What generator to run a 240v Split unit inverter A/C

Surfpath · September 2023

Hi,
Helping a retiree who moved to the islands and is new to off-grid.

Is it best to run a 240v inverter A/C unit using an inverter type generator? Or can a regular, brand name (like Ace's Champion), shop generator do?

Also,
Many 120v generators seem to come with 240v receptacles, but I'm guessing that a model like this would not work because they are 240v but 60hz, as opposed to the 240v 50hz that his small split unit requires.

Any advice appreciated.

BB. · September 2023

NOTE: See update below--I was reading "DC to AC inverter" and SP was talking about "inverter Air Conditioner" so did not really address his question fully.

You probably need to look for generators that are sold in your area... Given that you are between USA/North America (120/240 VAC 60Hz) and South America (typically 230 VAC / 50 Hz--I guess), you should be able to find something to meet your needs.

For example, in North America, smaller generators are 120 VAC / 60 HZ (3kWatt or less typically), and larger gensets can be 120/240 VAC, 120 VAC high current, or 240 VAC only--All 60 Hz).

Personally, I tend to suggest smaller (Watt) gensets for the typical home/emergency backup. Smaller gensets (1-2kWatt inverter-generators) will run 4-9 hours on a gallon of gas (25% to 100% of rated output)... Which for me, are almost all 120 VAC units (60 Hz).

For folks with larger power needs (HVAC, Well Pumps, Electric Water Heaters), then larger gensets with 120/240 VAC are widely available (3.5 kWatt+ or so).

However, if you are in a 240 VAC 60 Hz region, then typically you can find most gensets for local use in 240 VAC 50 Hz... For example, the Honda eu2200i a 2kWatt genset is 120 VAC only. However, pulling up a random website for eu22i -- A 240 VAC 50 Hz inverter-generator, is available (happens to be New Zealand, but whatever you find locally):

https://www.honda.co.za/power/eu22i

Now inverter-genset vs traditional gensets....

Most AC equipment does not care if the line voltage is 230 VAC +/- 5% and 50 Hz +/- 1 Hz. But if you are using an inverter-charger (for example), there are units that "sync" with the AC input and do not work/sync on XX Hz +/- 10% or greater frequency variation.

And there are AC inverter-chargers that can be switched between 50 and 60 Hz (or will even "auto sync").

When choosing an AC genset... Standard Gensets (there are different voltage regulation, RPM controls, etc.) tend to have variation in output voltage and frequency (typically dependent on AC loading). Fuel efficiency wise, they are "fuel efficient" at 50-100% of rated load.

And inverter-generators typically have more accurate voltage and frequency control... And they are relatively fuel efficient at 25% to near 100% of rated load (a "standard genset" can be more efficient at 75% to 100% of rated output). However, they do not (typically) have high surge current support (i.e., you run then at 10-20% more than rated load, the inverter cuts off and goes through "recovery").

For running smaller loads (computers, electronics, smaller pumps, etc.) that do not have high surge current--The inverter-generators are very nice... Inverter-Generators are very nice, because most people running their home don't really use that much power (Watts). They run some LED lighting, a fan, computer, washing machine, small water pump, etc.--I call these "solar friendly" loads).

If you are doing "construction", then running a circular saw on an a 2,000 Watt inverter-generator, may "trip" the genset and not start the saw (constant "restart").

With a Standard Genset, the output voltage and frequency may "droop", but the genset will "struggle through" at reduced output voltage/frequency until the saw is up to speed--Then all is good (saw starts up a bit slower, but does start "normally"--The inverter-generator may not start the saw "without help").

And looking at loads... Running your home on a genset (power failures), the inverter-generator can save lots of fuel.

More or less, I can run a home with a power blackout on a 1,600 Watt genset on 2-3 gallons of fuel per day. Because most of the loads are LED lighting and several refrigerators that run at 120 Watts at 50% duty cycle (on average).

I could get a 9,000 Watt genset that will run the whole home (including HVAC, all lights/TVs/Vacuum cleaner, Washer+Gas Dryers, etc.)... However that unit will probably take around 0.5 gallons per hour, or 12 gallons per day... Heck of a lot fuel to store/buy (I also store with fuel stabilizer and "recycle fuel to car once a year). 10 gallons of gas will run my small genset for 4-5 days or so. A "full size" genset, probably not even 24 hours.

With off grid solar, there is a good possibility you will need to charge the battery bank during stormy weather. In this case, charging a battery bank from 40% to 80% load is pretty much a "constant current" load. I.e., the genset will need to supply that battery charging power for 5+ hours (depending on bank AH capacity, charger current output, etc.). But a "cheap" standard genset sized to run at 50%+ output during that X hour battery charging cycle, will burn about the same amount of fuel as an "inverter-generator" unit (because loading will be at 50%+ loading on genset).

If you are looking for more generator information--This is a very interesting read (movie lighting newletter):

http://www.screenlightandgrip.com/html/emailnewsletter_generators.html

-Bill

BB. · September 2023

Oops, mistake on my part. Inverter A/C is air conditioning... Not a DC to AC Inverter or inverter-charger.

Need to measure the AC input current for the air conditioner. Some Inverter based units may have 0.95 power factor. Others may have as poor as 0.50 PF.

What this means (roughly) is--For Example--You have a 1,000 Watt A/C input unit. The current consumed (1,000 Watts, 230 VAC, 0.95 and 0.50 PFs):
AC current (0.95PF) = 1,000 Watts * 1/0.95 PF * 1/230 VAC = 4.58 Amp draw
AC current (0.50PF) = 1,000 Watts * 1/0.50 PF * 1/230 VAC = 8.70 Amp draw

Or almost 2x the current. Your AC wiring, the Generator output needs to be rated both based on power draw (1,000 Watts) and on PF (especially if "poor PF) where "good" PF is close to 1.00).

Also, the "old" standard A/C systems were typically "on/off" type units. On for XX % of the time and Off for YY % of the time to give you the "average cooling" power needed.

Depending on the brand and model of Inverter A/C unit--Many (some, many, all?) have the ability to slow down the compressor when cooling requirements are not that high. For example, if the room is 95F and the the control is set for 75F, the unit will run the compressor at full RPM and draw full rated power and current.

If you set the control for less temperature span (say start A/C in AM when room is at 79F and the set point is 75F), the A/C unit runs the compressor at slower RPM, and drawing less power/current. This could allow you to run on a smaller genset (and/or run other loads once the A/C unit has cooled the room).... Your unit could use 1/3rd the amount of power (Watts) at that point.

You can see this does affect the size of the genset--And possibly a choice of inverter-generator vs standard generator...

Note that PF (Power Factor) has many different implications... And depending on "what type" of poor power factor a load (A/C, Refrigerator, etc.) may have--It can have an effect on the genset choices.

If you get a Kill-a-Watt type meter (UK/International 230 VAC versions--May or may not fit your "local cord sets"):

https://www.amazon.co.uk/s?k=kill+a+watt+power+meter

If your unit has "good PF" (>0.90 PF), that is a "good thing". Will work pretty well on inverter-generators or standard gensets.

If your unit has "less than good PF" (say less than 0.65 PF), it can have some pretty interesting effects on your gensets.

The usual answer is to get a "good PF" A/C (computer loads, etc.) and an inverter-generator for highly variable loads (for lowest fuel consumption). You can size your gensets to your loads (do not oversize genset).

With poor PF loads, and heavy(ier) loads... You are sort of stuck getting a larger genset. Also loads the surge (power tools), may need a larger genset and/or "standard genset" (which can "ride through" higher surge current than a typical inverter-generator).

If you can get a Kill-a-Watt type meter (measure current, PF, over time and usage--i.e., "low power" average mode, or cycling "high power" operation) and measure the A/C unit (in store, or if you already have one, or access to a neighbor's)--You can get some useful data.

Or--If you have the A/C unit--Can you borrow or rent a genset (either type, or one each) for a day and see how it runs (and what the fuel consumption is).

Without data, it is difficult to give you good answers... And the choices are not great--Oversize genset, lots of noise and huge amounts of fuel costs (and possible storage issues). Undersize a genset--And it does not run your A/C--Waste of money there.

-Bill

JRHill · September 2023

Good stuff Bill.

BB. · September 2023

Thank you JR.

-Bill

Surfpath · September 2023

Hi Bill,

Both your replies had good advice within them. So, I think a non-inverter generator that is 240 V, but 50 Hz will not work. A lot of devices and appliances with digital displays – like air conditioners – don’t play well with the different frequency. Anything with a Digital clock in particular seems affected.

On the other hand, it seems like a non-inverter generator could work, although from what you say, it won’t be as efficient if the draw of the split unit AC is relatively low which we’re hoping it to be.

I’ve read on this form that they are quite a few small inverter AC units that draw between 500 and 740 watts. I’m hoping that we find one like this, and then it looks like we’re going to have to find a Honda 20i or equivalent to run it.

BB. · September 2023

Technically, the "new" unit is eu22i (200 Watts more) than the "original" eu20i/eu2000i.

Given that the Honda's are something like 3x-4x or more expensive than the current low cost inverter-generators--I would not worry about trying one of the Firman or other 2nd tier branded gensets.

I really like the fully sound isolated Honda euxxxx family (and other brands). Does make for quieter home/camping.

Things to watch out for--The Honda are known for their engine life (2,000-6,000 hours reported)... Just keep the oil changed, filters clean, fuel stabilizer/drained when stored.

Also, people have complained about Firman inverter generators--they draw air in through the bottom of the case and suck up dirt/sand/debris, and may run hot due to poor airflow... Keep on clean deck and/or spaced above ground (if needed).

Spending on the "inexpensive genset" may still be a good move--At least you get some experience about how loud, reliability, and fuel usage.

At least in my area, finding somebody to do warranty repairs seems to be hit and miss... So, for many brands, you will probably hold the bag if they have issues ,and why starting cheap, to see if things run correctly before laying out big bucks for next step up.

There are some neat tricks for some of these smaller gensets. Some (like many of the smaller Honda euxxxxi family) have an internal fuel pump. You can buy/convert the gas cap to have a fuel line that you can drop into a 5 gallon gas can and draw fuel from. Just fill the genset tank, and the pump will draw fuel from the large external tank (you do not have to raise the tank and siphon fuel into the genset).

https://www.amazon.com/extended-run-fuel-tank/s?k=extended+run+fuel+tank

(you can just convert the factory fuel cap, or buy a machined fuel cap with fuel port).

Different brands/models of gensets can have neat little hacks so you don't have to refuel every 4-9 hours (not all gensets have internal fuel pump, but you can buy some small crankcase vent power pumps for other gensets to convert, etc...).

Short fuel tank runtime is a drawback for these small portable gensets.

Then there is the gasoline/propane/diesel fuel questions. Look at estimated fuel usage, and genset life... Say you need to run the genset 8 hours in the evening/night... A "good portable genset" should run 2,000 hours or so:

2,000 hours / 8 hour per night = 250 days of estimated life for portable genset...

That is not a long life for a tropical climate genset that runs most of the year. At least 1 gallon of fuel per night... Total cost could be:

$5 per gallon (California pricing these days) * 250 days = $1,250 worth of fuel (need oil change, filters, spark plugs, etc. as needed)
$1,200 for genset (local pricing) + $1,250 for fuel = $2,450 for 250 days (at least) of operation
$2,450 total cost / 250 days = $9.80 USD per day for modeled usage

Not saying that this is your costs--Just more of an example of how I like to model operational costs to see if this stuff makes sense.

May make sense for home if lose power for a week or two a year from storms--But may not make sense for daily use... Your mileage will vary.

-Bill

Wheelman55 · September 2023

People are reporting good luck and long service life with the Champion inverters. Same deal with doing the maintenance for long life.

Dave Angelini · September 2023

I did not read what make/model inverter/charger your friends power system has? That is the key to a decent answer here.

Surfpath · October 2023

Dave, they have a SMA sunny island 5048 system that can produce about 3kw, tied to ~3200 watts in panels.

Dave Angelini · October 2023

I am not an "sma island" guy and too busy to look up. Find out if the dual islands can run and charge from a 120vac gen or require a 240vac gen. Many of the new models can run off either source. Many, older ones can't.

The split AC cooling does not care, it will run off the 240 inverter. The 240 splits have the best efficiency which is more hours at night off batteries offgrid.

Getting one installed in Mexico may be and issue and there are a few DIY choices that come and go. You want the highest SEER 20+.

Buena Suerte !

What generator to run a 240v Split unit inverter A/C

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