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05-04-2019, 02:05 PM
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#1
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Senior Member
National RV Owners Club Freightliner Owners Club
Join Date: Jul 2015
Location: Conch Republic
Posts: 2,532
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Onan generators all constant rpm?
I am curious. I am looking at used RV's and I see Onan generators that vary in size from 4000 to 8000. I have and a 4K "Microquiet" which is a constant RPM unit. I have had more than my share of troubles with it. Folks deride the constant RPM system. Are all of these constant RPM and are some better than others?
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33' 2008 National Tropical on a Freightliner chassis.We tow a 2001 XJ (Cherokee) RVM#189
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05-04-2019, 02:16 PM
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#2
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Senior Member
Join Date: Feb 2019
Location: So Cal Mountains
Posts: 331
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The Cummins/Onan Quiet Diesel 6000 in our 2018 Palazzo changes RPM with the load.
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2018 Thor Palazzo 33.2
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05-04-2019, 02:20 PM
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#3
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Community Administrator
Tiffin Owners Club
Join Date: Sep 2013
Location: DFW, Texas
Posts: 21,513
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The Cummins/Onan diesel generators 10k and larger are constant RPM. The 8k and lower vary with load.
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 2017 Phaeton 40IH XSH Maroon Coral - Power Glide Chassis with IFS
Previous '15 Tiffin Allegro RED 38QRA and '06 Itasca Sunrise 35A
'16 Jeep JKU Wrangler Sahara or '08 Honda Goldwing
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05-04-2019, 02:28 PM
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#4
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Senior Member
Join Date: Jul 2014
Posts: 35,415
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There are at least 2 Onan Quiet Diesel RV generators that have variable speed power producers but beside them, I haven't heard of any others that worked that way.
Most other models are constant speed. The generator head needs to turn 1800 or 3600 RPMs to produce 60 HZs. Some, like the 5500 unit will belt drive the generator head at 3600 RPMs but the engine will be turning 2400 RPMs. The slower RPM engine will be quieter, but need more HP to do the work.
A fuel injected, inverter style, 6000 watt generator would be a great RV unit. Don't know of any out there, yet.
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05-04-2019, 02:54 PM
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#5
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Senior Member
Join Date: Feb 2017
Posts: 1,037
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When the load increases it may sound like the RPM's go up but I'm not sure it does. AFAIK there is no constant velocity drive in these. There would be an oil change involved....
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'20 RAM 3500, '20 Heartland Road Warrior 430 https://thecastle.blog/ Also: Eagle Cap 950 Before:'17 Berkshire 38A class A https://dragonship.blog/ '11 Heartland Cyclone TH, '11 Lance TC, '05 Keystone TT, '76 Coachmen class A and a '16 DIY Transit conversion........
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05-04-2019, 03:02 PM
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#6
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Senior Member
Join Date: Feb 2019
Location: So Cal Mountains
Posts: 331
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Quote:
Originally Posted by oscarvan
When the load increases it may sound like the RPM's go up but I'm not sure it does. AFAIK there is no constant velocity drive in these. There would be an oil change involved....
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Good point, I'm not actually sure the RPM is increasing on our QD6000, but it sounds like it is. Similar sound change as my little Honda under a load verses not...
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2018 Thor Palazzo 33.2
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05-04-2019, 03:18 PM
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#7
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Senior Member
Join Date: May 2006
Location: SoCal
Posts: 1,123
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What you are hearing is a "bump" on the generator as the load increases. The rpm is for most gennies out the constant as explained in previous posts.
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2020 Grand Design Reflection 315RLTS
2019 GMC Sierra Denali Duramax
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05-04-2019, 03:28 PM
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#8
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Senior Member
Thor Owners Club Ford Super Duty Owner
Join Date: Jul 2011
Posts: 3,795
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Quote:
Originally Posted by HaRVey 74.5
Good point, I'm not actually sure the RPM is increasing on our QD6000, but it sounds like it is. Similar sound change as my little Honda under a load verses not...
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"Computer-Controlled Variable Speed Operation. Matches engine speed to load demand, minimizes noise levels."
The QD6000 is the only one I know of. Not sure how they made it work or how much the RPM varies. I was a firm believer in the 3600 RPM requirement until an owner schooled me.
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2006 Hurricane 31D built on a 2006 Ford F53
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05-04-2019, 03:37 PM
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#9
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Senior Member
Join Date: Jul 2014
Posts: 35,415
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HaRVey 74.5 may actually have a variable speed diesel generator.
As I mentioned in my ignored post, Onan has produced a few. Its described here in print, where it mentions variable speed, not a bump from extra load.
It uses the same inverter technology as small portable ones do. 
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05-04-2019, 03:44 PM
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#10
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Senior Member
Country Coach Owners Club Solo Rvers Club iRV2 No Limits Club
Join Date: May 2011
Location: Vancouver, WA
Posts: 37,725
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All the Onan RV generators except the 10 and 12.5 K are variable speed.
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2009 45' Magna 630 w/Cummins ISX 650 HP/1950 Lbs Ft, HWH Active Air
Charter Good Sam Lifetime Member, FMCA,
RV'ing since 1957, NRA Benefactor Life, towing '21 Jeep JLU Rubicon Ecodiesel
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05-04-2019, 07:51 PM
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#11
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Senior Member
National RV Owners Club Freightliner Owners Club
Join Date: Jul 2015
Location: Conch Republic
Posts: 2,532
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Quote:
Originally Posted by Sweetbriar
"Computer-Controlled Variable Speed Operation. Matches engine speed to load demand, minimizes noise levels."
The QD6000 is the only one I know of. Not sure how they made it work or how much the RPM varies. I was a firm believer in the 3600 RPM requirement until an owner schooled me.
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Thanks for that PDF. As I am looking for a DO if possible I can consider myself lucky if I get a QD 6 or 8 k unit rather than the propane one.
Are all of the Onans as quirky and prone to fail as the 4K or ore some more dependable?
__________________
33' 2008 National Tropical on a Freightliner chassis.We tow a 2001 XJ (Cherokee) RVM#189
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05-04-2019, 07:57 PM
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#12
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Senior Member
Join Date: May 2006
Location: SoCal
Posts: 1,123
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Mine (Onan 5500 Gold) is 13 years old and doing fine. Replaced fuel pump and filter and adjusted valves last summer, other than that air filters oil and oil filters. Trouble free
__________________
2020 Grand Design Reflection 315RLTS
2019 GMC Sierra Denali Duramax
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05-04-2019, 08:04 PM
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#13
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Senior Member
Holiday Rambler Owners Club
Join Date: Aug 2010
Posts: 9,746
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Quote:
Originally Posted by Kahoona
Are all of the Onans as quirky and prone to fail as the 4K or ore some more dependable?
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Only the variable RPM ones  !!
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Ben & Sharon
2008 43' Holiday Rambler Scepter PDQ
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05-04-2019, 08:55 PM
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#14
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Senior Member
Join Date: Feb 2017
Posts: 1,037
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Quote:
Originally Posted by Kahoona
Are all of the Onans as quirky and prone to fail as the 4K or ore some more dependable?
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That true?
QD6000 650 hours... oil and filters. Run, run, run.
__________________
'20 RAM 3500, '20 Heartland Road Warrior 430 https://thecastle.blog/ Also: Eagle Cap 950 Before:'17 Berkshire 38A class A https://dragonship.blog/ '11 Heartland Cyclone TH, '11 Lance TC, '05 Keystone TT, '76 Coachmen class A and a '16 DIY Transit conversion........
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