From my last post, you might have guessed that I had decided to look for an inverter generator. After doing a bit of online research and reading reviews I ended purchasing the Predator 2000 Inverter generator from Harbor Freight. This generator has a 1 gallon fuel tank and puts out 1600 running / 2000 starting watts. According to the specs it will run for 12 hours producing 400 watts. I haven’t tested it yet but have read where some have and got similar results. Based on running it some it does sip fuel. Weighing in at only 50 lbs the generator is also highly portable.
The front panel has two 120V receptacles and an odd shaped 12V receptacle. There is also a switch which puts the generator in “Eco” mode which throttles the motor down to the required speed. Included with the generator is a set of 12V leads that end in two squeeze clamps and some cheap tools. The generator is also able to be paired to another identical generator to generate twice the rated power output.
One nice thing about the generator is that they took all of the stuff that is actually important out of the owners manual, turned it into a sticker, and put it on top. There are steps for how to start it, the max load, and fuel type.
Both plastic side panels of the generator are able to be taken off by removing three screws from each side. From there the insides can be seen. As this engine has no oil filter I purchased a magnetic oil dip stick to collect bits of metal that are produced while the engine breaks in. I also added an hour meter to help keep track of runtime for maintenance. The meter runs off of 12V which I got by slipping wires on to the threaded studs on the back of the 12V receptacle. It sits inside normally and I’m able to view it when I remove the side panel. Ideally, it’d be nice to have it visible from the outside but I didn’t want to cut a hole in the generator case.One of the touted benefits of an inverter generator is that quality of the power produced. Using a step down transformer I measured the voltage with my oscilloscope. The picture below shows the results on the scope. The wave appears well formed with no frequency distortion. The frequency is almost perfectly 60 Hz.In case of a hurricane I’d like to be able to run a window AC unit, my refrigerator, and a few smaller items such as phone chargers and LED lights. The AC and fridge were my big concerns since they’re the largest loads. With this size generator I should be able to run both at the same time. If both were to start at the same time it may overload the generator but I figure that is unlikely to occur.
As I mentioned in my last post, when anything containing a motor starts up there is a short time large current requirement. This period of high current is called “inrush current”. A the period of inrush current the current will drop down to near or less than the amount specified on the data plate on the device or motor. My window unit lists the amps as 7.1 at 115V. As my voltage is around 120 the running current will actually be a little less. Power can the be calculated by multiplying the voltage times the amperage times the power factor. Luckily, power is already listed on the data tag. If the inrush current required by the AC is more than the generator can provide then it will kick offline and the AC will not start.
To measure the inrush current I used my Fluke 374 which has a special mode to do this. When in this mode it will wait for a large spike in current, take measurements for 100 ms, and then display the current. Below is a picture of one of the AC start ups I analyzed. Clearly, 30A is much larger than the listed 7.1A, At 120V and 30A, 3600 watts are required to start up the AC. For fun, I used my cheap current clamp and oscilloscope to show the inrush current. Below is the startup of my AC. The screen shot shows the current wave. As you can see, after startup, there is a period of much higher current. After this time the current then drops to the lower running level. Also displayed are two vertical lines which mark out 100 ms. The values onscreen are calculated in this window. The RMS value is 321.61 mV which converts to 32.1 A. The values are not identical (probably due to several reasons I won’t go into) but are close enough for what I’m doing here.
The ability to provide increased output for inrush current is called “Starting Watts” on generators. My AC needs around 3600 starting watts but the inverter generator only produces 2000 starting watts according to the rating. When I try to start the AC off the generator it starts fine though. When Eco mode is not turned on the generator doesn’t mind the AC starting at all. If Eco mode is on then the generator slows a little before increasing RPM. I’m sure the voltage sags when starting on eco mode but I haven’t measured it. Maybe later…
Even though the numbers say my generator shouldn’t be able to start my AC, it does. This is a good thing but it makes me wonder how the “Starting Watts” number is produced. I looked online and in the manual but there is no mention of it. I would think there should be a table in the manual that lists X number of watts can be produced for Y amount of time. Since there isn’t it’s a buy and try thing which is unfortunate. As far as I know, all generators are this way.
I was also worried about starting the fridge but it drew a much less amount of running and starting current. Thus, I’m not discussing it as it is similar to what was shown above but with smaller values.
So far I have about 25 hours of time on the generator. I runs well and I have no real complaints against it. I did replace the spark plug with an NGK because some people have reported issued with the Torch brand plugs. I’ve also never heard of Torch. The instructions do say to slowly turn the choke off and I’ve found this to be accurate. If the choke is turned off quickly the motor will stumble for a bit like any other motor.
Also, for those who may wonder I purchased the generator and it was not given to me to review. But if HF wants to send me the larger version of this one I’d take it.