"We went through all the highs and lows."

Fleet manager Alexander Hadersdorfer and technician Felix Jahn from ARRI Rental Munich developed a mobile electricity generator for the special demands of the film industry. Now, two years later, the Green Silent Generator is going into series production.

They say necessity is the mother of invention. Alexander Hadersdorfer (44) and Felix Jahn (23) can confirm that. Hadersdorfer, fleet manager at ARRI Rental Munich, and Jahn, a technician, weren't happy with the self-driven generators available on the market.

The issues: user friendliness and ease of maintenance. Conventional generators are loud, and if the surrounding air temperature is above 22 °C, they don't perform at their best. With many models on the market, the generator is integrated into the vehicle's chassis, which means that if you want to do repair work, you have to dismantle the interior of the vehicle and pull the generator out of the side door with a crane. "That means that when the generator has a defect, the whole vehicle has to go to the repair shop, and is not available for work," Jahn explains.

The two men wanted a removable power generator, to make repairs easier. They asked a number of manufacturers, but none of them wanted–or was able–to meet ARRI Rental’s requirements. This was partly because, in addition to wanting a plug-and-play AC electrical generator, the two men had a number of other ideas for the product. "Eventually we said: If nobody wants to make it for us, we'll make it ourselves," recalls Hadersdorfer, who is known by the nickname "Hadi.” They presented their idea to the ARRI Rental management, and it got the go-ahead.

Hadi and Jahn started work on their new generator in December 2015. They contacted the German branch of an Italian company that had responded some months earlier with a promising-looking generator system. Together with that company, they went in search of the right component suppliers. "We put our know-how into the collaboration,” says Hadi. “They had all the basics down, but had never built a self-driven generator before. We told them what was important and how it might best be done, and the project just evolved.”

So, the Green Silent Generator is an Italo-German co-production with a European cast: The generator's electrical system comes from Campania. The chassis comes from Mercedes in Wörth an der Isar. The distribution box, which is attached to the outside of the control element, comes from Indu-Electric Gerber in North-Rhine Westphalia, as does the active filter. And the whole thing is powered by a Swedish Volvo Penta motor, with a control panel from the Czech Republic and fuses from the German company Schneider Electric.

The cases into which the generators are packed are made in Swabia. But the vibration behavior of the materials had to be tested carefully, because the generator motor is jacked up on blocks inside the case, and like any other motor, it vibrates. These vibrations transmit to the housing, making the case act like a loudspeaker, passing the sound on and spreading it across a large area, which is problematic on a film set. So they had to find materials that swallow up vibrations, or that don't vibrate at all. Hadi notes: "The manufacturer let us have a few finished cases, and in the first test we put the unit into the case and looked to see which materials vibrated in what way, and which floors and walls made the least noise."

From the very beginning, Jahn and Hadi wanted a generator in which the cooling chamber and the engine compartment are separate. Their Italian partner was one of the only manufacturers in the world to offer this kind of setup. When these two areas are separated, the air only goes through the cooler and not through the engine as well. This means the engine compartment is no longer covered, and more importantly, the air isn't heated up by the motor before going into the cooler, and the cooling surface is larger. This means you can have full performance at even up to 55 °C air temperature.

The project was not without its teething problems. First of all there were delivery delays from one manufacturer, which pushed completion back several months. Then, when the prototype was finally in Munich, the real work began. In mid-2017 the Green Silent Generator went into its testing phase. Productions rented the prototype at friendly rates, tried it out, and gave feedback. Colleagues in other ARRI Rental branches also had valuable suggestions. For example, the Berlin team sent the message: Please install a second 125 A/400 V socket! "Berlin lighting technicians work a bit differently from their counterparts elsewhere in Germany,” explains Hadi. “They need a second 125 A socket so that they can build a ring circuit."

"That was a pretty stressful time, of course. Felix had to drive up to Cologne, for example, because the machine was running too loud for one production," continues Hadi. But it was really important to get direct feedback from people who had actually used the generator. "We technicians know how to work with the machine properly," says Jahn. "But on set, people usually don't do things the way we do here. For instance, a 100 kW unit generally runs at 6 kW or at most 10 kW on set."

That was one of the biggest problems with the original particle filter system: If a diesel generator runs at low load for a long period of time, it soots up much more quickly, especially the exhaust system, which then leaks, causing the engine to die because it doesn’t get enough air. So Hadi and Jahn decided to replace the plug connections in the exhaust train with welded flange connections. And because they had to remove the roof of the generator to do that anyway, they installed an active soot particle filter while they were at it, to replace the passive filter. An active filter incorporates a diesel-driven burner, which switches itself on and adds heat if the exhaust temperature falls below 400 °C. In that way, the filter doesn't fill with soot, no soot particles are emitted, and the amount of nitrogen oxides (NOx) reduces. What is more, the active filter has a working life of at least 8,000 hours, in contrast to the 400 hours of passive filters. Hence the name: Green Silent.

"We wanted an active filter system because environmental friendliness is important, and I am of the opinion that it will become compulsory sooner or later anyway,” says Hadi. “When it does, we'll already have it in there." Constantin Film specifically requested the prototype for a special project: SAUERKRAUTKOMA, which was produced as a "green film,” and received the 100th Green Film Pass from the Filmförderung Hamburg Schleswig-Holstein (FFHSW) state film fund.

So, there is demand for the Green Silent Generator, and that demand will most likely increase in the future. ARRI Rental therefore decided to go into series production. Hadi and Jahn kept tweaking the prototype for a long time, driving to the manufacturer in Italy, analyzing feedback from customers, performing tests. Sometimes the solution to one problem caused another. For instance, the redesign of the exhaust plant made the generator very loud. So they installed a bigger exhaust pipe with fewer swirls. On one trip to Italy, they also found a better material for the case. The new isolation swallows up more noise than GRP, is lighter, and easier to clean. “It looks better too," says Jahn.

Nonetheless, the lighter casing doesn't reduce the weight of a Green Silent Generator significantly. The prototype stands on an 8.6-tonne chassis, and the generator has a 10-tonne undercarriage, due to emissions standards. A 100 kW generator has the engine classification "Stage 3A,” and a six-cylinder engine is compulsory for this class, which is 450 kg heavier than the four-cylinder engine used in utility vehicles in the past. "That was a real brain-teaser: How can we get the generator to fit on an undercarriage of 7.5 tons?” says Hadi. “Together with the generator's manufacturer we calculated and calculated, and looked where we could reduce the weight, but after two months of intensive applied mathematics, we had to admit that we just couldn't do it. We needed a bigger chassis."

With an old Class 3 driver's license (now: Class B), you can drive a truck of up to 7.5 tonnes. For any chassis over that weight you need a Class C license, which not many people have. But you have to make concessions somewhere, was Hadi's succinct assessment. Safety first. “Either you have a small generator with less performance on a 7.5 tonne chassis that anyone with a B license can drive, or you have a big, high-performance unit that can even run at full capacity when the weather is hot, but you have to make sure someone has a license to drive a 10-tonne vehicle," he says. It's all a question of priorities.

"Getting a prototype to the stage where it can go into series production is really nerve-racking and sometimes extremely frustrating," says Jahn, and Hadi laughs: "Yes, we went through all the highs and lows." They look back on the experience positively, but react modestly to praise for their work. "There's no reason to put us on a pedestal," says Hadi, "We were honored that the company placed that much trust in us; there are considerable amounts of money involved." Jahn agrees: "The most important thing is that the customers are happy with our new generators in the future. If we managed that, then we consider it a huge success."

And we'll find that out soon. The new generation of Green Silent Generators hits the market in spring 2019.

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