Last month, we introduced the concept of inverters to power 240 volt appliances from batteries. Now it’s time to look at inverters for serious applications such as microwaves, refrigerators and possibly even air conditioners.
Larger permanently mounted inverters will need to be in the range of 2-3kW. It’s not easy to size an inverter for compressor loads such as refrigerators and air conditioners so always specify an inverter with a high surge current rating and with a power reserve. Some testing and evaluation will be necessary to specify the best inverter for your needs.
Larger inverters are capable of displacing small generators in their power output and have the advantage that they are silent in operation. These inverters invariably generate pure sine wave electricity which is obviously beneficial for most mains operated appliances.
Often they are integrated with a smart battery charger in the same package. This means that battery banks of up to 800Ah can be replenished when shore power or a generator, is available. The ultimate package is an inverter/charger system with intelligent shore power and generator power management.
Having decided to install a high power inverter or inverter/charger, the next consideration is how to install it. Larger inverters require careful planning especially with respect to the installation of cabling and mounting.
The inverter should be installed as close as possible to the battery bank so that DC cable runs are kept to a minimum. Adequately sized cables and terminals are imperative so that any voltage drops under load are eliminated. Most inverter manufacturers recommend operating from a 24 volt supply when the output is in excess of 2kw so that there is less DC current stress.
Unfortunately, mounting the inverter close to the battery could mean the risk of corrosive fumes contaminating the inverter, so, as for battery installations, the location must have adequate ventilation.
Although many high-end inverters have conformal coated printed circuit boards, it is essential to ensure the environment is clean, dry and at a stable temperature. Mount the inverter securely and not above the battery. The last thing you want is the inverter dropping across the battery terminals.
It must be emphasised that inverters produce potentially lethal AC power. Also, high currents on the DC side can generate high temperatures and arcing if incorrectly installed. Not only must 240 volt permanent wiring be installed by a licensed electrician but the input side should be configured by a person familiar with DC implications, especially cable sizing and fusing.
There are real safety issues with inverter outputs as the AC from an inverter does not have a neutral bonded to earth, unlike mains power. This means that a Residual Current Device (RCD) will be ineffectual unless a mains earth neutral connection (MEN) is established. This must be performed by a qualified installer and only with advice from the manufacturer. So issues with earth current leakage, shore power isolation and bonding are best entrusted to the experts.
These packages are the ultimate in power management. A high quality sine wave inverter is combined with a multi stage smart battery charger. Combining the two reduces wiring complexity and overall equipment costs. Both are controlled by a high speed AC transfer switch.
In the event of a shore power or generator disconnection, the AC transfer switch automatically activates the inverter and the boats loads are switched to the batteries. This can take place within 20 milliseconds so that continuity of power to sensitive electronics and appliances is uninterrupted.
Some inverter/chargers are capable of sensing a generator or shore power overload and cutting in the inverter to compensate. This can be of considerable benefit in the case of peak power demand for short periods such as the start up of an air conditioner or refrigerator.
The heart of any marine installation is the battery bank, so make sure that the battery bank and charging system are more than adequate for the expected inverter loads. Highly recommended is a battery monitoring system to keep an eye on the battery status, particularly in a high load environment. The only upside to an engine that won’t start due to depleted batteries is that at least the beer should still be cold!
*Gavin Sorrell works in collaboration with Aquavolt Electric Boat Parts.
Tel: 02 9417 8455 www.aquavolt.com.au