Using a generator to power a washing machine

NWCabin
NWCabin Registered Users Posts: 7
Hi Everyone,

I'm working on my off grid cabin and I need a little help finalizing some of the design.

Using a Kill A Watt meter, I measured how much energy to do a load of laundry. It took .28Kwh (280W) and drew a max of 600W.

I'd like to get a small generator anyway to charge the battery bank through the winter, but I'm also wondering if I can use a generator directly to power the washer. Will this work?

I've seen a lot of good information, and if this has already been answered but I missed it in the search, please post the link. Thanks!
«1

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using a generator to power a washing machine

    No reason why it shouldn't work.
    With numbers like that you could use one of the small inverter/generators, which produce very 'clean' power. Some of the big fixed RPM units can be a little unstable in the frequency department as loads come and go, which might confuse electronic controls on the washer.
    Even with an inverter/gen you'll want to switch the eco throttle off and run it full speed, as otherwise it will have difficulty keeping up with the sudden load changes.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Using a generator to power a washing machine

    My guess is that an Eu1000 would be not quite big enough to start a washing machine, especially under load. 600 running watts might be over 2 kw, may be 20 amps to start?

    A Eu 2000 would do it.

    There is no reason can't run a washing machine off a genny. Do realize however that charging a battery will tax some (potentially large) portion of the gennies capacity, so a small one may not due both at theme time.

    Tony
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Using a generator to power a washing machine

    The newer HE front loaders have very soft start 3 phase PM motors which are inverter controlled. Mine during normal wash cycle uses less than 200 watts with no surge, and in spin cycle, gradually ramps up to a bit over 400 watts. (Kill-a-Watt checked) Very impressed with it. Totally unlike the older "standard" washers. AND, it uses very little water compared to the old style top loaders.
  • peakbagger
    peakbagger Solar Expert Posts: 341 ✭✭✭
    Re: Using a generator to power a washing machine

    I dont know if this information is current, but many manufactures used to void the warantee on aplliances if they could prove that the unit had been operated on non utility supplied power. This was apparently a real issue with square wave inverters. Home Power commented about this issue on occasion in the past but with the prevalence of pure sine inverters it may not be as much of an issue. Staber washing machines used to be recomended for off grid as they had no limitations on power source.

    In reality, with a inverter based generator, I wouldnt expect much of an issue.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Using a generator to power a washing machine
    peakbagger wrote: »
    I dont know if this information is current, but many manufactures used to void the warantee on aplliances if they could prove that the unit had been operated on non utility supplied power. This was apparently a real issue with square wave inverters. Home Power commented about this issue on occasion in the past but with the prevalence of pure sine inverters it may not be as much of an issue. Staber washing machines used to be recomended for off grid as they had no limitations on power source.

    In reality, with a inverter based generator, I wouldnt expect much of an issue.

    For sure I would not remotely consider running my washer on MSW, regardless of warranty. It's one thing to have the recharger for a drill go up in smoke - - something totally different for a $900 washer!
    Thanks for mentioning that "peakbagger", sometimes those of us on pure sine forget about MSW and it's problems, because it's no longer something we have to deal with. Out of "sight", out of mind.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using a generator to power a washing machine

    To that end, the original question was about running a washer off a generator. Now all fixed RPM generators are sine wave, but some of the el cheapo inverter/generators are not! Beware! Buy quality or pay the price - twice! :cool:
  • NWCabin
    NWCabin Registered Users Posts: 7
    Re: Using a generator to power a washing machine
    The newer HE front loaders have very soft start 3 phase PM motors which are inverter controlled. Mine during normal wash cycle uses less than 200 watts with no surge, and in spin cycle, gradually ramps up to a bit over 400 watts. (Kill-a-Watt checked) Very impressed with it. Totally unlike the older "standard" washers. AND, it uses very little water compared to the old style top loaders.

    What make and model of washer is it?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Using a generator to power a washing machine

    I have a pair of ~6 year old Fisher/Paykel washer + drier machines. Standard top load washer (and a top load drier--which I do like) that both use poly phase Permanent magnet motors in them. I can not measure any surge power usage (kill-a-watt) and they both use around 0.250 kWH per load (drier is natural gas).

    Power is on grid--so I cannot say how they will do off-grid, but they should be OK.

    The pair does draw about 9 watts "turned off"--Which is about equal to the power needed to run them a couple times a week--So I turn them off with a power bar when I am not using them.

    I am not thrilled with the mold/mildew problems that I have seen and read about with front loaders (plus other issues)--So I stayed with the top loading washer.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NWCabin
    NWCabin Registered Users Posts: 7
    Re: Using a generator to power a washing machine

    This is the generator that I plan to use.

    http://www.overstock.com/Home-Garden/2000-watt-Propane-Generator/5986359/product.html?CID=208011

    This one has some good features, to me, and is in my price range. It doesn't say "Inverter Generator" and, to be honest, I don't understand the distinction between a generator and an inverter generator since they both output AC.

    When I go to the website for the product, it has an FAQ that says not for sensitive electronic equipment, which it mentions as TV, DVD, Computer. No mention of washing machine.

    My other use of this will be to run an IOTA DLS-30 charger with IQ4. Getting things set up for the first time, I still have a lot of work to do, but I want to get the battery bank installed and start working on the systems so that I can get moved and not be paying rent and mortgage.
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Using a generator to power a washing machine
    NWCabin wrote: »
    This one has some good features, to me, and is in my price range. It doesn't say "Inverter Generator" and, to be honest, I don't understand the distinction between a generator and an inverter generator since they both output AC.

    My guess is that an inverter generator has a motor that spins a DC generator and inverts its output to make AC, and a generator's motor spins an alternator that produces AC natively.
  • spanel
    spanel Solar Expert Posts: 36 ✭✭
    Re: Using a generator to power a washing machine
    ggunn wrote: »
    My guess is that an inverter generator has a motor that spins a DC generator and inverts its output to make AC, and a generator's motor spins an alternator that produces AC natively.

    Generally speaking.. an inverter generator output a pure sine wave output.. good for electronics and as well are generally built to last ALONG time as far as 1000+ hrs of use and more fuel efficient as they have electroic throttles.

    A regular genny outputs a modified sine wave.. good for power tools, etc and gennerally dont last very long (100-1000hrs use). Also, most run full speed regardless of load and drink gas.

    for a washing machine.. is it old school with no electronic stuff or one of the newer models with it?

    As well... how many amps is the IOTA?

    Chris
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: Using a generator to power a washing machine

    spanel,

    Regular generators use an alternator, which puts out Sinewave AC. These generally have good sinewave outputs, until the load gets heavier or has poor PF. Quality generators such as the Honda constant speed (traditional) types have good waveforms with loads approaching full load, when the PF is at/near 1.0

    An MSW outupt generator is uncommon, with the exception of the very inexpensive import inverter gensets.

    JMHO, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Using a generator to power a washing machine

    NWC,

    Personally I would avoid the genny you are looking at like the plague. These are pretty generic cheap generators with cheap engines. They spin fast, have little oil, and don't last very long. If it were me, ( and I couldn't afford a Honda ue 2000) I would go on CRAIGSLIST or eBay and find an older Honda ex series generator, used for about the same money. Built well, built to last, if not abused, will run thousands of hours.

    Tony
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Using a generator to power a washing machine

    An Inverter/Generator consists of:
    • "wild frequency" 3 phase alternator
    • Inverter which takes in "wild AC", turns it into high voltage DC, which is then "inverted" into 120 VAC 60 Hz (or 230 50Hz, etc.).
    • "ECO" throttle control which allows the engine to slow way down and use less fuel while powering "small" AC loads. ECO Throttle may be turned off (full engine RPM) when running loads with heavy starting current (such as an A/C system).
    So, the inverter generators are really nice for running smaller loads (lights, TV, refrigerator) which don't use 50% or more of the generator's rated load. They save a fair amount of fuel for most of us when we just need to run a few appliances during power outages.

    Also, it is difficult (and expensive) to maintain 3,600/1,800 RPM +/- 1% for 60Hz power. Inverter generators are electronic so it is very easy for them to keep the frequency and voltage more stable.

    The inverter can be a good TSW version, or it may be a cheap MSW... Most inverter gensets are not really clear if they are TSW or MSW.

    And, while the definition of the Sine Wave should be the output of a standard AC genset--There are lots of design issues/cost trade-offs (amount of iron, copper, voltage regulation circuitry, etc.) that some AC generators have worse waveforms than a MSW inverter (and the waveform can vary greatly depending on loads and load types).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Using a generator to power a washing machine
    NWCabin wrote: »
    What make and model of washer is it?

    Sears, sold in Canada, 2007 model # 907-C4706-00
    The name plate states 12 amps, but where they get that I have no idea.

    Re the inverter generators, the old, non-inverter type produce their power directly from usually their stator, fed it right to your load and is more of less sine wave, even if rather distorted. They could be of an extremely simple design, a couple of large magnets spinning on either side of air core coils, and no regulation of any kind, save the mechanical governor that tried to maintain engine RPM, and the "60 Hz" varied with engine revs. Most were designed to run at 3600 RPM had to run dead on that 3600 speed to produce 60Hz and for all intents and purposes none of them did, they wondered all over the place. The GOOD inverter generators work in a different way. Their alternator output is fed into a rectifier, converting it's AC, regardless of frequency, to DC, which is then fed to a pure sine inverter which in turn powers your load. The beautiful thing about these better ones, like the Honda so often mentioned, is that under light load, the engine can vary it's speed, reving right down to almost idle, and still produce enough power to run the inverter. So under light load, the revs are low, it's extremely quiet and it only sips at the gas. Beautiful machines.
    The cheap ones? You have no idea what you're getting. In some cases the word "inverter" is used as a sales tool, so to keep the price down, some of them are the poorest quality you could imagine, including the poorest of square wave outputs.
    Added after posting: I see after the fact that BB has described the inverter generator much better than I could. Guess I was still composing while he was posting. Hahaha
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Using a generator to power a washing machine

    Robert took some nice pictures of sine wave, modified sign wave, and square wave output from various devices:

    -Bill
    2manytoyz wrote: »
    I've been using a scope on my inverters & generator for a while also. I have a Yamaha EF2400iS inverter type generator. Very clean power, cleaner than the grid power at my house.

    Grid:
    grid1compare.jpg

    Generator:
    gen1compare.jpg

    Other tests of this generator here (along with a look at the DC output): http://www.2manytoyz.com/yamaha2400.html

    A pic of the waveform from a Vector MSW (400W) inverter:
    scope.jpg

    From a Xantrex 1800W Prosine inverter:
    1609.jpg

    From an old Tripplite squarewave inverter:
    upswaveform.jpg
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using a generator to power a washing machine

    Of course you have to understand about waveforms and their effect on AC power for the pictures to mean anything. ;)

    In the simple form, everything you plug in to a wall outlet is expecting 120 VAC 60 Hz pure sine power. Some things aren't bothered if the frequency or Voltage drifts a bit or the waveform is a bit distorted. Some things will act up. Some things will drop dead in a puff of smoke. The closer you can come to that clean "utility grade" power the safer you are with running anything. (To be fair, some utilities don't have power as "clean" as even the cheap generators.)

    Note about the propane gen you linked to: be warned that propane generators use lots of fuel compared to gasoline. Like Tony said, those el cheapos are pretty much failure waiting to happen. Better you should buy a used Honda than a new NoName.

    BTW: my Honda EU1000i had not been used for two years. I put gas in it. Pulled the rope 6 times. It ran. Not bad for something with over 6,000 hours on it, eh? :D
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Using a generator to power a washing machine

    You won't get accurate start currents from a Kill-A-Watt meter. There are some clip-on ampmeters that capture surge current number.

    The start-up of the spin cycle is usually the killer.

    I doubt a 1kW generator will run it.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using a generator to power a washing machine
    RCinFLA wrote: »
    You won't get accurate start currents from a Kill-A-Watt meter. There are some clip-on ampmeters that capture surge current number.

    The start-up of the spin cycle is usually the killer.

    I doubt a 1kW generator will run it.

    I completely agree.
    Didn't mean to imply that a 1kW gen would; I was just mentioning the old Honda as an example of a quality-built rather than low-dollar unit.

    Many washers have 1/3 HP high-torque motors in them. The start-up on these can knock out a even 2 kW generator, especially if you have something else running at the same time..
  • abrockca
    abrockca Solar Expert Posts: 72 ✭✭✭✭
    Re: Using a generator to power a washing machine

    Our Sears front load washer would not work while our prior generator was running; would give off lots of beeps and then not run.

    We have a Honda EU series now, a much better generator, and it seems to be ok with that. But we still avoid running it while the generator is running.

    So yeah, don't go with a cheap generator or you might not be happy with the results. (both of our generators have been propane)

    Anne
  • NWCabin
    NWCabin Registered Users Posts: 7
    Re: Using a generator to power a washing machine
    spanel wrote: »
    As well... how many amps is the IOTA?

    Chris

    The IOTA is the DLS-30-IQ4, from Northern Arizona Wind & Sun.

    http://www.solar-electric.com/dls-30.html

    It's a 3 stage charger with up to 30A at 12v.
  • solarbob
    solarbob Registered Users Posts: 1
    Re: Using a generator to power a washing machine

    I dont see why it wouldnt work I am all about low energy and green products here is something you should look into http://www.12volt-travel.com/generator-portable-electric-1500-watts-p-4775.html Its a generator that can run off many things but my favorite is solar panels give a look may be a cheper way for you to go in the long run.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using a generator to power a washing machine

    Welcome to the forum.
    solarbob wrote: »
    I dont see why it wouldnt work I am all about low energy and green products here is something you should look into http://www.12volt-travel.com/generator-portable-electric-1500-watts-p-4775.html Its a generator that can run off many things but my favorite is solar panels give a look may be a cheper way for you to go in the long run.

    Just to be clear, that is not a generator. It is a box on wheels with an inverter and batteries that can be recharged by solar panels. Or a generator.

    Chances are it would not power most washing machines, which tend to use really large amounts of current to get their 1/3 HP high-torque motors going.
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Using a generator to power a washing machine
    NWCabin wrote: »

    My opinion is that that generator will drop well out of spec on voltage and freq, and could even kick out, when the washer goes into spin. I also see a problem with the propane fuel. I think you're going to be a little disappointed when you find out how long a 20lb cylinder lasts running a generator at full load. There is absolutely nothing wrong with using a conventional generator to run a washer. You don't need an inverter generator. But I do think you would be better to get a little bigger one that what you linked to.

    From experience with them, and owning one, I can recommend a Champion 46539 if you are looking for a cheaper generator that's reasonably good quality. You can buy them direct from Champion Power Equipment thru Amazon dot com if you google it or search on Amazon, and the shipping is usually pretty reasonable.

    The engine in the Champion is basically a Honda clone. But I think they made some improvements in it that even Honda should sit up and take notice of. One is the rockers. The Champion engine has genuine cast-iron rockers on a real rocker shaft that provides more positive valve timing control than Honda's stamped rocker setup, and with less wear to the valve guides and end of the valve stems when you get a lot of hours on the engine:

    Attachment not found.

    I don't consider them too bad for a $450 generator. They have a two year warranty and Champion Power Equipment has customer support that is rivaled by nobody, including Honda. When I adjusted the valves at 2,400 hours and needed a new valve cover gasket, I called Champion to order one. They sent me a new gasket for free.
    --
    Chris
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Using a generator to power a washing machine
    Welcome to the forum.



    Just to be clear, that is not a generator. It is a box on wheels with an inverter and batteries that can be recharged by solar panels. Or a generator.

    Chances are it would not power most washing machines, which tend to use really large amounts of current to get their 1/3 HP high-torque motors going.

    And even worse, many of them have nothing more than a couple of little motorbike batteries to supply the power. But they sure look cool, and the marketing behind them is worthy of one of those famous Hollywood Film of the Year Awards.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Using a generator to power a washing machine
    I completely agree.
    Didn't mean to imply that a 1kW gen would; I was just mentioning the old Honda as an example of a quality-built rather than low-dollar unit.

    Many washers have 1/3 HP high-torque motors in them. The start-up on these can knock out a even 2 kW generator, especially if you have something else running at the same time..

    FWIW, some of the high-tech front loaders (which would not be happy with intermittent AC to their control boards!) use a direct coupled motor to spin the drum and use essentially an inverter or VFD to drive it. For those the speed ramp up of the motor does not cause a significant surge at any point (compared to the power consumption at full speed anyway.)
    SMA SB 3000, old BP panels.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using a generator to power a washing machine
    inetdog wrote: »
    FWIW, some of the high-tech front loaders (which would not be happy with intermittent AC to their control boards!) use a direct coupled motor to spin the drum and use essentially an inverter or VFD to drive it. For those the speed ramp up of the motor does not cause a significant surge at any point (compared to the power consumption at full speed anyway.)

    I'd bet that box on wheels is MSW too, and the more complex washers with their VFD and electronic controls won't like that either.

    Ain't no free lunch. :roll:
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Using a generator to power a washing machine

    I don't know about front loaders. But the other thing to consider with top loaders is that every time the drum reverses direction during the wash and rinse cycles it puts the equivalent of a surge load on the washer's motor. When our top loader washer is going I see the ammeter on our inverter bouncing all over the place like it has gone nuts. That wouldn't be good with a little generator that only delivers about 1.2 kW continuous power. The generator would get a severe alternating "grunt workout".
    --
    Chris
  • Surfpath
    Surfpath Solar Expert Posts: 463 ✭✭✭
    Re: Using a generator to power a washing machine
    No reason why it shouldn't work.
    With numbers like that you could use one of the small inverter/generators, which produce very 'clean' power. Some of the big fixed RPM units can be a little unstable in the frequency department as loads come and go, which might confuse electronic controls on the washer.
    Even with an inverter/gen you'll want to switch the eco throttle off and run it full speed, as otherwise it will have difficulty keeping up with the sudden load changes.

    For the past 4 months I have been running my Speedqueen washer off my Yamaha6300iSDE generator in Eco mode. It seems to do fine in ECO, even when the washer 'agitates' (I think that's the word). At the same time I run my fridge for a few hours (note: out of habit I always start the fridge in 'regular' gen mode and then switch it over to eco). But, because the fridge is trying to cool down from a warm state it probably only hard starts the compressor once, when it is started up.

    In ECO mode I also run about 100 watts of lights along with the washer/fridge. The led power meter on the Yamaha is usually blank or briefly goes on the 1st bar out of 5 bars. However I notice that if I put on another, say, 100 watts of lights they all slightly flicker when the washer agitates. The LED meter goes to the 2nd bar.

    I can understand that the smaller briefcase generators may have difficulty running a washer (esp in eco mode), perhaps the larger inverter gens, as in my case, can.
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Using a generator to power a washing machine

    I am a big believer in basic measurements... So, measuring the kWH total each time you run time it--And the amount of fuel used. Get something like kWH/Gallons (or liter) of fuel used...

    More or less, you are pretty efficient if you are getting 4kWH per gallon (or ~1kW per liter)... And not doing too well if less than 2kWH per gallon (or ~0.5kWH per liter).

    For example, the inexpensive generator that Chris Olson likes (the Champion 46539) is a 3.5kW unit with a 3.8 gallon gas tank that will (per specs) run about 12 hours at 1/2 load, or:
    • 3.5 kW * 0.50 loading * 12 hours * 1/3.8 gallons = 5.5 kWHh per gallon

    That is not too bad... The non-inverter generators tend to be more efficient at >50% load and the inverter generators tend to be more efficient (than non-inverter types) at less than 50% load--But that still does not mean that inverter generators are "that" fuel efficient--They just tend to be more fuel efficient running small loads than the big guys.

    And, I would suggest, that having two gensets--one large (perhaps purchased at a good price) for the larger loads, and a small genset for emergency/small loads is not a bad thing.

    The Honda eu2000i ratings are 1,600 watt full load, 4 hours at 100% and 9.6 hours at 25% on 1.1 gallons of fuel:
    • 1.6 kW * 4 hours * 1/1.1 gallons of fuel = 5.8 kWH per gallon
    • 1.6 kW * 0.25 loading * 9.6 hours * 1/1.1 gallons of fuel = 3.5 kWH per gallon

    Note, the above numbers are based on factor specifications--Chris Olson has posted some fuel usage numbers before. Anyone that different/better numbers, please feel free to post. These numbers are intended as a starting point for discussion. Here is one post from Chris (I did not find the others yet):
    ChrisOlson wrote: »
    That's assuming those fuel consumption numbers are even accurate. I did a measured fuel consumption test on my new EM4000SX and it burned 57 ounces of 91 octane gasoline with no ethanol in it in one hour @ 3.8 kVA continuous output, driving water heater elements.

    If you look on Honda's website it shows rated load for that generator at 3500 watts, max 4000 watts, iAVR 5000 watts. On the data tag on my generator it shows rated load 3800 watts, max 4000, iAVR 5000. On Honda's website it only shows a generic run time, which doesn't really mean much. But for rated load it says it will run for 10.1 hours. It also says the fuel tank holds 6.2 gallons.

    The tank was bone empty when I got it and the most gas I could get in it, filled up at the pump at the gas station when it was in the back of my truck, was 6.06 gallons, not 6.2. And according to my fuel consumption test it will run for 13.6 hours at 3.8 kVA output on that 6 gallons of gas. And that's assuming it could get every drop of fuel out of the tank, which it can't. There's a standpipe in the tank that draws the fuel at about 1/2" off the bottom of the tank, so I estimate that there will be about 1 quart left in it when it quits due to being out of fuel.

    Actual field test data is the only thing you can rely on. Taking figures off a manufacturer's website, from their sales propaganda, is a little "iffy".

    Also, reading the operator's manual for my new generator, not a single mention, chart or anything, relating to fuel consumption in it.
    --
    Chris
    • 13.6 hours * 3.8 kVA / 5.75 gallons of gas = 8.9 kVA per gallon of gasoline

    The big question here is what is the kW of the load--For a typical motor load it is not unusual for PF to ge in the 0.67 range--But for resistance heating for it to be in the 0.95 to 1.00 range... That will affect the kWH per gallon ratings... For example using 0.67 PF:
    • 8.9 kVA per gallon * 0.67 = 6.0 kWH per gallon of fuel

    Still not bad--But "different". But since I don't know Chris' loads--The above is just an excessive in math.

    There have been a few folks that have been running large genset with relatively small battery chargers--And that can get down towards 1kWH/gallon of fuel--And that gets real expensive real fast (running a genset at less than 25% loading can be really inefficient). If you are stuck trying to bulk/absorb the battery bank during bad weather--Sometimes it is just the cost of living off grid.

    If you have to do a lot of "low power" generator runtime, a smaller genset can easily save its costs in fuel usage alone over a couple years of operation.

    But the downside with thermodynamics is that smaller engines are almost always be less efficient than a similar engine type in a larger size...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset