«Energy Unlimited Reinout Vader Electricity on Board (And other off-grid applications) Revision 9 June 2011 Electricity plays an increasing role on board ...»
Electricity on Board
(And other off-grid applications)
Electricity plays an increasing role on board yachts. Modern navigation and communication
equipment depends on it, as well as the growing list of household appliances that are taken
This is the concept text for a booklet about electricity on board small and large yachts. The
intention of the book is twofold:
Firstly I try to cover in depth a few matters that over and again are subject to discussion and misunderstanding, such as batteries and management of batteries, or electric power consumption of refrigerators, freezers and air conditioning.
My second intention is to help designers, electricians and boat owners to decide on how to manage and generate electricity on board. Several new products and concepts have substantially broadened the range of alternatives here.
Together with some unavoidable theory, I use examples of small and large yachts to clarify the consequences of choosing one alternative or another. The consequences are sometimes so unexpected and far reaching that, writing it all down, I have also helped my own understanding!
Reinout Vader © Victron Energy Copyright © 2000 Victron Energy B.V.
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2. The battery: preventing premature aging The battery is the heart of every small-scale energy system. No battery, no storage of electric energy. At the same time the battery is a costly and delicate component. This chapter specifically addresses the battery’s vulnerability.
2.2. Battery chemistry 2.2.1. What happens in a battery cell as it discharges 2.2.2. What happens during charging 2.2.3. The diffusion process 2.2.4. Service life: shedding, oxidation, and sulphation
2.3. The most common types of lead-acid battery 2.3.1. Lead-antimony and lead-calcium 2.3.2. Wet or flooded versus starved (gel or AGM) electrolyte 2.3.3. The flat-plate automotive battery (wet) 2.3.4. The flat-plate semi-traction battery (wet) 2.3.5. The traction or deep-cycle battery (wet) 2.3.6. The sealed (VLRA) gel battery 2.3.7. The sealed (VLRA) AGM battery 2.3.8. The sealed (VLRA) spiral-cell battery
2.4. Function and use of the battery
2.5. The lead-acid battery in practice 2.5.1. How much does a battery cost?
2.5.2. Dimensions and weight 2.5.3. Effect on capacity of rapid discharging 2.5.4. Capacity and temperature 2.5.5. Premature aging 1. The battery is discharged too deeply 2.5.6. Premature aging 2. Charging too rapidly and not fully charging 2.5.7. Premature aging 3. Undercharging 2.5.8. Premature aging 4. Overcharging 2.5.9. Premature aging 5. Temperature 2.5.10. Self-discharge
3. Monitoring a battery’s state of charge. ‘The battery monitor’.
The battery monitor indicates a battery’s state of charge, and can also be used to automatically start charging systems, or indicate that charging is required.
With larger battery systems a monitor with an amp-hour counter is indispensable. To start charging once the “voltage drops” is simply too late. The battery is then discharged too deeply and harm will already be done.
3.1. The different ways of measuring a battery’s state of charge
3.4. Charge efficiency of a battery
3.5. Effect on capacity of rapid discharging
3.6. Is capacity “lost” at high rates of discharge?
3.7. Useful features of a battery monitor
4. Battery charging: the theory Different types of battery have to be charged in different ways.
This section reviews the optimum charging characteristics of the most commonly used types of lead-acid battery.
4.2. Three step (I U° U) charging
5. Charging batteries with an alternator or a battery charger The alternator with a standard voltage regulator as used in automotive applications is far from being the best solution, and certainly not where several batteries, separated by a diode isolator, need to be charged.
5.1. The alternator
5.2. When the alternator has to charge more than one battery
The daily energy consumption of continuous and long duration low power consumers (refrigerator and freezer) is often underestimated, while the energy consumption of short time high power consumers (electric winches, bow thruster, washing machine, electric cooker) is often overestimated.
6.2. Power and energy
6.4. Electric winches, windlass and bow thruster
6.5. A battery powered washing machine and dishwasher?
6.6. Ever thought that electric cooking on battery power was possible?
6.7. The diving compressor
6.8. How to deal with the inrush current of AC electric motors
7.1. AC generators 7.1.1. The diesel engine will last longer if it has to work 7.1.2. A hybrid or battery assisted AC system 7.1.3. Don’t forget the problem of limited shore power 7.1.4. 3000 rpm or 1500 rpm (in a 60 Hz environment: 3600 rpm or 1800 rpm)
7.2. DC generators
This chapter brings us to the central theme of this book: how to optimise safety and comfort, and at the same time reduce weight and size of the power supply system.
8.2. New technology makes the DC concept more attractive
8.4. New: the hybrid or battery assisted AC concept, or “achieving the impossible” with PowerAssist 8.4.1. PowerAssist 8.4.2. Other advantages when operating Multi’s together with a generator 8.4.3. Shore power
8.5. Thinking different
11. Up to 48 kWh required per day (2 kW average)
11.2. The major consumers
11.3. Energy generation 11.3.1. With an AC generator running 24 hours a day 11.3.2. Adding a battery for a generator free period 11.3.3. Using parallel Multi’s with PowerControl, and the DC concept for shore power 11.3.4. Multi’s with PowerAssist 11.3.5. The DC generator 11.3.6. Using a small auxiliary DC generator to reduce generator hours, battery capacity and fuel consumption
11.4. Conclusion 11.4.1. A 20 kW generator with generator free period 11.4.2. Implementing PowerControl and the DC concept for shore power, and adding an auxiliary genset to reduce battery capacity 11.4.3. Using a smaller generator with PowerAssist, the DC concept for shore power, and an aux. genset
12.2. The major consumers
12.3. Energy generation 12.3.1. AC generators 12.3.2. Adding a battery for a generator free period and battery assisted generator operation (PowerAssist) 12.3.3. Adding an 8 kW auxiliary AC generator
12.4. The alternatives for 10 kW average consumption compared
13.1. Consumption of electric energy on board
13.2. Energy generation
13.3. The DC concept
13.4. PowerAssist: the hybrid or battery assisted AC concept
13.5. The house battery © Victron Energy
1. Introduction Victron Energy has been supplying components and systems for autonomous energy supply for some 25 years. These might be systems for sail- or motorboats, inland navigation vessels, off-grid houses, for many types of vehicles, and a nearly endless range of other, often unexpected, applications.
We know from experience that generating and storing electrical energy on a small-scale is a complex business. The components of an autonomous system are costly and vulnerable. For example, the battery, that indispensable storage medium in a small-scale system, often goes flat quickly and unexpectedly, so that the “power fails” and eventually the harm caused by excessive discharge means premature investment in a new battery.
Developments in the field of autonomous energy-supply on board sail- and motorboats are exemplary. The amount of electric (domestic) equipment on board boats is increasing rapidly, while at the same time the space and weight available for energy generation and storage are being kept to an absolute minimum. It goes without saying that living space and sailing characteristics take a higher priority.
Growing demands imposed on autonomous energy systems have spurred the development of new products and concepts. This overview presents new products and concepts, with specific attention being paid to optimum system component integration and day-to-day operation of the complete system.
Where system components are discussed, brands are only mentioned if the products are unique, that is to say available exclusively under that brand, or if other brands are very hard to obtain. The unique Victron Energy products mentioned
Battery chargers with adaptive software to automatically optimize charging.
Parallel connection of inverters and combined inverter-battery chargers The parallel connection option (if needed even in 3-phase configuration) means that there are no limits anymore to the amount of AC power that can be supplied from a battery. As will be shown, this opens the possibility to run all kinds of domestic equipment, including the washing machine and the electric cooker, from the battery. Although the peak power consumption of such equipment is high, the amount of amp-hours needed is quite manageable and much lower than one would expect.
- PowerControl is an often overlooked but very convenient feature of the Victron Phoenix Combi and its even more versatile successor, the Phoenix Multi: by constantly monitoring the total power drawn from the on-board generator or shore supply, the Phoenix Multi will automatically reduce battery charging when otherwise an overload situation would occur (for example when high power household equipment is switched on).
The next step: PowerAssist. The revolutionary Phoenix MultiPlus, also an inverter-battery charger, actually runs in parallel with shore power or an AC generator, and uses the battery as a buffer to “help” the shore power or generator during periods of peak power demand.
The implications of PowerAssist are truly far reaching:
Traditionally the on-board generator had to be dimensioned to the peak power required. The use of power hungry equipment such as air conditioning, a washing machine or an electric stove would require a big and heavy generator and the required shore power capacity would often not even be available. With PowerAssist, shore power and the onboard generator can be reduced to less than half the rating that normally would be required!
While this overview is directed mainly towards boats, many products and solutions are also applicable in other autonomous energy systems such as can be found in off-grid houses, motor homes, or special purpose commercial vehicles.
I like engines. When they go wrong you can listen, and look, and smell, and then take them apart. Parts can be replaced, repaired or overhauled. Then put it all together again, and there they go!
With a battery you can’t do that. The battery is a secretive product. From the outside there is nothing to tell us about its quality, possible aging or state of charge. Nor is it possible to take it apart. It could be sawn open, but that ruins it for good and only highly qualified specialists could analyse the content and may be, in certain cases, they could trace the cause of failure.
A battery, when it fails, has to be replaced. That’s it.
A battery is expensive, bulky and very very heavy. Just think: with 10 litres of diesel (= 8.4 kg) and a diesel generator you can charge a battery of 24 V 700 Ah (energy content 24 x 700 = 16.8 kWh). Such a battery has a volume of 300 dm (= 300 litres) and weighs 670 kg!
Also, batteries are very vulnerable. Overcharging, undercharging, discharging too deeply, charging too fast, excessive temperature…. All these issues can occur and the consequences can be disastrous.
The purpose of this chapter is to explain why batteries fail, and what to do to make them last longer. And if you want to have a look inside a faulty battery, don’t open it yourself. It is extremely dirty work and for the price of a new pair of trousers (the sulphuric acid of the battery will ruin them) buy the standard work of Nigel Calder, “Boatowner’s Mechanical and Electrical Manual”, and enjoy the many close-up’s of failed batteries in chapter 1.
2.2. Battery chemistry 2.2.1. What happens in a cell as it discharges As a cell discharges lead sulphate forms on both the positive and negative plates through absorption of acid from the electrolyte. The quantity of electrolyte in the cells remains unchanged. However, the acid content in the electrolyte reduces, something noticeable in the change of the specific gravity.
2.2.2. What happens during charging During charging the process is reversed. On both plates acid is released, while the positive plate converts into lead oxide and the negative plate into porous, sponge-like lead. Once charged the battery can no longer take up energy, and any further energy added is used to decompose water into hydrogen gas and oxygen gas. This is an extremely explosive mixture and explains why the presence of an open flame or sparks in the vicinity of a battery during charging can be very hazardous. It is therefore necessary to ensure that a battery compartment has effective ventilation.
2.2.3. The diffusion process
When a battery is being discharged, ions have to move through the electrolyte and through the active material of the plates to come into contact with the lead and lead oxide that has not yet been chemically converted into lead sulphate. This moving of ions through the electrolyte is called diffusion. When the battery is being charged the reverse process takes place. The diffusion process is relatively slow, and as you can imagine, the chemical reaction will first take place at the surface of the plates, and later (and also slower) deep inside the active material of the plates.