problem worse.

I have other generator grumbles, but I've been nice and stayed on point.
 

GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I've heard that PV systems are pretty quiet:lol:

Some inverters hum very loudly. Especially when mounted on a stud wall with resonant frequencies.
That sort of noise in a quiet room can drive you crazy in a way that a generator might not. :)
 
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GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Let's look back at one basic: decibels. Did someone say 4 db wasn't much? WRONG. 72db is more than twice as loud than 68db- it's a logarithmic scale. 68 db is TEN times as loud as 58db.
But human hearing perception is also logarithmic. A 3db difference at any level (once you are above the background noise) is generally considered to be the smallest difference that can be reliably detected. Note that you can detect a sudden change in level a lot better than you can do separate comparisons of two different levels.
One of the problems of reducing noise a few db at a very high db level is that you have to absorb a lot more power than the same db difference at a lower sound level.
 

hurk27

Senior Member
Other then using a 4-pole alternator to run the engine at 1800 RPM's instead of 3600, the part of a generator that seems to make the most noise is the cooling fan which in many cases runs as fast as the engine, while I have seen a few belt driven fans, where the belt broke and you could almost carry on a conversation next to the generator without the fan running, if they would go to high volume squirrel cage blowers and run them at a lower speed, the rest of the engine noise could be dealt with by a better exhaust system, my car is so quiet sometimes I try to start it even when its running but a car engine running at 600 RPM's at idle is a big difference then when it is running at 3600 or even 1800 rpms, but thanks to the starter disable system on newer cars that keeps you from engaging the starter after the engine is running or I would be replacing a few starters.

I have did a generator that the homeowner built a double layer block wall around it leaving the side away from the house open, and they would put a slanted roof to allow heat to flow up and out of it, worked great as you could not hear the generator inside of the house, but the neighbors might not like it as it funneled all the sound toward their houses.

The main problem with putting the generator in an enclosure is getting rid of the heat, a 20kw generator engine will produce some where around 80k to 100k btu's of heat and the alternator another 5 to 10k of btu's, and thats allot of heat to remove which will take quite a bit of CFM's to remove it out of an enclosure not to mention make up air for combustion, I had a couple who wanted to build an underground concrete vault, but I told them I could not warranty such an installation because it would be to hard to remove the heat and provide fresh makeup air for the engine to run on although the make up air would have been much easier then the heat problem as you are not only removing the heat from the engine but also the alternator, I would think that most generator manufactures would void their warranty if it was installed like this.

An inverter output generator system would allow the engine to vary on load demand and would mostly idle at night when the least loads were used except when the air conditioner or electric heat would cycle, but inverters get very costly once you get above the 5kw range especially the full sine wave inverters which is all I would ever recommend because allot of electronics with switch mode power supplies don't like the modified sine wave, burned up a power supply in my computer once and a couple of my Dewalt chargers trying to run them on modified sine wave inverters, although all you have to do is throw a transformer with primary voltage taps on the output of the inverter and you will get a some what close to being a full sine wave output that can be adjusted if the inverter output voltage is a little low, but then you now have the loss of the transformer to add to the load on the inverter.

At one time I started designing a generator system with inverter output, that also used a battery or two feeding the DC buss to provide power to the inverter like the hybrid cars that the engine would shut off until the battery level got below a certain level or a heavy load kicked on, the efficiency over a standard generator would be almost cheaper to run than some utilities charge for electric like our utility (but I would have to have the numbers crunched to be sure), if NG cost stays as low as it is now, just think now you would be using the utility electric as a back up instead of the other way around, you could use any standard ATS just land the utility feeds on the generator lugs and the generator/inverter feeds on the utility lugs and since the generator would always be online and only started on battery voltage sense, the start circuit would be just disabled in the ATS, when the utility electric becomes cheaper then the NG just have a control to swap the system to use the utility as the supply and the generator as back up, add a few good sized solar panels on the roof or out in the yard and you lower the cost even more and might be able to stay off the grid with NG the only other source as the engine would not run as much.

Got as far as dating and notarizing the paper work but never got the numbers crunched or could find a low cost source for high output full sine inverters which getting up into the 10kw to 20kw range made the system not very good on ROI?
 

mkgrady

Senior Member
Location
Massachusetts
One supplier indicated that their generators (they sell several brands) all fall between 65-72 db and implied that that amounts to such a small difference that it doesn't matter. Anybody agree with that?
 

eHunter

Senior Member
One supplier indicated that their generators (they sell several brands) all fall between 65-72 db and implied that that amounts to such a small difference that it doesn't matter. Anybody agree with that?

No.
I have seen db specs that range from about 9 feet to about 50 feet for the sampling distance.
Not all db ratings are the same, some are weighted differently, some are not weighted at all.
I have about 30 years of experience with generators and the operating noise levels vary greatly.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
... At one time I started designing a generator system with inverter output, that also used a battery or two feeding the DC buss to provide power to the inverter like the hybrid cars that the engine would shut off until the battery level got below a certain level or a heavy load kicked on, ...

Yes, this is an interesting idea.

I recall a paper by ATT Canada on powering remote mountain top repeater comm sites (maybe 10 years ago). Original installation sized the generators big enough to meet peak loads and ran 24/7. Gens had maintenance issues, wet stacking during low load times, long hours (8760 hrs/year) requiring frequent rebuilds. Fuel costs were astronomical (consider delivery costs).

The project installed a battery bank suitable to run the repeater for 24 hours, The gen was fitted with a charger that fully loaded the gen (100%) System was setup/designed, such that the gen would run 4 hours/day to charge the batts. Generator shuts off and repeater is powered from the batts for the other 20 hours. So the gen is on, loaded 100%, or off - except for a short period topping the batts at the end of the charge cycle. Gen starts on low battery, and shuts off after completion of charging algorythm.

Pretty easy to monitor the condition of the batts - have the repeater report on the hours per day the gen is running

As I recall, the fuel savings paid for the project in like the first year (but maybe it was two)

I worked up a plan/design on changing out the charger and batts at my cabin, keeping the existing 3.3kw gen and 200w PV. I'd like a 65A - 100A charger instead of the 30A I have now. And change the batts from the 140AH set to 400AH. But being as I use less than 50gal/year, hard to justify any changes.

sigh - It would be kind of neat

If I find the paper I'll post it

ice
 

renosteinke

Senior Member
Location
NE Arkansas
Grady, whenever a salesman starts saying something doesn't matter, my BS alarm starts ringing. Think of the Yugo, where I'm sure the salesmen stressed how the Yugo had to meet the same safety and environmental standards as everyone else. Yet, did anyone really think the Yugo was the "equal" of a BMW?

Another comment I'll make about sales personnel is that their actual experience is often quite limited, and most can't afford what they're selling.

Hunter is correct; there's a lot of balderdash out there when it comes to noise measurement. Ever watch TV? Do the commercials seem louder? If so, by how much? For years,various studies 'proved' the commercials were no louder than the programming; last year they finally admitted that they were cranking the volume up after all. Who do you believe?

Having been exposed to generator noise under many different conditions, all I can say is that there IS a huge difference between generators, and the difference DOES matter. Some you can stand next to the pleasant hum and still talk normally. Others have a banshee wail that carries to the next county.


Quiet generators have other advantages. As demonstrated after Hurricane Hugo, the sound of a generator can act as a thief magnet. Others told tales of folks stringing cords for blocks, wanting to 'tie in.' People foolishly think excess noise means you have power to share. I've even seen the "authorities" going around and asking to borrow YOUR widget, just for the emergency, for the 'common good.'

"Quiet" isn't just about mufflers and padding. Often a well-designed machine will make less noise. Probably the best example of this is the Harley-Davidson motorcycle. Most folks don't realize that they come from the factory a LOT quieter than what you often see on the road. The new owners get "the sound" by actually damaging various parts.

It's no accident that the $150 Harbor Freight genny makes a lot more noise than the comparable $900 Yamaha or Honda. It's also no surprise that there are also differences in power quality, reliability, weight, and ease of starting.

Folks might tolerate a noisy genny right after a storm - but the weekly maintenance run,or prolonged running (as after a Sandy) is another matter.
 

mike_kilroy

Senior Member
Location
United States
I'd suggest u google "INVERTER DUTy GENERATOR noise comparison" or some such and LISTEN to different DB levels on inverter duty vs regular generators. When I did my research I found this Yamaha as the largest inverter model sold, so i doubt you will found a quiet inverter model in 10-20kw size, but at least u will hear the actual comparison of different DB levels.

then u would have a real life comparison of sound levels rather than theoretical 10x at 10db difference or 2x audible level at 3db differences.

I did this and bought a 6700w or so Yamaha inverter model and I can tell u it is like a car running in a garage compared to my 4kw 3600rpm put-on-ear-protection regular model. but I also paid $4000 rather than $ 400 for the same kw Harbor Freight model.
 
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