More Power from Small Generators

[Guy Holt]

Guy, could you clarify or expound on your statement, "For example, the 7500W capacity of our modified Honda EU6500is Inverter Generator can........" The Honda technical specifications state that the EU6500is is rated for full load (6500w) for 30 minutes or less, 5500w continuously. What modifications to the engine/generator/inverter have you made to produce the additional 1000w, without burning out the windings?

 

We are not just providing an additional 1000W, but 2000 more watts because the 7500 Watt load we put on our modified Honda EU6500is is a continuous load. How we modify the generator is proprietary information. What I can say is that our Transformer/Distro is able to provide 7500 Watts in a single 60A circuit because the capacity is already built into the machine by Honda. In order to understand how it is possible to get 7500W of continuous power in a single 120V circuit out of a Honda EU6500is generator, one must first appreciate three things about the continuous load ratings given for generators.

 

First, the factors generator manufacturers use to derive load ratings include not only the mechanical components (engine & alternator), and the electrical components (circuitry & wiring), but also the market for which it is intended (how it will be used) and the brand image of the manufacturer (life expectancy of the product.) A quick survey of the wide range of continuous load ratings (5000W-7000W) of generators, by manufacturers other than Honda, using the same Honda GX390 engine as the EU6500is supports this fact. Second, when Honda engineered the EU6500is it was not only for the North American market. Like a car, Honda engineered a base model for the world market that they then customize for the different national markets. The difference between the various national models is primarily in the power output panel, which is configured according to the electrical system and prevailing standards used in the national market in which the generator will be used. The 120V power output panel on the North American EU6500is is under-rated for the actual generating capacity of the machine. Finally, the continuous load rating of generators is what you can reasonably expect to get at the business end of the power panel allowing for all the vagaries associated with the load put on the generator. That is, the same engine and generator components will carry different continuous load ratings depending on its' intended use or the type of load (resistive, inductive, capacitive) that will be put on it. I would like to explain each of these in more detail.

 

When you compare how Honda outfits the base model of the EU6500is generator for the European and UK markets, where the standard circuit for domestic power is 230/240 Volts and 13 and 16 Amps, to how Honda outfits the same generator for the North American Market, where the standard circuit is 120 Volts and 15 or 20 Amps, one realizes that the continuous power rating of 5500w for the North American Model of the generator is under-rated. Where England and Ireland have not entirely conformed to the European Union Standard of 230 Volts, but still generate 240V power, Honda has engineered the base model to support a version of this generator for the UK market (the EU65i) with two 240V/16A circuits (3840 Watts/circuit). To support the UK market, the base model must be designed to generate at least 7680 Watts (2x3840W/circuit = 7680W). It is beyond the scope of this post to go into more details (those interested should contact me off list for a detailed side by side analysis of the wiring schematics of the two generators) but simple math (16A x 240V = 3840 W/circuit x 2 circuits = 7680 Watts) clearly demonstrates that it the base model must be designed to generate at least 7680 Watts.

 

To empirically test how much generating capacity the base model is capable of, we tapped an EU6500is in a similar fashion to the UK model, the EU65is, and used a step-down transformer to convert the 240 Volt output to a single 120 Volt circuit. We then used the generator's overload sensor to empirically test its' capacity with a load bank following the parameters as set forth in the manual:

 

"If the generator is overloaded, or if the inverter is overheated, the red overload indicator will go ON. When an electric motor is started, the red overload indicator may come on. This is normal if the red overload indicator goes off after about five seconds. When the generator is operating overloaded, the red overload indicator will stay ON and, after about five seconds, current . will shut offî

 

What we discovered about our modified EU6500is was startling. We found that we could power a continuous load (more than 30 minutes) of up to 7650 Watts without the overload indicator coming on. When we exceeded 7650 Watts, the red indicator blinked intermittently. When we exceeded 7800 Watts the red indicator came on continuously and power was cut off to the receptacles. Since, according to the Honda Manuel it is normal for the overload indicator to come on for short front-end loads, like electric motors starting, our results suggest that the continuous load capacity of the base model, or the EU6500is after our modification, is actually 7650 watts. And, when you consider that electric motors require up to three times more power to start than is required to keep them running, it suggests that the peak rating is actually well above 7650W.

 

Suspecting that it was not just coincidental that the actual continuous load capacity of 7650 Watts is the equivalent of two standard household circuits in the UK, we confirmed with Honda Motors USA that in fact the base model of the EU6500is generator is engineered to generate the equivalent of two UK circuits and has a continuous load capacity of 7650Watts. And, that when Honda configures the base model for the North American market with 120V circuits, it is not fully utilizing the power generating capacity they have built into the machine for the worldwide market. Since I am out of space, I will have to explain the second reason it is possible to run a continuous 7500W load on our modified EU6500is in my next post.

 

Guy Holt, Gaffer, ScreenLight & Grip , Boston

[Guy Holt]

Guy, could you clarify or expound on your statement, "For example, the 7500W capacity of our modified Honda EU6500is Inverter Generator can........" The Honda technical specifications state that the EU6500is is rated for full load (6500w) for 30 minutes or less, 5500w continuously. What modifications to the engine/generator/inverter have you made to produce the additional 1000w, without burning out the windings?

 

Continued from above:

 

Even though our test demonstrates that the inverter module of the EU6500is can support continuous loads of 7650W does not necessarily mean that the generator's engine can. Quite often, when you find yourself in the situation with a conventional AVR generator, where lights that have been running fine, suddenly fail when another light is turned on, it is because the generator engine bogs down because it is over loaded. As the engine RPMs drop, frequency and voltage drop as well, causing the HMI lights to cut out from low voltage. For this reason it is important to factor engine capacity whenever sizing a generator for a predominantly HMI load.

 

The power behind the EU6500is is Hondaís workhorse GX390 engine. According to Honda literature, the GX390 is a 13HP Twin Cylinder, Overhead Cam (OHV), Liquid Cooled gas engine with a Displacement ( Bore X Stroke ) of 389cc / 23.7 cu. inches and a Gross Torque of 20 ft-lb at 2,500 rpm. This same engine is used worldwide by manufacturers of all kinds of power tools, from pumps to roto-tillers, and is rated with a maximum output of 9600 Watts (13ps, 13bhp) at 3,600 RPM.

 

Surveying the continuous load capacity ratings of 5000W-7000W of generators by manufacturers other than Honda that use the GX390, one quickly realizes that the factors generator manufacturers use to derive these ratings include not only the mechanical components (engine & alternator), or the electrical components (circuitry & wiring), but also the market for which it is intended (how it will be used) and the brand image of the manufacturer (life expectancy of the product.) For these reasons we can only speculate as to the true power generating capacity of the GX390 engine.

 

To get an idea of the true power generating capacity of this engine we need look no further than the Coleman Model PM0497000 Generator. Coleman uses the Honda GX390 engine in this conventional AVR generator it manufactures for the construction market. Colman rates the Model PM0497000 Generator at 7000W continuous and 8750W peak load capacity. Where the Model PM0497000 Generator is manufactured by Coleman for the construction trades to run power equipment with high front end loads (3X) it is probably safe to bet that Coleman is under-rating the PM0497000 generator at 7000W continuous and 8750W peak load capacity.

 

Using Coleman's rating of the Model PM0497000 Generator as a conservative bench mark of the engine's true capacity, and taking into account that an inverter generator puts out 20% more power from each revolution of the generator core (thanks to its multiple coils and multiple magnets generating several hundred overlapping sine waves per revolution), it is probably safe to assume that the GX390 engine in an inverter generator is capable of generating at least 8400W of continuous and 10500W of peak power. Where Honda does not make this information public, there is no way of knowing for certain what the actual generating capacity of the GX390 engine is in an inverter generator like the EU6500is. We can, however, safely conclude that the GX390 provides a quiet and efficient power plant that more than compliments the 7650W continuous power output of the EU6500isí inverter power module.

 

Guy Holt, Gaffer, ScreenLight & Grip , Boston

[Guy Holt]

Guy, could you clarify or expound on your statement, "For example, the 7500W capacity of our modified Honda EU6500is Inverter Generator can........" The Honda technical specifications state that the EU6500is is rated for full load (6500w) for 30 minutes or less, 5500w continuously. What modifications to the engine/generator/inverter have you made to produce the additional 1000w, without burning out the windings?

 

Continued from above:

 

 

The third and final reason we can run a continuous 7500W load on our modified EU6500is is the most difficult to understand because it has to do with the vagaries associated with the load put on generators. If you haven't already, I would suggest you read the article I wrote for our company newsletter on the use of portable generators in motion picture lighting. In it I cover some of the basic electrical engineering principles behind harmonic distortion and how it can adversely effect generators. The article is available on our website.

 

The reason that the same engine and generator components (the engine/generator set) marketed to the construction trades carries a higher continuous load rating than that marketed for RV power or Home standby power is that the load that the construction trades put on generators is typically a "resistive load" - motors, heaters, etc - that does not create harmonic distortion of the power waveform. Where as, the same engine/generator set marketed for RV power or home standby power will carry a lower continuous load rating because the typical load put on it is a "reactive load" - computers, fluorescent lights, microwaves, etc. - that creates harmonic distortion of the power waveform. In our discussion above, the heat generated by electrical components operating on highly distorted power (the square wave above) is just one of many vagaries associated with load that manufacturers take into account in determining the continuous load rating of a generator for a specific market. Another consideration related to load, and the one that JD alludes to above, is overheating of the generator windings caused by high Total Harmonic Distortion (THD) levels.

 

Harmonic currents produce high frequency flux change in the generator's stator cores which can lead to them overheating. Higher magnetic core temperatures result in higher winding temperatures. Winding heating is, in fact, proportional to effective or RMS current squared. Rotor loss can also occur because harmonic currents in the stator will induce currents in the pole faces and windings. And, of course, harmonic currents cause increased resistive losses everywhere in the generator's electrical distribution, resulting in increased temperatures everywhere, not only in the generator windings. For this reason, if an engine/generator set is intended for a market whose typical load is reactive (either reductive or capacitive), the manufacturer will de-rate the inherent generating capacity - i.e. lower the continuous load rating - for that engine/generator set for that market in order to reduce flux change in the generator's stator cores that could lead to the windings burning out under "normal load." In other words, the lower Continuous Load rating builds in a margin of safety that allows for the harmonic distortion generated by reactive loads (both inductive and reactive.) Overheating of electrical components and overheating of the generator windings are just two of many vagaries of load related to high THD values that generator manufacturers take into account when rating generators. Other vagaries of load related to high THD values are generator voltage regulation problems, generator speed governor problems, and excessively hight returns on the nuetral.

 

An analogous situation is when a genny operator over sizes the plant and the size of the neutral return (a Super Neutral) when they know they are going to be dealing with a lot of non-PFC HMI or Kino Ballasts. Electronic square wave ballasts, in addition to pulling the voltage and current out of phase, also create harmonic currents that can stack on top of one another, creating very high currents returning to the power source on the neutral wire. If the nuetral return path has not been oversized to accomodate additinal current, these high currents can cause excessive heat on the neutral wire, and the neutral bus of the generator. Where the neutral of a distribution system is not fused, this excessive heat can lead to a possibly hazardous situation. For this reason it is a standard practice when powering large numbers of electronic ballasts on large film sets to size the neutral feeder of the distribution system to carry the sum of the currents of the phase legs times 80 percent (.8). Likewise, the generator is typically oversized to handle the higher return current.

 

The means by which the motion picture industry has more or less successfully dealt with harmonics - namely the over-sizing of generators, the over-sizing of neutrals, the incorporation of power factor correction circuitry in large HMI ballasts, and finally the use of generators with 2/3 pitch windings (Crawford Studio Generators) are generally not available to users of small portable generators as their primary source of power. That is because, productions using portable gas generators are using them by necessity. For budgetary or logistical reasons, it is simply not an option to upscale their generator and customize their distribution package to accommodate a dirty load. The only alternative is to de-rate the continuous load capacity of the generator and distribution equipment.

 

Unfortunately, much of today's lighting technology relies on electronics such as DC rectifiers (electronic HMI ballasts), silicone-controlled rectifiers (SCRs), capacitors (magnetic & electronic HMI ballasts), and high-frequency switching power supplies (the IGBTs of electronic ballasts). And since these kinds of load can have undesirable effects on the current waveform, many Gaffers will further de-rate the continuous load capacity over and above what the generator manufacturer has already de-rated the generator set. For example, the power waveform below left (from my article) is typical of what results from the operation of a 2500W non-Power Factor Corrected load (electronic HMI & Kino ballasts) on a conventional portable generator (a Honda EX5500 with a Barber Coleman Governor.) Where the severe harmonic noise exhibited here can cause overheating and failing equipment, efficiency losses, circuit breaker trips, excessive current on the neutral return, and instability of the generator's voltage and frequency, the conventional wisdom in the past has been to not load a generator beyond 75% for more than a short period (the maximum recommend continuous load on a 6500W generator, with a continuous load rating of 5500W, would be roughly 4000 watts.) Like the generator manufacturer, by de-rating the load capacity, the Gaffer minimizes the adverse effects of high THD so that the generator will operate more reliably.

 

Left: Conventional generator power w/ pkg. of non-PFC Elec. HMI Ballasts & Kino Flo Wall-o-Lite. Right: Inverter generator power w/ Pkg. of PFC Elec. Ballasts & Kino Flo Parabeam 400.

 

However, this conventional wisdom no longer holds true of inverter generators when used with Power Factor Corrected (PFC) HMI & Kino ballasts. For example, the power waveform above on the right, is the same 2500W load but with power factor correction operating on our modified Honda EU6500is Inverter Generator. As you can see, the difference between the resulting waveforms is startling. Even though the load is the same, the fact that it is power factor corrected and the power is being generated by an inverter generator, results in virtually no power waveform distortion. What this means is that an inverter generator can be loaded to capacity with PFC HMI and Kino Flo ballasts without its' stator core overheating from high frequency flux change, its electrical wiring overheating from excessive resistance, and its distribution panel overheating from a high neutral return. The substantial reduction in line noise that results from using PFC ballasts on the nearly pure power waveform of an inverter generator creates a new math when it comes to calculating the continuous load you can put on a portable gas generator.

 

Wide Shot of Night exterior scene lit with a pkg. consisting of PFC 2.5 & 1.2 HMI Pars, PFC 800w Joker HMI, Kino Flo Flat Head 80, 2 ParaBeam 400s, and a ParaBeam 200 powered by a modified Honda EU6500is.

 

We maximize the continuous load that can run off our modified Honda EU6500is inveter generator, by offering HMI and Kino Flo lights with Power Factor Corrected ballasts. For those of you not familiar with Power Factor Correction (PFC), a PFC circuit utilizes a RF Mains Filter to restrict the flow of harmonic currents back onto the supply service. In this fashion, the PFC circuit realigns voltage and current and induces a smoother power waveform at the distribution bus. Formerly only available in large HMI ballasts, this advanced electronics reduces voltage waveform distortion and contributes to a more economical use of power than typical HMI and fluorescent electronic ballasts.

 

The PFC 2.5 & 1.2 HMI Pars, PFC 800w Joker HMI, Kino Flo Flat Head 80, 2 ParaBeam 400s, and a ParaBeam 200 of our HD P&P Pkg. powered by our modified Honda EU6500is through our 60A Full Power Transformer/Distro

 

Where, in the past we had to de-rate portable generators because of the inherent short comings of conventional generators when dealing with the harmonic noise generated by non-PFC electronic ballasts; now you can load an inverter generator to capacity. And if the generator is one of our modified Honda EU6500is inverter generators, you will be able to run a continuous load of up to 7500W as long as your HMI and Kino ballasts are Power Factor Corrected.

 

According to this new math, when you add up the incremental savings in power to be gained by using only PFC HMI ballasts, add to it energy efficient sources like the Kino Flo Parabeam fixtures, and combine it with the pure waveform of inverter generators, you can run more HMI lights on a portable gas generator than has been possible before. For example, the 7500W capacity of our modified Honda EU6500is Inverter Generator can power a lighting package that consists of a PFC 2.5kw HMI Par, PFC 1200, & 800 HMI Pars, a couple of Kino Flo ParaBeam 400s, a couple of ParaBeam 200s, and a Flat Head 80. Given the light sensitivity of HD cameras, this is pretty much all the light you will need to light both the foreground and deep background of night exteriors.

 

A Distro System consisting of a 60A Full Power Transformer/Distro, 2-60A GPC (Bates) Splitters, 2-60A Woodhead Box distributes power from a modified Honda EU6500is. Even though the generator is 100' away to reduce noise, plug-in points remain conveniently close to set.

 

It is beyond the scope of this post to go into more details. Those interested should read the article I wrote for our company newsletter (mentioned above) on the use of portable generators in motion picture production. The article is available at www.screenlightandgrip.com/html/emailnewsletter_generators.html.)

 

 

Guy Holt, Gaffer, ScreenLight & Grip , Boston