Excerpt from:
MarineHowTo.com LiFePO4 on Boats:
Drop-In LiFePO4 (LFP):
Drop-In LFP batteries are often sold in standard lead acid case sizes eg: group 27, 31, 4D, 8D etc. and
they lack any external communication between the internal sealed BMS and the vessel.
Most of the
drop-in batteries have been Chinese in origin and this is not necessarily a bad thing. All LFP batteries that claim to be
Made in the USA are using Chinese made cells (Except Lithionics) so they are really just "Assembled in the USA".
Wheredrop-ins often
fall flat is in
marine specific engineering. These batteries, as a class, were originally designed for telephone pole mounting where light weight and “drop-in” replacements for lead acid were critically necessary for the solar powered street lighting industry. The demand for this type of battery, especially in third world countries, is staggering. I know many boaters
assume we are a large market but we are not and no, many of these drop-in manufacturers are not specifically building “marine” batteries for us, though they may be “marketing” them to us. The application of a “
marine” sticker, and perhaps even a well marketed brand name, on the plastic box, does not always denote a product that is well engineered for a cruising boat.
Most of the “A” graded LFP cells used in these Chinese drop-ins are sold into the street lighting industry. Sadly for boaters this can mean the low grade “orphaned” cells wind up in batteries that may look the same but are sold on Ali-xxxx, eBay or through other less reputable sources.
Drop-ins will likely be the future of LFP, and there are currently a few good manufacturers working to improve the shortcomings but, in my opinion, they are still not
prime time ready. When they have improved the engineering it will
definitely get mention on MHT.
Drop-In Pit Falls for Marine Use:
#1 Current Handling – The current rating of the internal switch that protects the battery is often too small for the task. These batteries routinely use multiple tiny little MOSFET switches that often can’t handle the loads imparted by many cruising boats. On board devices such as a bow thruster, windlass, large inverters, electric winches, electric cook tops, massive alternators, starter motors or chargers are very very common on-board cruising boats these days. These are exactly the devices many boat owners are hoping to see a gain in performance from when switching to LiFePO4. Look at the
contactor ratings companies such as Lithionics, ex Genasun, Victron & Mastervolt use/used for “
marine specific” LFP batteries. What you’ll often see are 500A continuous rated Gigavac, Blue Sea ML Series, Tyco or other similarly rated contactors being used. Companies building “marine specific” LFP batteries know what boats need. Companies re-stickering streetlight pole batteries, or simply copying them, do not use this type of contactor. What you’ll often find is some wimpy 50A continuous rated MOSFET switch installed inside a 300Ah LFP battery! Ouch. Here's a hint" If a manufacturer is trying to sell you a "marine" LFP battery and suggests not using it to start the motor... Well, you guessed it, look elsewhere....
#2 Vibration – Many of the cheaply sourced drop-ins are using 18650, 26650 or 32650 cylindrical cells inside the battery case. In a worst case, a 100Ah LFP battery, built from 18650 cells, would need a grand total of 364 cells with two connections per cell. Hows that math work?
18650 Cell = 1.1Ah (An Ah rating for an 18650 cell above 1.1Ah should be considered suspect)
91 Cells Make Up Each 3.2V cell
Four 3.2V Cells Make Up a 12.8V 100Ah Battery
91 X 4 = 364 18650 Cells
Positive & Negative
Connections Inside The Battery =
728
If the manufacturer uses 5Ah 32650 cells, and some do, we then only need 80 cells total, and 160 spot welds or bolted connections to potentially fail or work loose. (32650 cells are available in bolted or spot weld versions)
The connections, with 18650s’s, are almost always spot welded to
end boards that make up the individual cells. So in a single 100Ah battery, made of 18650’s, just to connect the cells, we have as many as 768 spot welds to rely on. Beyond that we have all the internal wiring and BMS connections. These
spot welded assemblies are often just dropped into the polypropylene case with no other support or vibration dampening material. To be safe always be sure to ask the battery supplier to furnish third party vibration testing results or testing to UL or IEC vibration standards. These days Ultrasonic or Laser welding is the preferred connection method for the automotive world and they have and are rapidly moving away from spot welding.
#3 Internal Wiring – It is not uncommon to open a 100Ah drop-in battery, rated at 1C, and find 10GA or 12GA wire feeding the main positive and negative terminals. When someone finds a 10GA or 12GA wire rated for 100A, under any safety standard, please let us know.
#4 BMS – Some of the
drop-in batteries lack a BMS altogether and others only have a single low rated relay that disconnects the bank on low or high voltage only. These batteries should also have temperature protection, for each 3.2V cell, but many don’t. The BMS protection relay (really just a MOSFET switch), as discussed above, is often rated at a ridiculously low amperage capability of around 50A and maybe as high as 100A, if you’re lucky. The drop-in manufacturers are essentially relying on you
paralleling multiple batteries together and
sharing the load across the questionably suitable, under-engineered, (for cruising boat use) BMS switches.
#5 Non-Communicable BMS – This one is perhaps the most dangerous aspect on-board a cruising boat. For a trolling motor? Who cares.. It’s not powering anything critical.. For a house battery, on a boat that ventures off-shore, and is powering critical navigation and safety equipment, this can create a dangerous situation. A
non-communicable BMS is one that cannot communicate externally with the vessels charge and load systems or even you the owner. It has no means of externally communicating or sending/sounding warning alarms or activating relays/triggers to properly and safely disconnect charge sources or give ample warning of an impending BMS disconnect.
Ask yourself what happens when your 150A alternator is in bulk, supplying all the current it can, and the internal BMS decides to “
open circuit” or disconnect the battery from the boat? I’ll help out a bit here.
A) The alternator diodes, unless avalanche style (pretty rare in high performance or stock marine alternators), can be blown and the alternator will be rendered non-operable. Two years ago we did exactly this. Using the alternator test bench here at CMI the alternator was running at full bore charging an LFP battery The “system” I set up had a 3A dummy load on to
simulate navigation electronics. With the alternator running at full bore I disconnected the battery just as an internal sealed BMS would do to protect the LFP cells.
Poof went the alternator diodes! Worse yet the voltage transient I recorded on the “load bus” (think your navigation electronics) using a Fluke 289 was 87.2V. This is enough to tosat just about any 12V electronic device... Ouch!
B) If the boat is wired, as is typical with drop in batteries, the voltage transient caused by the open circuited alternator will now directly feed the DC mains and potentially destroy your navigation equipment. A
properly designed BMS, in this case, would open a relay that would
de-power your charging sources on the input side, thus
shutting the charge sources down correctly and safely with no risk of a damaging voltage transient. For a large inverter/charger it would de-power the AC input side, for an alternator it would de-power the field wire or regulator B+, for solar it would open a relay in the PV feed etc. etc./ With a drop-in battery, that features a sealed BMS, you have no way to do any of this.
NO EXTERNAL BMS WARNINGS OR EXTERNAL COMMUNICATION CAPABILITY CAN BE DANGEROUS
#6 Series Wired System – In a parallel wired bank one battery BMS dropping out only creates problems when it re-engages into a different SOC to the rest of the bank. It can actually toast the internal mosfets if the banks are at a gross level of imbalance when re-connect occurs. Manufacturers such as Lithionics carefully control this with an
external BMS that communicates between paralleled batteries. With a series bank (or a single drop-in LFP battery) one batteries BMS taking itself off-line spells disaster at sea. I know an AliExxxxx buyer who hit a bridge abutment in his electric boat using a 48V series bank of drop-in batteries. It did a few thousand in damage to the boat, and his pride, but it could have been much worse. The owner had ZERO warning the battery was about to disconnect itself before he 100% lost power while going under a bridge.
#7 Fan Boys/Girls – Please, please, please when watching videos on YouTube or reading blogs showing cruisers touting LFP drop-ins, keep in mind this is a technology they may know very little about other than from the glossy marketing materials. Also, many of these installs may have been
HEAVILY SUBSIDIZED BY THE BATTERY MAKER. I know this because I am one of the folks who’s been contacted by companies trying to get web presence from high-view YouTubers or high reader volume bloggers. CMI/MarineHowTo.com will continue to politely decline these offers until they can get their engineering to a place we feel is of a safe design level for a marine application. Unlike an RV, cruisers can’t just pull over and call AAA from the middle of the Pacific Ocean when the $hit hits the fan. Bottom line here is don’t rely on the research of others, including this article and please educate yourself. Going into LFP blind can cost you a venerable
boat load of money....
#8 Catastrophe Level Protection Only - Owners considering purchasing any drop-in battery need to understand that the sealed in-built BMS offers catastrophe level protection only. What does this mean? It means the BMS is there to prevent thermal runaway and total destruction of the battery only. You will still need to have charge sources that can be custom programmed to ensure a "long life" charge algorithm, one suitable for LFP, and to never simply rely on the BMS to protect the battery for
cycle life longevity. We have had a number of drop-in LFP batteries come through our shop ruined in less than a few hundred cycles because the owner was led to believe they were just that "
drop-in". If you expect anywhere close to 2000 cycles it is not just
"drop in"...
What I’d like to see to support an LFP drop-in for a cruising boat?
#1 Externally Communicable BMS that can control charging sources safely when approaching a high voltage event.
#2 Internal BMS contactors / switches capable of the amperage’s used on cruising boats. A 50A continuous rating on an LFP battery is simply unacceptable and under-engineered for the specified use.
#3 Individual cells that have passed UL testing
#4 Third party vibration testing data or UL testing for the entire battery, not just the bare cells
#5 Verification of internal cell matching
#6 Transparency of what manufacturers cells are being used internally. There are a lot of questionable LFP cell makers in China these days.
#7 Internal wiring gauge specifications
#8 BMS warnings that can
externally warn of a trend towards a disconnect.
#9 BMS low voltage, high voltage and over & under temp protection for each of the four 3.2V cells in the battery
The Future of Drop-In?
I do believe we will see at least a couple of manufacturers step up the game on all these points. I have discussed this with a couple of them who are actively working on making these batteries safer and better suited for marine house bank use including heavier duty BMS switches and external communication to avoid dangerous and damaging voltage transients. Some are already using UL tested cells but most lack UL for the complete battery. Currently only Lithionics can supply a complete UL listed battery. If it seems to good to be true, especially if it is sourced from eBay or Ali xxxxx it probably is. At this point in time I still urge a strong
caveat emptor on LFP
drop-in’s for use on cruising boats. Safe enough now for a trolling motor on a bass boat? In some cases yes but, not quite ideal yet for a cruising boat.
PLEASE DO YOUR RESEARCH
When in doubt go with Mastervolt, Victron, OPE-Li3 / Lithionics system or potentially the new Trojan Trillium G-24 LiFePO4 with Canbus. These companies have well thought out marine specific systems.
NEW: In late October 2018 Trojan battery
officially announced their entrance into the LiFePO4 market. The initial formats are supposed to be a Group 24 92Ah 12V (w/CAN-bus) and a 110Ah Group 27 12V (no CAN-bus yet).
I was told the batteries will be using 26650 cylindrical LiFePO4 cells and the batteries, only the group 24 version initially, will be able to communicate externally using the CAN-bus protocol. Kudo’s to Trojan on developing a “drop-in” LFP battery that features external communication! On top of CAN-bus external communication the batteries have a 250A (G24) or 300A (G27)
continuous discharge / contactor rating. Trojan is using
real contactors not cheap mosfet switching, and they can handle as much as 350A (G24) or 400A (G27) for 30 seconds.
Robust BMS contactors is not something we’ve seen out of any of the Chinese “
drop-ins“ or even some "Assembled in the USA" LFP drop-ins. The Trillium batteries can also be charged at up to 1C or 110A for the 110Ah battery. Trojan has also addressed
cold weather charging and gives charging guidance,
in drastically reduced amperage, based on temperature. According to Trojan, the new Trillium LiFePO4 batteries were designed & engineered in the US and are currently being built & assembled here, at least for now.
The 26650 cells (26mm diameter X 65mm long) used inside the Trillium’s are not being manufactured by Trojan but, they are built to Trojan’s specifications under contract in China. In other words they are not just purchasing a commodity as others are and the cells are specifically manufactured to Trojans exacting specifications. The release date for the Trillium’s is slated for sometime in Q1 2019. We may possibly see them as early as Jan but an inside source hinted we may see some ship out before the end of the year. Pricing has not yet been disclosed (possibly by December 2018) but I was told they are supposed to be “
competitive” with pricing aimed directly at similar “
drop-in“ competitors. Warranty, if it stays at what we were told, seems excellent but it is not yet set in stone either.
Trojan’s entry into LFP, I believe, helps to legitimize the underlying LiFePO4 chemistry. I also know other “
reputable” US battery manufacturers are working on this too. Up until Trojan entering the LFP arena, the “
drop-in” market has been flooded with US based
sticker application companies not by actual experienced battery manufacturers who have a long term hard earned reputation to uphold.. As soon as I get more information on the new Trojan Trillium batteries I will be sure to let readers know. Until then stick with Victron, OPE-Li3/Lithionics or Mastervolt and you'll have a well engineered battery.
