Author Topic: Whats the minimum load a diesel motor should run at?  (Read 9627 times)

Simtech

  • Newbie
  • *
  • Posts: 18
    • View Profile
Whats the minimum load a diesel motor should run at?
« on: January 25, 2012, 06:13:14 PM »
How low can you load a listeroid before it begins to cause problems (not getting warm enough, coking up the injectors, etc)?
50%?  25%?  10%?

I've got a possible line on a 12/1 here in my local (ish) area.  Even derating it to 10HP it's putting out ~5000watts at max output.  

At 50% load its about 2500W.

After rectifying and conversion by a (in my case a Midnite Classic 200) charge controller thats:
208A at 12V
104A at 24V
52A at 48V
34A at 72V

At 48V and 72V to a battery bank the charge controller can handle that, but the size of a battery bank to take a 48V/52A or 72V/34A charge as its C/10 rate is rather large (and expensive).

I'm wondering if I reduce the load on the listeroid to match the charging ability of my planned battery bank I'm going to regret it down the road with increased maintenance problems.

I hope that made sense.
« Last Edit: January 26, 2012, 05:31:09 PM by Simtech »

BruceM

  • Hero Member
  • *****
  • Posts: 3054
    • View Profile
Re: Whats the minimum load a diesel motor should run at?
« Reply #1 on: January 25, 2012, 06:50:00 PM »
I think 50% is considered a safe minimum for long term.  I always try to keep my loads at least that.

I think an 8-1 is as fast as I'd want to spin a 'roid product from Rajkot, for both safety and longevity issues.  If you're going faster, you'd be better off with a slowed down modern diesel engine design. (Some very impressive jobs on that by folks here.)

What's the planned use (watt hrs/day) for the battery bank? What's your planned DOD? (Depth of discharge.)

AGM batteries will happily take very high charge rates and also have a much better charge efficiency, but of course you pay for the privilege.  I do use them and like them for some applications, but they were too expensive for my main battery bank.  Remember that the charge efficiency of the last 20% of charge on a wet battery is pathetic, like 50-60%. (Sandia Labs report.)  So PV/wind charging is a must for wet lead acid batteries, you don't want to be topping off batteries with a generator for regular operations.


 

bluesky

  • Newbie
  • *
  • Posts: 25
    • View Profile
Re: Whats the minimum load a diesel motor should run at?
« Reply #2 on: January 26, 2012, 12:00:36 AM »
 Even derating it to 10HP it's putting out ~5000watts at max output.  

At 50% load its about 2500W.



Pardon my ignorance, but is "derating" as used above accomplished by reducing engine RPM while still achieving required RPM at gen head? Would reducing an 8/1 to 650 RPM result in equal fuel consumption as running a 6/1 at standard 650 RPM?

ronmar

  • Hero Member
  • *****
  • Posts: 1227
    • View Profile
Re: Whats the minimum load a diesel motor should run at?
« Reply #3 on: January 26, 2012, 12:24:05 AM »
Pardon my ignorance, but is "derating" as used above accomplished by reducing engine RPM while still achieving required RPM at gen head? Would reducing an 8/1 to 650 RPM result in equal fuel consumption as running a 6/1 at standard 650 RPM?
Yes and Yes mostly.  A 6/1 and an 8/1 are pretty similar but I think the 8/1 has smaller lighter wheels.

50% is not a horrible load if you get and keep the engine hot.  So a 195 degree thermostat and a cooling system taylored to remove the correct ammount of heat(not remove too much)is reccomended.  Most folks need heat at some point, and hot water heating elements are relatively cheap, so you can quite easilly make an electric water heater/load bank.  Depending on what charge load you are running, this loadbank can be occasionally switched in, especially if you need heat, to add to the engine load and run it up closer to peak load for periods to cook the carbon out...  Or if you don't need heat, to just use occasionally as a maintenance exercise.
PS 6/1 - ST-5.

BruceM

  • Hero Member
  • *****
  • Posts: 3054
    • View Profile
Re: Whats the minimum load a diesel motor should run at?
« Reply #4 on: January 26, 2012, 01:19:07 AM »
Here's the Sandia Labs info on wet lead acid battery charge efficiency.  It's the same or worse than Nickle Iron (Edison Cells) over 80% full. 

http://photovoltaics.sandia.gov/docs/PDF/batpapsteve.pdf

If you need to charge 'em hard and fast, AGM's are your best bet. Even the small ones can take very high charge rates, with high efficiency.

cujet

  • Hero Member
  • *****
  • Posts: 956
  • Lister power rules!
    • View Profile
    • www.cujet.com
Re: Whats the minimum load a diesel motor should run at?
« Reply #5 on: January 26, 2012, 03:23:35 AM »
I have far more electrical capacity than I use. So, when I run my listeroid I'm typically at very low loads for much of the day. Same goes for diesel engines in all sorts of gensets. Quite often, they are at 10% to 25% load. With the occasional heavier load.

I'm not at all convinced long term heavy loads are required for any reason.
People who count on their fingers should maintain a discreet silence

deeiche

  • Full Member
  • ***
  • Posts: 240
    • View Profile
Re: Whats the minimum load a diesel motor should run at?
« Reply #6 on: January 26, 2012, 02:22:05 PM »
Here's the Sandia Labs info on wet lead acid battery charge efficiency.  It's the same or worse than Nickle Iron (Edison Cells) over 80% full. 
SNIP
wow, someone who actually reads SNL papers.  I thought we just produced them to show our managers we were working on something.   :)

Quinnf

  • Rest in peace
  • Hero Member
  • *****
  • Posts: 645
    • View Profile
Re: Whats the minimum load a diesel motor should run at?
« Reply #7 on: January 26, 2012, 03:35:30 PM »
Re: running at minimum load, fishing boats which run their generators long hours and depend on them heavily, frequently will run their deck lights whenever the generators are running, even in the daytime, in order to keep them loaded. 
Ashwamegh 6/1, PowerSolutions 6/1 "Kit" engine, and a Changfa R175a that looks like a Yanmar I once knew

BruceM

  • Hero Member
  • *****
  • Posts: 3054
    • View Profile
Re: Whats the minimum load a diesel motor should run at?
« Reply #8 on: January 26, 2012, 04:28:15 PM »
Deeiche, I know the feeling. When I worked at an AF simulator/training research lab, we generated a lot of tech reports we were pretty sure no one ever read.

As a gag (I was still in college), I developed a program that would generate technical gobblydegook of any number of paragraphs, given a structured list of topically appropriate keywords and phrases. I wrote a brief intro, then turned it loose for about 30 pages of techno-baloney filler. I did cherry pick some of the best paragraphs of nonsense for the first page, but not one sentence actually said or meant anything real, though the grammar and spelling was perfect.  Alas, the paper made the rounds, got reviewed and approved by a dozen senior staff scientists, and sent off to our headquarters for publishing before my horrified boss could stop it!

The Sandia Labs report on lead acid battery charge efficiency is very important, as before I read it I was also snookered into believing the often stated 85% charge efficiency of wet lead acid batteries.

We've all been waiting for the often touted breakthrough in batteries- yet 100 years later, we are still using the same old crap for bulk storage!  Everyone thinks all technology is like semiconductors, with a regular schedule of faster, better, cheaper.  If only it were so.




overbore

  • Full Member
  • ***
  • Posts: 162
    • View Profile
Re: Whats the minimum load a diesel motor should run at?
« Reply #9 on: January 26, 2012, 05:08:51 PM »
No Sandia lab report here --but-- I evaluated the flooded battery choices and set up a a 12 battery bank, #2Cable connected, of Crown 215ah 12v batteries charged and discharged through a Xantex 2400 inverter/ charger.  With an integral  digital readout I can confirm that the software is keeping the entire bank at 100% and  I limit the discharges to 50%.  I went with Crowns because they have been in the battery business for a long time and make their batteries with 100% pure lead and make their anodes 50% thicker than competition.

Laus Deo
overbore

bschwartz

  • Sr. Member
  • ****
  • Posts: 323
    • View Profile
Re: Whats the minimum load a diesel motor should run at?
« Reply #10 on: January 26, 2012, 06:36:32 PM »
I didn't realize you worked at sandia .  Our school district benefits from your outdated hand me down computers .
-Brett

1982 300SD, 1995 Suburban 6.5, 1994 F250, R170, Metro 6/ sold :( , Witte CD-12 ..... What else can I run on WVO?

deeiche

  • Full Member
  • ***
  • Posts: 240
    • View Profile
Re: Whats the minimum load a diesel motor should run at?
« Reply #11 on: January 26, 2012, 07:07:53 PM »
I didn't realize you worked at sandia .  Our school district benefits from your outdated hand me down computers .
yeah, it is amazing what we call "outdated hand me down".

I'm glad tax paying citizens can benefit, a lot of people here forget they work for their neighbors.

listerboy

  • Jr. Member
  • **
  • Posts: 97
  • I love the smell of diesel in the morning....
    • View Profile
Re: Whats the minimum load a diesel motor should run at?
« Reply #12 on: January 27, 2012, 01:06:23 AM »
BruceM,

After reading your story about the gobblydegook program you developed I think you'll appreciate this clip:

http://www.youtube.com/watch?v=rLDgQg6bq7o

BruceM

  • Hero Member
  • *****
  • Posts: 3054
    • View Profile
Re: Whats the minimum load a diesel motor should run at?
« Reply #13 on: January 27, 2012, 05:27:06 AM »
That was hilarious, Listerboy.  The actor did a great job.  My program didn't make up words, but the end result was just the same;  it seemed really technically impressive and meant nothing.


buickanddeere

  • Hero Member
  • *****
  • Posts: 807
    • View Profile
Re: Whats the minimum load a diesel motor should run at?
« Reply #14 on: January 27, 2012, 04:09:53 PM »
No matter the load the coolant temp should not drop below 195F. As  far as fuel efficiency is concerned. HP per gallon per hour drops rapidly when operated at less than 90% of max HP.