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Discussion Starter #21
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.
I believe that the Overkill BMS is a re-branded Chinese JBD or Ant BMS. But yes those are the "mid range" BMS that I was considering.
 

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Ironically, I also understand LiFePO batteries do not want to be stored for long periods at full.
Yes even for hours.

If course the use case may require it, so the "harm" just needs to be accepted.

But to the extent possible, only charge past say 70-80% when close to discharging time.

In storage for days or longer, no cycling needed, lower the better say 20-50% SoC

just make sure not going to discharge below say 3Vpc.

Self-discharge rates for good cells is very slow

so long as isolated and not too hot ambients.

Leaving BMS or other protective circuitry connected can quickly murder the bank via constant vampire loads
 

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I would use a cheap lead batt as a buffer for constant mains Float input keeping systems running when the owner is away from the boat.

Lead loves sitting at 100% Full, last for decades that way, but opposite of LFP quickly murdered allowed to sit below that, called PSOC abuse
 

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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.
Try the programmable Daly BMS with B/T. These are very well made BMS but you need to order the correct one with separate Charge/Discharge ports. Select the current by the maximu expected current draw from the battieries (windlass/bowthruster etc...) Can order it at AliExpress. About $140, as you want to be able to control max charge, min discharge and low temp cutoff.
Unfortunately, my preferred BMS - Victron - only work with Victron batteries.
 

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Try the programmable Daly BMS with B/T. These are very well made BMS but you need to order the correct one with separate Charge/Discharge ports. Select the current by the maximu expected current draw from the battieries (windlass/bowthruster etc...) Can order it at AliExpress. About $140, as you want to be able to control max charge, min discharge and low temp cutoff.
Unfortunately, my preferred BMS - Victron - only work with Victron batteries.
The Daly dual port BMS's can only accept 40A MAX charge current. Kind of minimizes one of the best features of LFP in my opinion.
 

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Discussion Starter #27
What charging level are you planning to have
I have no charge source capable of more than 40A. I have a small frame alternator and a 30a battery-to-battery charger off of the lead starting batt. small potatoes. I don't have solar yet, but that is inevitable. At this point I'm leaning towards foregoing the BMS like you. In my setup I'm not so sure a BMS would be "managing" much ... correct me if I'm wrong though!
 

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The following is just my opinion. A BMS should never be "managing" your batteries or the systems connected to them. Instead, it should be a last resort to save the batteries if everything else you put in place fails. Continual balancing of cells is over-rated, and likely unnecessary. It often requires holding the bank at a high voltage level to accomplish, and the cells wouldn't be unbalanced at a slightly lower voltage instead.

It would be foolish to go without any "battery management system" at all, but that doesn't mean one needs a dedicated centralized computer dialed into the entirety of the boat systems and imposing its will on everything. Instead, it could mean decentralizing functions to other components, with suitable alarms if those components are acting up.

For example, the alternator regulator could be programmed to charge appropriately and stop charging at the correct point. One could then make the decision that the alternator would never be running without a person on board, so decide to just put a simple high voltage alarm on it should the alternator fail at high output voltage. If the alarm goes off, then one just determines what is happening and shuts the alternator down manually. If the alternator fails at no output voltage, then the engine panel alarm will sound.

Likewise with other charging and load sources on the boat. Even your reefer/freezer have adjustable low voltage cutoffs that can be used to protect the batteries (many people don't know this). If you will be living aboard, then a simple battery monitor will tell you much about what is going on at all times.

I think it is worse to wire in a complicated centralized BMS and blindly trust it works while not understand what it is doing at all times than to fully understand your boat systems and how to set up and monitor them.

Mark
 

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I have no charge source capable of more than 40A. I have a small frame alternator and a 30a battery-to-battery charger off of the lead starting batt. small potatoes. I don't have solar yet, but that is inevitable. At this point I'm leaning towards foregoing the BMS like you. In my setup I'm not so sure a BMS would be "managing" much ... correct me if I'm wrong though!
My balmar regulator is set to 13.9
Solar regulztors are also set

You may or not motor a lot
I have and will again so the alt regulator is important to me
While i have a 110 dock charger set for my needs, its not used

If you dont want your nose and mind contiually into your batteries, you want to regulate charging...imo
Same with 110 dockside

Ive seen some dropin li systems that totally rely on bms set for 14.5 etc charging volts
So...all your chips would be on that bms

There are good, relatively inexpensive low voltage cutoffs availsble if you are concerned with hitting the bottom
Ive not added that

For me...totally a longterm solution for my projected needs
 

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At this point I'm leaning towards foregoing the BMS like you. In my setup I'm not so sure a BMS would be "managing" much ... correct me if I'm wrong though!
Your call, but have you never forgotten anything when out sailing? A BMS is there to have your back. Since lithium can be ruined, if not set on fire, I'll take the wingman any day.
 
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Battery Monitors exist, whole-pack level

some have midpoint balance monitoring.

But that would be a separate thread.
 

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LiFePo4 is hundreds of times safer than the LI chemistries used in screen devices and for propulsion.

Your statement is more true for lead.

IMO LFP with protective HV cutoffs separate from the primary charger regulation, is just as safe as lead.
 

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It is the high energy state that increases the danger factors.

The lower the SoC / voltage the safer they get.

And proper care means ensuring no surprises, generally lead only gets dangerous well after its EoL point.

Just keeping on using a bank until its failure symptoms become noticeable is asking for trouble.

Responsible owners proactively replace long before that, 80% SoH in industry, consumers often go down to 75-70%.
 

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It is the high energy state that increases the danger factors.

The lower the SoC / voltage the safer they get.

And proper care means ensuring no surprises, generally lead only gets dangerous well after its EoL point.

Just keeping on using a bank until its failure symptoms become noticeable is asking for trouble.

Responsible owners proactively replace long before that, 80% SoH in industry, consumers often go down to 75-70%.
Why would you not want hi and low voltage protection for those dangerous acid filled lead batteries
 

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The text you quoted is my answer to your duplicated question.

LVC is for protecting the batteries, ensuring their longevity, not for safety concerns.

When you are disposing of batteries, SOP is to ensure they are dead flat first.
 
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