Generator size needed to start 11,000 BTU truck camper A/C?

softdown · July 2019

So I bought a 1600 watt inverter Yamaha with 2000 watt surge. It would not start the A/C using a 110 outlet. Hoping the 220 outlet does the job. I had been running the AC off of grid power 110 so I "figured" it was about 12 amps ~ 1500 watts.

I'd just check but having some peculiar health issues. It is a 2012 Forest River Palomino truck camper rated at 11,000 BTU. FWIW - modern truck campers take a while to know your way around.

BB. · July 2019

The easiest temporary fix/trial is to get an old 50-100 foot light duty extension cord and plug it between the genset and the A/C unit and see if the added resistance will drop the starting current.

In general, inverter generators, have poor surge performance (past rated value)... Plain Jane gensets will simply lug through a "heavy starting surge". An inverter-generator is "electronic" AC output and can shutdown in milliseconds and will not "lug" through heavy starting surges.

-Bill

softdown · July 2019

BB. said:

The easiest temporary fix/tratrial is to get an old 50-100 foot light duty extension cord and plug it between the genset and the A/C unit and see if the added resistance will drop the starting current.

In general, inverter generators, have poor surge performance (past rated value)... Plain Jane gensets will simply lug through a "heavy starting surge". An inverter-generator is "electronic" AC output and can shutdown in milliseconds and will not "lug" through heavy starting surges.

-Bill

Great answer as always. I was hoping that simply using the 220 volt outlet on the genset would make the A/C work fine. Though that seemed suspicious for some reason. The genset "advertising" fails to even mention 220 volt applications.

If I can't make it work I can return it for a larger, cheaper and simpler unit that also accepts propane. Though propane is less energy dense and would lower the output by ~ 20% by my estimation. Shame in a way - I really like the inverter generator. Super quiet and seems well made. I just can't justify ten gensets. My others are too small or too heavy for truck camper usage.

BB. · July 2019

If it is the Costco inverter-genset:

https://www.costco.com/A-IPower-1600W-Running--2000W-Peak-Yamaha-Powered-Gas-Inverter-Generator.product.100343958.html

That twist lock connector is a 120 VAC 30 Amp unit intended for simple plugin to RVs that have 120 VAC / 30 Amp twist lock...

As far as I can tell, that is not a 240 VAC output on that genset.

-Bill

I am guessing it is in the NEMA L5-30P family...

https://www.amazon.com/L5-30P-Plug-NEMA-Locking-Amps/dp/B004XHWHHU

softdown · July 2019

BB. said:

If it is the Costco inverter-genset:

https://www.costco.com/A-IPower-1600W-Running--2000W-Peak-Yamaha-Powered-Gas-Inverter-Generator.product.100343958.html

That twist lock connector is a 120 VAC 30 Amp unit intended for simple plugin to RVs that have 120 VAC / 30 Amp twist lock...

As far as I can tell, that is not a 240 VAC output on that genset.

-Bill

I am guessing it is in the NEMA L5-30P family...

https://www.amazon.com/L5-30P-Plug-NEMA-Locking-Amps/dp/B004XHWHHU

That all makes perfect sense. No surprise at all though one tends to expect 220 volts from a 220 volt type outlet.

BB. · July 2019

That L5-30 is a common 120 VAC @ 30 amp connector... It would never (on purpose) be used on 240 VAC.

Besides RV, a lot of shops and construction use 120 VAC twist locks too.

-Bill

softdown · July 2019

Turns out that many voltage regulators have a tiny brass screw on the inside that easily adjusts voltage output. Changed my Onan 3500 from 103 volts to 123 volts by turning that tiny screw - many times.

The Onan 3500 was made in China using a pretty good knock off of a Honda 2000 motor. Other problems presented and the partnership was terminated in favor of Yamaha. Tried to find my old thread about the Onan and lacked the technique to find and update. Least I did something.

Some would say that my campers 11,000 BTU air conditioner may have a 3000 watt start up surge though I doubt this is highly accurate.

Blackda3 · July 2019

Perhaps the following will be of interest. I have a Dometic Cool Cat 10.5k btu air conditioner in my Aliner camper. I made three test runs to measure my surge and running values - see below. I used two 2017 Honda 2000 generators (the primary and the companion units). Since then I have added a MicroAir smart start which allows me to run this load on a single generator. According to the manufacturer the MicroAir learns the start-up compressor's requirements with a full load which allows it satisfy the compressor's requirements using a smaller power source.) I have yet to perform the same test with the revised system. I can report that it does work but the A/C used to start instantly and now it takes a minute or so before it ramps up to output cold air.

The Honda's provided 120 volts AC:

Start-up/Surge: 44.1 amps for less than half a second;

Running: 9.3, 9.87 and 10.0 amps (each run had a slightly different value);
Once the A/C cycled off the fan alone was drawing 2, 2.48 and 2.47 amps.

softdown · July 2019

Blackda3 said:

Perhaps the following will be of interest. I have a Dometic Cool Cat 10.5k btu air conditioner in my Aliner camper. I made three test runs to measure my surge and running values - see below. I used two 2017 Honda 2000 generators (the primary and the companion units). Since then I have added a MicroAir smart start which allows me to run this load on a single generator. According to the manufacturer the MicroAir learns the start-up compressor's requirements with a full load which allows it satisfy the compressor's requirements using a smaller power source.) I have yet to perform the same test with the revised system. I can report that it does work but the A/C used to start instantly and now it takes a minute or so before it ramps up to output cold air.

The Honda's provided 120 volts AC:
Start-up/Surge: 44.1 amps for less than half a second;
Running: 9.3, 9.87 and 10.0 amps (each run had a slightly different value);
Once the A/C cycled off the fan alone was drawing 2, 2.48 and 2.47 amps.

That start up surge is about 5300 watts. What size is your Honda? I've seen a number run their A/C with gensets over 2000 watts - that seems to be the size needed.

BrianMoser · November 2019

I do realize that this subject has been discussed many times here. As a matter of fact, I did a search and found a lot of information. However, most of what I found is for 13,500 BTU or 8,000 BTU AC units.

My unit is 11,000 BTU and I need to know how many watts will require to run on a generator. I searched the web and found the following technical information about my unit:
-->Electrical Rating: 115VAC/60hz/1PH
-->Compressor Loaded Amps: 9.5
-->Fan Motor Loaded Amps: 3.1
-->Compressor-locked rotor amps: 53.0
-->Fan motor-locked rotor amps: 8.8

According to the Honda website, click here, for an 11,000BTU unit, I need 1,600 starting watts and 1,010 running watts.

After playing with the Amps X Volts = Watts and Watts / Volts = Amps formulas, I can't come up with the same numbers, which is why I'm confused.

Based on my research, it seems to me like Honda generators are the king, however, I am also considering other manufacturers due to the cost of this investment. Size is also a big consideration because my Truck Camper doesn't have any storage big enough for a generator, so it will be mounted permanently outside and I want to keep it as small as possible.

mike95490 · November 2019

For an inverter generator you use both Fan & Compressor Locked rotor amps. inverter generators have little/no extra overhead.

For a old school alternator generator , you can likely use double the Fan and Compressor loaded amps, to calculate your starting watts

old school generators have a flywheel which can help the engine manage a 1 or 2 second overload

These are "seat of the pants" guesses, since every generator / air con combo will be a bit different, some stagger turning the two motors on, some don't

mcgivor · November 2019

Could you not rent, borrow or somehow aquire a Honda and test it to confirm it is up to the task? Information provided on websites whilst helpful, its not as valuable real world testing.

softdown · November 2019

I find that gensets over 2000 watts are a bit large and heavy to be putting into a truck camper. Not to mention the major space needed - especially if you have a slide out. I addressed this major issue with two inverter gensets that run in parallel.

Honda gensets are among the very best. If a user plans on racking up hundreds of hours of needed usage the Honda investment is likely to prove wise. Quality gensets are also attractive to thieves who tend to have discriminating tastes. Use locks as needed and plain covers instead of Honda covers.

Blackda3 · November 2019

Sorry - I didn't realize my post was repetitive to this thread. Apologies.

t00ls · November 2019

I am having good luck with my 6250 inverter generator from champion power equipment, plus the fact they are US made and a US company

they have some smaller units that can do bi-fuel https://www.championpowerequipment.com/product/100263-3400-watt-dual-fuel-inverter/#product-img-3

and the regular ones https://www.championpowerequipment.com/product/75537i-3100-watt-wireless-start-inverter/

or if you want smaller and do a parallel setup

Johnny_Lightning · December 2021

I think in this case that a soft start is going to be your answer. They're not cheap, about $350 as I recall and as far as I know there are 2 manufacturers but it reduces the "surge" at startup by charging a capacitor or two to provide the start up power. As stated above this is what accounts for the slight delay in the A/C starting, the cap or caps have to charge. This is a very common upgrade in the RV world, Good luck.

Ralph Day · December 2021

I have a Yamaha i2800. It starts and runs my 13K Dometic on the roof just fine. It's open frame, but quiet. I think any of the 2K - 2.4K suitcase inverter generator units would work. The place I purchased from let me setup the trailer in the parking lot and try the unit before I bought it. Just wish I'd asked to try the 2400watt suitcase model as well. I might have purchased a slightly lighter one if it performed well.

unyalli · September 2022

https://www.microair.net/products/easystart-364-3-ton-single-phase-soft-starter-for-air-conditioners

Bunkysdad · October 2022

I have a 11kbtu Coleman Mach 1 PS in my truck camper and a Honda 2200i (previously a Honda 2000i, but desired the xtra headroom) so there are some variables that the Honda site outright dismisses such as ambient temp (i.e. post compressor warm-up temp), elevation, eco-mode operation and wattage headroom…Yes, a 2000i will start and run the air conditioner, but may struggle a bit at higher elevations and with higher ambient temperatures (say, much above the lower-mid 90’s, f) which may preclude the more economical and quieter eco-mode operation (which RPM ramps-up slightly slower…).

My Coleman once warmed up can easily draw 9.5 amps with fan on low speed…Something else to consider is that starting amperage can easily, momentarily be 5’ish times or so greater during each compressor run call…Because I’m in Nevada, I’ve since added a soft start to the air conditioner which (unlike a standard start cap) greatly reduces start-up voltage sag (a welcome attribute when in eco mode), and the damaging associated high current to motor windings which may shorten motor life…

To be sure I’d go with the 2200i (2000i is no longer in production)…

Generator size needed to start 11,000 BTU truck camper A/C?

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