Lithium implementations A comparison between different implementations

Standard lead-acid installation

Standard lead-acid installation
Standard lead-acid installation

This drawing is provided for comparison. Note that usually charge sources and consumers are added at random somewhere on the single power bus (red wire). There is no separation between charge sources and consumers because there has never been a reason to do so.

Lithium only, no disconnectors, voltage based regulation

Drop-in lithium replacement
Drop-in lithium replacement

This is also called a "drop in replacement" as no modifications are carried out. Note that the lithium battery may have a BMS, but it is unable to offer much protection (if any at all) because it is unable to disconnect the battery in case of overcharging or overdischarging. Don't get lured into the false notion that the battery may have an internal disconnector. It doesn't, and if it had one, your equipment would fry at the moment the BMS activates the disconnector while the alternator is running.

Advantages

  • Single bus: No modifications necessary on existing wiring
  • No modifications necessary on charge sources
  • Drop in replacement. Cheap and easy.

Disadvantages

Lithium only, overdischarge protection

Lithium overdischarge protection
Lithium overdischarge protection

Advantages

  • No modifications necessary on charge sources
  • Protection against overdischarge

Disadvantages

Lithium only, overdischarge proctection, charge termination with interruptor

Lithium overdischarge protect, charge term. by disconnection
Lithium overdischarge protect, charge term. by disconnection

Advantages

Disadvantages

  • Dual bus: modifications necessary in wiring
  • Charge sources need to be able to operate without battery. Modifications/replacement of charge sources likely necessary.
  • When battery is fully charged, equipment immediately starts feeding from the battery.
  • No redundancy. If BMS erroneously activates the overdischarge protection, all equipment goes offline.
  • Lithium battery needs to be large enough to provide all reserve power, will thus remain most of the time in a highly SOC which is bad for its health.
  • No reliable balancing possible

Lithium only, overdischarge proctection, charge termination by communication

Lithium overdischarge protect, charge term. by communication
Lithium overdischarge protect, charge term. by communication

Advantages

Disadvantages

  • Dual bus: modifications necessary in wiring
  • Modifications/replacement of charge sources necessary.
  • No protection against malfunctioning/disobeying charge sources (BMS unable to disconnect the battery)
  • No redundancy. If BMS erroneously activates the overdischarge protection, all equipment goes offline.
  • Lithium battery needs to be large enough to provide all reserve power, will thus remain most of the time in a highly SOC which is bad for its health.

Lead-acid/Lithium hybrid

Lithium/Lead-acid hybrid
Lithium/Lead-acid hybrid

Advantages

  • Single bus: No modifications necessary on existing wiring
  • No modifications necessary on charge sources
  • Properly implemented charge termination
  • Protection against overdischarge
  • Protection possible against low temperature charging
  • Protection against malfunctioning charge sources (BMS just disconnects the battery)
  • Redundancy. If the BMS malfunctions, the system automatically falls back to the standard lead-acid configuration
  • Lithium battery can be smaller, thus gets discharged deeper, which is good for its health
  • When battery is fully charged, equipment will be fed from the charge sources
  • Reliable balancing possible without interrupting normal ship operation

Disadvantages

  • A hybrid installation is heavier than a a pure lithium installation due to the weight of the lead-acid batteries.

Conclusion

A lead-acid/lithium hybrid implementation clearly offers the most advantages.

Despite its clear advantages, the lead-acid/lithium hybrid implementation is relatively unknown. There might be a few reasons for this:

  • Ship owners want to get rid of the pesky lead-acid batteries and only focus on a total replacement by lithium batteries. A hybrid conversion might intuitively feel as a "job half done".
  • Lithium battery vendors want to sell as much capacity as possible.
  • So far there were no Battery Management Systems specifically designed for hybrid installations.

We hope to bring the advantages from lead-acid/lithium hybrid installations more into the well deserved spotlight. Read more about it on our article about lead-acid/lithium hybrid systems.


Comments

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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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