Generator

Hi,

I need a suggestions for a generator to charge my batteries after 3 cloudy days.

I have:

1. Outback VFX3648
2. Outback MX60
3. 16 Sunxtender AGM, for 700ah
4. 8 Sanyo Bifacial 186 W

Any help will be greatly appreciated.

Thanks,

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Generator

    Richard,

    Are the batteries each 12 volts? What is the bank voltage? 700AH bank or per battery? Fuel (diesel, gasoline, propane)? Local voltage required (Dominican Republic)? Any other large loads during day? Electric or Pull Start? Auto or manual start/run? Run often or rarely (low speed prime mover, or just an inexpensive "throw away" genset? etc...

    Generally, I would recommend the minimum generator size possible loaded to around 50% capacity to support your loads... Say you have a 700 AH 24 Amp battery bank and want 5%-13% rate of charge (sort of optimum charging conditions for various reasons), Assume quality battery charger with 80% efficiency:

    700 AH * 30 VDC charging * 0.13 max charge * 1/0.80 invert eff = 3,400 watts maximum load

    Assuming 50% load, ~7kW generator maximum, Around 3kWatt minimum generator (depending on battery charger ratings).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Richard Edwards
    Richard Edwards Solar Expert Posts: 27
    Re: Generator

    Bill,

    Thanks for your answer. I’ll try to clarify a bit:

    1. The batteries are 6v.
    2. The bank voltage is 48v.
    3. 700ah bank.
    4. Looking for gasoline with automatic electric starter, so I can program Mate and Flexnet to start generator automatically.
    5. Run rarely, I hope. We do get a lot of sun. I want it to run each time my batteries get to 50% capacity.

    Will not consider wind generators at all. I am not in a high wind area.

    Much obliged!
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Generator

    What model are those batteries?

    The way I see it: 6V * 8 = 48V, meaning two banks of 8 each. That's 700 Amp/hrs divided by two: 350 Amp/hr batteries?

    I don't see a model for Concorde Sun Extenders that meets that spec. :confused:
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Generator

    You can get details in the Battery FAQ...

    But I would recommend that you charge your batteries to at least 80-90% capacity. You will be able to pretty much run at maximum charge current (fuel efficient) and the battery will be back above the ~75% state of charge level where most batteries tend to sulfate and die over time (days, weeks+ of storage below ~75% State of Charge).

    Obviously, if the next few days are forcasted to be clear and your panels will bring the state of charge >75% -- then you can forgo the genset and waste of fuel to charge.

    Looking at the VFX3648 ratings:

    120 VAC Input: 60 amps AC Max, 54 to 66 Hz, 45 amps DC Max Charge output

    From the Manual (Page 47)--We need to figure out what kind of Battery Charger this inverter has, and its efficiency (Power Factor Corrected or not)...

    Max 120 VAC AC input current is 20 amps (18 amps default). Max DC output Charging Current is 45 Amps DC:

    Elsewhere, the manual says the charger is >80% efficient...

    Anyway, the maximum input charging current rating for the inverter sets the maximum useful genset capacity for charging of:

    20A * 120 VAC = 2,400 VA (VA is always equal to or larger than Watts--depending on type of AC load)
    • 2,400 VA * 1/50% genset loading = 4,800 VA Genset (or ~5kW "max" useful generator capacity)
    Any generator that is larger than this size will start to be a waste of fuel as most standard gensets use about 50% of maximum fuel flow whether supplying a 50% of capacity load or a 1% capacity load (I.e., roughly a 5kW genset will use approximately 0.8-1 gallon per hour at 100 % load and about 0.4-0.5 gallons per hour at 0-50% of load).

    Your minimum recommended size of genset (assuming 50% load, 5% battery rate of charge, and 80% charger efficiency would be):

    700 AH * 60 VDC batt Charge * 0.05 charge * 1/0.80 charge eff * 1/0.50 generator loading = 5,250 VA (~5,250 Watts)...

    So--for an "average" genset (only loaded to 50% maximum load for good life and fuel efficiency) would be around 5kW.

    In the US and Canada--you can probably find some nice used gensets from wrecked Recreational Vehicles that are in that range (Onans and such) that include auto-start, pressurized oil system, oil filter, quiet, etc.

    Or you can get a couple very cheap 5kW generators (primary and backup/spare parts) that will need to be replaced every few years (depending on how often you end up needing to run them)...

    The other end of the "useful range" of large gensets, based on your battery bank capacity and 13% charge rate (note, some AGM batteries will support more than 13% rate of charge--check your manual for details):

    700 AH * 60 VDC charging * 0.13 max charge * 1/0.80 invert eff = 6,825 watts maximum load

    6,825 Watts * 1/0.50 generator capacity = 13,650 Watt maximum useful genset capacity

    Now you are talking about larger gensets that are available in 1,800 RPM (low speed) Prime Mover rated capacity. These can last for a decade or more with reasonable maintenance.

    However, to charge your batteries at this high of current, you will need an external charge controller to output ~91 amps @ 60 VDC (48 volt battery charger)--perhaps a used forklift charger would be a nice choice. And larger chargers like this would be 240 VAC input most likely.

    And, if you don't run them often--you probably need fuel stabilizer/additive and need to rotate your stored fuel with fresh fuel at least once every year (assuming you put in fuel stabilizer).

    Another issue you will need to look at--the Outback supports a "two wire" electric start system... Some generators support a "three wire" or more starting controller--you may need to get an adapter in some cases.

    Once you nail down your requirements (price, performance, reliability, noise, etc.)... Then you can can look at what is available in your area.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Mangas
    Mangas Solar Expert Posts: 547 ✭✭✭✭
    Re: Generator

    Adding to Bill's comments, our engineers recommended an industrial grade 1800 rpm auto start genset to back up our system. They are efficient and very quiet with the sound accenuated cover option.

    Considering its current annual running hours, we expect to get 15 years or more out of it compared to a higher rpm gas powered unit which I estimated at less than 8 years.

    One reason we decided on propane fuel to power the 1800 rpm genny was our feeling it required less maintenance in most climatic conditions which vary here between say 0-110 degrees and our cost per gallon was less than gas. So far, all we've had to do was change the oil. After four years, plugs look brand new and so does the air cleaner.

    It cost a little more to install an underground propane tank, valves and fuel delivery line but once set up, we could supply the genny and the house from the same supply simplifying matters for us.

    Our off grid SW plus inverters are very flexible when it comes to charging the battery banks with the genny. We can program the inverters to charge the batteries at various amperage rates and running times depending on the system's size and operating conditions.
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • Richard Edwards
    Richard Edwards Solar Expert Posts: 27
    Re: Generator

    Hi,

    Your're right! Sorry. Sunxtenders, 3050T, 6v, 305ah x 2 = 610ah.

    I am trying to digest all the info. I'm relatively new at this. I believe then a 5000 k generator will do. Is that correct? Please advise.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Generator

    Yes, if you use the Outback internal charger (no other external chargers)--a 5kW genset should be a nice fit.

    A larger genset will probably waste fuel (try and get the fuel flow for various power levels to verify)... A genset smaller than ~3kW will be heavily loaded--and you may have to "program" back the maximum AC charging voltage.

    AGM batteries don't need "hard equalization"--so the 5% minimum charge rate can be cut back to 3% or 2%--but the genset will have to run for a long time to recharge the bank.

    5% (20 Hours to 100% recharge a bank) seems to be a nice minimum charging current size... If you discharge your bank to 50%, it will take ~8-10 hours to bring your bank back to near 90+% state of charge. That is probably enough generator noise/fumes in a day.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Richard Edwards
    Richard Edwards Solar Expert Posts: 27
    Re: Generator

    Thanks Bill. I think I will go for a Honda ei series. What do you think?
    I will probably run it for 4 hours a day and see what happens. Once I get me Mate and Flexnet up and running again, I will try to program it so it starts automatically.

    Much obliged, :D
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Generator

    I think the Honda eu2000i is about the perfect size for portable/reliable/efficient/basically one 15 amp 120 VAC outlet...

    However, you asked for auto-start. That bumps you up to a Honda eu3000i--but I am not sure that anyone really has set one with auto-start.

    Both are on the small side of charging your system.

    The larger Honda are good too-but I don't know much else about them.

    If you are planning on running the genset 4 hours per day--You probably want a better genset (a nice 1,800 RPM unit with pressurized oil filter, perhaps even water cooled).

    Also, you should have a good idea of how many Amp*Hours / Watt*Hours / kWatt*Hours you will need to recharge your bank (daily, monthly, seasonally).

    Getting too small or too large of genset can both be bad.

    Also, handling fuel--you are talking about a gallon or so of gasoline per day. Do you have any other "cost effective" sources of delivered fuel in your area (diesel, propane) which would store better and keep longer than gasoline?

    In any case--you should probably give your requirements (xx kWatts, auto start, fuel type, hours per month/year run-time) to a local generator supplier/knowledgeable local used equipment seller.

    I have no idea where you are located or what is available (including parts and service) for your area. Or--let people know here roughly where you are and perhaps somebody local can give you some more accurate information.

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