On Adagio we have a 24 v system for service batteries. The original system was six 12 v 100Ah AGM in series and parallel to get 24v 300Ah nominal and a usable capacity of 150Ah (when new). Our old AGMs started to be really tired so something needed to be done, one of the challenges was that our battery compartment wasn't possible to rebuild since it is build in thick aluminium and very solid, so we needed to find batteries or cells that fits in the old space.
A lithium system needs monitoring and protection from under voltage, over voltage and temperature protection when charging and discharging. It also needs balancing of the cells, for this a serious installation has a BMS to handle all of the parameters. Also the so called drop in batteries have a BMS under the shell. The BMS is designed to protect the battery primarily.
When the BMS detects that one of the parameters are outside of the value that triggers the BMS to protect the battery.
It simply cuts the energy, For example if the BMS cuts for low volt it means blackout on a sailing boat. You can have a rough indication on a battery monitor when this will happen but the longer time since the batteries where fully charged and the battery monitor where calibrated the more unreliable it gets. On a boat (espacially a sail boat) we think this needs to bee considered.
Many manufacturers of so called drop in lithium batteries have a bluetooth connection to monitor the state of the battery.
This can work especially if the bank is just one battery, it gets more complicated if the bank is built using several drop in batteries and you have to log on to every battery to be able to see the state of that battery.
This makes a bluetooth connection in practicality not so useful. One way to handle this is to use a battery monitor that has an alarm function (For example Victron BMV 712) and set the trigger value with a god margin so you get the alarm in time before the BMS cuts.
But on the other hand the more time since the calibration of the monitor the more wrong it will count, and maybe you have capacity left that you don't use because you think it's time to charge based on the battery monitor. This is important to notice if you consider how many Ah you get for the money you pay for the cells or batteries. We decided to not design our system like this.
When charging a lithium system compared to a AGM lead system its not a big differense in the charging profile except for the float state that is used when charging AGM batteries.
Lithium don't like float charging and this will shorten the life of a lithium battery.
We have a Masterwolt charger that have a lithium profile but it still has a float state.
To really take care of the lithium battery we wanted to completely stop the charging when the batteries were fully charged.
If we compare with the car industry and what they say about how EV-cars shall be handled when they are in stock, they shall have a state of charge between 20- 50% of the battery capacity and not have the charger connected.
They shall then be monitored at a certain interval so the battery don't drop to low.
This is for a brand I have worked with for several years, but I don't think it differs much between different manufactures.
On a sailing boat you often have different chargers and so do we.
A part from our shore charger we also have a solar charger and alternator.
The alternator is especially sensitive and it is important for the alternator to always have a battery to work against if you are not able to turn the charging off.
Some modern models like Balmar and Masterwolt has this feature and it can be managed by a BMS.
If this is not done and the alternator is charging only the lithium battery the BMS is going to protect the battery from over charging by turning the battery off. But if the alternator is still charging and have nothing to dump the energy to then the diodes in the alternator is going to get damaged and the alternator will stop working.
There is different ways to handle this,
one way is to have the alternator always connected to an aux battery, for example the start battery or the bow thruster battery and then charge the lithium battery from that battery via DC-DC charger.
An disadvantage with this is that it is not possible to use the benefits of fast charging directly from the alternator to lithium.
A lithium battery has very little internal resistance and the big benefit of this is that the alternator can deliver the energy it once was designed to do. Which in many cases it wont do when charging lead batteries due to the higher internal resistance.
A guideline for charging lithium is 0,5C in charging capacity without any effect on the battery.
For example if we have a 400 Ah lithium bank we can charge with 200 A.
Another thing that is important is to have a well ventilated engine room due to that the alternator is going to work harder charging lithium than lead batteries, especially at low alternator rpm when the cooling fan is less efficient than on higher rpm.
It's a good idea to consider extra ventilation to keep the alternator at its rated working temperature to not lose performance and lifespan.
Yet another thing to consider is that there is not many DC-DC chargers that have as high output as the alternator that is already installed.
And if we don't want to have float charge on the lithium battery we have to manage this on the DC-DC chargers as well as on the shore charger and the solar charger etc.
When we have considered different BMS alternatives and done a lot of measures on different batteries and cells we decided to go with lithium cells instead of drop in batteries and a BMS that had the features we wanted.
During this work we tried to match our list of functions and requirements that was important for us with existing components on the market and different BMS like Daly, BMS123, Victron BMS, Victron battery protect etc.
After we had done some different drawings and tried to match a system designed with these type of products we got to the conclusion that it wasn't possible to build a system after our list of functions with these type of components.
Instead we decided to install 3.2 V 310Ah LiFePo4 cells connected in 3P8S. Our nominal capacity is 930Ah 24 V.
This was the cells that had the best measurements to fit in our battery box. The BMS we decided to use is the X2 BMS from Battery Balance with external BMS monitor. In this system we don't have any mosfets, the system is controlled automatically by the BMS and the Gigavac relays that is designed to handle heavy loads.
The BMS control let us know the status of the battery and if we reach any critical battery limits by a three stage alarm with diodes, and before the BMS turn the system off an alarm will go off.
We can also easily turn on a lead battery backup, we use our 100Ah 24v bow thruster batteries.
The system combines both litium and lead batteries automatically and turns the float stage off at the lithium while the floats is still on at the lead battery.
The BMS is manufactured in Sweden and is "marine grade" CE marked. https://batterybalance.com
We have now used our system for almost two months including a summer cruise in Denmark for three and a half week and 580Nm without any need for any extra shore charging when reaching a port. We have only charged by solar panel 300w 24v and our alternator when motoring. We have our freezer and fridge running all the time and autopilot, navigation etc when we are sailing. We haven't measured exactly our consumption during 24 hours but an estimation is 150-200 A during sailing.
So far we are more than happy with the system and especially the increased performance on all of our chargers.
Now they really reach the performance that are specified.
We have added extra ventilation directly to the alternators for increased cooling, and this works well.
Br Daniel and Magdalena
