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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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Hi, I'm interested in your BMS! I’d be very interested in a 12v version. Please add me to your list. Dank u wel.
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I would like to build this project myself, any chance of sharing the software and schematics as suggested on Github?
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Hello Frans, I just want to suggest also to give a look at the BOS LE 200 manual that makes what you already designed with your BMS. https://www.manual.bos-ag.com/le300/ One interesting feature of BOS battery is the sleep mode to avoid deep discharge of the Lithium battery. I don't know if you have already thought to this with "Extensive voltage checking on cell level" or not, anyway I took the occasion to highlight the manual to you! Thanks again Daniele
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Hello Frans! I'm very interested in purchasing your BMS for my boat (if you are going to sell it, of course). I have also some contacts to distribute it in Italy, if you want :) Please let me know if you could be interested. May you have fair winds and following seas! Daniele
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Beste Frans, jouw aanpak lijkt precies datgene wat ik zoek: een LifePo4-aanvulling op mijn loodaccu's (360 Ah) die zonder heel veel gedoe kan worden ingepast in het (12V-)systeem. Lever je kant en klaar (met/zonder LifePo4-accu), en wat zou dit dan moeten kosten? Ik verneem het graag om zo de afweging te kunnen maken.
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In respect to Lithium-hybrid, I see two problems that difficult his implementation: *You need special alternators that can work with Lihium banks (with temperature sensors and external regulated). *Due to his different internal resistance, until the Lithium don't reach his maximum charge the lead bank will be unable to be charged.... that can result in a bad SOC of the lead bank during too much time.
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Hallo Frans,ik ben zeer geïnteresseerd in de door jouw ontworpen BMS en dan wel de Pro versie. Ik heb momenteel 420 amp loodaccu's en heb 8 cellen Eve 304 besteld. Verder heb ik 1600 watt solar panels.
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Any possibility of a 48v version to manage a bank for powering a propulsion motor (as opposed to just a "house bank")?
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https://www.zwerfcat.nl/en/bms-news.html Project was revived April 2022, according to that blog.
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I’m also very interested in this project but also cautious because of the lack of updates. Maar hé, wel een geweldig project!
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Hello I.m interested on the assemble version of the OHybridBMS. The project you made is great, thanks for the work, really usable
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Hi Frans, did you build this OpenHybridBMS? I want to buy it!
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Hi, I expressed interest in your BMS more than a year ago - maybe 2! I’d be very interested in a 12v version. Please add me to your list. Dank u wel.
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Hi...really useful, and a set up I hope to build into a new UK canal boat soon. However can anyone advise as to how we then monitor the combined battery, ie which do I watch, and how to know when charged (or needs charging). Expecting to use Victron BMV 702 energy display Thanks
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Hi Neil, I'm looking at fitting the hybrid system and wondered if you managed to get it up and running,and how it's doing?
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Is there any news with this BMS project? I'm very interested in either buying or building one.
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Goedendag, We zijn erg geïnteresseerd  in de pro-versie van de BMS voor 24 volt. Kun je een indicatie geven wanneer deze leverbaar is en wat deze gaat kosten?
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Is de pro-versie van de BMS beschikbaar? En werkt de hybrid Lithium aanpak zoals verwacht? Ziet er zeer doordacht uit en zou graag zelf willen ervaren.
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Its very iteresting concept. However in my opinion the voltage difference between lead-acid and lithium batteries will cause the lithium battery continiusly charging lead-acid battery. To stop that from happening you need a diode to be placed at the positive terminal of the lead-acid battery.
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No, the voltage of a fully charged lithium battery is less than the voltage needed to charge a lead acid battery. The lead acid battery will very quickly settle on the "float voltage" presented by the lithium battery, and current will stop flowing.
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Please note the depth of discharge graph in the top of the article (red line) shows discharge curve for lifepo4 (13.7V when fully charged) chemistry not traditional Li-Ion (12.6V when fully charged). Li-Ion chemistry has more linear dicharge curve that looks closer to Lead-acid. Therefore the Li-Ion therm in this artical is sort of mental shortcut more then actual chemisrty name.
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When talking about lead acid, does this include Gel and AGM types, they have slightly different charge profiles to typical Lead Acid chemistries, but will they still work in this situation for a hybrid setup?
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Is this a dead project? There's been no update on Github for 2 years and Frans hasn't commented for 6 months.
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Is de pro-versie van de BMS beschikbaar? En werkt de hybrid Lithium aanpak zoals verwacht? Ziet er zeer doordacht uit en zou graag zelf willen ervaren.
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Any chance of you publishing what you have at the moment on GITHUB? This would allow others to peer review, build, and suggest modifications.
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