Inverter generators power to fuel ratio

FreewilleyFreewilley Solar Expert Posts: 223 ✭✭
Chart attached.
Using a hybrid system, I often wondered where the sweet spot is for loading batteries per gallon. Generally, I had started drawing only 6 amps for charging on the theory that if I was not where the genny noise bothered me, longer running at lower power was more efficient (as it powered the house at the same time, killing 2 birds with one stone for at least some of the time.
Today I located the answer for my 8 year old genny, Yammy EF3000iseb, possibly similar for other brands?
So I am now doubling to 12 charging amps and running 1/2 the time...for about the same fuel. The change in noise is not that great...and there was no way to know this without this handy chart...


Mate, VFX 2812, FM 60 & MX 60, 2 Full River AGM 400 6v, 1400 watt Solar Array, Yamaha 3000iSEB inverter gen
12 volt Flojet water pump
off grid summer home in northern Ontario

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,514 admin
    If you are interested, you can also try 1/4 loading too...

    In general with gasoline/propane/natural gas power gensets (at least AC gensets with fixed RPM requirements), below ~50% loading, the fuel flow remains at about 50% number. So, the sweet spot seems to be be 50% or higher loading.

    With the Honda eu2000i and similar, because they can throttle back to lower RPMs at lower AC loading--They can be more fuel efficient at lower loading. However, near 100% loading, they may be less efficient (the inverter power conversion adds losses over a simple AC Alternator).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • FreewilleyFreewilley Solar Expert Posts: 223 ✭✭
    1/4 loading is 1/2 the power at 10% less fuel.
    So, I have moved to 1/2 loading to get DOUBLE power with a cost of 10% in fuel. I will run the genny 1/2 the time at a big fuel saving...plus less hours on the genny and less time with the noise level. NICE.
    Also I have now limited genny draw to 1/2 load. As most do, I run the genny as needed when running high loads. In my case, the loads rarely exceed 1100 watts (Dishwasher, hair dryer, iron, coffee pot). So while these items cycle or run for short time, my charging will reduce to 100-400 watts, but my fuel efficency will stay at the sweet spot and avoid a 50% increase in fuel consumption while the draw is high. 
    It all looks like less bought gas which is good on several levels....environmental, hassle, money for gas, time with high noise level.

    I am happy....
    Mate, VFX 2812, FM 60 & MX 60, 2 Full River AGM 400 6v, 1400 watt Solar Array, Yamaha 3000iSEB inverter gen
    12 volt Flojet water pump
    off grid summer home in northern Ontario
  • BB.BB. Super Moderators, Administrators Posts: 29,514 admin
    Just watch the "maximum loading" too. Many residential gensets really do not like running more than ~80% of rated power continuously or they can overheat the alternator wiring/components.

    With constant loads like battery charging--It is much easier to "sneak up" and fry a genset with heavy/continuous loads.

    Also--For stuff with poor power factor (motors, many battery chargers, some electronics)--It is VA rating that is usually the electrical limit and not Watts...

    Say you have a well pump motor that runs a 1,000 Watts and 0.67 PF--The VA loading would be:
    • 1,000 Watts / 0.67 PF = 1,493 VA
    So--You could be over current on the genset even though way under watts (and fuel flow is generally following the Watts loading, not the VA loading--because of a bunch of math).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • FreewilleyFreewilley Solar Expert Posts: 223 ✭✭
    Thanks Bill. I understand some of that.... :'(

    But I did hit a hitch....where in the Mate menus do I set the max draw from the genny? I know it is there, but just made lunch and found out I did not alter the correct setting....I am drawing 2700 total, 1500 charging
    Mate, VFX 2812, FM 60 & MX 60, 2 Full River AGM 400 6v, 1400 watt Solar Array, Yamaha 3000iSEB inverter gen
    12 volt Flojet water pump
    off grid summer home in northern Ontario
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    where in the Mate menus do I set the max draw from the genny?
    press the "setup" softkey.  The setting is in AC amps that you wish to draw from the generator.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.BB. Super Moderators, Administrators Posts: 29,514 admin
    I do not know the programming for any of these devices (I am grid-tied/on-grid, not off grid).

    You have to check the manual/instructions closely... I have read where some vendors when you set the max draw for the genny--there are several variables. There is the max AC branch circuit rated current, and there is the maximum charging current (which may be in 120 VAC Amps or in xx VDC amps). You may have one/the other/or both.

    The nicer inverter-chargers will even throttle back on DC charging current if AC Load + DC Charging Load exceed "branch circuit" rating.

    And when setting max AC branch circuit amps... You may set 20 amp "breaker" and the inverter will limit to 85% of branch circuit (17 amps in this case).

    There are no coherent standards out there--Each vendor seems to roll its own.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • FreewilleyFreewilley Solar Expert Posts: 223 ✭✭
    Thanks Vic
    Went thru the settings and I was right, BUT somehow the transfer control was to grid instead of genny. Changed that I my limit now applies correctly....
    Mate, VFX 2812, FM 60 & MX 60, 2 Full River AGM 400 6v, 1400 watt Solar Array, Yamaha 3000iSEB inverter gen
    12 volt Flojet water pump
    off grid summer home in northern Ontario
  • BB.BB. Super Moderators, Administrators Posts: 29,514 admin
    PF--Simple (I hope) way to understand Watts and VA...
    1. PF = 1.0 -- You are towing a car straight from front, no jerking on the cable
    2. PF = 1.0 -- You are pulling (from straight in front) with 500 lb constant force
    3. PF = 0.5 -- You are towing a car with a 60 degree angle to the side (Cos 60 degrees = 0.5)--Cable "feels" 2x more pull to move car forward
    4. PF = 0.5 -- You are pulling for 1,000 lbs for 1 second and 0 lbs for 1 second--Average is 500 lb pull but "jerking" puts more stress on cable.
    More or less, the "work" of moving the car forward is "Watts".... The total force on the tow cable is (again more or less) the VA (volts * amps).
    • Watts = Volts * Amps * PF (so watts is always equal to, or less than VA).
    • PF goes from 0.0 to 1.0 and "good power factor" is >~0.95 and "poor power factor" is 0.80 to 0.50 (or even worse).
    • CFL lights can have 0.5 PF
    • Induction motors can have PF in 0.6 to 0.8 range, if "power factor corrected" can be ~0.95 PF.
    • Filament Lamps (old fashion lights) have PF = 1.0
    • Electric resistance heters have PF = 1.0
    • Electronics can run from 0.95 (power factor corrected) to 0.50 or less (for non-power factor corrected).
    • Many times, things at "low power" (TV on standby, AC motor with no load) can have "poor power factor", but once turned on and loaded can have "better PF".
    The wiring, transformers, inverter internals "see" Volts*Amps (stress on the tow cable).... The battery stored energy, fuel usage by genset, etc. "see" Watts (moving car forward).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • oil pan 4oil pan 4 Solar Expert Posts: 766 ✭✭✭✭
    Also most of the consumer home owner units are not rated to run at more than half load continuously.
    My 7kw troybilt generator only had wiring capable of supporting just under 5kw continuously.
    I ripped out all the 12 gauge wire and replaced it with 10 gauge wire, because I use all 30 amps it can produce when I run my welder or plasma cutter.

    On powerfactor, even a seemingly high power factor, such as 0.08 can increase the demand for engine torque by 30% to maintain the load as compared to a load with a power factor of 1.
    I have also power factor corrected motors, usually you can not achieve .95 power factor on every motor. Usually you can get at least up to .90pf form a low .5 to .7pf which is a good improvement.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • oil pan 4oil pan 4 Solar Expert Posts: 766 ✭✭✭✭
    I looked it up the other day, went to post it and my wifi had dropped out, so I will repost it.
    I looked up a cheap no thrills, direct drive single phase 2-pole 3000w generator that runs at 3600rpm and they are claiming 0.36 gallons of fuel per hour at half load.
    So as long as you can run the generator on at least half load there is virtually no fuel savings over an inverter generator. The only advantage the inverter has is at light load.
    Otherwise you are buying a more expensive, more complicated, more expensive to repair machine that you don't need.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • FreewilleyFreewilley Solar Expert Posts: 223 ✭✭
    Oil pan
    But what about the noise level between the two gennys? I assume that the cheap one is twice as loud.
    Noise is a big factor for me, both for our peace and quiet and the neighbors. We are on mile wide lake and I can hear lawnmowers on the other side of the lake when enjoying the fresh air....super quiet is as important to me as inverter...
    Mate, VFX 2812, FM 60 & MX 60, 2 Full River AGM 400 6v, 1400 watt Solar Array, Yamaha 3000iSEB inverter gen
    12 volt Flojet water pump
    off grid summer home in northern Ontario
  • FreewilleyFreewilley Solar Expert Posts: 223 ✭✭
    Now that I am ramping up my charging power from the genny, I am aware that I have to be careful not to overcharge my bank...can someone advise the abosolute max rate of watts for 4 550 Surrettes?
    I did the calc a couple of years ago and figure it is around 1500...I have a 12 volt system (early mistake!)
    Mate, VFX 2812, FM 60 & MX 60, 2 Full River AGM 400 6v, 1400 watt Solar Array, Yamaha 3000iSEB inverter gen
    12 volt Flojet water pump
    off grid summer home in northern Ontario
  • BB.BB. Super Moderators, Administrators Posts: 29,514 admin
    Assuming this is the correct battery:

    http://pdf.wholesalesolar.com/battery-folder/surrette/S-550.pdf

    As always, get all the information you can find from the Mfg:

    http://rollsbattery.com/uploads/pdfs/documents/user_manuals/Rolls_Battery_Manual.pdf

    These are 6 volt batteries at 428 AH capacity (20 hour rate). You have 2series x 2parallel for a 12 volt @ 856 AH battery bank

    In general, we recommend 5% to 13% rate of charge and 10%-13% rate of charge is "ideal" (5% is needed for equalization and smaller weekend/seasonal folks will sometimes charge at 5% with few panels, smaller genset).

    If you have a current meter on your inverter-charger or a DC current clamp meter, you can adjust directly for your desired target current (say 10% or 85.6 amps for your bank).

    On the AC side with the genset you have have various issues to deal with. Depending on the genset (local temperatures, altitude, etc.) you have a maximum genset capability. Say you have an 1,800 Watt rated consumer genset... At the very much (cool weather, sea level) you would want 80% of the genset capacity or:
    • 1,800 Watt * 0.8 = 1,440 Watt max
    • 1,800 Watt * 0.5 = 900 Watt min (fuel efficiency)
    And note that for consumer gensets, generally maximum Watts = VA (volt*amps) rating. This means that "poor power" factor is also a limiting parameter too.

    You can measure the AC current directly (meter, clamp meter) and figure out VA:
    • VA=V*I
    • I = VA/V
    • 1,440 Watts(Or VA) max / 115 VAC genset = 12.5 amps (AC) max recommend
    • 900 Watts min / 115 VAC = 7.8 Amps AC minimum (fuel efficiency).
    You can also figure out (roughly) the math for AC to DC conversion--A typical "decent" quality inverter-charger may look like:
    • VA = 85.6 amps DC * 14.75 volts charging * 1/0.90 charger eff * 1/0.80 typical power factor = 1,772 VA (estimate)
    Charger Efficiency may run 80 to 95% efficiency. Power factor may run from 0.67 to 0.95 (power factor corrected supplies).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • FreewilleyFreewilley Solar Expert Posts: 223 ✭✭
    edited June 2016 #15
    Ok, I chewed on this....not really asking about what the genny setting should be, but what total VA would be (combination of genny and some sun). I am trying to avoid over charging when running the genny and there is limited solar. This would happen fairly rarely.

    From the last calculation, I think you are telling me exactly what I need.... the 1772 would be 10% of the capacity. And that is about the max that I would be doing on a cloudy day and running my gen at 1200 watts charging. All good, I think.
    But there is a safety factor built in, should the sun come out....if 13% is the maximum before possibly damaging the bank, an easy figure is I could increase the 1772 by 30% approx (reflecting 13% as opposed to your suggested 10%). So 531 plus 1772 equals absolute max of 2303....
    If I have understood that correctly, I feel fine that I would never see that 2300 mark as that would require 1100 solar watts and I need a bright mid day sun to get there....will not be running the genny on THAT day!
    Have I gathered up enough apples here to bake my pie? Or in urban talk, am I on the right track?

    And many thanks Bill for your generous donation of your time to my problem. Very, very kind of you.
    Mate, VFX 2812, FM 60 & MX 60, 2 Full River AGM 400 6v, 1400 watt Solar Array, Yamaha 3000iSEB inverter gen
    12 volt Flojet water pump
    off grid summer home in northern Ontario
  • BB.BB. Super Moderators, Administrators Posts: 29,514 admin
    The 13% rate of charge is based on taking a Flooded Cell Lead Acid battery from 20% to 100% state of charge (i.e., a fork lift battery) without active cooling/temperature monitoring/thermal management of the battery bank.

    For the solar side, we suggest ~50% to 80% or to 90% as a typical genset charging range. And 20% rate of charge for a genset based charging is not going to "fry" the battery--But it is something that I would monitor (especially the first few times) to ensure that the battery does not get above ~110F (hot batteries are unhappy batteries). Lead Acid batteries are "very efficient" charging below 80% state of charge--As the battery approaches full charge, the efficiency drops (current, instead of "charging battery" goes into making Hydrogen and Oxygen gasses, and heat). At 100% State of Charge, pretty much all charging current goes into gassing and heat (at 100%, it is very possible/likely to overheat a lead acid battery with 2-2.5% state of charge if done for too many hours at a time).

    For solar charging, having a remote battery temperature sensor (common option for higher end solar charge controllers, not too common for AC battery chargers--for some reason--cost, more wires to connect/fail/break?) helps prevent thermal run-away (as battery gets hot, charging voltage and, therefore, current is reduced).

    Since other than for active equalization which you should be monitoring closely (which should be monitored unless is it is a short time period "auto-equalize" cycle), people are not going to run the genset at 20-30% current very often or much over 80% state of charge (waste of fuel and generator wear and tear).

    I will stop here--I think this answers your question without and excessive amount of hand-waving (I hope).

    Very happy to help--All I ask is that you help others when you can.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • oil pan 4oil pan 4 Solar Expert Posts: 766 ✭✭✭✭
    Build an enclosure.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • mike95490mike95490 Solar Expert Posts: 8,377 ✭✭✭✭✭
    If you have not bought a generator yet, you might read this very long web page about inverter generator and what happens when the power load is "less than optimal" (power factor less than .99)  They act strangely, you need higher wattage gensets, and lots of good info there,
    http://www.screenlightandgrip.com/html/emailnewsletter_generators.html

    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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