In this post, I discuss the thought process on moving to lithium based batteries. This will likely be a multi-post approach. While I hope that I can managed to create an entertaining conveyance of information on this topic. Some of this may become technical and exceptionally boring to the non-engineering minded. I apologize.
I have been attracted to Lithium since before I owned the second Ventolines. As electric cars become more en vogue and the technology more pervasive, I watch with great interest for the opportunity to use these on boats.
Advantages
For off grid applications, such as a cabin or a boat Lithium has many advantages over AGM and lead acid batteries. Energy density: Lithium wins. Weight: Lithium crushes the others. State of Charge: Lithium. Recharge rate: Lithium. There just doesn’t seem to be an area that Lithium doesn’t win. Well there’s charging complexity, catching fire and of course the cost is at least an order of magnitude higher. The sticker shock alone will have you considering whether or not you need energy storage at all.
There are many formulations of Lithium batteries. Lithium Ion, Lithium Iron Phosphate (LiFePO4), Lithium Titanate. All have advantages and disadvantages. Some have higher energy density than others. Some deliver that energy slower or faster. These in turn have advantages and disadvantages for the boat. One characteristic we are looking for is stability. That is, under adverse conditions, will the chemistry have a melt down.
The chemistry that we chose are prismatic, LiFePO4 cells. They don’t have the highest density, but they are very stable. There are YouTube videos of them being shot, and not catching fire. This advantage is huge in a vehicle or boat.
Other features we like about LiFePO4 are its ability to deliver energy over a broad voltage range say 13.6 Volts down to 11 Volts. (we stop at 11.8, but that’s another story). The depth of discharge is advantageous as well. For instance, we routinely take them down to 20% or even 10% capacity. They don’t seem to lose any capacity. And we would never do that with our Flooded Lead Acid batteries. In fact, I doubt we ever went below 60% discharge state. Another advantage is leaving them unused or not attached to a charging source. For weeks, we have let them sit, when we get back they are still at 13.4 Volts. FLA’s don’t like this at all, which is why there are trickle chargers.
Downsides
There are downsides to the technology. First and foremost is cost. They are significantly more expensive in upfront cost. That sticker shock puts many people off. But when looked at from cost per cycle Lithium competes well. There are 2000 to 5000 cycles in a lithium bank, depending on how nice you are to them. Discharge them all the way, cycles go down. Over charge them, with no protection, and cycles once again go down. But surround them with technology that protects them, manage the temps they are used/charged in and you will approach that cycles found in lab testing.
That brings us to the second disadvantage. Treating them as a system of chargers, inverters and batteries versus just a battery. The lithium system includes lots of extra devices to keep you investment safe. Potentially new chargers and inverters, MPPT Solar chargers, a new alternator or a dump or a DC-DC Charger instead of an automatic charge relay. You may even wind up with a hybrid initial system to lower cost. Why all the new equipment?
Lithium must be protected from over discharge and over charging. The equipment that charges and discharges, or monitors the batteries have to be capable of changing their charge profile to support lithium. Most drop in replacement Lithium makers rely on the Battery Management System (BMS) to protect the battery, and it will. However… Not all BMS’ are created equal, some/most will shut down your battery in an overcharge condition, just at the time you need it, say taking on water while the alternator is spitting out 14.7 volts. Which, as it happens, occurred. Luckily, large whale manual pumps saved the day.
So by coordinating each charging source and load to support Lithium you hopefully avoid some of the pitfall or destroying your batteries.
Some areas to expect new equipment
- Shore power charger/inverter: The ability to adjust this equipment so it does not trigger the BMS to do its thing is critical. You want customization of the charge profile and the ability for the inverter to sense when voltage is low and cut off. We went with Victron Multiplus 3000 12V.
- Battery protect – Is essentially a contactor that is closed until a low voltage threshold is passed. When it does it disconnects the load. This is in additional to protection from the BMS. Most BMS will allow you to wire the contactor to it, so it is controlled by the BMS (or possible a remote battery monitor). We went with a Victron Smart Battery Protect
- DC-DC Charger. The main cause of our issue with our dumb alternator and lithium not playing well together was the Automatic Charge Relay. It simply sense if there is enough charge voltage an then connects house bank to starter bank. The DC/DC charger allows us to change the charge profile to support lithum and get rid of the ACR
- Solar controller.
Lithium Battery Build vs Buy
One has two choices with respect to acquiring LiFePo4 batteries. Buy them. Build them. Buying is by far the easiest to do. Just call BattleBorn (10% military discount, if that’s you), Dakota Lithium, Victron, or other drop in replacements. They aren’t cheap. But you get support and they work, oh and a warranty.
I built mine. But know that I am cheap. I am stubborn. I think I am an electrical Engineer, all evidence to the contrary. It is not that hard to do. But, if you have any hesitation at all, just buy prebuilt and call it a day.
I started by ordering 8 prismatic 3.2 volt lithium cells off Aliexpress.com. They are made by Varicore and sold by Liitakola. If you go this route, be prepared to wait 3 months to get them. The order will say shipped the first week, then no status until they show up.
I also ordered 2 XiaoXiang Battery Management systems. They are exactly the same as those sold by Overkill Solar. But… You get no support, so you need to love figuring things out on your own….
The cells themselves cost about $450 per pack (nominal 12V). Each cell is 280 Amp Hours, so both packs give me 560 or so Amp Hours.
Since this is getting kind of long, I will wrap it up. The next article or two, I will discuss building the packs and installing them.