Diesel Generator Sizing

Discussion in 'Off Grid Living' started by Asia-Off-Grid, Sep 28, 2018.

  1. Asia-Off-Grid

    Asia-Off-Grid RIP 11-8-2018

    If you were looking for a permanent generator to provide for your full power needs (not having to pick and choose between circuits), what size would you go with?

    Currently, a single 2,000 watts Honda inverter will provide the power needs we consume, minus one refrigerator / freezer with the "old technology" compressor. If I were to run both Honda EU20i's simultaneously, even that refrigerator / freezer could be powered.

    Truth be told, I didn't take one thing into consideration when I purchased these fancy Honda generators. That is, exactly how frequently we may start having power cuts. Well, the electricity gods knew when we moved here. Over time, the power cuts have slowly been growing longer and more frequently.

    Personally, I have grown tired of pulling out a portable generator, starting it, connecting it to the plug I installed in the main panel for it, and then throwing the double pole knife switch. Then, after mains power has been reconnected, doing that in the opposite order every time we have a power cut. We have them too often. It's even less fun in a full monsoon rain. For me, it is long past time for emergency power to automatically come online when needed and automatically switch off when no longer needed, without me having to do anything.

    The straw that broke the camel's back: I had to wait through a 4.5 hours power cut for the mains to come on the other night, before I could switch back to mains and power off the little inverter. So, I am not exactly happy. But, at least it wasn't raining. If I had a diesel generator with an automatic transfer switch, I could go to sleep knowing it will automatically switch over and power down, all while I sleep.

    At the time I was looking at the Honda Inverter (EU20i) generators ($888 each), I also priced a Denyo 15kva (DCA-15LSK) diesel powered generator ($3,500 USD each). This was about January of 2017. Hindsight being what it is, I am reconsidering buying a Denyo. They must be the cat's meow. I rarely (if ever?) have seen a bank building here without a Denyo unit attached to it.

    I'm just not sure if I should still consider the 15kva, or if I should go with a smaller unit. Smaller units are available in country - 13kva, 10kva, and 6kva. I just want it to power everything here, business as usual, during a power cut. I do not want to wire "emergency power only" circuits. I want one automatic transfer switch to disconnect from the mains, while powering the entire farm until the mains come back online.

    The one real difference among them is, all generators I listed above, with the exception of one, are Swirl Chambered. The 13kva (DCA-13LSY) is Direct Injected. Not sure if, or how much of a difference that makes between diesel fired generators. But, it does appear to be the most efficient unit, of those I am looking at. Efficient is good.

    So, if I may bother you good folk, how much additional power would you calculate you need, if sizing a generator for your entire property?
    Last edited: Sep 28, 2018
  2. DarkLight

    DarkLight Live Long and Prosper - On Hiatus

  3. Dunerunner

    Dunerunner Brewery Monkey Moderator

    Off hand I would recommend 80% loading of a diesel genset, allowing for starting currents and taking into consideration that it will be providing prime (continuous) power. Understand that in most situations like this, commercial power or a second genset provides an alternate or separately derived source to provide for maintenance activities.
    Asia-Off-Grid and sec_monkey like this.
  4. BTPost

    BTPost Stumpy Old Fart,Deadman Walking, Snow Monkey Moderator

    Ok, Lets look at your situation... 2Kw is running everything, except two old Refer units that can be accodated by using a second 2Kw unit... So, It would seem that 4Kw is your Total load which also includes any Starting Loads encoutered. Now figuring that you still need some headroom above that Load, for expansion and safety, likey 6Kw Genset would be the minimum size for purchase at this time. The long term issue is that any new Genset will likely be there for a couple of decades, you just might need to consider what your expected loads might be in 20 years. This is a long term purchase, and it you undersize the Genset, and down the road, find you need more power than you figured, then your Investment now, in the smaller unit would be not so prudent... Fortunately for you once you get passed the amount of Fuel (BTUs) used to just get the the engine running, the Fuel to Kw Output is a very linear ratio, for Diesel Fueled Gensets, and the difference between a 6Kw vs 8, or 12Kw Gensets in Fuel used before power generation is not all that significant... Things to look for in a Remote site Genset are:
    1. Naturally Asperated. (No Turbos)
    2. Maximum Rpm 1800 (60 hz) 1500 (50 hz)
    3. Totally Mechanical Direct Injection System (No computers in the Engine Control System)
    4. Auto Voltage Regulation of the Electrical Output
    5. Follow the KISS System (Keep it Simple, Stupid.) Make everything as simple as possible
    6. Use the same philosophy with your AutoSwitching System... KISS
    Hope this helps....
  5. sec_monkey

    sec_monkey SM Security Administrator

    @Asia-Off-Grid the issues with the grid in Cambodia are so bad that the ATS could fail :(

    they aint supposed to fail but they do

    we had at least one instustrial one fail on us

    the Denyo looks like a gud unit, but if ya want it to run reliably ya will have to take real gud care of it, plus have other backups

    it does run at 1500/1800 RPM which monkeys say is a gud thing (y)
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  6. Asia-Off-Grid

    Asia-Off-Grid RIP 11-8-2018

    Even if I purchased the 6kva unit, I am not close to an 80% load, currently. 60-65%, or so, if my calculations are correct. The only other load I see adding here, is a small home. Part of the power would be a trade off, though, as I would drop power requirements in the container, which would be transferred to the home, once construction was completed.

    Brother, I can only hope I will be alive in another 20 years. Very doubtful, though, in my mind. I'm 52. If I last another 10 good years, I will be happy. My pappy died at 63.

    Thanks for the advice, Bruce. Truly appreciated. Looks like I already have most of that list ticked.

    I imagine they make one that is pretty well bullet proof, even for this shitty Cambodian power. Like I said, banks across the country use these same generators. They too, are automatically switched. I would imagine (READ: hope) a Denyo ATS would be reliable as their generators. I imagine, going with one would be pretty costly, though.
    sec_monkey and Dunerunner like this.
  7. Dunerunner

    Dunerunner Brewery Monkey Moderator

    Having worked on and with these types of systems, slower running diesel engines are somewhat slow in recovering RPM as heavy loads hit them. That would mean that commercial power has failed, your genset detects it and initiates a start, there is a delay allowing the genset to reach designed speed and at that point, the transfer switch (ATS) is allowed to select the generator source. Transfer switches are powered by the source they are transferring to so, in this case, it would be your genset output. This is especially true of engines that are naturally aspirated (no turbo or supercharging) and utilize mechanical fuel injection systems.

    That all said, in your situation; you could put timers on your refrigeration (refrigerator/freezer/air conditioning) so that they do not try to re-start under a high refrigerant head pressure (increases starting current) or all at the same time. This gives the generator a period of time to recover before the next piece of equipment comes on line.

    Diesels like to be loaded down and hate being under worked so you will want to keep that in mind when sizing your equipment. I'm assuming the 2k set will be your back-up.
  8. BTPost

    BTPost Stumpy Old Fart,Deadman Walking, Snow Monkey Moderator

    Speaking of the ATS... I never use them here, I like to check the fluids and things every morning when I start the Gensets... I also use a 3 minute Warmup Cycle on the Genset, before I bring it onLine... and only use Manual Transfer Switching... but I have a 4Kw Trace Inverter on the Cabin,to keep ir alive even if the Genset is off... The rest of my Loads only are powered when the Genset is running... These include our four Freezers... we open them only when we need something, and usually that only happens when the Genset is runnin... I run the Genset only about 10 hous a Day... 7Am to Noon, and 5Pm to 10Pm. This is plenty of time to keep the Freezers Cold, Inverter Batteries Charged, and clothes Dryed, on Laundry Day...
  9. Asia-Off-Grid

    Asia-Off-Grid RIP 11-8-2018

    The way I have witnessed ATS's working in the past here, are they cause the generator to start and run at 1500 RPMs. Then, the ATS puts the generator online. When mains power is reinstated, the ATS keeps the generator running for X length of time (after transferring the load back to the mains), and before shutting down the generator. I can only assume this is how they work in the US, as well? (I have only seen them in "action", during my time in Southeast Asia.)

    Actually, we have 2 Samsung inverter refrigerators (one currently at the apartment in town), one old style compressor horizontal refrigerator-freezer, and one 1.5 hp Panasonic inverter air-con.

    I'm not 100% sure about the inverter refrigerators. But, the Panasonic air-con and the ref/freezer with the old style compressor, both have 5 minute delays built in. Aside from that, we only have one small water pump. So, no major draws immediately after switching to generator power. All of our inverter tech starts slowly, like a turbine, fortunately. I love inverter technology.

    Yes sir, I will.

    I have two of the 2k generators. They will serve for portable operations and as backup if we have a mains failure while performing maintenance on (what will become) the main generator.

    Well, thank God above, our generators aren't run that frequently. But, once or twice per week, is becoming the norm. One hour, to 4.5 hours thus far, have been the average run times needed. Enough so that we don't need to "exercise" them once per month, anyway.
    Last edited by a moderator: Sep 28, 2018
    Dunerunner likes this.
  10. ghrit

    ghrit Bad company Administrator Founding Member

    For a rupee's worth of useless thinking:
    Given the part time use and partial loading situations you are facing, I might rethink diesel vs. gas (or propane, or something else.) Diesels are not happy with partial and cycling loads. Just a perverse bamboo stick in your thought process. Auto start and delayed loading works no matter the engine.

    No matter the thinking, part time, emergency, and backup use is less taxing from an economic standpoint, so fuel efficiency counts for a lot less.
    Last edited: Sep 28, 2018
  11. sec_monkey

    sec_monkey SM Security Administrator

    yep yep

    @Asia-Off-Grid yer ideal load would be right around 80% fer diesel
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  12. oldman11

    oldman11 Monkey+++

    I have an older diesel 7.5 k generator that will run my house without any trouble,but make sure you get the right size to start with. The only trouble I have had was water formed in the fuel tank and rusted the bottom causing it to leak.The tank does not have a valve to drain water off the bottom.
  13. Dunerunner

    Dunerunner Brewery Monkey Moderator

    But it can be detected with a dip stick tipped with water disclosing paste, then pumped from the tank. I would recommend any fuel tank in a humid climate be lined or made of a non-metallic substance as condensation will happen.
    oldman11, sec_monkey and Gator 45/70 like this.
  14. BTPost

    BTPost Stumpy Old Fart,Deadman Walking, Snow Monkey Moderator

    Water is a MAJOR Issue for any Diesel Engine... This is why I designed my Fuel System with redundent Fuel Sources... My Main Tank is 550 USG and has a Drain Trough built into the bottom, that leads to an external Drain Ball Valve. This allows me to drain off any water that may form in the tank. Then I have a 55USG Secondary Drum Tank mounted above the Main Tank, that is filled by the Fuel Return Lines from the Diesel Gensets. This Tank has an Overflow outlet near the top, that allows Fuel to fill this Tank until it overflows, and when that happens a line then takes the Overflowing Fuel back to the Main Tank... Since the Fuel in the Secondary Tank comes from the Return Lines, it has been thru ALL the Engines Fuel Filters, and Injection System, and is Totally CLEAN FUEL... There is a second outlet from the Secondary Tank to the Genset Input Fuel Manifold via another Ball Valvue. This way, if the Main Tank should get contaminated, I can valve it off, from the Fuel Input Manifold, and open the Secondaty Tank Valve, and have a Known clean Fuel supply for the Gensets, for 72 Hours, while I investgate the issues with the Main Tank. This design comes from 30 years of operating the Powerhouse as my Winter Power System.
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  15. arleigh

    arleigh Goophy monkey

    I'd like to weigh in here even though I probably shouldn't .
    When we lived on the desert, we were off grid solar completely .
    I worked at a boat shop an they were supplying me all the cast off batteries I could use .
    During the winter months the sun was at such a low angle we needed a generator to keep them up but what worked most efficiently was a small engine an automotive alternator to charge the battery bank especially for the long winter nights,
    I built the system initially while living in the mountains and since the power went out unexpectedly I built my own UPS to protect our computer. 'so it ran on battery and the grid kept the battery up and the inverter ran the computer.. regardless of the grid ,
    A battery system can be charged by any thing . all you need is a large enough inverter or several of them to supply the batteries energy to your equipment, and if the grid is up charge it with the grid, if not charge it with any thing else you've got. but the batteries and inverters create a buffer zone should something else in the primary supply fails . shorts spikes brown outs.
    Though I don't get the wind I'd like I have a mill making it's contribution , along with the solar panels.
  16. Asia-Off-Grid

    Asia-Off-Grid RIP 11-8-2018

    I understand. But, that also puts me back to sizing the generator and making sure it will continue to be the correct size needed for some time to come. A rock and a hard place, me thinks.

    I am already on top of that issue. A stainless fuel tank is what will be manufactured, and will serve as the primary fuel supply for the generator I buy. The last thing I will be concerned about, is running low on fuel.

    EDIT: A drain petcock will work to remove any accumulated water in the tank.

    Everyone's input is always a welcomed addition to my threads.

    Um, not taking a shot at you, but this doesn't quite make sense to me. A boat shop in a desert?

    Similar to this 12vdc engine / generator resource that I uploaded a while back?

    I have 3 smaller UPS units that are online 24 hours per day. By smaller, I mean 600va - 750va. When I was stateside, I ran 1250va units. Regardless of the sizes, I'm glad I have them. I would go nuts having to constantly restart my internet, computers and other electronics, every time we have a quick drop in power, or a mains power cut.
    Last edited: Sep 29, 2018
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  17. Gator 45/70

    Gator 45/70 Monkey+++

    We always had Racor filters with a sight bowl in-between the tank and engine fuel pump, Easy to drain off the water with that set-up.
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  18. ghrit

    ghrit Bad company Administrator Founding Member

    Not really. Knowing that spark ignition engines are far more tolerant of part loading than diesel, you can oversize the gennie to accomodate future loads and know the engine won't give two hoots and a holler.
  19. Dunerunner

    Dunerunner Brewery Monkey Moderator

    Find or build a resistive load bank and wire it into a separate circuit panel in your generator shed. When you need to add more load, just flip a switch to add some. A few electric heaters could fill that niche.
  20. Asia-Off-Grid

    Asia-Off-Grid RIP 11-8-2018

    I won't find many electric heaters here. But, it wouldn't take too many water heaters to do the same job.
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