Lithium Ferrophosphate (LFP) is a flame retardant, stable, safe and proven cell chemistry that has a very good energy density around 325 Wh/L. This cell chemistry can be engineered for various applications by adjusting the ratio of elements to provide high performance characteristics. E.g. the DCS marine battery range runs 2C cells, which means our little 75Ah battery will discharge comfortably at 75Ah x 2C = 150A. The DCS 80Ah Extreme runs 10C cells which means the 80A can comfortably discharge at 80Ah x 10C = 800A but is of course limited to lower currents due the the Battery Management System.
LFP also has very good cycling durability between 2,000 ~ 12,000 cycles can be achieved depending on how well the cells are managed, and the lowest rate of capacity loss (aka greater calendar-life) compared to other lithium cell chemistries.
Battery cells are simply a bunch of resistors with the ability to store energy. A 100Ah battery pack has a different resistance characteristic compared to a 50Ah battery pack, that theoretical difference in resistance is 2:1. So if you connect a 100Ah battery in parallel to a 50Ah battery there is no way for these two batteries to equalise and therefore you can’t charge them correctly. So for example connecting a 60Ah calcium starting battery to a 120Ah AGM via a VSR (Voltage Sensing Relay) you cannot charge both batteries correctly and from that day onwards you are prematurely destroying both battery packs. Same theory applies with lithium’s it’s still a battery pack.
What’s the solution? A DC-DC charger, you now have a permanent point of isolation (meaning that both batteries are never connected to each other in parallel). The DC-DC charger takes the surplus power from battery A (engine) and chargers battery B (aux/house). This device now allows any battery capacity and or chemistry to be used.
Yes you can, but lithium’s have a different voltage curve, so you would still need to use a programmable VSR to dial them in correctly. You would also need to ensure the batteries are programmed to never exceed a 10%SOC variance, any larger and you risk damaging the BMS’s. These devices also draw a lot of power when engaged to so it’s best to run the two batteries in permanent parallel and run a load disconnect instead of a VSR.
Lithium battery cells have a super low resistance so are very easy to charge and very efficient. This level of efficiency means you can charge them at very high C rates. For example if you look at the charge rate of a 100Ah AGM battery the recommended charging current will be around 25A, which is a 0.25C charge rate. If you consider the DCS 12V 100Ah Lithium battery it can be charged at up to 70A which is a 0.70C charge rate. This means you no longer need to consider DC-DC chargers as you can connect our batteries directly to high power charging devices such as suitable alternators, or large buck boosters. For example our popular dual 90Ah battery system for boats and 4WD vehicles, can be connected to alternators up to 160A.
Because our batteries are internally voltage regulated and because our BMS has such a high sustainable peak discharge current they will do an amazing job of equalising very quickly.
When expanding battery packs in parallel to achieve larger capacity battery banks, does not mean that the charging and discharging capabilities are simply added together. For Example;
Considering 2 x DCS 12V 75Ah batteries connected in parallel, to make a 12V 150Ah battery bank. These batteries have a recommended charging current of 50A. So that would be 50A + 50A = 100A with two batteries in parallel. However you always have to work on a 20% safety margin for parallel connections, especially as batteries age over time. So it would be 100A less 20% = 80A. So it would be safe to configure chargers to a maximum of 80A.
The same 75Ah batteries have a maximum continuous discharging power output of 150A. So it’s 150A + 150A = 300A less 20% = 240A. 240A x 12V = 2.9kW. So for example these two batteries would be suitable to support a 3000W inverter.
Considering 2 x DCS 12V 180Ah batteries connected in parallel. Maximum charging current is 60A + 60A = 120A less 20% = 96A. It would be safe to configure chargers at a maximum of 96A.
The same 180Ah batteries have a maximum continuous discharging power output of 180A. So it’s 180A + 180A = 360A less 20% = 288A. 288A x 12V = 3.5kW. So for example these two 180Ah batteries would be able to support a 3500W inverter.
The same formula applies for 3 or more batteries connected in parallel. In the case of our 180Ah batteries it would be 60A + 60A + 60A = 180A less 20% = 144A for maximum safe charging. 180A + 180A + 180A = 540A less 20% = 432A for maximum continuous discharge. 432A x 12V = 5.2kW. So these three batteries could support a 5000W inverter.
The BMS will emergency open circuit the battery terminals to protect the cells. This means there is no longer any resistance in the system. The BMS needs a 12V supply with at least 1A of current to release and wakeup from a cell emergency protection state.
Most mains chargers with a lithium profile will do a slow recovery charge as will most solar regulators. Some chargers on the market today that are advertised as ‘lithium’ compatible still don’t have the firmware to do a slow recovery charge to release BMS’s. If you have a charger that will not wakeup the BMS, easiest way to wake it up is to connect a unregulated solar panel directly to the battery terminals, ensure all loads are disconnected before you do this. Having said that every system should have a suitable low cut off voltage to shutdown loads/accessories so that the batteries are not fully drained.
“Batteries cannot be left flat/empty, if the low voltage cutoff is triggered the battery pack should be fully charged as soon as possible. If access to a suitable charger is not possible, disconnect all loads from the battery terminals. The warranty will be void if the battery pack has been left in a low voltage cutoff state for longer than 14 days.”
Most important thing is to isolate everything from the battery terminals, as cables/loads connected to the terminals causes more power drain as the FET gates have to remain closed to cull the accessory standby loads connected to the battery pack + offset BMS standby power consumption.
Use the following settings:
Charged voltage 14.0V
Tail current 4%
Charged detection time 1min
Peukert 1.05
Charge efficiency 98%
Current threshold 0.1A
C rates: refer to the battery pack capacity
Fully charge to 100% isolate everything from the terminals and leave for max 3 months and then cycle (fully discharge and fully charge) and leave again for 3 months etc…. Minimum 4 cycles per year to not effect the cells capacity.
The reason many factory batteries fall over after 9/12 months is because modern/smart alternators typically drop the alternators voltage output to 13.5/13.6V. This voltage is not high enough to charge wet/calcium/lead acid batteries so from the getgo they are destined to fail prematurely. They are typically under charged to around ~80%SOC at these voltages.
So what happens when DCS Hybrid batteries are connect to smart alternators? Exactly the same thing they get charged to around the same 80%SOC. However because LFP has no memory effect that’s perfectly fine. By only charging to 80% you are further improving the service life of our batteries. It’s no not necessary to charge our batteries over 80%SOC. The only advantage is that you give the BMS a chance to detect full charge voltage and calibrate the SOC readout. So try to plug into mains once a week to fully charge your batteries, especially if your not running any fixed solar supply.
All DCS 12V cylindrical cell packs can be charged as follows:
Bulk: 14.4V
Float: 13.5V
The DCS 12V 180Ah Auxiliary prismatic cell packs (SKU: DCS-12V-180Ah) need to be charged as follows:
Bulk: 14.2V
Float: 13.5V
When the battery pack is discharged down to 11.50V the BMS resets to 0%SOC and now is placed in a relearning state – the pack must be fully charged continuously without stopping to calibrate again. Charge it on a mains charger to 14.60V.
Depending on the usage pattern, best to fully cycle the batteries once every 3 months to give the cells a refresh. To fully cycle a 12V pack discharge to 11.50V and charge to 14.60V.