Charge controller or Inverter for generator power?

New_Mexico_Will · November 2020

I'd like to add a generator to my system. I've ruled out auto-start for many reasons, mainly I don't trust what it might be doing when I'm not at home. I'm a homebody, so it's not a problem to just fire it up when I need it.

My charge controllers and inverter are capable of handling the generator power, so my question is: which one should I run the generator through? Is one inherently more efficient than the other? Or would it be better to use an AC->DC charger and connect directly to the battery bank?

I am 100% off grid, if that matters. It's a 48 volt system using Epever charge controllers and an AIMS 6,000 watt inverter.

mcgivor · November 2020

The generator AC output can't be used through a charge controller, the inverter would need to be an inverter charger.with AC input, othewise an external AC-DC charger of sufficient capacity would be required. Many generators have a DC output but the capacity is limited to a few amps of poor quality rectification.

mike95490 · November 2020

If your inverter has an AC charger in it, that's likely the best way, don't need to buy any new gear. Otherwise you are stuck with either small 15A 48V chargers, or big forklift 240VAC chargers.

New_Mexico_Will · November 2020

Ah, I'm now clear about things I didn't even know I was confused about. It IS an inverter/charger, so that'll be the way to go. Thank you gentlemen.

Can I just directly wire that, or do I need a fuse? I don't have the generator yet. I'm leaning towards a Westinghouse.

mcgivor · November 2020

The generator would have overcurrent protection rated by its output however if the conductors used are rated at less than that then a breaker of less capacity would be needed. Should the inverter charger be a split phase it may have a 240V AC input, details matter in selecting the correct generator, many portable ones have internal neutral ground bonding which needs to be taken into consideration as well.

mike95490 · November 2020

Westinghouse does not build generators, some company has licensed their name, to brand a generator.

First, look at the specs for the inverter/charger and see how many amps it can supply to your battery bank.   Does it need 120V or 240V to charge with ?
Generally, charging a battery bank from a generator, you want to have about 15% of the bank capacity, as charge current, you want to charge quickly and not burn more fuel than needed.   If you have a 600ah bank. 15% would be 90A, 10% would be 60A
Then look up the charger spec and see what the Power Factor (PF) is . Good inverter/chargers would be 0.97 or larger.   0.65 is pretty lousy, and you will need a larger generator for that.

Then figure the wattage needed .   90A @ 60V is 5400 and because battery charging is very demanding ( full load ) your generator should only be at 75% of it's continuous rating.   If your inverter has AC input Pass Thru to loads, your generator will be powering your house loads AND running the charger. More wattage.
So figure what size you need before you get invested in a brand.     Open frame contractor gensets work as well for battery charging as a fancy inverter generator, but half the cost and you get twice the wattage.

BB. · November 2020

You have to be very careful to understand the "ratings" of the various inverter-charger settings... Sometimes the Amp (current) limit is the 60 VDC max charging current, other places the current limit may be the 120 or 240 VAC Amp input current limit for AC1 or AC2, etc..

Also, on some other models (don't know about the AIMS)... If you program 20 amps for the "AC breaker rating" for AC or Gen AC input--Some mfg. will only draw 80% of that limit 20 amps * 0.80 = 16 Amps max input current).

That is a "good thing"... For North American fuses and breakers--Generally they are rated to not trip at 80% or less load (can take hours or days or never at 81%-99%), and will trip at 100%+ of rated current (again, depends on actual over current--100% may take hours or longer, 300% may take minutes or seconds).

-Bill

New_Mexico_Will · November 2020

Great information here, thank you. I need to go out of shopping mode and back to research mode on this project.

New_Mexico_Will · January 2021

I'm revisiting this topic, as I plan to buy the generator soon. My inverter automatically adjusts to match the power factor of the generator as long as it is within a voltage and hertz range, 95-127 and 58-64 respectively, so that shouldn't be a problem. It will accept up to 75 amps, which is more than I intend to feed it. It will only be for manual use when there are 2 really cloudy days, which isn't often around here.

I plan to wire the AC input of the inverter to an outlet on the exterior wall of the power house, so that I can roll the generator up to it and just plug in with a male/male cord. I'll be sure to use one rated for the amperage of course.

So, I think my last issue is neutral/ground bonding. The inverter is manual switchable, and is currently floating as it is hardwired to a panel that is bonded. So the generator should be floating too, correct?

Thanks!

BB. · January 2021

Sounds like you have the basics wired... Yes, float the genset, and ground bond in the main panel is the way to go.

Just to be clear, "Power Factor" (PF) is a specific electrical term. Voltage and Frequency, as well as waveform (pure sine wave, modified sine/square wave) is (more or less) power quality and is determined by the source (generator, PSW or MSW AC inverter, etc.).

Power Factor is a function of the load (AC loads, input to AC inverter-charger, etc.). It is "how efficiently" the AC waveform is "used" by the loads.

Sort of like how you pedal a bicycle... I you evenly press the pedals all away around, especially in the middle of the cycle on the pedals (most force to wheels) and not near the top/bottom of the cycle when little force goes to the wheels.

Bad power factor would be if you did most of your effort near the top/bottom of the cycle, or "jumped" on the pedals for part of the cycle and did no force the rest of the cycle, etc....

-Bill

New_Mexico_Will · January 2021

Thanks Bill, that's a great analogy for the slow learners like myself :-)

I understood that I needed to try to match the generator power factor to my inverter's, but apparently not so much. If I get to the point of needing the generator, the loads would be extremely minimal, as they typically are anyway, unless the water heating is running (it's on a timer). My inverter manual's instruction regarding this is attached.

I'm still leaning towards a Westinghouse. They seem pretty packed with features given the price. The model I'm looking at has a disconnectable netural/ground bond; just remove a wire. It's good to have options.

Bill, I see in your signature that you have a generator as well. Can I ask what you use, and if you're happy with it? My setup will be 3.2 kwatts when finished, similar in size to yours.

Image: https://us.v-cdn.net/6024911/uploads/editor/y5/pt4ayb2o5zw0.jpg

BB. · January 2021

I have a couple older Honda eu2000i--Pull start (5-10 years old) that have been "pickled" between uses (one short outage, another 2-3 days power outage)... They both worked great (running on stored fuel with fuel stabilizer, fuel recycled into cars once a year). Also used the "extended run" fuel cap (genset pulls fuel from 5 gallon gas can). The on for my inlaws ran a 1/3rd hp fish pond pump, 2x full size refrigerators and a full size freezer--All no-frost units. Used around 2-2.5 gallons per day.

https://www.amazon.com/s?k=honda+eu2000+extended+run+gas+cap (extended run fuel caps like these)

I think the Honda eu2200i use the same fuel caps as the eu2000i (tried my eu2000i syphon cap and it fit on the eu2200i).

And I just picked up a couple eu3000is (electric start, batteries on float chargers)--A bit larger with 3.x gallon fuel tank (the eu2000i are 0.95 gallons). Have not run them yet (pickled) and on float chargers. Marc Kurth recommended the eu3000is units as being very fuel efficient too...

I tended to go for the small/efficient gensets because I do not have much space for fuel storage (5 gallon cans), and have to recycle the fuel into my cars once a year... Also in a quiet neighborhood, and did not want to bother the neighbors either.

This website/newsletter has a whole lot of details about PSW/MSW and generators... Very nice read.

http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorSquare Wave Generators

There are a whole bunch of small/quiet/efficient inverter-gensets out there now. And it is pretty difficult to justify spending 2-3x more money for a "Honda"...

The older Hondas do not have remote start, power meters, gas gauge (on some units), float chargers, or bluetooth.... Although they are slowly adding features. The new eu2200i model may have bluetooth (now or soon?).

You do have to watch out for some of the new inverter-generators--Some may have MSW (modified square/sine wave) output---You really do not want that, and there are many PSW/TSW (pure/true sine wave) models out there, so no reason to get the MSW type.

I hope to get 2,000 to 6,000+ hours from the Hondas (not that I will ever run any of these that long in an urban area in my lifetime--I hope and pray)... And I would sort of expect 500-2,000 hours from the low cost units (many seem to be from the same overseas factory--Just paint and branding differences).

Just one little note--The newer Hondas (at least some models) are coming out with a carbon monoxide detector/shutdown module (looks to replace the 12 volt 8 amp battery charger output). My only concern is that if the CO detector fails, will the generator still run (CO detectors have a life of something like 10 years in general)... I read one review where the guy just unplugged the detector and the genset ran fine--So it appears that if you are between a rock and a hard place, you can get the genset running again.

If you are in the middle of no-where, can stand the noise... A simple genset (alternator) based unit without the inverter part will work fine, and probably be a bit more fuel efficient at heavy loads (such as charging a battery bank for 10 hours)... The inverter generators are generally much quieter and more fuel efficient if operated at less than 50% loads (down towards 25% loads). "Normal" gasoline/propane gensets run about the same fuel flow (gallons per hour) at 50% or 0% load--So lightly loaded gensets tend to really suck fuel (and same thing if you "oversize" the genset for its average loads).

I am sure there are a lot of folks here with lots more genset experience than I... They can give you some good feedback too.

-Bill

BB. · January 2021

And regarding PFC (power factor corrected) power supplies/equipment/battery chargers/etc. as loads--That is a very nice thing to get/have.

More or less, the wiring, plugs, transformers, alternator/gensets, AC inverter outputs need to be rated for VA (volts * amps). One equation for VA to Watts is:

VA * PF (power factor) = Watts

Power factor for "good PFC" units runs around 0.95 to 1.0 ... That is "efficient" of the AC current (AC voltage is a sine wave, AC current follows the AC voltage sine wave--In Phase). On those systems, Watts~VA (PF 0.95-1.0).

On "average" AC loads for a home (induction motors, computers, lighting, etc.), you may see a PF of ~0.80 on average... Some iduction motors may be down to 0.65. And some of the cheap twisty florescent lights, they get down to PF=0.5 ...

What does that mean... If you were lighting your yard with a 100x 13 Watt poor PF lights--Then:

100 * 13 Watts = 1,300 Watts
100 * 13 Watts * 1/0.5 PF = 2,600 VA

That means while your energy meter (battery usage, generator fuel usage) may be supplying 1,300 Watts (very energy efficient)--The wiring, transformer, AC inverter, AC generator (inverter or non-inverter) needs to be rated for 2,600 VA or in amps:

2,600 VA / 120 VAC = 21.7 Amps with "poor" power factor loads
1,300 Watts / 120 VAC = 10.8 Amps with "perfect" power factor loads

The reason "good power factor" loads are very nice for small gensets... An average (cheap) AC battery charger may have a PF (and efficiency) of 0.65 whereas a nice (not cheap) charger may have a PF (and efficiency) of 0.95

If I am running a small 1,800 Watt genset--The difference in Watts to charging a battery could be:

1,800 Watts rated power
1,800 Watts rated * 0.8 derating for residential gensets = 1,440 Watts max continuous power recommended
1,400 Watts * 0.65 PF = 965 Watts to battery charging with "poor" PF charger
1,440 Watts * 0.95 PF = 1,368 Watts to battery charging with "good" PFC charger

For you home/AC power system... We pay for kWatt*Hours--Poor power factor is not charged (for residential usage--Commercial can be a whole different kettle of fish). Poor "PF" is generally not an issue (again for homes).

However, if you are running on an AC inverter or genset--Poor PF--You have to design for a heavier genset (burns more fuel) and wiring/plugs because of poor PF (say large well pump and/or AC/Heat Pump systems, or poor PF for AC battery charger).

Please feel free to ask more questions... This is actually a very complex subject and I have run together many sub-issues into one quick explination.

-Bill

mike95490 · January 2021

New_Mexico_Will said:

......
I plan to wire the AC input of the inverter to an outlet on the exterior wall of the power house, so that I can roll the generator up to it and just plug in with a male/male cord. I'll be sure to use one rated for the amperage of course...........

NO ! Spend the $90 and get a proper generator Inlet port and Transfer switch

That's my 5 cents

PS - A small generator will only have a single 120V output and will only energize half of a household 240 split phase panel

BB. · January 2021

Mike does bring up the whole transfer switch issue... You cannot just plug a genset into an AC main panel without transfer switch(es) and interlocks, or similar...

The basic systems only allow one AC source "ON/Connected" to the AC main buses... There are multiple ways to do this.

The inverter-charger can have an AC or AC1/AC2 input... And the genset (or AC mains) would plug in accordingly...

Then there is the whole question of having an AC inverter bypass... To allow you to power the AC panel with the AC inverter disconnected (failure, for service, etc.).

It is not "rocket surgery"--But you do need to have a workable schematic and choose the right parts/components.

The "suicide plug" (extension cord with maies at both ends) is not a great idea... The "sex" of the AC(or AC2) depends on what you are connecting (is it input only, or can it be energized by another AC source)... Nice/weather proof/fully shielded plugs/receptacles are not cheap.

Do you have a plan?

-Bill

New_Mexico_Will · January 2021

Well "suicide plug" does not sound like something I want!

Thanks for the detailed response Bill. I'm dipping my toes into unfamiliar water here, so bear with me. I did read the article referencing generators in the movie industry, and that definitely had some great info.

I'm seeing plenty of good options out there for a generator inlet box, clearly the way to go.

Just to clarify, I'm not planning to run the generator into the AC panel, but rather into the AC input of the inverter/charger. I'm wondering if a transfer switch is necessary? Also, I'm off grid and 120v only. Here is a section from the inverter manual:

Synchronized Power Transfer
When a load is transferred from inverter AC output to another backup AC source of power through the transfer switch, there will be a finite interruption of power to the load for the transfer to take place. A mismatch of phase and frequency of the inverter AC output and the backup AC source in transfer is likely to damage the backup AC source / a reactive load. With sophisticated circuitry design, our inverter will first lock on the frequency and phase of the input shore power/generator power and make a smooth and safe transfer at the zero voltage point to minimize the impact on the power modules.

Transfer Delay
There is a 15-second delay from the time the inverter senses that continuously qualified AC is present at the input terminals to when the transfer is made. This delay is built in to provide sufficient time for a generator to spin-up to a stable voltage and frequency and avoid relay chattering. The inverter will not transfer to generator until it has locked onto the generator’s output. This delay is also designed to avoid frequent switching when input utility is unstable.

After talking to a few friends yesterday, I'm leaning towards an auto start generator setup, which my inverter is capable of. I'm guessing that the inverter is handling the transfer switching, and that no additional switch is needed?

Also, I'm never looking for the cheap way out. I'm very happy to pay for what is required for a safe and effective system.

BB. · January 2021

Generally (as always, read the installation manuals), if you use the AC input to the AC inverter--It will take care of all of the AC transfer requirements--And you can uses a standard male plug for input to the inverter (no AC present from inverter, just from genset).

Most of the inverter-generator Hondas use a manual choke--So they are not really suitable for auto/remote start (and Hondas really do need the choke to start--Some folks setup a solenoid to make an auto/remote choke).

The "siren call" of an auto start generator setup is strong... But the issues and complexity of auto start systems does give pause.... It is more than just a relay from the inverter auto start controller to the genset... The generator generally has a fairly sophisticated controller that monitors cranking time/choke-mixture/oil/temperature/re-try cranking/monitoring RPM/cool down/weekly test/etc...

And the auto start needs to monitor battery state of charge and AC frequency/voltage from genset.

Also watch out for other design issues--One of the World Trade Center 9/11 issues--NYC had gensets a couple floors up in one of the buildings with their incident command centers hit by debris--The fuel line(s) were severed and the fuel pumps (on backup battery power) continued to feed fuel into the fire(s).

If you do your own design/install of the auto start genset--You will eventually become and expert in figuring out the system design and debugging.There are just so many wild and wonderful ways a "fully automated" system can fail.

Looking at the newer remote start inverter-generator generators seem to have the auto start/engine management part working... And the smaller ones are certainly much less expensive. (cheaper to replace if/when failure occurs).

One thing in my earlier post I forgot to add--Inverter-Generators generally have farily poor surge capacity. Because they are AC inverter controlled output--They can only surge 10% or so "extra current"--And will quickly shutdown the output if overloaded.

The standard gensets can surge more current, and if nothing else, the engine will slow down (and lower frequency/voltage) until the surge passes/engine gets back up to speed--They "ride through" heavy surge currents better (if you have lights/other appliances on the genset, they may not "like" the surge sag).

Then you look at AC Inverters that have "generator support" function... The inverter uses battery energy to help the generator ride through surges and even higher than generator rated AC output power (such as a well pump) for short term loads. Allows the use of smaller/more fuel efficient gensets on larger systems.

-Bill

New_Mexico_Will · January 2021

It seems to be very hard to find generators that state MSW vs PSW output. Honda is the only "reasonably" priced one that even mentions it in my searches so far. It also seems hard to find auto start/stop as a feature on a portable generator. The search continues. Thanks again Bill and Mike, you've been most helpful.

New_Mexico_Will · January 2021

I found these add on kits for Honda generators. Anybody have experience with these?

http://www.generator-line.com/index.html

Charge controller or Inverter for generator power?

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