Minimal or maximal or in-between? The old time sailors say keep it simple and watch every amp. But we like our comforts and our modern devices too much. The days in which I might have sailed without modern conveniences are gone. Now we are a power hungry lot that wants to have hot water, computer, refrigerator, radar, radios, and electric autopilot, to name a few energy gobblers. A primary source of diesel-generated electricity is required!
In developing the electrical system design for Beatrix it was necessary to look at all components from a systems viewpoint including all sources and sinks of energy. This involved analyzing our expected electrical needs, both AC and DC, determining how much battery capacity we needed, and considering the type and capacity of the DC charging system. Daily cycles of use and battery charging at anchor, at sea, and at the dock were factored into the equation. We hopefully see ourselves spending days or weeks at anchor in quiet tropical harbours and DON’T want to be running the main engine to recharge batteries.
In considering alternative energy sources such as solar, wind, or towed systems, and with our own experiences and in talking to others, the conclusion is that they function best as supplemental or backup sources of power, unless you have minimal power needs.
At the time we needed new batteries, a new refrigeration/freezing system, and we had not yet bought a watermaker so we were able to make some choices. In refrigeration we had the choice of mechanical drive or using AC or DC power. We chose DC throughout. We also wanted the ability to quietly charge the batteries and run these systems from an auxiliary power source. We don't need or want air conditioning, which is the main use for an AC generator. All compressors (reefer, airco, SCUBA) take LOTS of power to start up and a fair amount to run. DC reefer systems aren't as bad because the compressor capacity can be sized to the job. (We do have a SCUBA compressor, but it is gas-engine driven).
Thus, having a DC generator and high-output alternator became the center of our electric system planning. We feel a DC generator is a much better way to go than an AC generator UNLESS you want air conditioning on the boat. Four or five times as much DC can be made with direct generation than using an AC generator to power a battery charger.
An exceptionally quiet generator is important so it can be run it at anchor without bothering us or anybody else. If not motoring (i.e. sailing or at anchor or at a dock without shore power) we would have a daily charging cycle during which we also pull down the refrigerator/freezer cold plates, make the daily water with the 12V Spectra watermaker, and heat domestic hot water (using the inverter -- the water heater is AC 750 Watt). After the initial bulk phase, switching on more DC loads makes efficient use of the generator.
When I saw the Panda AGT 4000 at the 2000 Seattle boat show I knew we had a solution. This genset is the big "splurge" for us (it's quite expensive). The Panda AGT 4000 is a VERY QUIET 12 volt generator. It puts out a max of 285 amps of 12 volt DC power. (Compare this to the charging capacity you could get from a 4KW genset/40A charger combo). It's the same 4KW but without the charger power loss.
The Panda is actually an AC generator with a "diode box" that rectifies the AC to DC. This works well because, unlike AC generators, the output is balanced to the load; i.e. if you need less power, the Panda slows down and produces less power. There are cheaper DC generators that use alternators. None are as quiet as the Panda. We are locating the Panda under a custom seat that replaces the ladder in the aft companionway. Access is really easy and all fuel, water, power, and exhaust fittings neatly pass through the aft cabin-engine room bulkhead. Fuel consumption for the daily charge should use between 0.25 and 0.35 gallons of diesel fuel.
NOTE: AFTER YEARS OF TRYING TO MAKE THIS DEVICE WORK I REMOVED IT FROM THE BOAT. The Panda AGT single-cylinder genset has no place on a cruising boat. It's design is seriously flawed and a 1-cylinder engine does not have the lifetime required for daily use onboard. The system is overly complex, prone to failure of both electrical and mechanical components. Reports from other cruisers confirm this. If it had ever performed to specs, it would have been a beauty. Sadly not. Our new charging routine involves using the main engine, then a Honda EU2000i gasoline portable "inverter" generator, and solar panels. We got used to this when the Panda wasn't working (as it usually wasn't working) and decided to stick with it. In my opinion the ideal genset would product DC power with a 2-cylinder diesel, alternator and regulator.
We have a 175A dual-belt Balmar alternator for the main bank and a 100A Balmar single-belt. They are regulated by a single Balmar MaxCharge 612 Regulator. This regulator has an option for ½ power and a switch to disconnect the field wire allows us to turn off the alternator altogether should we desire. I have incorporated this feature into a single DPDT switch that sets zero-half-full power for each of the alternators. The starting battery is an Optima spiral-wound battery charged with a "Digital Duo-Charge", also from Balmar, which only charges the starting battery when the voltage climbs to over 13.1V.
I rejected lead acid batteries because 1) the batteries are not fully accessible for topping up and 2) AGMs can accept 4 times the charging amps of lead-acids, thus using up to the full 285A capacity of the generator. The combo of the AGM batteries and the DC genset allow for faster charging (about 1.25 hour per day).
We wanted the batteries in the bilge below the companionway. This puts the weight low and centered in the boat and keeps the heavy-duty cable runs as short as possible. Because they are mostly inaccessible for servicing this dictated using gel-cel or AGM type batteries. AGMs are superior for other reasons, having a huge acceptance rate, long life, and deep cycles. They are perfectly matched to use with a high-output charging source. There only drawbacks are a higher initial cost and the fact that they can be damaged by charging at too high a voltage level. They are cost-effective over the lifetime of the battery and modern control systems should prevent overcharging.
In the under-floor location there was room for only 3 AGM 4D batteries, with 630 AH of capacity. This was enough. Removing the non-structural “web” between the two floor hatches and replacing it with a removable piece allowed us to easily drop the each battery into place to rest in a custom-built aluminum tray. The 4Ds are lighter weight than 8Ds and thus much easier to handle. (I have since determined there is space for a fourth 4D AGM if it is laid on its side, but it really isn’t necessary as long as the Panda is functional).
The first bank lasted 9 years. The second bank lasted less than 1 year. The 4Ds have been replaced with 8 6-volt AGM batteries at the recommendation of the manufacturer.
I have since learned that parallel battery strings seriously degrade the lifetime of batteries. I have reduced the current configuration to 3 parallel strings (plus 1 spare string). The NEXT bank will be 6 2-volt AGM cells and should last a long time.
The Trace 2500W inverter/charger is for shore power charging and, of course, AC loads such as kitchen appliances and power tools. It could theoretically power a small AC motor (2 HP) but would draw a huge drain on batteries so in that case you would have to run the DC generator to power the inverter at the same time. That is not the intended use. The inverter will easily run the water heater (750W) during the daily charging cycle and the water heater is insulated enough to hold hot water for 24 hours.
The Trace is a “modified sine wave” (MSW) inverter, which means that the wave form of the power only approximates the “pure sine wave” (PSW) that is delivered by the power company. MSW inverters are suitable for nearly every use on a boat including household appliances such as televisions, VCR's, power tools, microwave ovens, washing machine, freezers, and computer and inductive loads such as heaters. A PSW inverter produces power comparable to that produced by the local power company. On a boat PSW power is only required for laser printers and a few of the small battery chargers that you get with power tools and cordless devices. (You can test these by plugging them into an MSW inverter – if they don’t heat up, they are OK to use with MSW power). PSW inverters are more complicated, less efficient, more expensive, and the charger component is not useable with 50HZ power.
Since purchase of the Trace 2512 in 2001, the Trace Company was purchased by Xantrex. Xantrex also purchased Heart Interface and ProSine, effectively locking up the marine inverter market. Fortunately since then other competitors have come to the fore, notably Victron and Mastervolt, both high-end competitors. We have decided to purchase a second, smaller PSW inverter (250 – 300W) to power a laser printer only.
Electrical Generation System - DC Genset
Last modified: November 23 2015 04:29