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lifepo4 independent and combined battery banks

SV Lyric

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Oct 11, 2021
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***Parts of this post were originally posted as a comment in another section but I have moved it here after receiving a suggestion to start a new thread***


Hello all. I'm a new member here with a solar system on my sailboat and I am looking to upgrade away from lead acid.

I wish to switch to lifepo4 but I have concerns if a single cell should die or if a battery bms shutdown should occur at a critical time eg poor weather. I am trying to design a independent but shared load 2 bank lifepo4 system with a lead acid start battery to replace my tired all lead acid system. My hope is with two (semi) independant lifepo4 systems I will lessen the likelihood of a sudden loss of power to navigation equipment and my beer fridge. :)

A basic schematic I have started is attached. I would appreciate knowledge and feedback anyone has to offer that could simplify the system or errors I might have with wiring or device use.

My schematic at this point for simplicity does not depict switches or fuses.
I already have bms(s) and the lifepo4 cells on hand and would prefer to use them for this build.
 

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Those Victron Argo diode splitters are not needed, too complex and something else to fail.
Connect the battery inputs together and the outputs together. Feed all chargers to the batteries and take your loads from the parallel connection of the batteries.
You dont need the isolated version of the Orion, the non isolated version will be OK for your design.

With the Overkill BMS you can control the batteries via the app if required. Should any failure occur within one of the batteries the other will take over.

The 30 A Orion takes up to 40 amps from the charging system, operating two chargers could overload the alternator at low engine speeds.

Do you have power winches or power windlass or power inverter?

Mike
 
Those Victron Argo diode splitters are not needed, too complex and something else to fail.
Connect the battery inputs together and the outputs together. Feed all chargers to the batteries and take your loads from the parallel connection of the batteries.
You dont need the isolated version of the Orion, the non isolated version will be OK for your design.

With the Overkill BMS you can control the batteries via the app if required. Should any failure occur within one of the batteries the other will take over.

The 30 A Orion takes up to 40 amps from the charging system, operating two chargers could overload the alternator at low engine speeds.

Do you have power winches or power windlass or power inverter?

Mike
Thank you Mike. I have a powered dc windlass. I need to check the amperage. I don't use much inverter power beyond the needs of a laptop/tablet or a cell phone.

The alternator is a concern that I have. I have a "new" never-used Balmar ARS-5 from circa 2012 (will need Valeo mod kit) that I had planned to use to limit the alternator and monitor alternator and lead acid temperatures. Won't the ARS-5 protect the alternator during low rpm and derate as temperature increases?

If I understand correctly you suggest that I use a 4s2p configuration, to cut out most of the gadgetry, each having it's own bms but sharing charger input. If one cell fails I will only lose half my amp capacity. Is there a concern of charge issues due to internal differences in each string of cells leading to a unbalanced and undercharged system? That was at least my fear and reason for only combining the two banks output with the Victron diode combiner but not input. (I assume that the Orion or Syklla should be programmed to cut charging prior to the bms limit settings.)

I had also considered to separate house banks where only one bank could be utilized at a given time but that required battery switch flipping to charge or use the appropriate bank. The boat had something similar with lead acid when I bought it but I wasn't a fan; the batteries have a tendency to run low when switching is inconvenient.

-Matt
 
I have a powered dc windlass. I need to check the amperage.
The starting current will be much higher than the running current, this could be a problem with the BMS/cells, although you may be OK( the Overkill BMS allows short term overload).
Won't the ARS-5 protect the alternator during low rpm and derate as temperature increases?
should do, not quite sure how the Orion would respond. You may need some way of selection one or both Orions, easy control via the H and L control pins.
leading to a unbalanced and undercharged system?
reports on this forum suggest that the packs in parallel 'share' within a few%. With the BMS app its easy to keep a watch on the batteries and if necessary take action.
where only one bank could be utilized at a given time
could lead to an imbalance, but would be easy to implement as you can turn off the BMS charge or discharge path via the app.
However for safety and maintenance a mechanical isolation switch on the output of each battery would be useful.

Mike
 
Mike I have been thinking about your windlass question. The present windlass is underpowered for the boat and when it dies I would end up with something bigger. At present it is on a 12v 50A separate circuit from a previous owner. It is so old I actaully don't have any documentation on it.

Perhaps longterm the overkill bms is not my best choice and maybe I should look into the new REC bms as I have heard it can integrate with Victron equipment.

At the moment I already have 2 overkill 12v 120A bms so I would like to give it a go rather than shelf them. My lifepo4 cell wiring build options as I see it are:

▪︎Option A: two 1P4S (12v 200amp/hr each) each with a bms and combined at the main bus terminals
▪︎Option B: a single 2P4S (12v 400amp/hr) with 1 bms
▪︎Option C: a single 2P4S (12v 400amp/hr) with 2 bms in parallell

I have attached sketches depicting options A , B and C.

I would love to hear people's take on the pros/cons of each setup. (safety, issues with charging or balancing cells, max current draw limitations). I wonder how option C would work with cell balance and voltage SOC sense or if one bms would need active cell balance disabled. Has anyone tinkered with this?
 

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I would use option B. I see 2 separate banks and 2 BMS as added complication that is not necessary.

As far as C, why would anyone ever use 2 BMS on one bank? Makes no sense to me.

If you want a BMS that works well with Victron equipment look at Electrodacus. Not current limited and an excellent BMS.
 
The rational of double BMS's was to increase amperage. My normal loads are small fractional C rates way within the BMS safety range but Mike brought up the good point of potential high startup currents for a windlass.

B is definitely the simplest.

Thank you for the tip on Electrodacus; I haven`t heard of them. I will read up on them.
 
The rational of double BMS's was to increase amperage. My normal loads are small fractional C rates way within the BMS safety range but Mike brought up the good point of potential high startup currents for a windlass.

B is definitely the simplest.

Thank you for the tip on Electrodacus; I haven`t heard of them. I will read up on them.
Electrodacus - and a few others - control charge sources and loads without the current traveling through them. To my mind a much better way to go. From the beginning I didn't understand the logic of a conventional BMS - Daly, etc.

My main system is Electrodacus. I am making a portable powerpack for an electric trolling motor for a dinghy and am using an Overkill Solar BMS for that but it will always be quite low current.
 
You may want to watch Emily and Clark’s YouTube channel. Clark is a creative engineer-tinkerer who is currently developing a BBMS- battery bank management system to do a mixed/multiple bank system similar to what you describe. He strongly advocates for a FLA/LFP mixed system for charge profile reasons and reliability which seems to be your very valid concern.

DF
 
I do believe that keeping a traditional battery between the alternator and the lifepo4 side is good insurance against unintentional voltage spikes from what I have read. I guess the holy grail is a bms that shuts down the alternator prior to cutting off charge to protect the batteries. I can`t go that way completely so the lead acid battery in the middle is my compromise.
 
Victron Orion Tr Smart DC to DC charger question...Does anyone here have experience using the Orion to sense a running alternator? If so, how well is it working?
 
oops.... delete this post... wrong place for my reply (now erased)
 
You may want to watch Emily and Clark’s YouTube channel. Clark is a creative engineer-tinkerer who is currently developing a BBMS- battery bank management system to do a mixed/multiple bank system similar to what you describe. He strongly advocates for a FLA/LFP mixed system for charge profile reasons and reliability which seems to be your very valid concern.

DF
anyone else got thoughts on the BBMS concept? Looks like with my scenario in needing Lead still in an aux. bank (cause of large electric winches do not like Lithium in general) with an alternator made to handle heat of full working load in the heat of Afghanistan in the middle of a fire fight..... that the bbms may fit my needs well.
 
Well I have decided to shelf my overkill bms's and I will buy a REC active bms (victron compatible model). It is able to communicate with the victron gear thru the canbus and external relays can be used as well.
 
anyone else got thoughts on the BBMS concept? Looks like with my scenario in needing Lead still in an aux. bank (cause of large electric winches do not like Lithium in general) with an alternator made to handle heat of full working load in the heat of Afghanistan in the middle of a fire fight..... that the bbms may fit my needs well.
Are you talking about the BBMS from Clark of the sailing video blog? They just came out with those. I bought one because my best solution involves keeping some lead acid in parallel too (wind turbine, etc.). Bought the plus version with the screen, but it will be awhile before I get the other components and set it up. So I'm curious of others' experience too.
 
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Are you talking about the BBMS from Clark of the sailing video blog? They just came out with those. I bought one because my best solution involves keeping some lead acid in parallel too (wind turbine, eyc.). Bought the plus version with the screen, but it will be awhile before I get the other components and set it up. So I'm curious of others' experience too.
yup talking about theirs. I've purchased a Plus version as well. Looking at setting up an install configuration service for mostly Overland rigs with his product(s) once he is able to secure more mass production
 
Victron Orion Tr Smart DC to DC charger question...Does anyone here have experience using the Orion to sense a running alternator? If so, how well is it working?
I’ll be using one to keep my starter battery maintained (went with the 18A isolated unit as it was the cheapest. Given how flat the charge curve is on LiFePO4s, I don’t think the built in alternator detection will work too well. Instead, I’ll probably hook something up through the automation tools available on the Cerbo (relays, and some Node Red programming under Venus OS Large).
 
You will definitely want to think through your implementation. The only reasonable option from the ones proposed is option A (essentially building two drop-in replacements and hoping the internal BMSs don't drop both batteries out of your system at the same time - which is the major problem with any of the options outlined).

We spend about a year designing a system, with our designs migrating from building multiple individual batteries with Overkill (like) BMS system to installing a fully integrated system with a REC BMS controlling everything (victron multiplus, victron MPPT, and Wakespeed external regulator). In our final system, the REC BMS controls all charge and discharge sources via CanBus communications, and each device fails gracefully if CanBus goes down.

The following is a list of recommended internet resources to consult.
The following are a number of resources I have consulted in developing my LiFePO4 house bank.

https://marinehowto.com/lifepo4-batteries-on-boats/ - One of the best overviews of the subject by an industry expert.

https://mvdirona.com/2017/06/a-more-flexible-power-system-for-panacea/ - excellent case study by a Nordhavn owner that did his own system a few years ago - probably overly conservative.

http://www.mvtanglewood.com/search/label/Lithium Batteries - Another Nordhavn owner with an extensive blog that build a LiFePO4 system for an off-grid home as an experiment for his N68 under construction. Again, lots of great information, but took a more technical route than is warranted for coastal cruising (IMHO). Really liked the idea of using a PLC as a BMS, but in the end the (for us) the REC BMS did what we needed at a reasonable cost.

https://seabits.com/victron-wakespeed-battle-born-power-system/ - Local marine technician that installed a system using drop-in replacement LiFePO4s from Battle Born. I like a number of things he did in this install (but drop-in replacements are an expensive option). I believe this install also assumes that charge and discharge devices will behave, as I don't recall any fail-safes for all batteries dropping out of the system due to over charge or over discharge situations.

The major decision points and obstacles for using LiFePO4 as a house bank:
Decision - DIY bank, drop-in replacements, or commercial system (Victron, Mastervolt, etc...).
Obstacle - How to charge bank with alternators without overheating (Options - regulated alternator, Alternator to Battery Charger, Charge Lead Acid with Battery to Battery charger).
Decision - DIY Bank - What sort of Battery Management System

Keeping a FLA bank in the system can solve some problems, but that too needs to be carefully designed as LiFePO4 banks in parallel with FLA can create problems due to the charge acceptance rates and discharge rates of LiFePO4 batteries.
 
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