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Cummins-Onan MDKBM generator
Cummins-Onan QD MDKBM

Zanshin's Onan MDKBM generator The 9.5Kw Onan generator (Model MDKBM) installed at the factory aboard Zanshin
[46°51'52.61"N 1°1'55.8"W ]
Zanshin's Onan MDKBM generator

Zanshin has many electrical systems on board which use a lot of electrical power. While the alternators on the main engine can re-charge the battery banks, when heavy AC loads such as the air conditioning, the watermaker or the electric oven are used the inverter and batteries really aren't up to the heavy requirements one needs a powerful generator to produce the AC power. We take electric power for granted on land, just plug in whatever device you need and switch it on; the power used is always there, always reliable and very cheap to use. On a boat things are very different and having constant DC and AC electrical power is a luxury that few have. On Zanshin the diesel generator is a Cummins-Onan 9.5Kw QD MDKBM unit producing 230V/50Hz (European) AC with a maximum output of 9.5Kw, this is a lot of power and the equivalent of running 4 hair driers and 2 espresso machines at the same time (these devices draw about 1.5Kw apiece).

The heaviest AC power consumer is the air conditioning, which I rarely run when not attached to shore power at a dock. The trade winds at anchor align the boat so that she gets optimal ventilation, but at a dock that is usually not the case and most marinas are situated where they are optimally protected from the weather which also means that there is little wind so air conditioning is necessary in tropical marinas. The next biggest drain is the oven, which is electric on Zanshin. If I only use one or two of the hobs the inverter is capable of supplying that power from the batteries, but if I were to bake something in the oven and use the hobs at the same time that would exceed the inverter's capabilities and I would need to turn on the generator. The same thing applies to all the other AC loads, while they can be supplied from the reserves of the battery bank, it is better to use the generator for these loads as putting power back into a battery bank involves losses, i.e. when I remove 100amps from a battery I might have to put 150amps back into the battery in order to get the same charge level.

9.5Kw at 230V can be used to charge the batteries - the charger I have allows me to charge the batteries with 120Amps@24V, which uses about 1/3 of the generator's output but lets me recharge my batteries very quickly. This compares favourable to the 80Amp alternator on the main engine, plus the generator is optimised for producing electricity quietly and efficiently at 1500RPM while the main engine is better used to move the boat. The generator uses about 2 litres of diesel per hour at 1/2 load so is quite efficient and miserly on fuel as well as being almost soundless.

My previous generators were German Fischer Panda models aboard Solitaire and Zanshin I. These a lot smaller in size than the Onan, but they achieved this by running at double the speed (3200RPM, a bit fast for a diesel) and thus had more vibration and noise and generally shorter life spans. This generator is a bit oversized and thus I hope that it runs well for a long time without getting overloaded.
