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Discussion Starter #1
I've got quite modest electrical needs, and have decided to build a 280Ah LiFePO4 bank (4s, aluminum cased cells)

I need a BMS of course, but there is a bewildering array of options from ~$25 up to hundreds. I'm just wondering if anyone has recommendations on brands or models.
 

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I have a Victron BMV712 that I am very happy with. It is at the higher end of the price range, but I think it is worth the extra cost. What I like most about it is the Bluetooth connectivity. I installed the monitor itself beside my batteries, and I can connect with it using my phone or tablet using the Victron Connect app. That allows me to check battery status, SOC, real time amperage, historic amp and volts graphs etc from anywhere in the boat, or even on the dock next to the boat.

Sent from my SM-G981W using Tapatalk
 

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So what is a BMS, Big Money Sieve?
 

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Discussion Starter #6
So what is a BMS, Big Money Sieve?
Battery Management System. To manage and protect the cells.

Hes talking about something else.
I dont use a bms on my 360ah li bank
I didnt think that running without a BMS was an option ... do you monitor individual cells manually? or just let it be?
 

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Battery Management System. To manage and protect the cells.



I didnt think that running without a BMS was an option ... do you monitor individual cells manually? or just let it be?
I dont have great battery demands, dont charge near the top and stay away from the bottom
Im not exercising them near their limits, so not exposing any slight differences between the cells...
...at least thats how i look at it
I check them individually about every 6 months...prompted by threads like this
Last check show max diff/spread between the 8 cells was .003v.
3 years or so in use...never plugged into a dock

Do your own research. Your use and needs will vary from others
 

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Emmalina
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I have a Victron BMV712 that I am very happy with. It is at the higher end of the price range, but I think it is worth the extra cost. What I like most about it is the Bluetooth connectivity. I installed the monitor itself beside my batteries, and I can connect with it using my phone or tablet using the Victron Connect app. That allows me to check battery status, SOC, real time amperage, historic amp and volts graphs etc from anywhere in the boat, or even on the dock next to the boat.

Sent from my SM-G981W using Tapatalk
That is not a BMS thats a battery monitor !
 

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Yes a BM = battery monitor, SoC gauge + bank-level voltage display.

BMS is different, for LFP banks specifically, for ensuring cell-level voltages don't go too high or low

may include temperature-based protection

may with expensive ones include charger control

and many try to handle cell balancing as well.

Many BMS failures are what kills LFP banks, "Battery Murdering Systems", especially with cheap ones, build quality can be horrible QA non existent.

It is a huge and very contentious topic, many do go without "a BMS" as such, but do automate some functionality with known-good OTS products.

Close attention by the owner, "human BMS" is a good idea in any case.

Many say Chargery's are "good enough".

Orion
Energus
Emus
Elithion
EPS
ZEVA

also have pretty good reps.

See the "bluetooth BMS" thread on Endless-Sphere for reco's on some cheap-chinese units.
 

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This thread is an example of were we all get into trouble using acronyms and initialisms without first spelling out what we are using the acronyms and initialisms to represent.
 

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I'm fairly convinced I will move to LiFePO one of these days and know just enough about them to be dangerous, so far. I'm fairly convinced I would never operate a cruising system, without a BMS. I guess one could try to stay within the guard rails themselves, but there are too many distractions, when cruising, to trust that would work for me. Beyond the base quality of the BMS manufacturer, I understand there are load limits on different BMS. This has to be paired properly to the vessels demand (charge and draw). I also have the beginnings of an understanding that the BMS can disconnect charge input, to prevent an overcharge/voltage event, and that could cause an alternator to burn out, if its running against no resistence. I think there are ways to rig a sacrificial lead acid battery to take this charge, but perhaps there are other, more sophisticated ways I'm still trying to understand.

I've read articles that make the point that any battery can catch fire, if improperly charged. I know that is true. However, I rarely hear of lead acid batteries doing this, perhaps because they naturally accept less and less charge over time. LiFePO will take full charge untill essentially full and (disclaiming a good scientific understanding here), seem a bit more susceptible.
 

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LFP is much harder to ignite than other LI chemistries, except maybe LTO.

Really only need to worry about during charging.

Redundancy is the key, usually a good charger can be adjusted as to when it will auto-stop.

That setpoint should be well below the maximum voltage on vendor data sheets, for LFP 3.45V is good, but I would adjust that a bit according to the C-rate, if getting maximum capacity were important - it usually is not.

Then an adjustable HVC circuit can be set at a slightly higher bank-level voltage than the charger setpoint, to act as a failsafe for if / when the its regulator fails.

A high-temperature cutoff is also a good idea, and nit just for while charging.

Notice none of these functions need necessarily be provided by "a BMS".

But if you did use one, its HVC would be based on the first cell/group to reach the setpoint

even better than using full bank voltage.
 

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Emmalina
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If you use a battery protection model like a victron BP220 and then connect a programmable voltage comparator for you LVC HVC then add a programmable thermometer to switch on some fans if the batts get to hot and a 4-5 Farad capacitor to protect your alternator in case of OC from the BP .. All covered.
 

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Discussion Starter #17
Well I had hoped someone would have experience with some of these battery management systems (BMS), the internet is littered with them! There are tons of "reviews" of various BMSs out there but they only look at the ease of setup or the slickness of the UI. I haven't found any "long term" tests or reviews that address the quality, reliability and longevity of these devices. I think that there is a lot of legitimate crap out there and I'd like to avoid that. On the other hand there surely is decent stuff too.

If I had invested thousands in name brand lithium cells it would be a no-brainer to spend hundreds more on name brand BMS (Orion, Victron, etc) .

But I've built a 280ah pack with aluminum cased prismatic cells from china for under $350. They arrived in perfect condition, appear never used, bar code intact, listed as grade A, appear well matched (all within .004v out of the box) and "tested" at 105% of listed capacity. I don't have 1000s of dollars of test equipment or decades of experience with these but so far I'm happy with them and as best as I can tell they are quality cells.

I have small electrical demands and never have high discharge rates. I don't need to squeeze every last AH out of this bank. But for me, I think I need low temp charging protection. I leave the boat plugged in for periods in the winter and here winter means occasional below freezing temps (and LiFePO4 batts won't tolerate charging in sub freezing temps). Most of the low end BMS do not have low temp charging cut off. there are a few mid price units that do.

If I were in the tropics, or even FL, I would consider going without a a BMS like Registered User does.
 

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I've been researching this a bit myself. You might want to check out the DIY Solar forum. A lot of people there like the Overkill Solar BMS. I have no direct experience with it.
 

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I leave the boat plugged in for periods in the winter
Ironically, I also understand LiFePO batteries do not want to be stored for long periods at full. I could be wrong, I'm just learning this new to boating chemistry.
 
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Discussion Starter #20
Ironically, I also understand LiFePO batteries do not want to be stored for long periods at full. I could be wrong, I'm just learning this new to boating chemistry.
Yes you are right. It's a great point and Im not sure of a good way to manage this.

I think I can configure the charger to charge to a set voltage .... say a low value representing ~50%. I suppose this could be a another step in the winter decommissioning/commissioning?
 
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