Lithium but-whatabout... Common marketing inspired mistakes

Misconceptions

These days, everyone has experience with Lithium powered consumer electronics and these experiences might make it hard to believe that Lithium batteries will easily last more than 10 years on a ship. Also, many have heard about Lithium batteries exploding and/or catching fire, and the last thing you need on the middle of the ocean is a big heavy Lithium battery bursting into flames.

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There are a few explanations for Lithium batteries not living up to their promised performance and luckily none of these issues apply to ships. One key difference is that, unlike on boats, consumer electronics rarely use LiFePO4 batteries. Especially with mobile phones and other gadgets, size is everything, and LiFePO4 batteries just don't posess the best size-to-power ratio. So other types of Lithium batteries are used, which are optimized for size, but not for durability and safety. On a ship however, the Lithium battery doesn't have to fit into a ridiculously thin briefcase and even the "not smallest" LiFePO4 batteries are way much smaller than the lead-acid batteries people are accustomed to.

Durability

If you are like me, you leave your laptop almost always plugged in, and after a year when you want to work "cordless" you discover that the "hardly used" battery doesn't last very long anymore. Also, after one year of use, the battery of the mobile phone lost a significant amount of charge capacity as well. Why is this?

Safety

Lithium batteries are generally very safe. If something goes badly wrong, there is always some type of mismanagement or abuse involved, (like overcharging, overdischarging, shortcutting), or physical damage (like dropping, overheating). LiFePO4 batteries are the most tolerant as they don't get easily into "thermal runaway" territory but just start venting when they are being abused. There are video's on YouTube where people fire bullets into LiFePO4 batteries, shortcut them, and throw them in fire bins. The LiFePO4-cells just start venting but they don't explode or burst into flames.

In consumer electronics there is usually not much security against malfunctioning of the battery management system. Most of the time, there is no safeguard at all, so if the BMS gives up the ghost, there is nothing left to pull the plug and the battery will either be seriously overcharged or changed into a timebomb by overdischarging. Also, usually batteries are used which are less safe than LiFePO4 batteries.

On a ship, you can (or should have) a secondary BMS which takes over if the primary BMS fails. And you really should stick to LiFePO4 cells. And never ever use cells which have been overdischarged; they are no longer safe to use, even if they appear to have "recovered". In practice this means that you should only buy Lithium cells which are new and buy them from respected sources.

What about a 45mm calibre anti tank weapon?
What about a 45mm calibre anti tank weapon?
Fully charged cells are punched through simulating the shoot-through from a 45mm calibre anti tank weapon. Test was performed by the Chinese army to determine the safety and stability of the lithium cells.

As visible from the photo, the cells remained complete, did not burn, did not set on fire and did not explode.

How do they get away with it?

Ok, you have heard about that company which produces this wonderfull "replacement" Lithium battery which is supposed to be just a drop in replacement for a lead-acid battery. How is this possible?

A drop in replacement means that the Lithium battery can not be disconnected when it becomes fully charged because that would fry your alternator. So apparently this wonder battery doesn't get disconnected at all. I deliberately use the word "get" instead of "need to". If the battery would not need to be disconnected when it is fully charged this would imply a major break through in the Lithium battery world and the manufacturer of that kind of break-through batteries would not bother to try to sell this battery to sailors at all but would aim its marketing towards bigger and more rewarding consumers like the electric car manufacturers and the space and aviation world.
In reality, the number of companies producing big Lithium cells is extremely limited. Practically all Lithium cells are produced by the following three companies: Winston, CALB and Synopoly. They produce the raw cells and one of these brands is typically used by battery manufacturers to assemble "their" battery. There exists no small marine company creating magical cells themselves which deviate from the characteristics described above.

All LiFePO4 cells, regardless of manufacturer, exhibit the same characteristics, clearly described by the respective manufacturer in its specification sheets: The cells get damaged when the charge current is not terminated after the cells become fully charged. There are no exceptions!

So how can the a drop-in replacement at least seem to work for a while?

Firstly, the majority of the boat owners are not live-aboards. Their boats reside in marina’s most of the time, and the batteries are kept in a "float" condition by the shore power battery charger. A float condition decreases the lifetime of lithium batteries but it won't become dangerous very quickly because the output of the charger is usually quite limited and the Lithium battery converts the excess charge current into heat, which is neglible if the charger is not very powerfull. A more caring boat owner just pulls the plug of the charger and powers down the boat completely when docked in the marina. In most cases the Lithium battery is oversized to the needs of that boat owner so he won’t discover anywhere soon that his wonderfull Lithium battery detoriated quickly to less than 50% of its rated capacity. Even then, most people are, sadly, used to the fact that in just one year time the Lithium battery of their smartphones and laptops also shows signs of aging, so although it is a disappointment, it doesn't come fully unexpected.

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Things get however more problematic in the cruisers and live-aboards world. Sometimes it works on small ships with a small solar charger and an owner who doesn't run the engine for anything more than manouvring at the anchor spot. But many cruisers install big output alternators, 140 Amps is not rare. Double that for catamarans with their dual engines. And the engines are often not used just for manouvring in the marina or to "get home" from a one hour distance, but sometimes run nonstop for days to escape from a large no wind zone on the Pacific. No way you can keep feeding this amount of power nonstop into a fully charged lithium battery without risking a meltdown.
The other power sources are just as unpredictable. Solar arrays are ideally oversized to provide enough power in partly clouded situations, but provide way too much power during a sunny day, especially when the owners are out shopping of exploring some island and not consuming any power. The more one optimizes the situation, the less likely the drop-in Lithium battery is going to fulfill its expectations.

Then of course there is the risk of overdischarging which turns lithium cells into timebombs, which will inevitable happen at some point because the BMS (if there is one) is incapable of disconnecting the load because there is simply no disconnection-relay in the circuit.

Common mistakes

The following, often marketing inspired, mistakes are often made:


Comments

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So, when the lithium pack switches off because of low voltage, how does it recognize that it is ok to switch on again? Manually? If you have two circuits (charge and discharge) like usually with LF packs, you will need to redesign a lot.
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We both seem to have adopted exactly the same approach. I too use esp8266 and wireless connection for everything including remote displays, web interface, remote monitoring, etc etc.i have the hybrid BMS as a stand alone unit that can perform all required protection and control of the battery environment and that communicates via MQTT with a Pi and direct to other esp control units including proportional dump load control and various other power control and optimising systems. I think hybrid rocks!
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Dank je wel voor een zeer interessant artikel!
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Frans, finally someone who sees a hybrid system with the same view! I have been struggling with some of the same questions, even the same thoughts about hardware for a BMS. I would enjoy hearing more as you move forward, and could possibly work on the Pro a bit. I am not an EDA expert, but I have worked with it a bit.
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Frans we zijn zelf bezig met het voorbereiden van een li ion verhaal. Wat ons nog niet duidelijk is, is hoe je omgaat met je alternator. De meeste alternatoren branden door als ze li ion laden zonder dat er een regeling is in functie van de temperatuur ten gevolge van de hoge laadstroom? Hoe vangt jouw systeem dat op? Voor ons is juni 2021 of 2022 de vertrekdatum en hopen we jullie ergens in de pacific nog te ontmoeten. Bert (schip: Evarne)
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