It has taken a long time to decide on the generators but we finally have. Fir was initially fitted with two 100KW Detroit Diesel 671 generators that rarely ran at the same time. They could be paralleled but more often one was used to run the crane and the other was used to run the house systems. We want to replace one of the 671s with a new unit that is more energy-efficient and far less noisy. Also, we want to take advantage of the more modern systems such that the generators can be monitored and controlled by the Wheelhouse.
When Fir was in service her electrical load was fairly consistent. Her duties were predictable. The complement of sailors aboard, the demands from the galley, day-part schedules, the sanitary system were all predictable. Our repurposing creates a much different situation. We may have a few staff on board at anchor. We may have a hundred on board for an event. The previously installed system would certainly cover our anticipated needs, yet the generators would be running at less than 30% capacity for long periods. This is not inefficient, it is bad for the motor. We need a scalable system that allows us to run each generator at its optimal capacity without wasting fuel. And, we want a largely automated system that does not require numerous engineers to oversee.
We determined that the most basic operations (wheelhouse controls, steering, and starting the main engines) require about 32KW. The greatest demand comes from the air compressors and inductive heaters required to start the mains. We added in the fire pumps/dewatering pumps as these demands have to be covered at all times. At rest, 32KW is more than enough to cover the lights, galley equipment, potable water pumps, hot water, and sanitary system. Further, with some minor scavenging of the house system loads in an emergency, one can start the mains, fight a fire and dewater the boat. We decided that a 40KW generator (operating at about 80% of demand) best meets our needs. We will install two of these units so we have an additional layer of protection.
After some study, we settled on Northern Lights and Kohler as the preferred vendors. Northern Lights makes a great system. The Luger motor is rock solid. The controls are mechanical so they are very predictable, reliable, and repairable at sea. Kohler makes their own motors which are great for systems under 50 KW (John Deer probably make the best motor above 50KW). Kohler uses a circuit board controller called the Decision Maker 3500. It is available on generators above 16KW. The drawback with a circuit board controller is that you could need an electrical engineering degree to fix it and a software degree to program it. So, going with Kohler requires one to have a spare controller and there is a learning curve.
Because we are looking to scale our system based on demand, we wanted a system that can automatically parallel several generators. Fir’s existing system can be operated in parallel but, each time the two generators are joined, a person must manually synchronize the phases. This does not work if the generators are being brought on and offline based on demand. Both Northern Lights and Kohler offer automated solutions. Northern Lights offers a third-party package that will parallel two generators of the same output. Kohler offers an auto paralleling system that is built into its Decision Maker 3500 controller. One critical difference is that the Kohler system can parallel generators of different sizes which may be something we require when we get further into air conditioning. The Kohler system can organize the generators to best match the current load.
Worth noting here is that we intend to work with Victron and/or Tesla to develop a battery management system. The goal of the battery system is to have the generators run at 75% capacity whenever they are called online. To the extent that actual demand is less than production at 75%, the excess will be used to charge the battery system. Further, the battery system ought to smooth out spikes in demand, spikes caused by various motors, and short-lived operations.
Based on all of the above, we decided to go with Kohler. The Decisionmaker 3500 has been out for many years and field-tested. The unit comes from a single vendor so there will be no arguments about who is to blame for a problem. Since it will join generators of different outputs, the Decisionmaker 3500 is more flexible and the customer support feels right. Kent Prentice is our guy at Boatswain’s Locker and Kurt is our guy at the distributor( A1 Transmission). They have been helpful and responsive concerning system topography (Wye vs. Delta configurations). We have a good feeling that the system we designed on paper is going to show up in person. So, Kohler is our choice.
