Yamaha EF2400iS Generator




This is generator #4 for me.  The first inverter type I've owned.  Unlike the predecessors, this one is VERY quiet, lightweight for its power, thrifty on fuel consumption, frequency is not RPM dependent, and it runs at idle until the load requires more power.  The RPMs increase incrementally, to meet the load demand.

I bought this online through Wise Generator Sales.  Cost was $1147, then received $100 rebate through Yamaha.  No tax since it was an out of State purchase, no shipping fee.  Had it in about a week.

My buddy has two Honda 2KW generators.  He bridges them together with an additional piece of hardware, which syncs the frequency, and combines their power output.  This Yamaha has the same ability also with additional hardware. 

They key selling point for me was this Yamaha was designed to start & run a 13,500 BTU A/C unit alone.  It takes two Honda 2KW generators to do this same job.  From all I've read, this is the only generator on the market that fills the niche of a single, small, lightweight, quiet generator, capable of running an RV A/C unit.  You could buy a bigger generator to do the same function, but the noise, weight, and price start going up rapidly.  Pay close attention to the rated noise level.  Ever 3dB doubles the sound energy.  Every 10 dB, the ear perceives a doubling of the noise level.  This one is rated at 53-58 dB.  It'll put out 16.7 Amps continuous, or a 20 Amp surge.

There's a lot of talk about what will or won't run on a generator this size.  I decided to do some testing myself.


The AC Waveform...


Sorry these pictures are a little out of focus, but you can see the difference between the power coming out of my wall (grid) vs. the output from my generator (on the right).

Clean generator power.  Smooth sine wave, where the waveform from the wall (on the left), is slightly distorted.  Note, this was with the generator running at idle.  It produces 60 Hz electronically.  A conventional generator does this mechanically, so it is speed dependent.



First Test, A 5000 BTU Portable A/C Unit

I started out by putting the generator outside.  Many people have died from carbon monoxide poisoning from having one in the house or garage.  What you can't see is a large fan blowing the exhaust gases away from the garage.

To measure current with a clamp-on type meter, you must isolate one wire, the black or white.  If you put the clamp around all 3 wires the flow in/out is balanced, and you won't see any current flow.  As you can tell, this is a home brew item and easy to make.

I hooked up the meter and turned on the 5000 BTU A/C unit.  After a few minutes I shut it off, then immediately tried restarting it.  This is the worst case scenario, and not what you should do.  Restarting too fast can stall the compressor as the pressure in the system is still maxed.  Ideally, you should wait several minutes, allowing the pressure to drop.  This isn't an issue when allowed to cycle normally.  I wanted to challenge the generator.

 This tiny A/C pulled over 18 AMPS starting current!  My generator momentarily picked up RPMs, then dropped back to an idle.

The running current is just below 5 Amps, just as stated on the label.  The generator is still at idle.

With the compressor off, and blower on high, it draws a measly 0.2 Amps.

Using a digital IR meter, I measured the ambient temperature in my garage at 83 degrees.

The condenser coils measured 124.5 degrees.

The output air was 60 degrees and dropping.  That's better than a 20 degree delta.  Oh, this will keep 1 room nice during an outage.  Again, the generator runs at idle once the compressor has started.

I had to repair the generator when it first arrived.  The exhaust port didn't line up with the hole in the case.  It had apparently been dropped in shipment.  I took it all apart, and straightened the motor mounts.  I could have returned it, but that would have taken weeks to sort out.  The plastic no longer melts since the exhaust is now in alignment. 


If you're going to buy a generator, these two simple tools can give you an idea of what you will/won't be able to run all at once, or various combinations.  Make a log of running & starting currents.  The breakout plug can be made for a few bucks, the meter was purchased at Harbor Freight on sale for all of $9!

In a power outage at home, I can run this A/C unit all night on 1.5 gallons of gas.  The generator will be at idle, running whisper quiet on my patio.


Update:  Finally bought a Fluke meter with an "in rush" feature.  This is how much current it takes to start this small A/C unit.  A small generator might run it, but probably can't start it.  Can't run it if it can't start it.  The EF2400iS started this A/C unit easily.

Comparing the running current between the expensive Fluke meter, and the cheap Harbor Freight meter.  The downside of the HF meter is it lacks the in rush feature.



Second Test, The RV & 13,500 BTU A/C Unit

The setup.  I connected the generator to our camper.  Using a clamp-on meter, as shown in the previous test, I could measure the load.  The A/C unit is a 13,500 BTU Dometic brand.

A/C is powered off, the converter/charger is up and running.  So base line is 3 Amps.

I turned on the A/C unit's fan to high.  Compressor still off at this point.  So the blower on high draws 1.5 Amps.  Total so far, 4.5 Amps.

Compressor switched on, blower on high, converter/charger running.  11.5 Amps.  Deduct 3 Amps for the c/c, the A/C on high is drawing 8.5 Amps.

Note, I did watch this figure increase/decrease over several hours.  The highest I recorded was 13 Amps for a brief period (compressor engaging I suspect).  With a rated 16.7 Amps continuous, 20 Amps surge, this generator is ideally suited for my RV.  I'll have to turn the A/C compressor off momentarily when using the microwave.

In the low 90s today.  Yes, it's October here!  The A/C was putting out sub-50 degree air.  Didn't take long to chill the camper down.

I left the generator and A/C running for several hours today while I worked on the new RV.  The generator never even had a hiccup.  I also tested the onboard entertainment system.  No indications of noise on the Dolby 5.1 surround system, or on the 19" LCD TV.

The generator works as advertised.  During this test, it ran at 1/2 - 2/3rds throttle according to my ear.  That's about right, considering the load it had.  With the windows closed to keep in the cool air, the generator could not be heard inside.  Outside, it was quite bearable.  Could easily talk over the noise.


Third Test, Recharging A Battery

With the generator allowed to cool, gas cap on tight, and fuel valve off, it easily travels inside my SUV.  No gas smell.

The generator has a built-in 8 Amp battery charger.  Not a fast charger for a big battery, but convenient as it's always with the generator, and takes up no space.

The jack on the generator looks similar to a two prong AC jack, but the pins are slightly canted.

The DC power cord was included.

Our boat lives at a storage facility.  No power available to keep it charged up.  During the Winter, the boat didn't see much use, so I used the generator to top up the battery.  I later installed a removable solar panel on the boat, but that's another story.

Using a clamp-on DC Ammeter, I found that it was charging near the 8 Amp rating.  Note, the waveform of the DC output does have an AC ripple until the battery is connected.  Consequently, if you connect a DVM to the DC output of the generator, with no battery, you'll get an inaccurate reading that appears to be very high.  Connect the battery, then measure the Voltage.  If you need to charge a large battery, use a big external charger.  It'll be much faster than the built-in charger.  But in a pinch, this one does work as advertised.


Fourth Test, Running An Electric Chainsaw

Since I only have a few trees to worry about, I can't justify a gas powered chainsaw.  The upside of having an electric saw is they don't degrade when sitting on a shelf for a long period, unlike their gas counterparts.  This is a Poulan 18" Model 400E, 4-Hp (peak).  It pulls over 16 Amps with no load, according to my Kill-A-Watt meter.

For this test, I used a 25' 14-ga power cord.  I sliced up the stump from a small Maple tree.  Though the RPMs on the generator ramped up to meet the demand when the trigger was pulled, the chainsaw had no lag.  It jumped to full speed almost immediately, just as if it were plugged into shore power.  Plenty of power, no bogging down at all.

The slices were deep enough that the remainder of the stump would be below grade.  A crowbar was used to pop out the chunks.

Other than cleanup, the job is done.  So if I have to do a cleanup of fallen trees after a hurricane, I KNOW my generator will be able to run the electric chainsaw.


Fifth Test, Running An Air Compressor

Okay, I was running out of things to plug into the generator, so I got out the air compressor.  Don't let the small size fool you.  This compressor uses a huge 1.2 HP (rated, not peak) motor.  No soft start.  Pulls over 15 Amps.  It overloaded the Kill-A-Watt trying to measure the startup and running currents.  Consequently, this is the one thing I've found that the generator would not start.  It tries for 10 seconds, before going into overload.  The compressor rolls over slowly, and won't spin up to full speed.  Induction motors, like the one in this compressor, are notoriously hard to start.

So this one was a no go.  The generator runs everything else I've tested without any problems.  I could likely add a hard start kit, but my intent was to find the limits of my generator, not make all my equipment generator compatible.  I already have a heavy duty 12V air compressor for when 120VAC is not available.  Check out my Q-89 dual piston 12V air compressor.

I borrowed a meter from a coworker that will measure "in-rush" current.  The number of Amps it takes to start things like motors.  I drained the air out of my compressor, so it didn't have a head pressure to push against.  It took 53.8 Amps to start this motor!  That's a 6500 Watt surge.  So a portable generator won't likely start this compressor.

Induction type motors are notoriously hard to start.  I've since ordered one of these meters, and will measure what it takes to start some of the items tested above.  Check back!

Point here is to TEST anything you intend to run from a generator.  It might run it, it might not.  You won't know for certain until you try it.


Sixth Test, Running Power Tools

After letting the generator warm up for a minute, I connected a Makita 7 1/2" circular saw.

I sliced up a piece of 5/8th plywood for shelving.  The generator quickly jumped up to about 1/2 throttle, the saw went to full speed with no hesitation.

It easily sliced through the wood, generator easily handled the load.  The saw operated as though I was using grid power.

The specs on the circular saw.  13 Amp motor.

An easier challenge.  A small variable speed drill.  The generator stays at idle, even when drilling into concrete.

The specs on the drill.  Only 3.3 Amp motor.



Seventh Test, Testing The DC Output

Okay, we already know it can recharge a battery with the built-in charger, but there were questions on the RV forum regarding its performance.  Apparently some other generators must be taken out of the economy mode to use the built-in charger.  This model doesn't have an economy mode, it decides how fast to run based on the load.  So here's my setup.  A small oscilloscope running from its own battery (keeps everything isolated), a DVM, a clamp on Ammeter, a garden tractor sized LA battery, and the generator.

With no load, the DC output of the generator does have some ripple on it.  Common for many battery chargers.  Fancy filtering isn't needed as the battery flattens the ripples anyway.  This was verified once the battery was connected.  The waveform was pure DC with no AC ripple.

I hooked up the DVM to the battery to get a baseline Voltage.

The battery measured 12.64 before charging.

With the (included) battery charging cables connected, the battery Voltage increased to 15.53 Volts immediately.


The initial charge current was 5.33 Amps, and slowly decreased as the battery charged (normal).  See Test 3 above also.  My boat battery was at a lower state of charge, and pulled almost 8 Amps, the rated capacity of the charger.

The generator remained at idle speed the entire time.

Final proof that the generator has the ability to charge from idle.  The no load Voltage of the DC output measures almost 24 Volts.

The built-in charger is a nice to have feature.  It gives you the ability to charge an automotive or marine battery without having to haul another piece of equipment.  Years ago during a camping trip, my friend's truck died while we were out in the boonies.  We both had generators to run our A/C units on our Popup campers, but neither of us brought a battery charger.  But his generator had a built-in charger, and he successfully charged up his truck with it.  If you need to charge a battery quickly, then bring a big charger, and use the generator's AC side to do the task.  Otherwise, carry the included battery cable, and you may find that the wimpy 8 Amp charger might save your butt when you least expect it!


Here's an example of how quiet this generator actually is.  At a rest stop during a recent camping trip, I parked the truck, dropped the tailgate, started up the generator, and ran the 13,500 BTU A/C unit.  It was a very hot day, and being able to sit comfortably in the camper while having lunch was a nice benefit.  Even though the microphone is very sensitive, the exhaust can be barely heard from a distance (note the birds singing in the background).




So How Much Current Do Things Draw?

As a quick check, you can always look at the manufacturer's label on the back of the device.  Typically specified as a Wattage rating.  Power (Watts) is equal to the Current (I - Amps) times the Voltage (E).  So P=IxE, or P/E=I.  A 60 Watt light bulb, for example is 60 Watts divided by 120 Volts, or 1/2 Amp.

I bought a Kill-A-Watt plug in Voltage/Current meter.  Very slick and easy to use.  My other clamp-on works just as well, so either method will work.

There are charts online that will give you generic Power ratings for various products.  I would rather have an accurate listing, so I started measuring things around my home.  This list will grow as I get time.  I suggest you do the same.  Whether it be for a power outage situation at home, or RVing on the road, you'll know exactly what you can and can't run from your generator.

20" TV.  CRT type tube with built-in DVD player.  3 Watts off (parasitic draw), 39 Watts on.

Analog Cable Box.  32 Watts on or off.  Might as well leave it on!

32" TV.  CRT type tube.  No current draw when off.  112 Watts on.

Bedroom TV, cable box, UPS unit, and desk light:

UPS unit on or off: 32 Watts

Desk lamp with 2 CFL bulbs: 77 Watts

32" Sony LCD HDTV: off = <1 Watt, on = 123 Watts

Digital Cable Box on or off: 20 Watts

Everything powered up: 252 Watts

Bread machine.  548 Watts during bake cycle.  Run time 3.34 hours.  Total Wattage 0.29 KW (only bakes a brief portion of the total time).

Ice Tea machine. 700 Watts for about 10 minutes.

Toaster.  750 Watts for about 5 minutes. 

5000 BTU portable A/C unit.  600 Watts with compressor engaged.

Refrigerator in garage: Not running but on: 0 Watts.  Compressor running: 114-140 Watts.  Total per day: 1.15 KW, 47.92 Watts per hour average.

Refrigerator in house: Compressor running: 146 Watts.  Defrost: 572 Watts.  Total per day 2.15 KW, 89.58 Watts per hour average.

Microwave oven running: 1670 Watts on high (13.91 Amps).

13,500 BTU Dometic RV A/C unit.  Up to 1200 Watts running current.  The starting current is the reason for the much larger generator requirement.


I've used StaBil in my fuel for a couple of decades.  This has eliminated any fuel issues that I've experienced in prior years.  But recently, my generator started the dreaded surge at idle.  The gasoline I use is a 10% ethanol blend (only fuel available here), and 87 octane.  It was about a year old, but had been treated when it was first purchased.  Should have been fine.  StaBil now claims their product will keep gasoline fresh for 1 year, but if you double the dosage, it can extend the life of gasoline to two years.

So what to do?  I ended up disconnecting the fuel line, and dumping all the old gas into a large mason jar, later used it in the mower (1/2 mix with fresh gas).  Put everything back together, used fresh gas treated with Seafoam.  Seafoam claims to liquefy gum and varnish deposits.  Still on the first gallon of treated fuel, and the results are amazing.  No more having to pull the choke out to try and smooth out the idle.  This product was purchased at Wal-Mart.  See for yourself.



I have no affiliation with anyone.  I'm just impressed with how well this product worked.  I'll definitely keep a bottle of this on my shelf from now on.



Just when I was celebrating the success of using Seafoam, the dreaded surging returned with a vengeance.  I already had Seafoam in the fuel.  Okay, Plan B.  I removed the float bowl, it was clean, and the float operated smoothly.  This time the issue didn't appear to be on the fuel side, but rather the air side.  Think a piece of grit was clogging one of the metering jets.  I took the air filter off, and sprayed each jet, one at a time, with Gumout carb cleaner.  The motor would stumble, and then return to the dreaded surging.  I finally sprayed the jet to the right of the butterfly valve.  If you don't want to watch the entire 10 minute video, showing the entire process, jump to minute 6:40.  One good shot to the jet, and the issue is solved.  A couple of follow up shots to make sure the issue is gone, then time to button it up.  Make sure to wear a faceshield.  Carb cleaner doesn't do your face or eyes any good!

So Seafoam works great on the fuel side, but Gumout carb cleaner solves issues on the air side.  I'll be keeping BOTH in my garage from now on.  I hope this helps solves the common surging issue for you too.


I recently had a question from someone that visited my webpage, asking if I had tried my generator with construction type of equipment.  Things like a chopsaw, tablesaw, or even a small air compressor.  I didn't have a small air compressor handy, but I did try a Ryobi compound miter saw (chopsaw), and a portable Ridgid tablesaw.  The material being cut was 5/4 x 6" pressure treated decking material.  Both of these tools have universal type motors, which are hard to start with a generator.  Most times the chopsaw would start fine, but one time it didn't, and the generator had to be shutdown just long enough for the overload to reset.  I left that in the video so you could see the good and the bad.  It had no problems with the tablesaw.  Unlike other generators, there's no switch to take it out of the economy mode.  So when it tries to start a motor, it begins at idle and has to increase the RPMs on the generator to try and start the load.  Usually it does fine, sometimes not.



It performed about as well as I expected.  Also note that the generator continues to run smoothly, with no more carb issues since I started using SeaFoam.




I have a Lincoln Weld Pak 100HD MIG welder.  Purchased it at Home Depot years ago, later bought the optional gas kit to go from simple wire welding to true MIG welding.  It'll handle up to 1/4" steel, though most of my projects are limited to 1/8".  This welder is small/light enough to make it mobile.  It'll easily fit in the back of the truck, or even in the golf cart.  It'll operate on a standard 120VAC 15Amp household outlet.  That's fine at home.  How do I provide power when on the back of the property, or out in the boonies?  On paper, the Yamaha generator could run this.  This issue is it might not have enough initial current to get the arc started.

Only one way to know for sure.  As it turns out, it works fine for welding.  For the first second during the weld, the initial weld sputtered, and smoothed right out as soon as the RPMs on the generator increased.  I did crank the heat up one click to handle the heavier 1/4" steel I was attaching a 1/8" thick spacer block.  Yea, my welds ain't pretty but that's the operator, not the equipment.  Bottom line, the generator works well with my small welder.



Some prefer two Honda 2KW generators.  Easier to lift 50 lbs twice, than 70 lbs once, so they say.  That setup is double the cost when you add in the hardware to bridge the two generators.  Also twice as much to put in the back of the truck.  And when comparing fuel consumption and noise figures, remember, it takes TWO Honda 2KWs to do the work (running a 13,500 BTU A/C, etc.) of the single Yamaha. 

You could go with a quiet 3KW generator.  But the weight doubles (70 lbs vs. 140 lbs).  And the EF2400iS uses the same size engine as the 2.8KW & 3KW models.  But the 2400 uses an aluminum block to reduce the weight.  According to Hayes Equipment, the EF2400iS has been load bank tested to hold a 25 Amp load for 10 seconds, giving it a 3KW surge.  This is still not enough to do everything, but it'll run anything I've tried, with the exception of my air compressor.

The Yamaha EF2400iS does what the manufacturer claims in my testing.  It's the ideal generator for emergency power at my home, or running my RV while camping in the boonies.  I don't get a penny for the sale of a single generator.  Personally, it doesn't matter what you buy, but some will find this information useful.  I included enough pictures of my testing, and enough data, you can decide for yourself if this model will suit your needs.  Just don't buy a cheap contractor grade, thinking you can simply strap a new muffler on it later to make it quiet.  Not going to happen.  Do a Google search, many have tried, including me, and the results are very disappointing.  Pay once, cry once...

Had this generator SIX years now.  Still works great.  Still not heard from Yamaha... But I've heard from thousands of fellow Yamaha owners worldwide!



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Last updated 9/16/12  All rights reserved.