NicaSol: Off grid generator and SW+2524 inverter-charger configuration

This discussion was created from comments split from: Synchronising an inverter/charger with a generator.


  • NicaSolNicaSol Registered Users Posts: 32 ✭✭
    edited October 2020 #2
    A bit late to the party but this thread appears relevant to my inquiry.

    I will be buying a generator as a backup to our hybrid grid/solar battery system. (Xantrex SW+ 2524 inverter/charger still chugging along; 800Ah AGM battery bank; 2.4 Kw panels; 2 Tristar MPPT 45 controllers)

    The Xanterx manual states: "The generator should provide a stable voltage and frequency output for the inverter to synchronize with."

    When Bill (BB) says that genset inputs (Xantrex 2524 has an AC2) generally take care of synchronization themselves and then states "acceptable voltage and frequency something else", could someone (or Bill if you are here) kindly expand on that.

    To what extent, then, does "synchronization" take care of itself  and/or is limited by voltage and frequency range? In another thread (Problem with Xantrex Inverter/Charger; Jan 16) Bill stated "If the generator frequency or voltage is out of range, the inverter-charger will not "connect"."

    In my research for a generator (non inverter type), some mention having digital voltage control (Honda) and some with mechanical governors (Ford, Pulsar) to stabilize voltage (and many not mentioning anything at all). Having used a generator with power tools and directly connected to loads during power failures (pre RE system), there is a very audible change in its operation as appliances/tools power on and off.

    Another question is do these fluctuations reflect voltage and frequency changes that could cause the generator to disconnect ("de-sync") from the inverter/charger?

    At a guess I would think that all sorts of generators have been used as backup to RE systems over the years. Will any generator basically work or are there features I should be looking for?

  • BB.BB. Super Moderators, Administrators Posts: 32,015 admin
    IN GENERAL--A generator AC input accepts somewhere around 108 to 134 volts @ 60 Hz +/- 5 Hz or so.

    The AC1 input for a Hybrid AC inverter (and GT inverter) is generally programmed for something like 108-134 VAC (or 216 to 264 VAC for 240 VAC units), and 60 Hz +/- 0.5 to +/- 1.0 Hz and the AC input must be stable (within specifications) for >5 minutes.

    Mechanically governed gensets... +/- 5 Hz is probably as good as they get (over load range/operational temperature/etc.). Inverter Gensets can do much better.

    And depending on the Inverter, some are programmable for acceptance range (the GT settings generally require a factory password and possibly an OK from the utility).

    A Kill-a-Watt type meter (or some more complex AC Voltmeters) does a nice job of showing frequency.

    And one of the tricks for "stabilizing" a genset was to put a 100 Watt filament lamp or small heater load on the genset (sometimes helps the waveform and frequency).

    And specifically, do you have or can you find the manual for your specific AC inverter?

    Sorry for the generic answer (I am certainly no expert here). Does this help NicaSol?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    The AC2  settings of the SW allow extremely wide acceptance values, in the case of my SW 2524 - 230 the voltage is 170 - 270 VAC, frequency 40 - 70 Hz, this is for a 230V 50 Hz version, the 120 VAC 60 Hz version is equally generous. Once qualified there is a gradual increase in load to prevent voltage/frequency sags, this along with the wide parameters will accommodate most generators in decent working order as long as the maximum charging current is set to within the generator's rated output, which itself is adjustable. All the information is in the manual, including defaults, however to adjust the settings additional equipment is needed, SCP, Combox etcetera,  as there is no on board keypad interface.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • NicaSolNicaSol Registered Users Posts: 32 ✭✭
    Bill, mcgivor,
    Yes, thanks, answers my concerns. And also for the bump about the manual - although always close at hand, twigged me to look a little deeper. Like, what totally escaped me, the spec appendix. For the 2524 SW+: AC input voltage range - 80-150 Vac; AC2 Input Frequency Range - 54-67 Hz; Display Menu 04I Frequency Hertz - This menu item displays the frequency of the active AC source (inverter, grid or generator). This value may drift slightly until the inverter fully synchronizes to an external AC source. Once synchronized, the inverter follows the frequency of the AC source. The "old" Xantrex 2524 SW+ (when Xantrex was still Xantrex) does have an onboard display panel and keyboard interface for the set up of an extensive array of settings and inputs.

  • Dave AngeliniDave Angelini Solar Expert Posts: 6,032 ✭✭✭✭✭
    The xantrex SW  either the standard or "+" does not have the range or adjustability that the newer Schneider CSW inverter/chargers do.
    This gets mixed up all the time and Schneider should have picked a less confusing name for the newer CSW line. 

    A good way to test an old SW is with a honda or similar inverter based genset. If your old SW will not lock-up and charge then you probably have  a defective input relay, or circuitry. Try the other input.  A picture often helps avoid the confusion.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • NicaSolNicaSol Registered Users Posts: 32 ✭✭
  • RCinFLARCinFLA Solar Expert Posts: 1,398 ✭✭✭✭
    edited October 2020 #8
    Although AC2 has a wider absolute frequency range the inverter will still not lock on if there is too much wobbling in generator AC output frequency due to an unstable generator govenor control.  The lock bandwidth on inverter is a lot narrower then absolute freq range.. Similar problem if generator boggs down with surge load causing inverter to disconnect from generator because generator freq dropped too fast for inverter to follow even if lowest freq it dropped to is within overall acceptable frequency range.

    Listen to generator.  It should be smooth even sound.  If you hear a 'wha-wha' sound its rpm's is varying too much. The govenor instability can be caused by a number of generator issues but many times can be corrected with slight adjustment to fuel mixture needle valve set screw on carborator.  Other common cause is a dirty, partially clogged inline fuel filter.  If old gas has been left in generator a fuel additive carborator cleaner may help clear out a gummed up carborator.

    An inverter-generator has different issue.  You may not be able to use it in ECO mode.  For an inverter-generator the freq is perfect but if using ECO mode there is a lag time for engine to rev up on additional AC load.  During this time the peak voltage on sinewave output will clip at a lower voltage which can cause hybrid inverter to disconnect.
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,032 ✭✭✭✭✭
    Really, would you use "eco" mode offgrid to charge batteries on a small "typical" 2 or 3 kw inverter based genset?

    Just pointing this out as an inverter gen is a great way to test these old inverters that keep getting sold on ebay with age issues.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • NicaSolNicaSol Registered Users Posts: 32 ✭✭
    RC, Dave - living in Nicaragua I have a very limited choice of available generators (4 out of 6 are inverter). Inverter generators are very expensive (eg $1700 for Honda EU2200i). But, the cost could be recovered in as little as 100 hours of use in gasoline savings especially if Eco mode could be used. When charging my battery bank from the grid I have observed the input amps from an AC source to the charger decrease from 20 (max for 2524 SW+) to about 9. Keeping in mind RC's caveat, would not this decrease in power demand be well suited to Eco modes and fuel savings?

    Dave - your first sentence; are you just asking or a bit skeptical? But then you follow up with saying inverter gens are a great way to test old inverters. (and in terms of my needs, hopefully work compatibly with them)  For my knowledge benefit (maybe others) and the purchase decision I have to make, could you kindly expand on how they are a test? Many thanks.
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,032 ✭✭✭✭✭
    edited October 2020 #11
    An inverter genset is great to test the old SW and SW+ because they are the correct frequency. You know if the SW wont start charging, the SW has a problem. Alot of non inverter genset in the low price range, have issues with frequency stability.

    Most people, charging batteries, just do a bulk charge and do not spend much time in absorption because of fuel cost. This is the reason that ECO mode is not needed.  A typical user might run a bulk charge in the AM, and let the solar finish the charge in the afternoon.

    Always a skeptic of blanket statements.

    We had 6 months anchored in some of the beautiful spots on the west side down there. You are lucky to live there!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • NicaSolNicaSol Registered Users Posts: 32 ✭✭
    Thanks Dave. Did the land yacht (RV) odyssey 20 years ago out of Canada. Was a one way trip. Great country, people. Difficult political and economy issues now, but where doesn't. The reason for getting the genset as a backup as decent panels and batteries are difficult to get now and may be impossible heading into next year's election.
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,032 ✭✭✭✭✭
    The politics were bad when we were there also. Seemed to be good for a long time until the last 5 years. Guessing on that. Can't you go into Costa Rica / Panama and get one or is it border and customs ?

    I did not mean to knock the ECO mode. It can be very good for times when you want long runs with a possible large load like toast & coffee. They have inverter 2kw known brand names now at costco for $600 US. Even a little 1 kw for about 300.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited October 2020 #14
    Off topic I understand  but worthy of information, none the less.

    When I went to Nicaragua in 1989 the exchange rate in the morning was 6 million to one US $,  by the end of the day it was 8 million, I made the mistake of exchanging  $20, nobody wanted the  Cordoba, had to trade a pair of jeans for fuel for my motorcycle, the millions got me a plate of rice and beans, Gaiiio Pinto. The roads were free of all vehicles except the odd farm tractor trailer "bus" and in excellent condition, Managua was a ghost town of skeleton buildings with people on horseback.

    My return in 2001 was vastly different, the development was like night and day, but to be honest I liked the first visit, something about it I can't explain, simplicity has a quality all its own, then again I was just a visitor, not a resident.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • NicaSolNicaSol Registered Users Posts: 32 ✭✭
    mcgivor - you'd be further amazed in 2020. There's still that "je ne sais quoi". Although chaos seems to prevail, the pace of life, in our experience, is considerably relaxed (perhaps leading to the chaos) and folk always have time for family, friends and fiestas.

    No benefit price-wise to Costa Rica or Panama. I'd also be paying import/sales taxes on top of the such taxes already paid in those countries. Borders (flights) are closed with no apparent opening anytime soon. And I've just been told the 2 Yamaha inverter models I was considering are no longer available nor will be restocked. So I'm down to a Honda EU22i, a Honda EU30is, a discontinued Yamaha EF2600 and an A-ipower 4250 from Pricesmart (like a Cosco, Sams Club). The A-ipower gets good reviews in the US, and is 1/4 the price of the EU22i, but there is no warranty or repair service through Pricesmart other than a 30 day return. I have some inquiries out at the moment if the A-ipower and Yamaha are "sufficiently generic" that any electric motor/generator repair shop could repair them.
  • BB.BB. Super Moderators, Administrators Posts: 32,015 admin
    Some of the questions I ask about generators (including my own):
    • Does it need to be quiet (inverter generators are typically MUCH quieter than standard gensets)
    • Do you run >50% loading on genset (suggest 50%-80% loading is ideal for residential gasoline/propane gensets in terms of fuel usage). Standard gensets >~50% loading can be as fuel efficient or even more fuel efficient than some inverter generators.
    • Diesel gensets are much more fuel efficient than standard gasoline/propane gensets at less than 50% loading (Diesel cycle). However, they should be run (typically) over 50% loading for much of their life for longer life (avoid cylinder glazing from low combustion pressure, carbon and wet stacking from cool operating temperatures--Although, newer gensets should not have wet stacking issues--So I have been reading).
    • Repairs--Check your local generator/small engine repair place and see what they feel most comfortable repairing. "Simple" standard gensets--not as hard to repair. Inverters and electrical on the "nicer" inverter gensets, auto start, etc. can be difficult to get parts for (many of the less expensive units you cannot even get parts for).
    • Inverter generators generally do not have the higher surge rating of standard gensets... A 3,000 Watt inverter generator may run at 2,600 to 2,800 Watts and surge to 3,000 watts. Simple gensets will generally surge a lot more (and you may have some voltage and frequency drop, but that can still rid through starting a well pump--as an example).
    • With oil changes and good maintenance, a Honda may last >6,000 hours (some say 10,000 hours+). An inexpensive genset may last 1,000-2,000 hours--Although some folks have reported upwards of 10,000 hours on their "cheap gensets".
    • Price--Yea, a Honda or similar inverter generator may coast 2-3x as much as a standard generator.
    I don't know what the answer is for you... But if you can charge at ~50-80% (of generator's rated capacity) and charge from 50% to 80% battery state of charge (typically "bulk charging", or maximum AC charger current for lead acid batteries) on the genset (when needed--heavy loads, bad weather, etc.), and let solar panels take you to over 90% state of charge (absorb stage as batteries draw less charging current, at least a couple times a week)--That is usually the most fuel efficient/least amount of genset runtime.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NicaSolNicaSol Registered Users Posts: 32 ✭✭
    Bill thanks for helping get my thoughts in order.

    Noise is less of an issue. Diesel is simply not available/reasonable at a home scale. Nicaraguans can be amazingly resourceful at repairing things. Yea, cost is a bit of an issue. But, hey, not like we are spending a lot traveling or getting out this year so there's a saving there.

    Our house loads are pretty simple; small fridge, small freezer; gas stove; a couple of fans; pool pump (3A); internet connection and computer electronics; security cameras and lights. All has run well on 2.4kW of panels, an 800Ah bank and occasional grid assist for years. Our concern is the grid assist part, as a potentially "disruptive" national election next year could have power cuts as a measure of civil disorder control (it has happened before).
    Just to make sure I'm thinking correctly...

    The Xanterx 2524 SW+ has a max charge current of 20 Adc. During Bulk charging the max wattage would be 20A x 28.8 = 2016 watts. That is more than the EU22i's (EU2200i) 1800 watts continuous. If we were to go with an EU22i I can reduce the max charge amps (to 17.8) to match the EU22i output. But, that would be 100% of its capacity; would a reduction to 80% be better (but slower)? Doesn't leave anything for overhead but loads could be turned off. Or have the generator power some loads directly and reduce the load on the battery bank.

    At 2016 watts that would be 47% of the A-Ipower 4250 genset (5000 watts surge); but capacity for house loads.

    Posts about generators and charging batteries in the Wind & Sun forums also refer to power factor correction, which I know nothing about, including for the 2524 SW+ charger, but suspect it could mean even the numbers above may be "off."

    Also, on the subject of surge capability, I would like to refer to a link ( I believe you provided (can't find that post) to an interesting article  about generators used for powering  lighting equipment in the movie production industry. Other than my very basic understanding of electricity, most of that article, as interesting and enlightening as some parts were, was way over my head. One conclusion that stuck with me was that due to the structural and circuity differences of inverter generators they are able to better handle the surges of high power lighting turning on. Is this the case only for that particular application? In a home environment with electric motors (and maybe heating elements) are standard (non-inverter) generators still the better option?

    Many thanks to all for your thoughts and help with this.
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,032 ✭✭✭✭✭
    "The Xanterx 2524 SW+ has a max charge current of 20 Adc. During Bulk charging the max wattage would be 20A x 28.8 = 2016 watts."

    Ah hmm... better check your math/manual above.  Also SW2524+ has alot more DC current than 20 adc when charging unless you limit it.

    A small genset,  eu 22i will surge and run "your" loads with this inverter fine. You may not be able to run all loads and charge batteries at the same time.That is why people who live up in your old haunts of Canada use a larger genset to charge and run all of their big loads at the same time. You do not need to do this near the equator. If you added cooling you might. There are many offgrid strategies for minimizing fuel and when you run the genset for different apps.

     Most offgrid folks would run the minimum loads the first hour of gen run to let the batteries bulk up a bit and then start using more loads as the charge current decreases. They would shut down the genny when at bulk voltage or run a bit longer into absorption for various reasons.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • BB.BB. Super Moderators, Administrators Posts: 32,015 admin
    edited October 2020 #19
    You ask lots of good questions here NicaSol,

    Your AC loads, it sounds like a 2,000 Watt genset would power them pretty nicely (powered 2x full size refrigerators, and 1x full size freezer, plus a koi pond pump+aerator, plus a few lights) for a few days on an old (but never run) Honda eu2000i genset during a power outage (just about reliable maximum). With an extended runtime fuel cap, hose, and 5 gallon gas cans (you use a sealed cap on the eu2xxxi genset, the fuel pump draws a slight vacuum in the genset tank, and pulls fuel from a nearby large gas can/tank).

    Power factor correction... Here is a nice technical explanation:

    And here is a simple analogy:

    You have a car that needs to be towed. If you stand in front of the car and pull on the rope--Say 200 lbs moves the car. Pull 200 lbs straight on, 200 lbs to move the car forward.

    Now stand 60 degrees to the side and pull. Only a fraction of your pull is moving the car forward. the rest is trying to pull the car sideways. To pull 200 lbs forward while 60 degrees off to the side:
    • Cosine 60 Degrees = 0.5
    • 200 lbs forward / 0.5 = 400 lbs needed to pull forwards with 60 degree offset. to "pull forward on the car with 200 lbs of force"
    We look at the electrical power equation of Power = Voltage * Current

    While that is true in the simple sense, in the complicated AC Voltage/current sense it is not always true. Some loads (like resistance heating) the "phase angle" -- The current is always in phase (zero degree angle--Like pulling on a rope) for simple loads like the heater. 
    • Cosine 0 degrees = 1.0
    And the "real" power equation is:
    • Power = Voltage * Current * "Power Factor" = Voltage * Current * Cosine phase angle
    • VA (volt amps) = Voltage * Current (notice that PF/Cosine is not involved
    For things like Induction Motors, the phase angle runs something like a Power Factor = 0.6 to 0.8 or so... Or a phase angle of:
    • Cosine *-1 (inverse) 0.6 = 50 degrees (poor power factor)
    • invCos 0.8 = 37 degrees (typical power factor)
    • arcCos 1.0 = 0 degrees (perfect power factor)
    inverse Cosine, invCos, arcCosine -- All the same thing, just different wording.

    More or less, the amount of fuel (or energy consumed from a battery bank) is based on Power.

    Wiring, transformers, fuses/breakers are based on VA

    So if you have a "3 amp" induction motor @ 240 VAC (I am not sure if you are 120/240 VAC split phase or 230 VAC or so single phase for you), the answer is:
    • 3 amps * 240 VAC * Cosine 37 degrees (typical) = 3 amps * 240 VAC * 0.8 Power Factor = 575 Watts (power/rate of energy usage)
    • 3 amps * 240 VAC = 720 VA (volt amps)
    So, for solar energy, generator fuel usage, you would use 575 Watts of "actual work".

    For wiring and transformer and such, you would use the 720 VA (heavier wiring and transformer because of the higher current of a non 1.0 PF load).

    Most residential AC inverters and Gensets the Max Watt rating also is the Max VA rating. For commerical generators, they can use 0.80 PF for the ratings:
    • VA = 10,000 VA genset rating
    • VA * 0.8 PF = 8,000 Watt generator power rating
    With a typical voltmeter, you are measuring AC voltage (sinewave or DC) and AC Current (sinewave or DC)... So, technically, because the meter is not measuring the "phase angle" between the voltage and current, you are measuring VA (volt amps).

    If you have a power meter (your utilty meter, a Kill-a-Watt type meter), those do measure the phase angle and can give you Watts (and most will give you Volts, Amps, PF, Frequency).

    Some loads (LED and CFL) lamps, they can have a PF of 0.5 -- A very "poor PF" load.

    For most of our needs.. Using V and A measurements is "close enough--0.80*VA of "real power readings").

    From reading the Movie generator pages... You can see some generators have poor wave forms, and others have good waveforms.

    Most modern Inverter generators have "sine wave" output ("pure sine wave" is typically <5% harmonics.... >5% harmonics is not pure sine wave).

    Your loads more or less define if you need sine wave power or not (MSW inverters are Modified Square/Sine Wave). Heaters, filament lamps, don't care... MSW or PSW are fine.

    Induction motors can only use the "fundamental frequency" (60 or 50 Hz) to provide rotational power/torque. Any "harmonics" are more or less turned into waste heat (motor/wiring/transformers run "hot").

    A "good" AC generator should output a "Pure Sine" wave voltage output. And PSW inverter generators should too.

    A standard genset will have a simple circuit breaker that will let 2x more current through for a short period of time (seconds or a bit more)--Good for starting motors.

    AC inverters and Inverter Gensets can have breakers/fusees--But they also have electronic protection. And they can shut down the output if the output current exceeds the rating even for a fraction of a second, the inverter can shut down imediatly (AC inverters tend to be rated for 2x power rating for a few seconds to a few minutes. Inverter generators seem to not be rated nearly as high--Maybe 20% or so surge current)...

    I don't have a lot of real world experience (or testing) of genset or inverter gensets--But I would "avoid" loads (running and starting surge) that exceed the inverter genset rating. Standard gensets, better surge rating/support (they may sag, but they will not immediately shutdown the output).

    AC power is actually quite a complex subject. For the most part, if we stay with sine wave inverters/generators and use the typical rules of thumbs, we can ignore the complexity.

    I can give you an example of where it does matter--Running a battery charger off a genset. You have a large battery bank, that is discharged well below ~80% state of charge, the battery can take the full charging current of a battery charger and load the generator for hours at a time....

    Lets take your present 800 AH @ 24 volt battery bank.... That is a pretty good size bank and sounds like a good fit for your needs (the pool pump--need more details there--voltage/current/hours per day of running, etc.).

    A typical system would be designed to run 10% to 20% or so rate of charge from a generator. Let's pick 15%. And we want to run the generator at 50% to 80% of rated load. And assume the battery charge has a PF of 0.8 (some are worse, the good ones are 0.95 PF). Lets also assume the battery charger is 90% efficient (engineers are hated because we always through in these various "losses" which make systems more expensive).
    • Battery charging current: 800 AH * 0.15 rate of charge = 120 Amps @ 29.0 volts
    • Battery charging Watts: 120 Amps * 29 Volts = 3,480 Watts
    • Fuel Usage Power: 3,480 Watts * 1/0.90 efficient battery charger = 3,867 Watts AC power load from battery charger
    • AC Generator load: 3,867 Watts * 3 hours of bulk charging = 11,601 WH of genset AC energy (assuming 3 hours of bulk charging)
    • Generator Gasoline usage (assuming 50-80% loading): 11,601 Watt*Hours / 4,000 WH per gallon (decently eff genset) = 2.9 gallons of gasoline
    • Generator sizing: 3,867 Watts * 1/0.50 (50% loading) = 7,734 Watt rated genset (50% loading)
    • Generator sizing: 3,867 Watts * 1/0.89 (80% loading) =  4,834 Watt rated genset (80% loading)
    Now need to look at VA ratings... Assuming residential genset where Mas Watts = Max VA (whichever is "worse" or higher value, is how to pick the genset)
    • VA load: 3,867 Watt AC load * 1/0.80 PF = 4,834 VA rated load
    • Genset sizing: 4,834 VA / 0.50 loading = 9,668 VA 50% load genset
    • Genset sizing: 4,834 VA / 0.80 loading = 6,043 VA 80% load genest
    So you can see, using an "OK" PF rated battery charger, 1/0.80 = 1.25 -- The genset has to be ~1.25x larger to supply the extra current because of the 0.80 PF.

    Now--The above numbers are all made up--But sort of bracket what your system could be. Most people do not have the VA, PF, etc. ratings, and your charger may not output 120 Amps @ 24 volt battery bank--Or perhaps you can program it to supply less current (10% rate of charge) and use a smaller genset.

    Also, older inverter chargers can have worse power factor vs the "newer" inverter-chargers...
    • Older inverter (example): AC deratings = 0.8 PF * 0.9 eff = 0.72 overall VA "efficiency" (not a real term--But gets the idea across of how much the total "losses" can be
    • Newer inverter (example): AC Deratings = 0.95 PF * 0.95 eff = 0.90 overal VA "efficiency"
    I will stop here--The above may be getting way to deep for your needs... I.e., tell us what inverter charger or AC battery charger you want to use, rate of charge to battery bank (if adjustable), etc... And just go for it.

    And there is the math based on your loads, battery bank sizing, hours of sun per day, etc... Another post--If you want to go down that road. Just from a quick glance, your system looks to be OK for solar+battery and probably for your loads.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • notesnotes Solar Expert Posts: 52 ✭✭
    RE: above post, 
    • Battery charging current: 800 AH * 0.15 rate of charge = 120 Amps @ 29.0 volts
    • Battery charging Watts: 120 Amps * 29 Volts = 3,480 Watts                                                                                     .Trying to confirm math for Let’s say charging batteries only with out loads for proper generator sizing. Would it be 3480 watts /  120 ac volts =  29 ac amp minimum generator @ 0.15 rate of charge? So you would be needing a 4kw generator for battery charging only?
    4-Canadian Solar CS330 in series/TraceSW4024/Midnite Classic 250 with Whiz Bang jr/8 L16370ah 4S2P/ Propane Honda EU2000/Propane Champion3800/Propane refrig/Wood heat/Propane tankless water heater.
    Off grid in Upper peninsula Michigan
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,032 ✭✭✭✭✭
    Actually Bill I am doing very little installation and my business is based on DIY installs. It is not big bucks!  It is structured in a design fee for everything one would need to go offgrid. The second fee is for me having the equipment sent in one shipment most anywhere in the world. My equipment prices are not mark-up because I have zero overhead. I do have over 30 years experience eating my own offgrid cooking. This is the value I add as I help get the system installed/configured, and can do that remotely.

    I try and use the store here for Arizona clients as well.

    I think there are now 2 people in this post so maybe "notes" should have their own post.

    Better top off your gas jugs  :*

    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
    E-mail [email protected]

  • BB.BB. Super Moderators, Administrators Posts: 32,015 admin
    Per Dave's suggestion, I have split NicaSol's discussion into a thread of its own... NicaSol, feel free to continue your posting here about your system.

    Dave, sorry--I was just teasing you a bit. People who have done a lot of work in their field and learned along the way--They just make their jobs/businesses look easy. But that was gained through those years of hard work.

    Poster "Notes"--I am sorry, I missed that you were not NicaSol, and your question was about your system.

    If you know your system is drawing 29 amps (use a current clamp meter is the easiest/quickest method to confirm), then I suggest running a non-commercial genset at 80% of maximum load for battery charging and other continuous loads (hours of running at 80% loading is usually about the maximum the genset can take without overheating the engine or alternator).

    If you get into Watts/volts/amps from the DC side of the charger  vs VA on the AC input side--Then there is another factor (Power Factor--Typically around 0.80 to 0.95, but can be in the 0.60's for some equipment--It just depends on the charger system design) thrown into the equation. And if you do the question based on Amps*VDC of the battery charging current, then you have to toss in the losses from charging system too (typically somewhere around 85-95% efficient). Doing this one step at a time:
    • 120 Amps * 29.0 volts charging = 3,480 Watts DC into battery bank (note battery voltage can range from ~24 volts to ~30 volts--So V*I=P can vary as the battery gets charged, or the charger can increase the current at lower battery bank voltage--Constant Watt charging). Using 29v*120a as more or less "worst case load")
    • 3,480 Watts DC * 1/0.95 charger eff (high efficiency number) = 3,663 Watts AC into charger
    • 3,663 Watts * 1/0.90 Power Factor (pretty good) = 4,070 VA (this represents the total current through the AC wiring and Alternator)
    • 4,070 VA / 0.80 max residential genset suggested loading for battery charging) = 5,088 VA minimum suggested genset rating (here we can also use Watts=VA for rating purposes when talking to genset dealer)
    If, for example, your inverter-charger or charger is rated at 30 Amps AC maximum input (and/or you have measured the actual worst case current with a current clamp DMM), then you can skip the earlier math as you already "know" the VA:
    • VA (AC charger input loading) = 120 VAC * 30 Amps measured (spec'ed) = 3,600 VA (takes % eff and PF into account)
    • Amps into battery bank (just for example): 3,600 VA (AC side) * 0.95 AC charger eff * 0.90 AC charger PF * 1/29.0 VDC charging = 106 Amps DC charging current for battery @ 29 volts (all things being equal, and my "fudge factor" numbers being accurate)
    • Minimum Genset = 3,600 VA * 1/0.80 max loading for residential genset = 4,500 VA (or Watts) minimum rated genset
    As you can see, the answers differ depending on where you start, and what assumptions you make.

    A couple of examples of DC Current Clamp DMMs (digital multimeters, and really AC+DC current clamp--they do both): (example of low price--good enough for our needs meter) (nice mid price clamp meter)

    Note that prices are all over the place at this moment (trade issues with China, COVID-19). Also there are AC only current clamp meters too--They are very nice meters, but for working with battery/DC systems, we want the AC+DC current clamp meters.

    Notes, please feel free to start a new thread about your system if you want to continue the discussion. It makes it easier to keep the Q&A related to your system and needs.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 32,015 admin
    And one of my posts did not get moved to the new thread (Internet/Cloudflare error). This post should be somewhere in front of Dave A's #21 post. -Bill

    BB. Super Moderators, Administrators Posts: 31,011 admin
    Looking at the SW + 2524 manual--It looks like the inverter-charger can charge a 24 volt battery bank at a maximum of 70 Amps DC...

    And to figure out the 120 VAC charging current for the 24 volt unit:
    • 70 Amps max DC charging charging (on 24 VDC bank) / 3.5 = 20 amps max charging current (120 VAC) setting
    • 70 Amps / 800 AH battery bank = 0.0875 ~ 9% rate of charge (max for SW+2524)
    • 20 amps * 120 VAC = 2,400 VA (or Watts)
    • 2,400 VA / 0.80 max suggested AC genset loading = 3,000 VA / Watt genset minimum suggested (best fuel economy)
    • 2,400 VA / 0.50 min suggested genset loading = 4,800 VA / Watts genset maximum suggested (avoiding less than 50% loading and approaching "not good" fuel economy)
    • 2,400 Watts (close enough) / 4,000 WH per gallon--pure guess = ~ 0.6 gallons of gasoline per hour (rough estimate of 3,000 to 5,000 kWH per gallon for "typical" gensets >~50% rated load)
    If you have a second AC battery charger (you run in parallel with the SW+2425 inverter-charger), then you would need to take that into account... But at this point, your inverter-charger is limited to 70 Amps max charging current...

    And, obviously, if you plan on using the genset to run some AC loads during this charging period, you need to take this into account.

    For example, say you get a 4,800 VA/Watt maximum genset so you can both charge, and use the "excess power" for your local loads (i.e., doing washing/water pumping/vacuuming while the genset is running--Why not).
    • 4,800 Watt genset * 0.80 suggested max loading = 3,840 Watt max continuous power
    • 3,840 Watts continuous * 1/120 VAC = 32 Amps @ 120 VAC max
    Set the AC1 or AC2 generator input to 32 Amps--If the AC loads (and battery charging) exceed this amount, the charging current will be cut back/and or the AC inverter will start using battery current to support the AC loads (generator support).

    Note that charging batteries can draw max AC current for hours recharging the battery bank... I always suggest that you run 1.25x (NEC derating for continuous loads). If you set for 20 max (3,000 Watt genset) then I would suggest the 120 VAC branch circuit wiring and breaker from genset to inverter AC input be rated for:
    • 20 Amps * 1.25 NEC derating = 25 Amp rated wiring and circuit breaker (to prevent false trips/hot wiring)
    I used this manual for the Xantrex SW+2524 information:

    I am certainly no expert in this stuff (no practical experience)--Just reading through the manual.

    I may be wrong on 70 ADC @ 24 VDC / 20 AAC @ 120 VAC as the max limit for the SW+2425 inverter-charger... Dave A. says it should be higher than that.... I could have the wrong manual or misread something.

    That is why folks like Dave A. get paid the big bucks for designing and installing off grid power system.  

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NicaSolNicaSol Registered Users Posts: 32 ✭✭
    Bill, thanks. I was just about to reply to your post #19 when the thread was moved and there have been a few more posts. I go through those and get back. Yes, correct manual,  the SW+ 2524 has  20VAC passing to the charger and a continuous charging rate of 70VDC.
  • BB.BB. Super Moderators, Administrators Posts: 32,015 admin
    Just to clarify

    20 Amps AC @ 120 VAC from genset to charging function in inverter-charger

    70 Amps DC @ 24 VDC to battery bank from inverter-charger

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,362 ✭✭✭✭✭
    My 1930's single cylinder diesel & 5kw harmonically stabilized alternator, work just fine with the XW inverter I use.  So a generator would have to be pretty rough to not be qualified..   Some have a high unloaded AC voltage, and you might need to use a 100W incandescent bulb to suck some power down, to bootstrap start the inverter lock.  But once the inverter locks on and loads the genset down, the bulb could be disconnected
    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

    gen: ,

  • NicaSolNicaSol Registered Users Posts: 32 ✭✭

    Bill - many thanks for your power factor and sizing explanation. Certainly have a better (entirely new actually) understanding.

    (post #19) Just to keep straight in my mind the terms/concepts used. Early in the post Power is defined as V*C*PF and VA as V*C. A fair bit down there is the bullet point "Fuel Usage Power...". In that line the  Watts are calculated as V*A (V*C?) modified by an efficiency factor (1/0.90). Is "Power" the correct word here? A few lines down the VA load is modified by a PF.

    With respect to the generator sizing calculations, I will be using the Xantrex 2524 SW+'s charger - 20 amps AC for charging with 70 amps DC continuous charge rate. The max charge amps AC provided to the charger can be set from 1 to 20 amps AC.

    Regarding the calculations, and please correct me if I'm looking at this some weird way, post 19 (corrected for now know amps - 70 instead of 120) used  watts on the output (DC) side of the charger (Battery charging Watts: 70 ADC * 29 Volts = 2,030 Watts), whereas post 23 used watts on the input (AC) side of the charger (20 amps * 120 VAC = 2,400 VA (or Watts)). Not a small difference. Is there a benefit one way or the other?

    For generators it will be between the EU22i (1800 rated/2200max)  and the A-Ipower 4250 (4250 rated/5000 max). I won't really know until I show up to buy one or the other - an overnight trip planned around covid precautions. Phone calls/email on inventory availability can be very nuanced here - as in yes we have that, only to arrive and find out it will be next week or is on order for whenever.

    The A-Ipower seems to be the "obvious" choice with regard to the above calculations  (post 23).  But, I would like to give the EU22i a chance even if it means a more hands-on and limited use operation. Both you and Dave feel that the EU22i would be fine for the loads that we have. With regard to charging though, and the calculations provided in post 23, is charging with the EU22i even a consideration? Even if loads were shut off and with AC2 Amps and Max AC Charge Amps set appropriately would charging be use-ably slow, painfully slow, lead to an early death, not at all. An alternative would be to use it just for loads and let solar charge the batteries. The more I look at it I like its quality reputation, the fact there is service center, its fuel efficiency, ready propane conversion (gasoline shortages),  and would probably come to appreciate quiet operation if used daily over a long time.
  • BB.BB. Super Moderators, Administrators Posts: 32,015 admin

    Just some clarifications... Are you looking for ~230 VAC @ 50 Hz (eu22i) or 120 VAC @ 60 Hz (eu2200i)? (larger/different generators can have 120/240 VAC @ 60 Hz split phase power for typically North America).

    Much of the rest of the world is 230 VAC @ 50 Hz (Japan and a few other other countries can be different yet).

    The AC calculations and AC power connections to your inverter are (usually) only one or the other...

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NicaSolNicaSol Registered Users Posts: 32 ✭✭

    120 VAC @ 60 Hz used in Nicaragua. And it is badged EU22i although not easy to find on the internet, but basically a EU2200i.

  • BB.BB. Super Moderators, Administrators Posts: 32,015 admin
    OK--Sounds good--Got to love those marketing people and their love of new/different model numbers. I did look up the eu22i, and they did seem to be very coy about the voltage/frequency specifications that I could find.

    Note, you can put 2x eu22i together in parallel, and get 2x1,800 Watts. You can get a second eu22i "companion" (if they sell one in your area) that has a 30 amp @ 120 VAC socket (for more power)--And, I believe, you can make a Y cord that plugs into each genset, and put a 30 amp connection in the middle for full output.

    Some other things that are just coming out... The new models of the eu2200i (and other eu family generators) are replacing the 12 volt @ 8 amp DC output for battery charging with a CO (carbon monoxide--"CO-MInder") sensor that will shut down the genset if CO build up in the area (such as you put the genset in a barn or garage). I don't like the idea of something that shuts down the genset if it thinks something is wrong. And CO detectors generally have a lifetime (something like 10 years is typical) when they need to be replaced. A person did a quick test and found that unplugging the CO detector would allow the genset to start/run without issue (so it seems--good temporary fix to get genset running again).

    And, just coming out is the Bluetooth equipped eu2200i gensets:

    Have not seen the Bluetooth equipped gensets yet (not that I go looking for them--I am not in the market for a new genset at this time).

    So, if you wanted to use an 1,800 Watt eu22i genset, the math would look something like this:
    • 1,800 Watts / 120 VAC = 15 amps @ 120 VAC max continuous
    • 15 amps * 0.8 "Bill's" genset derating factor = 12 amps max continuous battery charging load
    • 12 amps @ 120 VAC / 3.5 Xantrex 120 VAC to 24 VDC conversion factor = 42 Amps @ 24 VDC charging current (assuming you set the max generator AC charging current to 12 amps @ 120 VAC)
    • 42 amps / 800 AH battery bank = 0.0525 = 5.25% rate of charge
    That is on the "light side" for charging an 800 AH battery bank--Generally 10%+ rate of charge is nominal specifications for many flooded cell deep cycle battery mfgs.

    If you, in general, have mostly sunny weather--Yes, you could get away with 5% rate of charge and use the solar charging for most of the year.

    The size of solar array for a 10% rate of charge:
    • 800 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,506 Watt array minimum
    • 800 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 3,013 Watt array nominal
    • 800 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 3,917 Watt array "typical" cost effective maximum
    So, at 2.4 kWatt of panels, you are getting:
    • 2,400 Watt array * 0.77 panel+controller deratings * 1/29 volts charging = 63.7 Amps about best charging current (at 29 VDC battery voltage on cool/clear days)
    We have not discussed your average daily loads... Based on battery bank sizing, 2 days of storage and 50% max planned discharge (rule of thumb design for flooded cell lead acid battery):
    • 800 AH * 0.85 AC inverter eff * 24 VDC battery bank * 1/2 days storage * 0.50 max discharge = 4,080 WH per day battery discharge (i.e., dark stormy weather and/or over night loading)
    And based on hours of sun for your location... Managua (?), fixed array:

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 78° angle from vertical (12 degrees from horizontal:
    (For best year-round performance)


    A 2,400 Watt array should supply around (on average) assuming 5.37 hours of sun average minimum:
    • 2,400 Watt array * 0.52 end to end solar AC efficiency * 5.37 hours of sun per day = 6,702 WH per day (August average)
    Of course, for your base loads (things that must run every day such as a fridge/freezer, LED Lighting, cell phone charging, a little laptop computer usage, home water pumping) assume 50% to 65% base load fudge factor:
    • 6,702 WH per day (August average * 0.65 base load fudge factor = 4,356 Watt*Hour base load suggested
    Of course, on sunny days, you can run your "optional loads" (water pumping, clothes washing, vacuuming, etc.).

    Anyway--The rest of your system looks to be pretty well balanced... If you want to avoid buying gasoline, reducing loads (more efficient loads) and enlarging the array to 3,013 to 3,917 Watts or so--That will certainly reduce the need for a genset during bad weather/heavy load days.

    Today--Do you need to use a genset much for your average days?

    Just to give you an idea of running a charge from 50% to 80% state of charge for FLA batteries--A 5% rate of charge and filling "30%" of the battery capacity (80%-50%=30% recharge on genset):
    • 30% / 5% rate of charge (small genset) = ~6 hours of runtime (no other loads) on the little eu22i.
    For running some of the EU family gensets (those with the eu22i "vented gas tank", you can get (or convert a spare eu22i gas cap) and extended runtime fuel cap (fitting+hose) and connect to an external gas tank (genset fuel pump draws slight vacuum in tank and draws fuel from an external tank):

    An eu2200i will run (from Honda website):
    • 3.2hr @ rated load 8.1 hrs @ 1/4 load
    • 3.2 hours * 1,800 Watts (full load) * 1/0.95 gallon tank = 6,063 WH per gallon (full load)
    • 8.1 hours * 1,800 Watts * 1/4 load * 1/0.95 gallon tank = 3,836 WH per gallon (1/4 load)
    6,063 WH per gallon--Sounds a bit on the optimistic side... 4,000 to 5,000 at "full load" is more typical (I have not done any testing--So this is just Honda's website)... If we take 4,500 WH per gallon:
    • 12 amps AC * 120 VAC * 6 hours = 8,640 WH for 50-80% battery charge
    • 8,640 WH / 4,500 WH per gallon = 1.92 gallons of fuel (estimate)
    Anyway--Several ways to cut the math--Just some examples of what you can be looking at... 5,000 WH per gallon is pretty efficient for a gasoline genset.

    As you see, running a larger genset at lower loads (typically less than 50% rated output), the fuel consumption (WH per gallon) goes down... One good reason to not "over size" the genset.

    There are other ways to approach the problem... There is the old saying for survival... 3 is 2, 2 is 1, and 1 is nothing... So for a critical installation, you should have 2-3 "backup sources" for your power. You could always get the eu22i and get an old but good 4-5 kWatt noise maker (standard genset) and have 2 backups for your system... Run the quiet one normally--And run the large/noisy one for those times the eu22i failed, and/or you need more power (running shop tools, repairing home, pumping large amounts of water, etc.).

    And here are the components for using an external fuel tank with the eu22i family of gensets (or you can take an extra eu22i fuel cap and put a hose fitting into it):

    No direct answers--But hopefully some ways you can figure out what will work best for you.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NicaSolNicaSol Registered Users Posts: 32 ✭✭
    edited October 2020 #31
    Bill (and all) thank you very much for the information and analyses you have provided. Far beyond my original inquiry and very helpful and educational.

    To answer the question you asked (need to use a genset for your average days) the answer would depend on the time of year - rainy (May-Oct) or dry (Nov-Apr) season. We currently use the grid as a backup source. In the dry season with very little or no cloud cover we can turn off grid power and power the house only on the RE system - all day time loads, including pool pump, have the batteries at 85-100 SOC going into evening/night and the next morning at 70-80 SOC. In the rainy season with considerably more overcast/hazy days (but beats a Canadian winter) we generally stay connected to the grid to supplement charging.

    Additional panels are on the to-do list. They are reasonably priced for here ($350-400 for 340ish watt panels). The only hold back is I would prefer to use another Tristar or Prostar MPPT controller ("play-togetherness" compatibility) but are only available in Costa Rica and the borders are closed.

    I fully get the 3-2, 2-1, 1-0 analogy as it applies to our home security system as well. Our concern is going into next year's elections there could be considerable civil unrest and disruptions in energy sources, except for the sun. Thus our planning for alternatives now - generators (if gas, then gasoline storage; propane conversion if possible); additional panels; spare inverter/charger (retire the Xantrex 2524 as the spare); perhaps replace an aging battery bank.

    Thanks for the information provided. It certainly helps with the decisions to be made. Don't know the timeline for those decisions right now. It will likely be weeks, possibly months. Just the way things move here. In any event I'll get back to the forum/post with updates when possible. Thanks again.

    P.S. My first thought is to go with the A-Ipower 4250 and put the $1200 saved into additional panels. But that EU22i keeps calling to me...
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