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

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 is similar to PWM.  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.

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.

Summary

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...

Last updated 07/22/08    All rights reserved.