Discussion of ZwerfCat’s hybrid LI/FLA design

[Utahsailor]

A recent thread linked to ZwerfCat’s articles on his hybrid battery system. After carefully reading all of them, his concept and accompanying BMS seemed like a very good approach to adding Li batteries to an existing FLA system. I have looked for a discussion and comments on his approach and can’t find any.
Is there already a thread about this?
Does anyone have ideas (positive and negative) on the concept?
Is an open source BMS a realistic idea (I see s/v Jedi is working on one)?

I’m hoping that a DYI winter battery project is possible.

[Pete7]

Certainly an interesting idea and might suit a small yacht with say 100-150A of LFP and perhaps a small gel battery since the charging voltage is lower than say FLA or AGM.

What will this achieve on a small yacht? well allow the use of short term but high consumption electrical items like a kettle, induction hob or mains hoover which I am loath to do on a pair of FLAs at the moment.

I am still ploughing my way through the website which is here for anyone interested:

https://www.zwerfcat.nl/en/lithium-hybrid.html

With a bigger yacht what do you think are the advantages? Do you have a genny, if so LFP has to be a serious consideration.

perhaps some safety if you connect the auto pilot, FHF and CP to the house bank and the LFP shuts down the lead acid battery can take the load until you sort it out.

I would consider the lead acid battery expendable in a LI/FLA design because the charging regime isn't ideal but so what, one battery every 3 or 4 years isn't going to break the bank.

Pete

[Dsanduril]

A good companion to ZwerfCat's info is the articles on Nordkyn Design's website. He hasn't updated things recently to account for different equipment availability, but the overall schematics are still valid and he also contends that a hybrid system is the easiest way to contend with some of the issues, albeit at the cost of carrying around some lead.

I haven't seen any updates on Frans' OpenHybridBMS page in some time. I have haphazardly taken on a winter project of seeing if I could move things along. I'm inclined toward using an SoC (system on a chip, not state of charge) battery fuel gauge instead of the analog I/O Frans proposes. TI and Analog Devices both make some interesting units that are < $20 and can monitor individual cell voltages, currents, temperatures, and do Coulomb counting all on a single device. Tie that to the ESP8266 and things get interesting. Will see what I can get done myself in the next couple of months.

Being able to use a (relatively) small SLA battery as a "buffer/capacitor" in the system means you could drop in LFP without modifying charge sources and also maintain use of late-day solar capacity rather than dropping it because your LFP is full and you don't want to float it. All makes sense to me, but of course, the devil is in the details.

[Utahsailor]

Why bother with Lithium batteries when you already have a big FLA bank?

I want to gain experience with Lithium batteries and BMS. Many members have projects creating smart controllers that seem superior to commercially available offerings. I’ve purchased an Audrino experimental kit but not a very good EE. This will be a good winter project.

Daily usage varies between 150 and 200 AHr. The 1,100 AHr FLA bank rarely gets out of absorb, so charging is slow and inefficient. The lithium battery will accept full charge from dual Balmar, Xrantex inverter/charger shore power or Honda and the 840 W solar array.

Big current draws drop the FLA voltage. This is annoying with inverter use and may contribute to problems with our ITR diesel heater.

The plan is to make a 200 AHr lithium battery from Winston cells in year one and learn how it all works. This battery should cover most days consumption, charge rapidly and leave the FLAs as a buffer and a 3 days of gloom backup. If lithium prices drop, I can replace additional FLA batteries as wanted. The FLA bank is a 2S5P setup with 6V golf cart batteries.

[Pete7]

Originally Posted by Utahsailor

Why bother with Lithium batteries when you already have a big FLA bank?

The plan is to make a 200 AHr lithium battery from Winston cells in year one and learn how it all works. This battery should cover most days consumption, charge rapidly and leave the FLAs as a buffer and a 3 days of gloom backup. If lithium prices drop, I can replace additional FLA batteries as wanted. The FLA bank is a 2S5P setup with 6V golf cart batteries.

Interesting.

I have just been reading this article by Jimmy Connell and its not good reading for a project. Surprised me, I would have thought someone could have got the sums close enough before they started. Certainly don't want to be in that position.

https://cornellsailing.com/2020/12/electric-shock/

The other document I found recently was this from Victron written by the retired owner of Victron a decade ago, but none the worse for that. The first 7 chapters are the basics but in lots of detail. Ch 8 is a DC boat concept which is what most small yachts have and Ch 9 starts putting some numbers down on paper which look pretty close.

https://www.victronenergy.com/upload...limited-EN.pdf

Having fitted a freezer in addition to the separate fridge last winter, I don't really have a good handle on our new daily usage. The 3 week summer cruise was spent hiding from 3 storms and needing to revert to shore power for heating and dehumidifying, in August One thing for certain, we could do with a more capacity than the 2kw house bank has at present. It's just which way to jump. The known simple solution is just add a pair of gel batteries and change some settings, job done for 8 years. The more interesting science project solution is a hybrid LFP bank.

Pete

[rgleason]

Frans' OpenHybridBMS
Nordkyn Design's website
Stan Honey's Design Description and Diagram (PDF) below is helpful and practical

PowerGate's site used to have an excellent article for a specific Marine Design, but I can no longer find it.

Smart Mosfet Switches
PowerGate LiFePo4 AD-09262017-1-R5
PowerGate LiFePo4 AD-07102019-1-R2
PowerGate Li

[rgleason]

There are very good reasons to have separate charge and discharge/load buses if you want to continue using the LiFePo after a HVD, which is better for the LiFePo and allow operation to continue. Also it allows the battery to be charged by Solar or Alternator after an LVD. This means you need a dual port BMS.

I still have not figured out the relay on a single bus setup is reset after a HVD.

[rgleason]

I found the S/V Mai-Tai "Endless Power" article that is no longer on the PerfectSwitch website (PowerGate Mosfets below, which are expensive but unique). This article is quite good. What I learned:

1. All charge devices have LiFePo regulators that protect the LiFePo bank and stop charging before any protective charge relay needs to operate. This applies to Alternator, Solar, Wind and Shore chargers. All regulation should be changed to conform to LiFePo requirements (Unless you intend to use the ZwerfCat preferred solution with one relay and paralleled FLA.)
2. A charge bus and discharge/load bus are needed to fully utilize the LiFePo when the charge relay has been triggered. (This should only happen very rarely.) -But I still don't know how you reset the BMS and system so that you can use the power in the LiFePo!
3. He used 3 specially configured PerfectPower Mosfets to solve his external system needs, also with a BMS for the LiFePo

Below is the article, if the PDF is small enough.