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Basic backup generator questions

Discussion in 'Home Power and Microgeneration' started by Mike Ruskai, Sep 3, 2007.

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  1. Mike Ruskai

    Mike Ruskai Guest

    I'm looking for some basic information about automatic backup
    generators to run on liquid propane.

    My house has 200A service, and I'm not interested in a generator that
    requires me to pick a fixed number of circuits. The whole house needs
    to be on backup. I'm not sure at this point what my power needs would
    be, but my preliminary guess is that a generator in the 10-15KW range
    would be sufficient.

    My questions:

    1) What's the lowest power output that's available for whole-house

    2) How important is liquid cooling versus air cooling in a normal NJ

    3) How large a propane tank is best? Besides the future generator,
    there's an existing oven/range and a future gas grill to consider. I
    already have a tank for the oven, of course, and I believe it's
    capacity is 200 pounds. It's oversized because after our initial
    propane company let us run out of gas on Xmas Eve day a few years
    back, then wanted a $100 emergency fill fee to come and rectify the
    situation, we requested a tank with a gauge (if possible) from the new
    company. I expect the 200-pound cylinder is the smallest they had
    with a pressure gauge attached.

    I'm comfortable doing research on details myself, so I'm only looking
    for basic pointers, and appreciate whatever helpful answers towards
    that end that I get.
  2. Per Mike Ruskai:
    If I were in your place, I'd either spend some money on a device
    that measures total consumption at the meter - or take the time
    and figure out how to deduce consumption by timing the
    revolutions of the meter disc.

    Then I'd fire up as many appliances as I thought constituted a
    full load and see how much they're drawing at the meter.

    Then I'd be able to shop for a specific capacity.
  3. Mark L

    Mark L Guest

    it's plenty.

    I just had a Trane A/C with multiple compressors installed and the stage1 compressor
    runs at 1260w, start load under 3kw. When the local utility power is down, I simply
    lock out the larger compressor, although it runs at just 3480watts with a start load
    under 5kw.

    how large is my generator you ask? it's a 5.5kw honda and it runs my central AC very
    well with 4kw left over for other things.

    have run it during times of total blackouts lasting several days and family has been
    cool, enjoyed cold milk and plenty of lights and computer/TV use.
  4. Vaughn Simon

    Vaughn Simon Guest

    Well, lets see... You have to figure in power factor, add in the square
    root of 3, correct for RMS, rub your chin for a while and furrow your brows
    whilst consulting your slide rule and your trig tables, and finally you end up
    with something like...48 kW. Did I make that clear?

    Seriously, it is very unlikely that the OP needs anything approaching 48

  5. Mark L

    Mark L Guest

    larger compressor is a 3 ton, the smaller 1.5 and I have run the 3 ton fine just fine
    with the 5.5kw generator, no tweaking needed, the only items I did not run were water
    heater and multiple burners simultaneously on stove
  6. Mike Ruskai

    Mike Ruskai Guest

    I do have fuel oil heat, but I don't know what kind of fuel oil it is.
    Only certain kinds are suitable for use in diesel generators. I've
    also not seen any automatic backup generators that run on diesel. I've
    no doubt they exist (or can be devised), but it may be more difficult
    than going with readily-available LP-powered ones.

    I'll just have the propane company put in a bigger tank, and maybe
    also get a gas dryer (not sure how the economy works out on that).
  7. Guest

    Which brings to mind the question

    "Can we use the 'waste heat' from the genset?"

    This might be 80 % of the fuel's heating value.

  8. no spam

    no spam Guest

    I'm looking for some basic information about automatic backup
    Yes and no. Fuel oil is a lower quality than diesel. You can pump fuel oil
    directly out of your tank and into your generator but I wouldn't. At the
    very least I'd want a couple of filters and a water separator between the
  9. A Diesel Genset will run on ANY fuel, that you can run a Fuel Oil
    Heating System on.

    Bruce in alaska
  10. You

    You Guest

    If you really think the above is true, then you need to ReEducate
    yourself on the differences between grades of Kerosene, Jet50A, #1
    Diesel, and #2 Diesel, and then go ask your local Diesel Mechanic
    what will run in the typical Home Backup Diesel Genset. Your in
    for a Major Education.
  11. More like 60%..... Rule of Thumb for beginners is:
    33% of the BTU's Energy goes out the Wires
    33% of the BTU's Energy goes out the Radiator/Cooling System
    33% of the BTU's Energy goes Up the Stack

    75 - 85% of the Cooling System BTU's are recoverable
    45 - 55% of the Stack BTU's are recoverable

    You paid for 100% of those BTU's, so anything recovered from
    the Stack or Cooling System, is Money in your pocket.......

    Bruce in alaska
  12. The Question isn't what size the Service Entrance Box is, BUT
    what are the LOADS, that the users is typically going to be
    using, and the Duty Cycle, those Loads bemand for Total Operation.

    If you have a 200 Amp Service Panel, I would expect that your
    actual Total Loads are significantly LESS than 200 Amps, and
    at any one time your Peak Load will be less than 150 Amps.

    The only way to know for sure, is to have equipment to Monitor
    you Loads over a couple of months, and see what Peak and
    Average Loads are during summer and winter for that Service.

    Most Urban and Suburban Residential Services can get by on
    15Kw very easily.

    Bruce in alaska
  13. no spam

    no spam Guest

    Yes and no. Fuel oil is a lower quality than diesel.
    I never said it wouldn't. I just said that I would not pump fuel oil out of
    a home tank right into the fuel tank of any diesel engine I own. If need be
    I'd use it but only after a lot of filtering.
  14. Perhaps you are thinking of bunker fuel. The typical home fuel oil
    furnace runs on #2 diesel, with maybe a bit of #1 and/or kerosene mixed
    in to keep it flowing when cold. Oh, and it comes with a boatload of
    dye so the taxman can tell if you were running it your OTR Kenworth,
    Dodge, Chevy, Ford, Volkswagon or Mercedes. He won't care if you run it
    in your genset.

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