Practical Questions about LiFePo4 Power Systems

[alctel]

My BMS (Orion JR) can control several different relays - I have the alternator regulator power on one, which cuts off before the main charge disconnect relay goes.

This cuts the alternator safely before the charge relay goes and cuts ALL charge sources.

They both work on cell voltage and the alt relay goes at 3.475 v and the main charge one trips at 3.5v.

[Dockhead]

Originally Posted by rgleason

I believe the Victron Overcharge Disconnect has a Field disconnect included.
What are the interruptions from? Sorry haven't read the whole post.

Perhaps the lead acid battery could also have 24hr loads such as Bilge and other essential loads that might run the Lithium down if a float gets stuck or something.
That is one disadvantage to the proposed wiring for my boat.

The BMS systems most people over here use have relays to disconnect loads when there is undervoltage and all charging when there is overvoltage.


The Victron BMS is only for Victron "batteries" AFAIK -- part of the BMS system is built into the packaged cells which Victron sell.


Allowing bilge pumps to run batteries down is not essential in my opinion. If the bilge pump hasn't save your boat by 23.02 volts it's not going to save it. This doesn't bother me. But I wouldn't want to give a device the authority to shut down my nav systems, radar, depth sounder, nav lights, without my participation. Which might happen because of some voltage spike or glitch, especially.

[alctel]

Originally Posted by rgleason

I believe the Victron Overcharge Disconnect has a Field disconnect included.
What are the interruptions from? Sorry haven't read the whole post.

Perhaps the lead acid battery could also have 24hr loads such as Bilge and other essential loads that might run the Lithium down if a float gets stuck or something.
That is one disadvantage to the proposed wiring for my boat.

On mine I have the main bilge pump on the battery side of the discharge connector but on the other side of the main 'oh crap' connector.

Meaning it'll keep running after everything else gets shut off, but will get shut off before it gets the batteries MEGA low and damages them.

[Dockhead]

Originally Posted by alctel

My BMS (Orion JR) can control several different relays - I have the alternator regulator power on one, which cuts off before the main charge disconnect relay goes.

This cuts the alternator safely before the charge relay goes and cuts ALL charge sources.

They both work on cell voltage and the alt relay goes at 3.475 v and the main charge one trips at 3.5v.

Thanks -- that's very logical and useful. I wonder if other work that way as well?

[john61ct]

Oops, sorry, messed up editing a typo

[rgleason]

Allowing bilge pumps to run batteries down is not essential in my opinion. If the bilge pump hasn't save your boat by 23.02 volts it's not going to save it. This doesn't bother me. But I wouldn't want to give a device the authority to shut down my nav systems, radar, depth sounder, nav lights, without my participation. Which might happen because of some voltage spike or glitch, especially.

Agreed. I suppose I should put the bilge and anchor light on the reserve battery which is much smaller, or perhaps have a voltage sensing relay to disconnect those loads. With LiFePo4 controls that protection is built in.

Is there normally a visual/audible alarm with under voltage or overcharging?

It the Victron LiFePO4 too integrated and proprietary? If so, what is the best BMS to use?

[Takamoana]

Regarding the concern of an automatic shutdown of nav instruments etc, in my experience, these systems are usually only of critical importance while underway. My BMS (Housepower) gives a warning signal, which I use to activate a piercing alarm and LED indicating HVE or LVE, well in advance of isolating the house bank. Whilst underway we always have a watchkeeper so there is time to respond to an alarm and take remedial action before hitting the critical point and losing the battery.

[john61ct]

Whether a "Full enough" event shuts down the charge source or just isolates the LFP from that buss,

is a system design decision, or perhaps an option the user can select as tge situation requires.

Keep in mind you should not be letting it get near Full (however you define it) unless loads are running ready to start pulling the SoC down, should not let LFP sit at high SoC for long.

But you may want the charge source to continue carrying a very heavy load until it's done.

Getting everything automated makes for complex and fragile systems, more likely to fail.

But some human regulators and switches are more reliable than others.

There is no one "correct" SOP way.

[a64pilot]

Question, what are you guys calling a BMS?
What I am used to monitors individual cells for temp and voltage, it will discontinue charging of each cell independently of any other, balancing each cell and of course will discontinue charging and I think disconnect the pack if it gets over a set temp.
With a BMS, the bank is like any other battery functionally, feed charge power to it all you want, the BMS disconnects charge, no need to terminate at the source, of course that could cause issue with the alternator though.

[john61ct]

I do not consider per-cell functionality essential to a DIY system, but it certainly seems to be included in all commercial designs.

To me only pack-level or whole-bank level are required
LVD
OVD
Overcurrent protection
High temp protection

Low temperature protection is often left out altogether.

Cell-level is "would be nice, but make it easily disabled"

[Dockhead]

Originally Posted by rgleason

Agreed. I suppose I should put the bilge and anchor light on the reserve battery which is much smaller, or perhaps have a voltage sensing relay to disconnect those loads. With LiFePo4 controls that protection is built in.

Is there normally a visual/audible alarm with under voltage or overcharging?

It the Victron LiFePO4 too integrated and proprietary? If so, what is the best BMS to use?

Well, read the Victron catalogues. Victron LiFePo systems are probably not "too" anything except expensive. But yes -- they are completely integrated and proprietary, and other than expense, that's a GOOD thing -- it means the system has been developed by real professionals and no doubt some of the best in the world. What we have been waiting for, for this technology. But the cost doesn't make sense for many of us, therefore we "home brew".


As to the issue of unexpected interruption of critical gear -- I had an idea about that just now.


Why not give the BMS two different modes -- operator present, and operator absent. Or if you like -- Underway. And Not. When the operator is present, the BMS is deprived of authority to disconnect loads automatically, but will give appropriately loud alarms so that the operator can make a decision, and disconnect loads SELECTIVELY, and resolve the overall issue if he can. Then, when the vessel is not underway, the system is switched over to do it automatically.





Otherwise, you can connect critical systems to a reserve FLA bank. Something like -- comms gear, nav gear, nav lights, boat network. That adds complexity, which is undesirable, but on the other hand this is a GMDSS requirement anyway, and adds safety. The reserve bank will need its own charger, monitor, some kind of connection to the alternator (diode splitter?) or battery-to-battery charger -- somewhat painful and expensive complexity, and added complexity in operation. But it solves two problems, and even adds yet more battery capacity (never a bad thing). On my boat (dual alternators), I could make this bank 12v instead of 24v and charge it from the engine start alternator -- isolating a bit more from the house side.




But the fact that we are discussing all of this is another downside to LiFePo that I had not imagined before a few days ago.

[Kenomac]

I ruined the small Lipo battery on my drone controller so easily that I’ve put off even considering the switch to lithium for the boat another 10 years until they get it right.

Dockhead,

I thought you have wet cell batteries.

[Dockhead]

Originally Posted by Kenomac

I ruined the small Lipo battery on my drone controller so easily that I’ve put off even considering the switch to lithium for the boat another 10 years until they get it right.

Dockhead,

I thought you have wet cell batteries.

I do have wet cells; described earlier in the thread, and elsewhere.



Also the reason for considering this switch is described -- it's not just for the inherent advantages of LiFePo, but for reasons of some deficiencies in the architecture of my current system.


My own opinion, for whatever it may be worth, is that there is still no good reason to switch to LiFePo if you are able to install a sufficiently large single bank of golf cart batteries. Also I think that those with solar installations of decent size have little to gain with LiFePo.



My use case falls between the cracks of those parameters, and so I don't think I will replace my current batteries with more of the same. I thought I might be in a new boat by the time these batteries were worn out, but now it's looking like that might not be the case, so this project is back on the front burner.

[travellerw]

Originally Posted by Kenomac

I ruined the small Lipo battery on my drone controller so easily that I’ve put off even considering the switch to lithium for the boat another 10 years until they get it right.

Dockhead,

I thought you have wet cell batteries.

The battery on your drone is a completely different chemisty than LiFePO4. You are making a mistake thinking that they are comparable.

[john61ct]

The comparability is the fact that one easy accidental "event" can instantly turn an expensive battery into scrap.

Much harder to do with a FLA bank.