Energy Unlimited by Victron

10.6.4. PowerControl and PowerAssist

Using Multi’s and PowerControl together with a generator has the following advantages (see also chapter 8):

- Uninterrupted AC supply. When the generator is off, 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. The reverse will happen when the generator is stopped. The PowerControl feature will eliminate any risk of overload on the generator. The battery charge current will automatically be reduced if, together with other consumers, power demand by the Multi’s (which with 2 Multi’s could be as high as 2 x 70 A x 30 V = 4.2 kW) would otherwise result in an overload. Thanks to PowerControl the generator discussed in section 10.6.4. can be downsized from 12 kW to 8 kW (installation with electric stove) or from 6 kW to 3 kW (without electric stove). PowerAssist : the MultiPlus as generator booster This is the option on the Phoenix MultiPlus to allow parallel operation with a generator or with shore power (see also chapter 8). - Operating 2 Multi’s in parallel with the generator would increase continuous AC output from 6 kW to 11 kW, and increase peak output to more than 15 kW. This brings the electric stove back on board. Whenever power decreases to less than a pre-set limit (which in our example would be 5 kW for the 6 kW generator, in order not to run the generator continuously at full load), the Multi’s would take the surplus power from the generator to recharge the batteries, at up to 2 x 70 = 140 A. Similarly, when operating in parallel with shore power, which would be rated for example at 16 A (In Europe this would amount to 16 x 230= 3680 W, or 3,7 kW) the 2 Multi’s would increase available AC power on board to some 8 kW. Let us first look at parallel operation with a generator, for example the 6 kW generator on the yacht under sail from the previous section.

No need anymore to start the generator in the marina!

10.6.5. The AC generator on a relatively small boat: conclusion

Sizing a generator to the peak power that may be required results in a big and heavy machine, and the shore power connection needed will be well above the rating that is generally available. If, in addition, a 50/60 Hz shore converter is needed the system becomes extremely expensive and cumbersome. Instead of compromising with regard to comfort on board, new technology can be used to reduce cost, size and weight of the power supply system.

By adding a 24 V 800 Ah battery, 3 Multi’s with PowerAssist and a 50 A battery charger to the system we have been able to:

Introduce 2 generator free periods per day of in total 20 hours.

Reduce the rating of the generator from 12 kW (3 phase) to 6 kW (single phase).

- Reduce shore power required from 8 kW (3 phase 16 A) to a mere 1.3 kW (6 A 230 V shore outlet)

Eliminate the need for a 50/60 Hz shore converter

Achieve uninterrupted AC power on board

Substantially increase redundancy and therefore safety.

10.6.6. The DC generator

Next to conventional 50/60 Hz AC generators, some generator suppliers are also offering DC generators. Outputs of up to 10 kW, that means a battery charging current of up to some 300 A at 28 V, are available. DC generators are smaller and lighter, and have a higher efficiency than AC generators. Moreover, engine speed can be harmonised with power demand, so that efficiency remains high even under partial load. The idea is to use the DC generator to charge the batteries, and use inverters to supply the AC load. Sizing of the DC generator is a question of acceptable running hours per day. With 14 kWh of electrical energy required per day, a 6 kW DC generator, for example, would run for 2-3 hours per day.