DuroMax Electric Start,Dual Fuel Portable Generator

On the surface the DuroMax XP5500EH looks pretty good. Looking deeper, though, it is barely good enough. The surface view includes starting, running major household loads, and spot checking those loads. The most important of those loads were a ½ horse well pump and non-digital refrigerator and freezer. Next most important were network gear, computers, and phones to check emergency conditions. The good news was that the well pump DID start and bring our pressure tank back up to full. Our setup allowed us to run that all by itself, then switch over to running other loads. More seeming good news was that the battery backup alarms would turn off once we had the generator on. The light on the battery backup would also turn off. It was also unquestionably good news that the propane setup worked as advertised. Hookup was easy, using included pieces and tools. The generator started on the first try for every test. The included plug made switching our old 10 gauge house attachment cable to match THIS unit simple. Wheel assembly was a snap. Handles were a little sprung, but not too hard to attach. Weight was a mixed bag. On the plus side the DuroMax weighed about 20 pounds less than our old unit. On top of that, if the unit needed to be moved after filling, there could be 30 more pounds of gasoline in the tank. With the DuroMax on propane the generator would remain around 130 pounds of dry, well-balanced weight to move, with a 40 pound full tank to shift separately. But the 20 pounds of weight reduction came at quite a cost. This is why the DuroMax XP5500EH only rates a “barely good enough.” We suspect much of the 20 pounds was rotational mass that would have improved the quality of power out of the generator. Getting past “skin deep” required some tools. Two of these tools allowed us to quantify and visualize the quality of the power coming out of the generators. One other tool allowed us to get more information than is available from the battery backup lights and beeps. The battery backup tool was first up. We use a linux application called “apcupsd.” The key feature we used was a log of all the messages the battery backup sent out. The key finding was that the battery backup kept detecting power failures the entire time that it was powered by the generator. The battery backup did not always consider the failure enough to warrant switching back to battery. But the generator power quality was poor enough that it clearly did NOT meet the desired input requirements of the battery backup unit. The log seems to indicate that the battery backup WILL charge its batteries while on the generator, but will not LIKE being there. We will not be leaving those systems connected to the generator for any longer than absolutely necessary. So, the battery backup test showed that the DuroMax XP5500EH power quality was clearly not very high. To quantify this power quality we used a relatively inexpensive Uni-T UT243 that we got before the price almost doubled. A better meter would give more accurate results, but this meter was good enough. The first obvious problem was that the DuroMax XP5500EH did not maintain a consistent frequency. Power from our utility is so consistent that a plot of frequency over time is pretty much a straight horizontal line. The first picture a plot for the DuroMax at different wattage loads. The closer the load came to the rated 4,275 watts (on propane) the closer the frequency got to nominal 60Hz. The frequency WAS more stable under the highest load, but still varied around half a cycle. Variation in Hz ranged from a bit over 5% to around 3%. This alone would have been enough to cause the battery backup to fluctuate as it did. But this was not the only problem. Utility power provided a nearly pure sine wave, with a little distortion around three times the fundamental 60Hz. Total Harmonic Distortion (THD) for utility power is usually very low, perhaps in the 1% range. The DuroMax XP5500EH showed THD up around 15%. The SECOND picture shows power put out by the DuroMax at 20 different multiples of the fundamental AC frequency in red. A generic example of utility power is in green. The volts scale is logarithmic, to emphasize the difference in power quality at higher multiples of the fundamental frequency. The numbers were not very good. But the goal of generator is to provide a “good enough” copy of the alternating current waveform we take for granted from the utility company. We used the inexpensive Yeapook ADS5012h oscilloscope to look at that waveform. We used the open source “Engauge Digitizer” to make photos of the ADS5012h screen usable in this review. The THIRD picture compares DuroMax XP5500EH power to utility power. The unfortunate thing is how hidden it all this is. First of all, the THD is not specified with in the generator documentation. We were surprised at this. The documentation even includes a circuit schematic, along with other useful information. Extensive searching on Amazon and the Internet showed that VERY few generators of this wattage rating showed THD specifications. And this gets to why a generator that is “Barely Good Enough” gets even three stars. Finding a generator with: 1) electric start 2) propane capability 3) enough wattage to run a ½ horsepower well pump 4) L14-30R plug AND ability to ground properly with a generator interlock 5) Low THD 6) low enough wattage to NOT require many refueling trips in an extended outage is hard. In fact, the DuroMax XP5500EH seems to be pretty much “state of the art.” This does not say much for the state of the art. The much older, heavier, recoil-only gas-only unit we had only came up to 5% THD. It did NOT trigger power outage sensing in our battery systems. But it was a big engine, and problems maintaining a seldom-used gas system, with ethanol, that seemed to become MOST cranky right when we needed it… well, see the six requirements listed above. This is, for us, an EMERGENCY generator. In a prolonged outage it MAY damage some of the things we have connected to it. We suspect that, in such an outage, we will be grateful to have ANY power. We also believe, after a lot of looking, that finding a generator that meets all six requirements will cost more than the things that might fail would cost. If that means paying a couple thousand to have a burned-out well pump replaced halfway through an extended outage… that would be unfortunate. More likely this generator would get us through an reasonably likely emergency. So, despite its problems, we are keeping this because even if it is “Barely Good Enough,” it is STILL at least “Good Enough.” NOTES: 1) Call-outs on the tools above are NOT endorsements of those tools 2) We specifically do NOT state how we connected those tools because those connections are inherently risky and we do NOT recommend such connections. 3) Tools are named ONLY so that readers can form their own opinions on the accuracy and repeatability of results cited in this review.