Lithium battery system
1. Capacity requirement
Consider the capacity requirement with regard to the charging capacity. Although the charging capacity is large to recharge quickly, the capacity must be dimensioned after the charge limitation <0.5C. This means that if the solar, alternator and others can charge 150 A together, the capacity of the battery must be at least double (> 300 Ah) and preferably by a margin, ie in this example ≥400 Ah. Charging faster than 0.5C shortens the cells service life.
Consider capacity needs with respect to energy balance including any solar charge. Note that the X2 BMS makes it possible to safely utilize 95-97% of the true capacity when needed, which explains why the capacity does not have to be as large together with the X2 BMS compared to other BMS ‘in the market. However, it should be added that the capacity can not be too large because lithium does not need to be fully charged in each cycle which is the rule for lead batteries.
2. Battery compartment
Plan the installation and placement of the battery. It is always easiest to use existing battery compartment with regard to cables. It also simplifies installing one Cell Pack. However, if there is a need to divide the battery into two (or more) Cell Packs, there is the possibility of an extra X2 BMS unit and relays (common BMS Control).
Lithium batteries can be charged up to +45° C and discharged at temperatures up to +55° C. These limits include margin and are the setting of the X2 BMS and therefore recommendation that the battery compartment does not exceed +45° C. There is also a limit for charging in freezing degrees which for X2 BMS is set to +2° C and should be considered as well.
Measure the dimension of the battery compartment. Please note, height may be a limitation. Prismatic cells should be placed upright (according to all cell manufacturers).
Make a sketch of the location and consider the dimensions according to step 3 when choosing the Cell Pack. Also consider compression plates and how to attach. It is important that the Cell Pack is clamped efficiently so that it does not move, which can otherwise stress terminals if they are given the task of mechanically holding.
3. Choose Cell Pack
+ Compare dimensions on Cell Pack and decide which model. When ordering from batterybalance, make a request where the battery terminal (+/-) connection is desired (which side of Cell Pack).
4. BMS and Relays
Choose a system that suits existing installations. X2 BMS manage all devices of different brands. Consider how much current the system can handle. If there is a continuous (>30 min.) Current > 100 A or peak currents > 200 A, we strongly recommend choosing a mechanical relay (contactor) instead of SSR as for example a remote controlled Victron BP (= MOSFET based electronic switch). FETs are often the weakest link in the system.
Between the consumers (incl. nav.instruments and autopilot) and lithium battery there is a “switch” for all BMS’ and if it is a MOSFET, all current passes 1 pcs (or 2-3 pcs) small silicon that is only a few millimeters large. If it breaks, it will be blackout.
A mechanical relay can handle 500+ A and without losses. An SSR has large losses at high current but advantage with low hold power and relatively cheap. X2 BMS has an output for connecting a latching (bi-stable) relay that does not continuously draw hold power and X2 BMS also has a built-in pre-charge to protect the relay.
Select the type of relay that the X2 BMS should control.
+ Select BMS Kit (with or without Gigavac relays).
+ Select the desired length (m) of cable between BMS unit and BMS Control
+ Select the desired length (m) of tap wires between cells and BMS unit.
System might require extra busbar, main fuse and signal relays.