Energy Unlimited by Victron

both sides of the Atlantic.

- A 20 kW generator running 24 hours a day would have an average load of only 2 / 20 = 10 %! Not good for the generator and not good for fuel consumption. Adding a second, smaller, generator would increase this figure to some 20 %. Better, but still bad.

- And then of course the noise, vibration, smell and pollution 24 hours a day…(and do keep in mind that there are more and more marina’s and nature reserves where running a generator is forbidden).

11.3.2. Adding a battery for a generator free period

This alternative brings us back to 10.6.3, but with more power required.

Battery sizing Battery capacity will depend on the required generator free period, and especially on whether at all, or how much, air conditioning is required during the generator free period. Let us assume here that the generator will be running at least twice a day, whenever the electric stove & ovens are in use, when the water maker is on and during washing and / or dishwashing. In other words: during some 8 hours per day. Furthermore, we assume an average battery load during the generator free periods of 1.5 kW (= 63 A), which results in 1.5 x (24 – 8) = 24 kWh or 24 kWh / 24 V = 1000 Ah taken from the battery per day. Applying the rule of thumb from sect. 8.5.2, a battery of 2000 Ah will be needed.

Of the 48 kWh required per day, in this example 24 kWh is supplied by the battery, and the remaining 24 kWh directly by the generator.

The generator The generator will have to recharge 1000 Ah within 8 hours. We then need a recharge current slightly exceeding 1000 / 8 = 125 A, for example 175 A. For the generator this means a load of 175 x 30 = 5.25 kW. This can be done with the 20 kW generator mentioned earlier, provided the battery chargers are switched off when peak power is required for cooking plus some other electric appliances being used at the same time.

The energy to be supplied by the generator will be 1000 Ah x 30 V = 30 kWh for the battery, plus the 24 kWh directly to the AC appliances, total 30 + 24 = 54 kWh, battery charge-discharge losses included.

By adding a 2000 Ah battery to the system, we have: - achieved 2 generator free periods per day of on average 8 hours each - reduced generator use from 24 to 8 hours per day - increased the average load of the 20 kW generator from 2 kW to 54 / 8 = 6.75 kW, battery charge- discharge losses included.

But we still need a 15 kW shore power connection and a shore converter.

11.3.3. Using parallel Multi’s with PowerControl , and the DC concept for shore power: - for automatic generator load dependent battery charging - to reduce required shore power to 3.5 kW - and have frequency conversion nearly for free

Installing 5 Multi’s in between the 20 kW generator and the battery will result in the following:

- Instead of a three phase generator, a single phase model could be used: shore power will also be single phase (see below) and phase balancing problems will be eliminated.

- The Powercontrol feature will eliminate any risk of overload on the generator. The battery recharge current will automatically be reduced if power demand by the Multi’s (which could be as high as 5 x 70 A x 30 V = 10.5 kW if a fast recharge is needed, but would in general be limited to 5.25 kW) together with other consumers would otherwise result in an overload. - Uninterrupted AC supply. When the generator is off or power is needed for the bow thruster, the Multi’s will supply AC on board. After the generator has been switched on the AC load will automatically be transferred to the generator and the Multi’s will switch to battery charger mode. - By implementing the DC concept, shore power can be reduced from 15 kW to 3.5 kW (in Europe this would mean a single phase 230 V 16 A shore connection instead of a three phase connection) and frequency conversion is a built-in feature of the system. To implement the DC concept, shore power should be connected to a 100 A battery charger (or, for redundancy, 3 off 50 A chargers) which charge(s) the battery, and all AC consumers on board will be supplied by the 5 parallel Multi’s. The 5 parallel Multi’s are rated at 10 kW continuous output power and 15 kW short term. At first sight 100 A might seem a bit tight: the 48 kWh required per day translates to (48 kWh / 24 h) / 24 V = 83 A. But on the other hand being able to run the ship on a 16 A shore outlet is