System Overview

12v Engine Battery

A conventional vehicle battery is provided for engine starting and axillaries, this battery is charged from an engine mounted alternator through the standard Beta wiring and controls. The auxiliary systems such as the tunnel and navigation lights and bilge pump are powered from the engine battery when the engine ignition is on. This ensures the ability to navigate safely even if there is a problem with the Hybrid system or the 48v Propulsion battery.

To avoid draining the engine battery when the ignition is turned off this supply is disconnected from the engine battery and connected to the Domestic 12v system (see below).

A Victron Blue Power IP20 7A 12v battery charger is provided to keep the engine battery topped up while in the marina or on other shore supply.

48v Propulsion Battery

The 48v battery supplies power to the Hybrid system for Electric propulsion and is recharged by the system when the Diesel engine is running.

The same battery also connects to a pair of Victron Phoenix Multiplus 48/3000/35 Inverter Chargers to provide AC Domestic power and when connected to the shore line provides up to 70A of battery charging (dependant on shore line capacity).  PB Batteries have supplied and installed the 450Ah @C5 traction battery in Chelonian, see below for further info and for details of the various charging systems used on the 48v system.

12v Domestic Supply

12v Domestic supply is obtained from two Victron Orion DC - DC Converters.

A 48/12/360w (30A) unit provides the main 12v domestic supply including lighting, water pumps, Fridge etc.

A separate 48/12/100w (8A) unit is used for the Eberspacher boiler, this avoids some long 12v cable runs, and stops the volt drops caused by the pumps in the Eberspacher which often cause the lights to flicker.

230v AC

A standard Shore Supply connection feeds a Victron Blue Power IP20 7A 12v battery charger which charges the engine battery and a  pair of Victron Phoenix Multiplus 48/3000/35 Inverter Chargers which charge the main 48v Battery.

The Phoenix Power assist function allows a shore supply that is typically limited at 6 or 8A to be used with varying loads without tripping the breaker. The Input current is simply set on a control knob and the Multiplus looks after the rest. Take a look at the Victron site for more info.

The pair of Multiplus units provide 6Kw (12Kw peak) of AC Domestic power which is more than enough for the entertainment, wood pellet stove and lighting systems and is capable of providing power for an onboard Washing machine and Electric cooking.

48v Battery Charging Systems.

Chelonian has three methods for charging the main propulsion/domestic batteries, two driven from the engine and one from the shore supply.

Hybrid system Charging

The Hybrid Marine system operates as a battery charging system when the engine is running. This system provides a multistage charging system providing up to 5Kw of bulk charge (approx 100A). This system is capable of rapidly recharging the main battery system while the engine is running and would be the normal method of battery charging when cruising.

Backup Charging from Engine mounted alternators

When the hybrid system was being planned it was necessary to provide an alternative 48v battery charging system to provide a 48v supply before the Hybrid system was installed and to cover for times when the hybrid system is being worked on.

The solution designed Hybrid marine is two earth free 24v 60A alternators wired in series. The alternators are connected to the batteries at three points the 0v and 48v point and also at a centre tap 24v point. This configuration ensures that the 24v regulators in the alternators operate correctly even if the two alternators are not completely matched.

This charging solution is a simple constant voltage solution which will put a significant charge (60A) into well discharged batteries but its efficiency quickly falls off as the batteries charge up. This system is a backup solution and was tested over a week in October and worked well enough to provide domestic power from a daily charge from the engine.

Shore supply Charging

The Victron Phoenix Multiplus units provide a sophisticated multi stage charging system including equalisation and storage modes. The Multiplus units can provide up to 70A of charging but this will usually be limited by the available shore supply. It is expected that the shore supply will be used regularly to provide an equalisation charge for the 48v battery to maintain its condition.

In theory it would be possible to provide an equalisation charge using the hybrid system, but this would require prolonged running of the diesel engine at light load which at best would be inefficient.

Battery systems

Various battery systems could be used with the Hybrid system, but they must be able to withstand the high charge and discharge currents needed by the system, and provide a reasonable service life.

The Charge and discharge currents needed by the Hybrid system are in the region of 70 - 120A and these may be maintained for several hours.

A typical days use could consist of 4 hours of propulsion @75A a similar period of charging at up to100A charge rate.

Effective Battery capacity varies with the discharge rate, with the capacity reducing as the discharge rate increases. Battery capacity is therefore quoted at a particular charge rate and it is important when comparing batteries to use the quoted capacity at the same charge rates. Typically Leisure batteries are quoted at the 20 hour rate (C20) while traction batteries for industrial applications are usually quoted at the 5 hour rate (C5) to allow comparison I have quoted the C20 rate wherever possible.

Semi-Traction or Leisure Battery's.

This is the type of battery usually fitted to narrow boats to provide domestic power. typically 3 or 4 batteries of 100 - 140Ah (@C20) are provided.

Unfortunately this type of battery is not designed to provide the sustained high discharge rates needed by the system, and would also be ill suited to the high charge rates provided by the system. Using this type of battery would result in extremely short service life and high maintenance (water replenishment).

AGM  (Gas recombination Cells)

AGM batteries such as the Odyssey Batteries offered by Hybrid Marine are "sealed for life" and require no routine maintenance. These batteries are similar in size to the Semi Traction batteries and offer similar capacity at the 20Hr rate. The PC2250 battery offers 126Ah @C20.

This is however where the direct comparison ends. Odyssey batteries are capable of maintaining high charge and discharge rates without damage. The PC2250 offers a 1 hour rate of 80A and can accept a charge rate of 100A without problem. Service life is quoted at 400 cycles to 80% discharge.

Using a bank of 4 x PC2250 Odyssey Batteries with the Hybrid Marine system would allow 1 hour of electric propulsion and a similar period on the diesel to recharge the batteries. So on an 6-8 hour day this would be 3 - 4 charge cycles plus an additional cycle overnight for domestic use resulting in a service life of around 100 days operation. For a typical Narrow boat used for 20-30 days a year this would give a service life of around 3 years with a replacement costs of around £1,200, or around £400 a year.

A boat used intensively over the year would need more frequent battery changes possibly several times a year.

 

Traction Batteries

Traction batteries are typically used in industrial applications such as for Lift trucks. They provide high charge and discharge rates plus can offer large storage capacity up to many hundreds of Ah. Typically they are available as individual 2v cells which are then combined to provide the necessary battery voltage (24 cells for the 48v battery needed for the Hybrid Marine Solution).

Installation of Wet Traction cells is more complicated than with the AGM batteries with provision needing to e made for watering and for ventilation to remove the hydrogen produced during charging and this will add around £700 to the initial installation as a one off cost with only the cells needing replaced at future replacements.

By increasing the battery capacity it is possible to reduce the number of cycles per day, and or reduce the depth of discharge both of which extend the battery life.

The Traction battery fitted to Chelonian was supplied and installed by PB Batteries and consists of 24 x 2v 450Ah cells (at C5 rate) this battery provides over 4 hours continuous electric cruising depending on boat speed. This allows for a single charge discharge per day. The system supplied by PB batteries includes a special cap fitted to each cell that provides automatic watering and gas venting. The gas fom each cell is collected into a seperate tube which is vented overboard without the need for fans and forced venting of the battery compartment,

At the expected rate of useage this would give a life in excess of 400 days or on a 30 day per year usage over 10 years with a replacement cost of around 2,200 or around £220 per year.

A more intensively used boat should still get a service life of several years from these batteries, and if the average discharge was limited to 50% this could extend to around 5 years.

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