This post in full was written by an non professional that had no real life experience of using LiFePO4 on boats. This just us sharing our thoughts that we when through when planning for LiFePO4 batteries on our boat. Since this post was written we have gained a lot more knowledge regarding LiFePO4. These were our thoughts when choosing batteries.
Last summer, we had issues with getting the batteries to last while cruising in a for us an extraordinarily warm summer. This was our first summer with Liv, and we had no real experience of how and what to expect from the existing batteries.
What we did know was that the batteries were not in very good shape. With a test tool, the marina measured the batteries at 40% to 44% capacity. We did not think this was going to be an issue since the house battery was massive compared to our previous boats. Our batteries consisted of a starter battery of 110Ah and a house battery bank of 460Ah. The batteries where all AGM deep cycle batteries, and the house battery bank consisted of three 110 Ah and one 130Ah battery. Even at only 40-44 % capacity, they should give us around 200Ah as a house battery.
Since we discovered that we have an insulation issue with the refrigerator, we had to run the refrigerator on manual at a high setting. In the spring, when the weather was colder, we could run the refrigerator on automatic at a much lower setting. All the electronics on the boat is also drawing much more power than what we are used to on our previous smaller boats. The end result was that we had to stay shorter periods at moorings or use shore power / run the engine to charge the batteries.
I had also noticed that the wiring to the batteries were not optimal. But I will write about all the rewiring and improving the insulation on the fridge in another post.
Our original plan was to use a 12V 180Ah LiFePO4 house battery consisting of two Winston 90Ah batteries. A simple solution that would easily fit in the existing battery compartment. But since we have decided to go for an extended cruise in 2020, we realized that we would need a much larger battery bank.
Initial requirements for new batteries:
- Increased capacity
- Faster charging
- Must fit in the existing area for the batteries
Increased capacity and faster charging are easily solved by switching to LiFePO4. Even if some are talking about triple the capacity with the same amount of Ah compared to regular batteries due to the faster charging. I expect twice the capacity.
When I started investing and doing research on what type/brand to use and everything related to LiFePO4 batteries on boats, I realized that the best solutions would either be Mastervolt MLI Ultra or Victrons LFP-Smart with Victron’s VE.Bus BMS. The only problem with both Mastervolt and Victron is that they are costly. They would make a significant dent in our budget, and we would have to skip a lot of other stuff if we choose either of those products. Since neither of them doesn’t fit at any suitable location on our boat, the decision was easy.
First, I was considering drop-in batteries imported from China. The prices were very low, and the options seemed endless. But the more I investigated, the more skeptic I got.
The information that I could get was either very limited and, in several cases, contradicting. You were supposed to be able to charge them a shorter time than what the BMS would be able to accept. Unclear about what type of cells that were used. Unclear how they were asssembeled. I found a couple that seemed pretty good. But since I had already started being skeptical, I knew that I would never be able to shake off that feeling.
If you would choose drop-in batteries from a well-established manufacturer such as Victron or Mastervolt, you would probably be ok. They have a good track record with these batteries and have the needed options for a complete system. There is just the issue of cost with choosing these systems.
Supposedly there are some good US brands of drop-in batteries as well. But none of them are present in our market. There is also Makspower and Super-B that are present in our market, which seems like good batteries. But neither of them fit, and I have no detailed knowledge of those.
BMS, battery protection and cell balancing
A BMS is a Battery Management System. It is not a Battery Monitoring System, and it is NOT “finely balanced cells with identical performance”. Anyone stating that “finely balanced cells with identical performance” such as Winstons 12V batteries would automatically equip them with a BMS is not being honest. I have only heard good things about these batteries from people using them, and they would be our choice if I could fit enough of them. I just do not like the marketing of these batteries by a local reseller claiming that they have a BMS. Winston and all other resellers are extremely clear that they don’t have a BMS.
A BMS is a good thing, no question about that. The question is if the drawbacks with a BMS for DIY outweigh the positive things with a BMS.
Marine-grade and open circuits
Getting a good BMS for DIY is not that simple. Yes, there are a lot of good BMS’s. But I have not yet found a BMS for DIY that are marine grade and can handle large discharge currents. Open circuits BMS boards on the battery terminals in an marine environment is not a good fit. Might be ok if you are mainly at the docks with the dehumidifier running on shore power or in a less humid climate. Where we are going, we expect to get a lot of corrosion and the climate to be very humid. The risk of the BMS being the cause of an issue is too high with open circuits. But then again, I am no expert. Maybe it is fine to have unprotected open circuits on a sailing boat, even in very warm and humid climate…
Maximal discharge and charge current
A lot of BMS systems have current limits, especially regarding discharge. The current from the start motor or windlass is fairly high, and most BMS cannot accept this load at the same time, also handling all the other loads. When I wanted to a use one-battery-bank solution, I had very few options for BMS’s.
There is a lot of debate about balancing of cells and not balancing cells as well as automatic balancing, manual balancing, top, and bottom balancing if you are balancing your cells.
It seems like well-produced cells such as Winston and CALB from the same batch with matched capacity have very little need of balancing after the initial balancing. That does not mean that they would never need balancing—more of a question of balance all the time or just every other year.
At the dinner table one evening Susanna asked me:
How often and how difficult will it be to check the balance of the cells? I don’t want to have a big project every day, checking the balance of the cells.
She also asked:
What would happen if we have an imbalance when we do an ocean crossing?
This got me thinking. I had originally planned to check manually using a digital voltmeter. If I found an imbalance, I would connect a spare battery and balance the cells by connecting them in parallel with the risk of a very long balance time. Maybe this was not the best option.
Our conclusions / requirements for our boat
The existing space for our batteries is a protected area that can handle a fairly high intake of water into the boat. It is also fairly center and low. And the best place regarding wiring. Our choice was to get as many Ah that can fit in the battery area by using individual cells from a trusted manufacturer.
We wanted bulletproof protection for under-voltage that would also not draw power after being triggered. While we are on the boat, an alarm for over-voltage and an early warning for under-voltage is enough. We can then take mitigating actions. But when we leave the boat, we wanted the possibility to disconnect everything from the battery.
No BMS, easy monitoring and easy balancing
The question of the need for a BMS still remains. There is also no good marine grade BMS available that we could find at the time. But we still wanted to easily see the balance of the cells and be able to do a manual balance of the cells, even during an ocean crossing. What we finally did choose is not what we consider to be a BMS. Even if we have under-voltage protection, over-voltage protection, manual cell monitoring, manual cell balancing.
Our system that we will install
- LiFePO4 battery: 12V 320 Ah with 8 x 160Ah Winston Wide cells in a 2P4S configuration
- Over voltage, temp and under voltage warning: Victron BMV-712 battery monitor with alarm activated
- Under-voltage protection: Battery Brain Type 1, switches off everything at 11.8 V and 0 consumption at disconnect with a manual override
Secondary under-voltage protection at 11.5 V with relay functionality from BMV-712 disconnecting the battery using the ML-RBS battery switch.
- Over-voltage protection: Relay functionality from BMV-712 disconnecting the battery using the ML-RBS battery switch at 14.6 V.
- Main battery switch: Blue Sea ML-Remote battery switch with easy accessible remote switch
- Circuit breaker for MPPT: Blue Sea circuit breaker
- Cell balance monitor: ISDT BattGO cell logger with pre-wired cables to the battery to easily check individual cell voltage
- Balancer: Evlithium QNBBM 4S/12V with pre-wired cables to the battery for easily balancing when needed
The 320Ah is more than we had hoped to fit. Some smaller cells that would give us enough Ah would still not fit. By first parallel connecting four pairs of cells and then serial connecting the four pairs to a 12 V battery will reduce the risk of an individual cell imbalance to the same as risk as using four larger cells.
The choice of using Battery Brain for under-voltage protection is because it can handle both charge- and load current compared to e.g. Victrons Battery Protect or Alfatronix PowerTector that can only handle either a load or a charge current. This is hard to accommodate with a charger/inverter combo unit. The Battery Brain is triggered at 11.8 V and has a manual override button. This is more than enough to start the engine at sea.
The BMV-712 battery monitor will be configured to warn when both the charge current is too high or give early warnings of under-voltage, before the Battery Brain is engaging.
When leaving the boat, we will switch off the battery with the ML series remote switch. The switch will have an easily accessible remote switch at the DC panel. All positive cables are connected after this switch except for the sensor cables for the battery monitor, alternator, and charger.
Even if the MPPT is configured for lithium, we will install a circuit breaker to be able to disable the solar panel from charging when SOC is 100%. This will completely disconnect the MPPT from the rest of the system.
EDIT: We later choose to install a DC isolation Switch instead to disconnect the panels from the MPPT:s.
On the cells, we will pre-wire connections for both the BattGO and the QNBBM. When we check the balance, it is just by simply plugging in the connection to the BattGO. This neat little device will indicate the individual voltage of each cell and clearly show if there any imbalance or not.
If there is an imbalance that needs to be balanced, the QNBBM will be connected and will start to balance all the cells. The balancer will balance at 10A peak and 6A long term continuous current per cell. This is a much higher balancing capacity than what most BMS systems can provide.
Even if the balancer is not marine grade, the balancer will only be used when and if there is a need to balance the cells. When the balancer is not used, it will be stored airtight with silica gel bags.
Keep in mind that these are our thoughts only. What is best for you might be something completely different. We are not professionals or experts. These are just our reasonings and thoughts that we went through when choosing a LiFePO4. All cabling, switches, circuit breakers, fuses, shore power chargers, alternators, alternator regulators, solar panel regulator, etc. must be considered when using LiFePO4 batteries.
When everything is installed, and we have more experience of using the system, we will share this in later posts.
Below is a great article that goes into more technical details of LiFePO4 on boats