Amel owners, as a group, are highly suspicious of changes to design decisions made by the builder. This is a good thing, as a rule, because almost all of the decisions made by Amel in the design and construction of their boats are excellent ones. There are areas where technology marches ahead and it is appropriate to revisit the original ideas.
In our case, it was time to revisit things in our electrical system. As we have previously reported, a lack of required spare parts pushed us into deciding to retire our old Onan. We took a step back and evaluated how we used this unit, and if there were better alternatives for us and the way we used our boat.
What we had…
Our Amel is not especially complex for a cruising boat of her size these days. We have 220VAC power outlets in each cabin, two air conditioners, clothes washer, space heaters, and a water heater. Unusually, Amel installed a parallel 120V AC system that we feed only from a 2kW inverter. Other than a few specialized items, this is mostly used for the microwave in the galley.
When away from the dock, we have been running our 6.5kW Onan for about 2 hours every other day to charge batteries, and make water for our routine use. (We have a 40 litre/hour watermaker that draws about 25 amps at 24V). Once a week or so, we’d add another hour to the cycle to run the laundry and make the extra water needed for that.
The Onan fed 220V AC to two battery chargers, one 70Amp unit in our Victron inverter/charger and a 100 Amp unit from Quick. The highest output I ever saw from these units combined was about 120 Amps in total, or about 3200 Watts, about half the capacity of the Onan. In five years of cruising on Harmonie we have run an air conditioner away from shore power exactly once. So we have never really used any more than half the output of the generator.
Our 3kW Victron inverter charger easily drives all of our routine AC needs, including startup loads for the air conditioners. We didn’t need a 6.5kW generator to keep us in the life style to which we have become accustomed.
What We Wanted
Once we realized we were looking at a unit significantly smaller than the original installation, many options were open. Our criteria looked like this:
- Minimize fuel use to extend our operating time away from supplies.
- Reduce weight
- At least 95 amps of 24 Volt charging capacity. (Minimum recommended charge rate from out battery manufacturer)
- Minimum capacity of 3kW
- At least as quiet as the old unit.
- Minimal modifications to existing infrastructure.
- Good integration with our existing Victron monitoring equipment.
What We Got
We settled on a generator quite a bit different than the original. We decided on a WhisperPower M-GV 2 variable speed DC generator. Here is a bit of the thinking involved:
- Since we were using our generator almost exclusively as a battery charger, doesn’t it make sense to have a generator actually DESIGNED primarily to charge large battery banks?
- The capacity of the unit was well matched to what we were looking for, 150Amps at 24 Volts, or about 3.5 kW.
- The weight of 140 kgs was very attractive, as was the specified fuel usage. A reduction of about 100 kgs, this has put our boat on an even keel for the first time.
- The drive engine for this unit is a 2 cylinder Kubota Z482 engine, a well known and very common system of proven reliability.
- WhisperPower is a Dutch company spun off from Mastervolt a number of years ago when Mastervolt decided to get out of the generator business. They are not well known in the US, but are a significant presence in the European yacht and alternative energy market, especially as a high-end OEM supplier.
- Connecting to our Victron system with a simple relay connection, our main electrical monitoring panel can start and stop the generator either manually, or automatically based on the state of the batteries.
- The permanent magnet alternator technology is far simpler than the field coil system used in synchronous generators. No routine maintenance is required on any moving parts other than the Kubota engine.
- Being fully water cooled means a full sound shield can be installed and the engine room is cooler, and quieter than before.
- We are able to use the waste heat from the engine to heat our domestic hot water, giving us hot water while away from the dock for “free.” This used to be done from our main drive engine, but that was of limited utility since we didn’t really need much hot water underway, and never ran the drive engine at anchor.
How We Will Use It
Based on our testing so far, if we start charging when the batteries are about 30% discharged (70% SOC) and run them up with the generator to 7% discharged (93% SOC) that will take almost exactly 90 minutes of run time to put 107 Amp-hrs (3 kW-hrs) of recoverable energy into the batteries. This would have the generator start off at full output for about 30 minutes, and then taper down to about 25% output over then next hour. This will keep the engine running at its most efficient for most of the cycle, with a chance to cool down a bit at the end before shutting down.
Based on our historical usage, this will happen every other day or so. On a good sunny day, the batteries will then be fully topped off with the solar panels by the end of the day.
How much of this we will automate, we have yet to determine. The Victron monitoring system lets us to automatically start and stop the generator based on state of charge of the batteries, DC power usage, AC power usage, Battery voltage, inverter temperature, inverter overload, … Pretty much anything except phase of the moon! Automation has its advantages, and potential problems. We’ll see how those play out in the real world.
If you want more of the gory technical details, see this link on our project pages…