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
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.
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.)
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.
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.
"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.
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 firstname.lastname@example.org