Friends of mine have a DJ set up consisting of (4) mackie SR1530's at 500w each, (2) mackie 15' 500w subs, and maybe 500w of computer, mixer, mic, etc. They say when they turn it up to a moderately high level the sound levels drop during heavy bass track, then rise during brakes in the bass line. Of course, they don't want it to do this.
I think Shawn is correct that his problem is voltage drop, but it is a kind of voltage drop that cannot be compensated for by increasing the wire gauge of his distro cable. Where the DJs are concerned about hearing the noise of the generator during quieter songs, I would bet they are operating the generator with its’ Eco-Throttle. The Eco-Throttle used in conjunction with a “spider-box” (what I would call a “splitter box”) may be causing sensing errors on the part of the generator’s microprocessor engine control.
What makes the Honda EU6500is incredibly quiet, as well as more fuel efficient, is what Honda calls its’ microprocessor controlled Eco-Throttle.
Eco-Throttle is simply the marketing name Honda uses to describe two of the characteristics that make inverter generators considerably quieter than conventional Automatic Voltage Regulated (AVR) generators. First, with their multi-pole rotors and small stator, inverter generators produce more electrical energy per engine revolution than is produced in conventional AVR generators. Their greater efficiency, and the fact that the frequency of the power they generate is not linked to engine speed, means they can run at much slower RPMs for a given load than a conventional AVR generator.
The second reason that inverter generators are quieter is that their Pulse Width Modulated (PWM) inverter modules permit their engine speed to vary with load. Which means that, at less than full load, the engine can slow down which tremendously reduces the noise it generates. Put simply, an inverter generator is much quieter because the engine speed is load dependent – it does not have to run at full speed constantly as is the case with conventional AVR generators (use this link for more details:http://screenlightandgrip.com/html/emailnewsletter_generators.html#anchorProduction%20Features (http://screenlightandgrip.com/html/emailnewsletter_generators.html#anchorProduction%20Features).)
(http://www.screenlightandgrip.com/images/generators/Pro_Sound_EU7000is_Voltage_Charactistic_Curve.jpg)
It also means that the voltage generated by the inverters is load dependent. Above is the Characteristic Curve of the voltage output of the Honda EU7000is’ inverters as a function of load. As you can see here that without a load the voltage generated by the inverters start out at about 125/126V and then drops gradually as the load on the inverters increase and reaches 120V at full load.
In order for the Eco-Throttle to function properly, it requires a fairly balanced load. This is because Honda has designed the EU6500s with two inverters. To provide more 120V power, the generator has a 120V/240V selector switch, which when set for 120V, aligns the two inverters in series for greater 120V capacity (see illustration below.) To provide 240V power, the 120V/240V selector switch, set for 240V, aligns the two inverters in parallel at a phase angle of 180 degree to generate 240V, but at the expense of 120V capacity. In both cases, the two inverters see the same load and are balanced. In 120V mode with 120V loads the two inverters see the same loads. Since 240V loads are by nature balanced loads, in 240V mode, the two inverters see equal loads on each. As such, when the engine control unit (ECU) varies the speed of the engine and hence the power (as a function of load), both inverters receive the same power.
(http://www.screenlightandgrip.com/images/generators/Op_Man_Circuit-Diagram.jpg)
Given this design, you run into trouble when you start to split-out 120V circuits from the 240V receptacle and load them unevenly. If you don’t meticulously balance your loads over the two legs (two inverters), then one inverter will be over powered while the other is underpowered when the ECU sets the rpm of the engine for the average of the two. In this case, since the bass woofers in the Mackie SR1530's draw 300w each (500W is the load of the whole system) and the 15” sub woofers in the Mackie SR1501s draw a full 500w, if they are not meticulously balanced (one SR1501 and two SR1530s on each inverter), when the load between the two inverters is averaged and the engine rpm adjusted accordingly, the inverter carrying the higher load (the 15” sub-woofers) will be under-powered and the inverter carrying the lessor load (the SR1530s) will be over-powered. Consequently, the voltage on the underpowered inverter will drop in accordance with the Voltage Characteristic Curve discussed above and the voltage on the over-powered inverter will not. Since it is the sub-woofers that are throwing the system out of balance, the voltage-drop on one inverter and not the other exhibits itself as dampened bass frequencies. Increasing the gauge of wire serving the load will not compensate for this voltage drop because it is not a function of cable resistance, but voltage droop of just one of the inverters as a function of the greater load.
One benefit of using our Transformer/Distros in place of a spider box is that it assures that the generator’s inverters are evenly loaded. Basically nothing more than a tricked out 240V-to-120V step-down transformer, our Transformer/Distros split the 120V load plugged into their secondaries evenly between the two legs of their primaries. Since the Transformer/Distro’s primary is the generator’s load, and not the 120V loads on the Transformer/Distro’s secondary, the generator’s two inverters are perfectly balanced. As such, when the ECU adjusts the engine rpm for the average load of the inverters, each inverter is fully powered.
A good example of this benefit is the Rap Music Video production pictured below. For this video, our Tranformer/Distro was able to power both a 4k HMI Par (36A w/PFC) and the amplifier for the monster stack of speakers on which the girls are dancing (22A) without either load being affected by the disparity between them. It did so by creating a single 60A/120V circuit from the two 30A/120V circuits of the 240V twist-lock receptacle. Where neither the 4k HMI Par, nor the speaker amplifier, could be operated on the 120V circuits of the generator's factory equipped power output panel, they could be operated on the larger 60A/120V circuit because the Transformer/Distro split the combined load evenly over the generator’s two inverters (29A a piece.)
(http://www.screenlightandgrip.com/images/generators/Boomtown_Scene_Comp.jpg)
2010 BET Hip Hop Awards "Director of the Year" Nahala Johnson, aka "Mr. Boomtown", directing his latest Rap Video: an outdoor dance party with DJ and dancers on top of a speaker stack (upper left.)
Our Transformer/Distro not only enabled the production to get more useable power out of the generator; but it also greatly simplified the distribution of power on set. To run power around the Rap Video set, breaking out to 20A Edison outlets at convenient points, we used standard 60A Bates extension cables, 60-to-60 Splitters, and fused 60A GPC-to-Edison Breakouts (snack boxes) with our 60A Transformer/Distro (see pictures below.) The best part about using a transformer as a Distro in this case was that no matter where in the distribution system we plugged in the 4k HMI, speaker amplifier, set monitor, camera battery charger, or DIT station in the course of the day (it changed from set-up to set-up), the Transformer/Distro automatically balanced the load on the generator, so that we didn't have to spend the time to meticulously do so.
(http://www.screenlightandgrip.com/images/generators/Boomtown_SetUp_Comp_Web.jpg)
Our modified Honda EU6500is supplies power to set (far left.) Our 60A Full Power Transformer/Distro compensates for line-loss of 300' cable run (left center) to assure 120V line level to 4K HMI (far right), Speaker Stack Amplifiers, Set Monitors, Battery Chargers, & DIT station (Center.) 60A Bates Splitters, Extensions, and Gang boxes distribute power from Transformer around set (right center.)
Our Transformer/Distros can also eliminate "Line-Loss" from long cable runs without resorting to larger more expensive gauge wire. A common problem with portable generators, even the super quiet Honda Inverter generators, is that by the time you move them far enough off set that you don't hear them, you have significant "Line Loss" (often referred to as "Voltage Drop") from the long cable run back to set (if you use regular cable.) To the problem of line loss, as we saw in the Voltage Characteristic Curve of the generator above you have the added problem that as you add load, the voltage drops on the generators. For this reason we tap our Transformer/Distros so that you can boost the voltage their secondaries in 5% (6v) increments. This feature enables you to operate the generator at a distance without suffering from voltage drop.
(http://www.screenlightandgrip.com/images/generators/Select_Transformer_Switch_Sm.jpg)
"Select" Models allow you to adjust for line-loss to maintain 120V on set
This Rap Video is also a good example of the benefit to being able to boost line voltage with our Transformer/Distro. Even though the generator was 300 ft away, the boost capacity of our Transformer/Distro assured that line level on set did not drop too low. By comparison, had we run 300' of standard 14 Awg electrical cord to set we would have experienced severe line loss.
(http://www.screenlightandgrip.com/images/generators/Boomtown_Distro_Comp.jpg)
Our 60A Full Power Transformer/Distro is outfitted with a 60A Bates receptacle so that you can use standard film style distro such as 60A Bates Splitters, Extensions, and Gang boxes to distribute power around set.
Our Transformer/Distros greatly simplify set electrics so that you don't have to be an experienced electrician to distribute power on set. The iMonitor display on the EU6500igenerator control panel makes it especially easy to load our modified Honda EU6500is inverter generator to full capacity. Simply plug in lights. When the load wattage displayed on the iMonitor reaches 7500 Watts you are fully utilizing the power capacity of the generator. An overload alarm on the iMonitor display will tell you if you inadvertently overload the Transformer/Distro. It is that simple.
Guy Holt, Gaffer
ScreenLight & Grip
Lighting Rental and Sales in Boston
Cell 617-224-85634
[email protected]
I'm sure that Honda and Yamaha inverter generators are constantly monitoring current and can go into limiting mode, much like our modern power amplifiers do to protect their output stages.
A while back I tested both the Honda EU6500is and the Yamaha 6500 for limiters with a load bank and came up with some interesting results. Both machines have an electronic master breaker upstream of the overcurrent protection of the individual circuit breakers. Where the master breaker in the Yamaha 6500 trips at 54A (6500W at 120V), the breaker in the EU6500is does not trip until 65A (7800W at 120V.) Further testing of the EU6500is with a load bank suggested that the actual continuous load capacity of the EU6500is is 7680 Watts. Where that is much higher than Honda’s stated continuous load rating (5500W) for the EU6500is, let me explain how we arrived at that figure in more detail.
First we modified the generator in order to tap the output of the inverters upstream of the individual branch circuits. Then following the load parameters as set forth in the manual, we used the generator's overload sensor to empirically test its' capacity with a load bank. The load parameters as set forth in the manual are as follows:
"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 off"
Gradually increasing the load with the load bank, we found that we could power a continuous load of up to 7680 Watts without the overload indicator coming on. When we exceeded 7680 Watts, the red indicator blinked intermittently. When we exceeded 7800 Watts the red indicator came on continuously, the limiter kicked in, and power was cut off to the receptacles after 5 seconds. Since, according to the Honda Manual it is normal for the overload indicator to come on for short front-end loads, like electric motors starting, our results suggested that the continuous load capacity of the EU6500is is actually 7680 watts (at first glance it seemed an odd number, but made perfect sense after further investigation.) When you consider that electric motors require up to three times more power to start than is required to keep them running, the manual suggests that the peak rating is actually well above 7680W.
Since our load bank tests suggested that not only is the limiter much higher than one would expect, but also that the inverter modules of the EU6500is generator are in fact capable of generating more power than is provided to us by the North American Power Output panel, we investigated the capacity of the EU6500is further and found that, in fact, it is engineered to generate 7680W of continuous power. In order to understand why it is possible with a modification to get that much continuous power out of a Honda EU6500is generator, one must first appreciate two 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 prevailing electrical codes of the market for which it is intended (where & 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 standards and prevailing codes of the national market in which the generator will be used (use this link -http://www.screenlightandgrip.com/html/emailnewsletter_generators.html (http://www.screenlightandgrip.com/html/emailnewsletter_generators.html) - for more details on how generator manufacturers arrive at their continuous load ratings.)
When you compare how Honda outfits the comparable UK model of the EU6500is generator, the EU65, for the UK markets, where the standard circuit for domestic power is 240 Volts and 16 Amps (3680/3840 Watts), to how Honda outfits the same generator for the North American Market, where the standard circuit is 120 Volts and 20 Amps (2400 Watts), one realizes that Honda does not give us access to all the power available from the generator. That our empirical testing of the EU6500is revealed that it will power exactly two UK 240V/16A circuits (3840 Watts/circuit x 2 circuits = 7680W) is not just a coincidence. An examination of the wiring schematics for the UK version, the EU65, reveals that the 7800W master breaker and load sensor alarm setting of 7680W are set for the equivalent of two UK 240V/16A circuits (2x3840W/circuit = 7680W.) It would make sense that Honda would engineer the base model to generate more power for national markets, like the UK, India, Australia, etc. that use 240V power. Unfortunately the power output panel of the North American model, the EU6500is, does not give us ready access to this power without the use of a transformer/distro because of our electrical standards and prevailing codes. Based upon these results, I can say with confidence that the OPs problem is not related to a limiter.
Guy Holt, Gaffer
ScreenLight & Grip
Lighting Rental and Sales in Boston
Cell 617-224-85634
[email protected]
All this talk of harmonics and neutral heating got me thinking about the differences between inverter generators such as the Honda units discussed here, and old-school constant speed generators with nothing but spinning copper and magnets…
The primary factors limiting the use of non-linear loads on portable generators are their inefficient use of power and the harmonic currents they generate. Because of their radically different designs, inverter generators, like the EU6500is, and conventional AVR generators, like the ES6500, react very differently to these factors. The harmonic currents generated by non-linear loads, in fact, have less of an adverse effect on inverter generators than they do on conventional AVR generators and so do not require de-rating as conventional AVR generators do.
Harmonic currents cause two major problems in conventional AVR generators: heat and voltage waveform distortion. The first problem is that harmonic currents generate heat in the windings, core, and in the electromagnets of the rotor of conventional AVR generators. Since generator ratings are limited by allowable temperature rise, harmonics act as derating factors. In derating, the magnitude of the current is of obvious importance, because losses are proportional to the square of the current. Increased frequency causes increased core losses and increased copper loss from skin effect. 5th and 7th harmonics are the offenders here because they are in the 600 Hz range.
The second difficulty caused by harmonic currents is voltage waveform distortion. According to Ohm’s law, as each harmonic current encounters the impedance of the power distribution system, it will cause a voltage drop at the same harmonic voltage. Because, the capacitors of switch mode power supplies only draw current at the peak of the voltage waveform, this voltage drop occurs only at the peak of the voltage - leading to a flat topping of the voltage waveform.
The more harmonic content in the current, the more voltage distortion occurs throughout the distribution system. This includes the output terminals of the generator where the generator’s source impedance (particularly the subtransient reactance or “Xd”) will create the greatest voltage drops. If the flat topping distortion at the generator’s output terminals is severe, it can cause voltage regulator sensing problems (Self-Excitation or SE) and inaccurate instrument readings.
The effect that harmonic currents have on the generators is factored into the rating limits given them. How rating limits are affected by load can be illustrated in a “Limit Characteristic” graph that plots kVA and kW versus Power Factor. The fluctuations in the kVA line in the illustration below represent the generator’s operating limits depending on whether its load has a leading or lagging Power Factor. It is important to note that a generator’s Limit Characteristic graph will vary by the type of generator. The illustration below (courtesy of Caterpillar) is for a conventional AVR generator. Since the power quality of an AVR generator is intractably linked to its' engine - the effect of harmonics on the engine's governing system is the primary limiting factor. How the engine and its' governing systems are affected by lagging and leading power factor loads is illustrated by the engine kW limit line below.
(http://www.screenlightandgrip.com/images/generators/R_Gen_Rating_Limits.jpg)
A Limit Characteristic graph for a generator illustrates the effect of leading
or lagging Power Factor on the generator's output.
What this generator’s Limit Characteristic graph tells us is that, operating a capacitive non-linear load (the leading power factor quadrant right of the Unity Power Factor center line), this AVR generator first reaches a thermal limit as a consequence of heat generation in the generator's rotor from harmonic currents. And since, conventional AVR generators regulate voltage by means of a power feedback loop from the generator Stator (via the Sensor Coil), through the Exciter (Voltage Regulator), to electromagnets in the Rotor, Armature flux generated by harmonic currents in the Stator leads to erroneous Self-Excitation (SE) and therefore voltage. Put simply, lower power factor loads cause instability of the generator’s voltage output. Finally, since there comes a point as the Power Factor of the load decreases, when harmonics inhibit the successful operation of the generator’s Automatic Voltage Regulator all together, and hence the generator’s capacity to generate any power at all, the kW output eventually drops to zero. Since the voltage instability in conventional AVR generators is a function of the non-linear loads they power, the conventional wisdom is to limit the amount of non-linear loads it can power by roughly half of the generators capacity.
(http://www.screenlightandgrip.com/images/generators/EU_Gen_Rating_Limits.jpg)
The Limit Characteristic graph for an Inverter generator.
Note the negligible effect that leading Power Factor loads have on the generator's power capacity.
As the Limit Characteristic graph for an inverter generator above illustrates, it is a completely different situation with inverter generators. Because the speed of the motor is always changing, inverter generators cannot maintain voltage output by the conventional means of regulating the excitation current in Rotor electromagnets. Instead, inverter generators use permanent magnets in place of electromagnets.
A permanent Magnet is an object made from a material that is naturally magnetized (Neodymium in this case) and hence creates its own persistent magnetic field. Since permanent magnets do not require an excitation circuit, armature flux created by harmonic currents will not cause voltage instability as it does in conventional AVR generators.
(http://www.screenlightandgrip.com/images/generators/waveform_elec_ballast_AVR-I.jpg)
Left: Conventional AVR Generator w/1200W non-pfc electronic ballast. Right: Inverter Generator w/1200W non-pfc electronic ballast.
And since the generator’s inverter completely processes the raw power generated by the permanent magnet (converting it to DC before converting it back to AC by means of a micro-processor), the AC power it generates is completely independent of the engine. By switching IGBTs according to Pulse Width Modulation control logic, an inverter generator is much better able to sustain output voltage against transient loads and, therefore, it has a much lower internal reactance compared to conventional AVR machines. Finally, since the Impedance encountered by harmonic currents that causes voltage waveform distortion is a function of the internal reactance of the generator’s engine to changes in load, a second benefit to using permanent magnets in place of electromagnets in the generator’s Rotor is that as is evident in the oscilloscope shots above, inverter generators consequently are much less susceptible to voltage waveform distortion.
(http://www.screenlightandgrip.com/images/generators/Inverter_Gen_Comp_Chart.jpeg)
TABLE COURTESY OF KIRK KLEINSCHMIDT.
The end result is that leading power factor loads do not cause voltage regulation errors in inverter generators as they do in conventional AVR generators. Inverter generators are able to hold their voltage stable within ±1% of the mean voltage, as opposed to the ±3% of conventional generators using analogue AVRs and are much less susceptible to voltage drop and AC Frequency (Hz) as a function of load (see table above.)
The rock solid power and low sub-transient impedance of inverter generators enable you to operate larger non-linear loads on them than can be operated on conventional AVR generators. For instance, we have struck 6kw HMI Pars on a modified Honda EU6500is inverter generator without problem.
These power quality issues have been vexing film electricians for years, to learn more about how we have learned to remediate the adverse effects of harmonics read a white I have written on the use of portable generators in motion picture production available at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html (http://www.screenlightandgrip.com/html/emailnewsletter_generators.html).
Guy Holt, Gaffer
ScreenLight & Grip
Lighting Rental and Sales in Boston
Cell 617-224-85634
[email protected]