Generators and Motors
[Home] - [HELP] - [Forums] - [Library] - [Photo Gallery] - [Groups] - [Classified Ads] - [Subscribe] - [Links] - [Books] - [Sponsors] -

Go Back   SmokStak > SmokStak® Vintage Electrical Equipment > Generators & Electric Motors General Discussion > Onan Generators
Forgot Password? Join Us!

Notices

Onan Generators Restoring, operating and maintaining vintage Onan generators. When asking new questions about your generator, ALWAYS give your model number AND serial number.

Onan Generators

How Many KW to Run a...


this thread has 57 replies and has been viewed 1683 times

Reply
 
Thread Tools Display Modes
  #41  
Old 06-25-2019, 08:41:32 PM
Vanman Vanman is online now
Subscriber
 
Join Date: Aug 2011
Location: Mission Viejo, California
Posts: 5,751
Thanks: 9,057
Thanked 2,646 Times in 1,789 Posts
Default Re: How Many KW to Run a ...

Roughly speaking, no load fuel consumption is going to scale with engine size, assuming the same speed.

Above that, the fuel converted to useful output will be approximately the same efficiency for all of them.

From this it can readily be seen that low loads are REALLY inefficient.

Both figures will be better for diesel vs gas, overhead valve vs flathead, low speed vs high speed.

Keith
Reply With Quote
The Following User Says Thank You to Vanman For This Post:
Sponsored Links
  #42  
Old 06-25-2019, 08:56:53 PM
Wayne 440 Wayne 440 is offline
Registered-III
 
Join Date: Nov 2004
Location: Kentucky
Posts: 7,213
Thanks: 464
Thanked 6,602 Times in 3,090 Posts
Default Re: How Many KW to Run a ...

Quote:
Originally Posted by Railroads View Post
...I am still curious about what size generator is really too big for practical use?...
First, you must define "practical", while being aware that the definition can change with time.

For instance- in the past 10 years, my RDJC has run 47 hours, with maybe half of that for actual outages. It has had 4 oil and filter changes, and is due for one, so let's say an oil change every 2 years. The RDJC holds about a gallon of lube oil, and about a gallon an hour of fuel to run my house, with electric heat. For the sake of convenience, let's say all 47 hours are "loaded" by my house load.

A rough list for fuel, oil and filter cost over 10 years- $150 (fuel) $75 (oil) $50 (oil filters) $25 (fuel filters) so call it $300, or $30 a year for my 15kW set.

Now, say I buy an 80kW set. A DSFAE will use about 2 GPH diesel at 18kW load. Holds 3 gallons of oil and has practically the same filter costs as the RDJC. 300+225+50+25=600, so $600 or $60 a year for "run any #$%^ thing you want to" standby power.

Either one is easily "practical" for my actual use to date - but I would save $75 a day with the RDJC presuming a week long outage. Either one will be less expensive than the cost of putting my family and dependent in-laws up in a hotel for a week. After that, I would be looking for some reasonable way to get by with one of my smaller sets (maybe ).
Reply With Quote
The Following 3 Users Say Thank You to Wayne 440 For This Post:
  #43  
Old 06-25-2019, 09:40:56 PM
brianh brianh is offline
Registered-II
 
Join Date: Dec 2004
Location: South Bend, Indiana USA
Posts: 171
Thanks: 12
Thanked 95 Times in 56 Posts
Default Re: How Many KW to Run a ...

After experimenting with my DJE, I have found that the voltage regulator configuration makes a HUGE difference in the motor starting ability.
Most of our Onans (and most generators that I am aware of) typically only sample one leg of the 120/240 (or 120/208 three-phase) for the voltage regulator. This allows for more flexibility in strapping for different output voltages, but is a distinct disadvantage when you are trying to start a large 240V load and the regulator is only sampling half of the output. The voltage regulator had failed in my DJE and I put in an SX-460, setting it up to sample off the 120 feed to the old regulator. It worked, but struggled to start my 2 ton heat pump.
So a few weeks ago I took it apart and rewired the regulator to sample the total 240V output and reset the regulator for 240V input. BIG improvement. The regulator now sees the total voltage sag when the big high-voltage load is thrown on the generator. In addition, the 120V leg voltages are much closer with an unmatched load, like when my freezers or sump pumps cycle on and off, unlike when the regulator was only watching the voltage on one leg.
I would have built the capability to configure the regulator either way into the generator, to allow the installer to configure it to respond to the largest load, whether it was 120 with the windings paralleled, or 240 with them in series.
Just my $.02.

Brian
Reply With Quote
The Following 2 Users Say Thank You to brianh For This Post:
  #44  
Old 06-25-2019, 09:44:04 PM
len k len k is online now
Subscriber
 
Join Date: Jun 2012
Location: Manchester, New Hampshire
Posts: 18,661
Thanks: 625
Thanked 7,086 Times in 5,073 Posts
Default Re: How Many KW to Run a ...

I bought a gen because ~ 10 years ago a MASSIVE ice storm hit ALL of New England (NJ to MAINE). We are in LARGEST city in NH, yet neighborhood behind me was out for ~ 1 week solid in cold WINTER. I needed to be able to make electricity for my oil furnace for heat

Relatives in Maine were out for 3 weeks solid, and other areas ~ 5-6 weeks solid. Smaller gen conserving your available fuel supply can become very important sometimes. Lots of cash, but no fuel to be had.

Even in towns by me some fuel trucks were not able to supply houses because of ice on more rural hilly roads.
.

Last edited by len k; 06-25-2019 at 10:40:31 PM.
Reply With Quote
The Following 3 Users Say Thank You to len k For This Post:
  #45  
Old 06-25-2019, 10:02:37 PM
Zephyr7 Zephyr7 is online now
Registered-III
 
Join Date: Mar 2017
Location: Davisburg, Michigan
Posts: 2,280
Thanks: 703
Thanked 1,342 Times in 903 Posts
Default Re: How Many KW to Run a ...

Quote:
Originally Posted by Railroads View Post
Angry, 8 or 9 is on the border of obsession or something.
You're aware of our shared obsession on this forum, right?

A few of us are regulars in more than just the Onan section even...

For BrianH: careful optimization of the gain (sensitivity) of the regulator will also help with motor starting ability. You want just barely below the edge where you start to see oscillation.

Bill
Reply With Quote
The Following User Says Thank You to Zephyr7 For This Post:
  #46  
Old 06-25-2019, 11:44:51 PM
AngrySailor AngrySailor is offline
Subscriber
 
Join Date: Apr 2017
Location: West Prince, Prince Edward Isand, Canada
Posts: 1,883
Thanks: 784
Thanked 1,372 Times in 746 Posts
Default Re: How Many KW to Run a ...

Quote:
Originally Posted by Railroads View Post
Angry, 8 or 9 is on the border of obsession or something. You guys take them to tractor shows?

Robert
We used to show one or two a year but haven’t for a while. A few are workers, Dad is restoring the first 8n he ever bought right now. We’ve got at least one of every model 9,2&8n I felt a little bad about my 7 Fordsons until I saw this guy!

http://www.my9n.com/8nman.htm
Attached Thumbnails
Click image for larger version

Name:	718435FD-3AA1-4B9E-8DF5-66E8E60AABB6.jpeg
Views:	32
Size:	27.1 KB
ID:	337885  
Reply With Quote
The Following User Says Thank You to AngrySailor For This Post:
  #47  
Old 06-26-2019, 09:50:28 AM
zuhnc zuhnc is offline
Registered-I
 
Join Date: Nov 2013
Location: Macks Creek, Missouri
Posts: 350
Thanks: 5
Thanked 263 Times in 149 Posts
Default Re: How Many KW to Run a ...

I have a '51 8N-C, acquired when we bought the property. Not very well cared for. Rebuilt a lot of stuff on it, as well as the Bush Hog (tm) brush cutter. Still have the hydraulics assemblies and brakes to go, but it mows the pastures decently. A learning curve for maintenance and operation . zuhnc
Reply With Quote
  #48  
Old 06-26-2019, 11:44:05 AM
Leon N. Leon N. is online now
Registered-III
 
Join Date: Oct 2009
Location: N. Chelmsford, MA, USA
Posts: 4,603
Thanks: 812
Thanked 2,745 Times in 1,622 Posts
Default Re: How Many KW to Run a ...

Brian I will have to think about your findings. Don’t you think the Onan designers knew that?
Reply With Quote
The Following User Says Thank You to Leon N. For This Post:
  #49  
Old 06-26-2019, 12:35:35 PM
Zephyr7 Zephyr7 is online now
Registered-III
 
Join Date: Mar 2017
Location: Davisburg, Michigan
Posts: 2,280
Thanks: 703
Thanked 1,342 Times in 903 Posts
Default Re: How Many KW to Run a ...

Quote:
Originally Posted by Leon N. View Post
Brian I will have to think about your findings. Don’t you think the Onan designers knew that?
They probably made a design trade off knowing the pros and cons of their choice. That doesn’t necessarily mean it’s not possible to optimize the system for a particular set of operating conditions.

120v sensing will be ok for 240v loads, but will act like a slightly reduced gain since it will see smaller voltage changes with load changes. 120v sensing is worst for very unbalanced loads. 240v sensing splits the difference, will have the best response for 240v loads, and most even response for unbalanced 120v loads.

If 240v sensing gives better performance in your particular application, there is no reason NOT to use it.

Bill
Reply With Quote
  #50  
Old 06-26-2019, 02:35:50 PM
Leon N. Leon N. is online now
Registered-III
 
Join Date: Oct 2009
Location: N. Chelmsford, MA, USA
Posts: 4,603
Thanks: 812
Thanked 2,745 Times in 1,622 Posts
Default Re: How Many KW to Run a ...

OK, thinking about Brian's assertion that he gets better performance with 240 volt sensing why I think his reasoning is flawed. Yes, maybe he does get better performance but I do not think it is for the reason he postulates.

Now, we are talking about 1960's generator technology, meaning there is no fancy electronic voltage regulators or such things like synchronous governors, so I reason this way:

The voltage generated is directly affected by the RPM ( speed) of the machine. Yes there are other factors besides RPM. However, one important factor is the voltage regulator tries to hold the terminal voltage within 3% of the specified FL rating that is, monitoring the 5% droop governor tabs on the fluctuating RPM. So it does not matter where the gens output voltage is sensed.
Reply With Quote
  #51  
Old 06-26-2019, 03:01:23 PM
Birken Vogt Birken Vogt is offline
Email NOT Working
 
Join Date: Sep 2009
Location: Penn Valley, California, USA
Posts: 2,518
Thanks: 2
Thanked 876 Times in 612 Posts
Default Re: How Many KW to Run a ...

I don't see how 120v vs 240v sensing will give any different response to 240v loads. Yes the gross voltage drop is smaller but the proportional drop is the same.
Reply With Quote
The Following User Says Thank You to Birken Vogt For This Post:
  #52  
Old 06-26-2019, 04:39:23 PM
Zephyr7 Zephyr7 is online now
Registered-III
 
Join Date: Mar 2017
Location: Davisburg, Michigan
Posts: 2,280
Thanks: 703
Thanked 1,342 Times in 903 Posts
Default Re: How Many KW to Run a ...

Quote:
Originally Posted by Birken Vogt View Post
I don't see how 120v vs 240v sensing will give any different response to 240v loads. Yes the gross voltage drop is smaller but the proportional drop is the same.
Effective delta V seen by the regulator will be higher with 240v sensing. That's the only difference I can see, aside from the obvious issue with severely imbalanced loads.

Bill
Reply With Quote
  #53  
Old 06-26-2019, 05:10:10 PM
Leon N. Leon N. is online now
Registered-III
 
Join Date: Oct 2009
Location: N. Chelmsford, MA, USA
Posts: 4,603
Thanks: 812
Thanked 2,745 Times in 1,622 Posts
Default Re: How Many KW to Run a ...

Take my JB for example, if the frequency/speed stays within the 5% droop, then the VR is specified to keep the 120 volt and the 240 volt outputs within + or - 3% with. 2 second recovery to the specified 3% range.

Onan also provides a NL voltage adjustment over a very small range. At least for the magneciter, the voltage regulator operates over a very narrow voltage and frequency range.

The major
Reply With Quote
  #54  
Old 07-05-2019, 03:51:47 PM
len k len k is online now
Subscriber
 
Join Date: Jun 2012
Location: Manchester, New Hampshire
Posts: 18,661
Thanks: 625
Thanked 7,086 Times in 5,073 Posts
Default Re: How Many KW to Run a ...

Ran voltage sag test on 7NHM that was converted to 120/240 output. Reg only sensed off 1 hot. (120 V). Test was full winding rated amps on 1 hot and none on other.

Max difference in voltage between hots was ~ 12VAC (~ 10%), which is acceptable. Possible, but unlikely, one hot would be fully loaded while other was no-load.


........................................sensed hot ..........unsensed hot......... Difference
no-load on either hot ......... 121.8V ................... 121.8 ................. 0

full load on sensed hot ...... 120.1V ....................132.4 ............... 12.3

full load on unsensed hot .... 122.5 .......................110.1 ............. 12.4

Test data from post 54 of https://www.smokstak.com/forum/showt...=113775&page=3


While 132 V and 110 sound unusual , they are ~ +-10%, and I believe they are within IEEE spec that someone posted here. Think I saw even 136 is listed as OK by Onan manual for a NH gen.

I think there is a IEEE spec of +-5% for "sensitive equipment" loads. But these days many electronics have switching power supplys that are happy on even wider voltage ranges ~ 90-160 and can take even scrappy square waves.
.

Last edited by len k; 07-05-2019 at 04:24:00 PM.
Reply With Quote
The Following User Says Thank You to len k For This Post:
  #55  
Old 07-05-2019, 04:57:11 PM
Birken Vogt Birken Vogt is offline
Email NOT Working
 
Join Date: Sep 2009
Location: Penn Valley, California, USA
Posts: 2,518
Thanks: 2
Thanked 876 Times in 612 Posts
Default Re: How Many KW to Run a ...

A while back the utility here was having regulation issues and the neighborhood was wavering between 210 and 255 at different times of day. Normally things run a bit on the high side here anyway.

The only thing I noticed at 210 volts was my ancient UPS started beeping and shaded pole fans ran a bit slow. Everything else was fine and we ran for days like that. LED/CFL lamps seemed to not change output at all. Air conditioner currents were well within nameplate. A few DIP switches and the UPS was happy. The computers did not care.
Reply With Quote
  #56  
Old 07-05-2019, 05:03:05 PM
Wayne 440 Wayne 440 is offline
Registered-III
 
Join Date: Nov 2004
Location: Kentucky
Posts: 7,213
Thanks: 464
Thanked 6,602 Times in 3,090 Posts
Default Re: How Many KW to Run a ...

There is talk of a revision of ANSI C84.1-2016 in June 2020.

Here is a good reference page

https://www.pge.com/includes/docs/pd..._tolerance.pdf
Reply With Quote
The Following 2 Users Say Thank You to Wayne 440 For This Post:
  #57  
Old 07-05-2019, 05:44:49 PM
Vanman Vanman is online now
Subscriber
 
Join Date: Aug 2011
Location: Mission Viejo, California
Posts: 5,751
Thanks: 9,057
Thanked 2,646 Times in 1,789 Posts
Default Re: How Many KW to Run a ...

With 240 volt sensing, and loading only one line, you will still get the same ~12 volts difference between the two, but only half of it on each line. So if regulating right at 240 line to line, you'd see about ~114 on the loaded line and ~126 on the unloaded line. This is the only way I'd have it.

Quote:
Originally Posted by len k View Post
Ran voltage sag test on 7NHM that was converted to 120/240 output. Reg only sensed off 1 hot. (120 V). Test was full winding rated amps on 1 hot and none on other.

Max difference in voltage between hots was ~ 12VAC (~ 10%), which is acceptable. Possible, but unlikely, one hot would be fully loaded while other was no-load.


........................................sensed hot ..........unsensed hot......... Difference
no-load on either hot ......... 121.8V ................... 121.8 ................. 0

full load on sensed hot ...... 120.1V ....................132.4 ............... 12.3

full load on unsensed hot .... 122.5 .......................110.1 ............. 12.4

Test data from post 54 of https://www.smokstak.com/forum/showt...=113775&page=3


While 132 V and 110 sound unusual , they are ~ +-10%, and I believe they are within IEEE spec that someone posted here. Think I saw even 136 is listed as OK by Onan manual for a NH gen.

I think there is a IEEE spec of +-5% for "sensitive equipment" loads. But these days many electronics have switching power supplys that are happy on even wider voltage ranges ~ 90-160 and can take even scrappy square waves.
.
Reply With Quote
  #58  
Old 07-05-2019, 10:29:09 PM
Zephyr7 Zephyr7 is online now
Registered-III
 
Join Date: Mar 2017
Location: Davisburg, Michigan
Posts: 2,280
Thanks: 703
Thanked 1,342 Times in 903 Posts
Default Re: How Many KW to Run a...

Typical utility voltage spec is 110-125v. Most utilities shoot for around 120v average, which usually means people close to the substation run near 125v, and those near the end of the line will be closer to 115-120v. Voltage regulation happens only in tap changers at the substation and sometimes also in voltage regulators located along very long runs of primary (usually 4.8-14.4kv) lines. Everything in between those sees a varying voltage depending on load and distance from the substation.

I agree with vanman too, 240v sensing splits the difference between the two legs and gives the best overall voltage regulation performance for all conditions.

Bill
Reply With Quote
Reply

Bookmarks


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

F o r u m Jump


Use "Ctrl" mouse wheel to change screen size.
All times are GMT -4. The time now is 08:37:54 PM.

Smokstak and Enginads site search!


All use is subject to our TERMS OF SERVICE
SMOKSTAK® is a Registered Trade Mark - A Community of Antique Engine Enthusiasts
Copyright © 2000 - 2019 by Harry Matthews P.O. Box 5612 - Sarasota, FL 34277