Technology: When are lithium batteries suitable for starters and bow thrusters?

Lithium batteries are extremely powerful and ideal consumer batteries, but there are still some applications that push them to their limits or where lead is still the better choice. The best example is the engine battery: as it is only used for starting, it is always fully charged. Optimum conditions for the long life of a normal battery. Lead technology easily manages the high currents required for starting. In addition, a large capacity is not required.

The most important argument in favour of the lead starter battery is its voltage level. As soon as the starter motor is running, the battery voltage drops to below ten volts. However, this voltage drop, which is often seen as a disadvantage, is taken into account in the design of the starter. With lithium batteries, the voltage does not drop so much under load, so the starter motor gets considerably more power than intended. Prolonged starting attempts can then end with a burnt-out starter motor.

Special variants

In addition, a special lithium battery would be required. The BMS of normal consumer batteries cannot cope with the starting currents of the starter motor. The usual protective circuits only supply around 200 to 300 amps. Liontron and some other suppliers therefore have special variants in their programme that are designed to deliver up to 1,200 amps. The power supply for bow thrusters is similar to that of the starter motor. The manoeuvring aids have the same problems. The input power of several kilowatts generates enormous starting currents, and the motors are already operated in overload with lead batteries. The lack of a voltage dip with lithium is therefore likely to lead to even faster temperature shutdown. Both Sleipner and Vetus explicitly recommend AGM batteries.

More articles on this topic:

• What you should know about lithium iron phosphate batteries
• Safety risk? Lithium batteries vs. iron phosphate systems
• How lithium batteries can be optimally charged
• What to consider when choosing a larger energy storage unit
• What DOD and SOC mean when using lithium batteries

Inverters can lead to false alarms from the BMS

Only the modern brushless versions can also be powered by lithium batteries. However, as the continuous current output of the cells depends on the capacity, the batteries should not be too small. The operation of inverters can be tricky.

"Some models are equipped with very large capacitors that are charged in milliseconds when they are switched on. This means that starting currents of over 1,000 amperes can flow," says Michael Kögel from Philippi. The BMS then sometimes senses a short circuit and switches the battery off as a precaution. In this case, the only solution is to switch to an inverter model, in which the capacitors are charged more slowly.

To the beginning of the article series:

• What you should know about lithium iron phosphate batteries