Who should be in control?

[s/v Jedi]

Originally Posted by SaylorMade

No more red wine for this gentleman tonight

I prefer something stronger than red wine

[s/v Jedi]

Originally Posted by nfbr

They bottom balance and BMS cuts off charge when one cell hits top limit.
More important in cars to get range accurate than get last few % capacity.

Boat house loads tend to opposite.

There you go, that’s BMS tasks. But does the BMS in cars control the charger?

[wholybee]

Originally Posted by Jef & Marin, Netherlands

I understand that it is best to not charge an LFP bank to 100%.
You might want to charge it to a SoC (State of Charge) of for instance 50% or 80% or whatever, depending on how the bank's capacity and the next charging (for instance by the sun tomorrow).
When your desired SoC is reached, you want to minimize the current going in or out of your bank.
Both the SoC and the current of the shunt are known by the battery monitor.
This information should be used by a (any) controller to fix the output current of your chargers.
Note that at 50% or 80% SoC you are in the almost flat part of the battery curve. So voltage is a complete useless criterium.



Let me describe my current situation and my desired situation.
In the current situation, after reaching absorption voltage, the solar controllers go in float at 13.31V. (this is by the way around 99% SoC)

Then I switch on the hot water boiler. This will draw 60A. The voltage drops, the solar controllers compensate after a minute or so, and the draw drops to 10A. Even when the solar controllers have enough sun power to supply more than the required 60A. That is because float of the solar controllers is voltage controlled.


My desired situation is that I want to have a battery monitor that outputs current and SoC, for ionstance Modbus. This information is read by a controller (Raspberry Pi). The raspberry pi instructs the solar controllers (2 Morningstars) by Modbus about how much current they should supply.
The Morningstar MPPT60's have a slave mode, controlled by Modbus via Ethernet.
The software on the Raspberry pi (Node Red maybe) measures the momentary consumption, and changes the Morningstar slave current real time to force the battery bank current to zero.
This way you avoid minicycles on the LFP bank. That will cause wear.



Another thing I would like: the same controller should automatically switch on the hot water boiler at a certain SoC.



To realize the above, I lack only 3 things: the battery monitor, and sufficient time and knowledge of the programming of my Raspberry Pi. So I have to learn and invest time. After the current refit....



Of course, also this system is not perfect:
- The autopilot uses rapidly varying current. You can not regulate the slaved solar current to zero fast enough, I think. Same for the induction hob.

- In case of high current consumption (making tea using 2000W) the battery is still depleted. The solar controllers will go out of slave mode to replenish the battery from 79% to 80%.


To summarize my view, the chargers should be controlled by the battery monitor.



2 Morningstar MPPT60's with 960 + 890W of solar. 920 Ah 12V LFP bank. We have seen 60+60A of charging at noon sometimes. Even here in New Zealand in winter, we see more than 40A in sunny spells, between the rain showers

You are over thinking it. I did the same thing when I first installed, just wanting to protect my investment. I agonized over what the best settings were, and how to not charge more than 70%.

To extend life, you do not want the batteries at 100%. And, you want to not charge to 3.65Vpc. So, charging to 90% or 95% at 3.5V-3.55Vpc has nearly the same benefit at charging to only 70% (70% is still a little bit better for the life of the battery, but not a great deal)

Also, at 70-80%, because you are in the flat part of the curve, you can not balance your cells. If you turn on a balancer in this area, you will actually bring your cells out of balance. Because of that, only charging to <80% isn't a good idea for the long term. You could do it has a temporary thing, or if you want to put your battery into long term storage, planning a top balance cycle when they come out of storage. Some Victron chargers have a storage mode, which is a great feature for this.

There isn't any reason to have any control of charge sources to tell them what current to deliver. Set float at 13.6V (3.4Vpc) which is about 80%. Your batteries will charge to "full" (In quotes because you can set full to whatever you are comfortable with), then when the chargers go into float, charging stops. You then run off battery for a short time until they get to 13.6V. This is best for the battery so you are not storing them for any period of time at a high charge. Then, when they reach 13.6V, charging resumes. Nothing needs to control anything, at this point the batteries will stay at 13.6V, and all current will supply your loads with none going into the battery. Simple-Simple.

Some people like to charge to "full", but then instead of a daily cycle want to go several days until the battery is at a very low SoC. That way they battery cycles from 10% to 95% every few days instead of 70%-95% every day. This really extends life a lot. That can be achieved with a Victron BMV connected to a Victron Battery Protect or a contactor. Again, pretty simple and no need for CAN, Modbus, or BMS control. You could also you that setup to control charging to stop at any SoC you want, even in the flat part of the curve. But, as I stated before, you can't balance there.

[wholybee]

Originally Posted by s/v Jedi

There you go, that’s BMS tasks. But does the BMS in cars control the charger?

I don't know the answer to this question. I do know that the "car" does communicate with the "charger", the charger being that thing on the wall or the pedestal the care plugs into. But, there very well may be the "real" charger as another device in the car.

I don't think it matters. Car batteries are a different chemistry, with different charging requirements, and different safety concerns. The "charger" is tasked with charging multiple cars of unknow varieties and unknown chemistries. The battery is also in a different application, traction vs storage. While the answer might be interesting, I don't think it translates to a house battery on a boat.

[CaptainRivet]

Originally Posted by s/v Jedi

There you go, that’s BMS tasks. But does the BMS in cars control the charger?

In Tesla yes it does, you regulated via the smartfon app how high you wanna charge on your household chargers. The tesla also gives the signal impulse to stop charging.
But here you talk about propulsion setups which is a totally different animal in spec for BMS then our house bank setup on a boat is closest to a off grid or RV install for energy storage.

[CaptainRivet]

Originally Posted by wholybee

You are over thinking it. I did the same thing when I first installed, just wanting to protect my investment. I agonized over what the best settings were, and how to not charge more than 70%.

To extend life, you do not want the batteries at 100%. And, you want to not charge to 3.65Vpc. So, charging to 90% or 95% at 3.5V-3.55Vpc has nearly the same benefit at charging to only 70% (70% is still a little bit better for the life of the battery, but not a great deal)

Also, at 70-80%, because you are in the flat part of the curve, you can not balance your cells. If you turn on a balancer in this area, you will actually bring your cells out of balance. Because of that, only charging to <80% isn't a good idea for the long term. You could do it has a temporary thing, or if you want to put your battery into long term storage, planning a top balance cycle when they come out of storage. Some Victron chargers have a storage mode, which is a great feature for this.

There isn't any reason to have any control of charge sources to tell them what current to deliver. Set float at 13.6V (3.4Vpc) which is about 80%. Your batteries will charge to "full" (In quotes because you can set full to whatever you are comfortable with), then when the chargers go into float, charging stops. You then run off battery for a short time until they get to 13.6V. This is best for the battery so you are not storing them for any period of time at a high charge. Then, when they reach 13.6V, charging resumes. Nothing needs to control anything, at this point the batteries will stay at 13.6V, and all current will supply your loads with none going into the battery. Simple-Simple.

Some people like to charge to "full", but then instead of a daily cycle want to go several days until the battery is at a very low SoC. That way they battery cycles from 10% to 95% every few days instead of 70%-95% every day. This really extends life a lot. That can be achieved with a Victron BMV connected to a Victron Battery Protect or a contactor. Again, pretty simple and no need for CAN, Modbus, or BMS control. You could also you that setup to control charging to stop at any SoC you want, even in the flat part of the curve. But, as I stated before, you can't balance there.

In boat installs, unless its a very small bank, the calendar aging has the most effect as you are cycling it very soft and the reat you can only screw it up.
Only charging to 70% ruins top balancing and cells gets more stressed then so not enforcing lifespan.
Healthy comprise is 3,55V and you normally have a constant draw on it so it actually stays very short time at 3,55V unless solar is massivly oversized which is rarely the case,mostly underdimenioned.
I simply have my hot water boiler permanently on as dump load when not running electric galley, watermaker or washing machine and try to get bank full till the evening. Then before dinner the active balancer sorts unbalance and it gets discharge by around 15% (on anchor) or 30 (ar pasaage) overnight till in morning when solar kicks in again but gets further discharged to around 60%SOC as solar is not that strong to cover usage till 10-11.
So its naturally mostly in the 60 till 80% SOC range

[sv_isara]

Originally Posted by s/v Jedi

...
Personally, we first replaced one battery bank with LFP and went for 10.25kWh of the best available and cruised for two seasons with only that. We found that it was more than what is the minimum required for us, so we replaced our second battery bank also with 10.25kWh of LFP, this time some of the cheapest available. We know we can get away with that because we could do just with one battery as we proved for two seasons, but I also think they will perform the same… mostly. I mean, my Winston based battery never required balancing other than the initial balance and the new battery may be balancing every day, but I simply don’t know because it’s BMS is silently doing it’s work inside it.
...

Very curious about your different lithium battery types and how they've been holding up. What are the makes, and how are they performing compared to each other?

[CaptainRivet]

Originally Posted by sv_sharky

Very curious about your different lithium battery types and how they've been holding up. What are the makes, and how are they performing compared to each other?

Cells been on market long time:
Top notch no1 Winston
Best value for money: EVE or Lishen 272/280/304AH cells. Storage cells best use <=0.3C
Best quality with reasonable price: calb, especally the 100-240AH sizes.

There are dozen others but these are the well known and proven ones.
Drop ins of different brands/no name you find a lot EVE cells from A+ till junk grade, mainly the 100AH or 200AH cells.

[sailorboy1]

Originally Posted by wholybee

Some people like to charge to "full", but then instead of a daily cycle want to go several days until the battery is at a very low SoC. That way they battery cycles from 10% to 95% every few days instead of 70%-95% every day. This really extends life a lot. That can be achieved with a Victron BMV connected to a Victron Battery Protect or a contactor. Again, pretty simple and no need for CAN, Modbus, or BMS control. You could also you that setup to control charging to stop at any SoC you want, even in the flat part of the curve. But, as I stated before, you can't balance there.

I do that by controlling the Sun. I turn it off at night and let my batteries discharge. When I get up next day I just turn the Sun back on. This operates the batteries between 70-100% and some days I adjust the Sun dimmer switch and let the batteries go down lower for a day or 3.

[s/v Jedi]

Originally Posted by sv_sharky

Very curious about your different lithium battery types and how they've been holding up. What are the makes, and how are they performing compared to each other?

The good one I built myself from eight 400Ah Winston cells in series so 24V 400Ah or 10.25kWh. Perfection.

The cheap one are two 24V 200Ah Father’s Day special batteries from LiTime so also 24V 400Ah or 10.25kWh. They work for almost a year nowbut we haven’t been out cruising with them yet.

So in total I have 20.5kWh

[sailingharry]

Quite a bit of discussion about balance. I get the balancing is important, as it allows you to uniformly bring all cells to full charge so that you can then uniformly discharge them to a nearly uniform bottom of charge. The closer they are to balance, the more available power. I'm not disputing the value.

But a comment upthread about leaving them in storage for a lengthy period of time, where there is no opportunity for balancing, got me wondering. Is there a fundamental problem with being out of balance? If you run your cells say 60 to 80% for months or years on end and they get significantly out of balance, is that inherently bad? I don't know if this question has a real world application, but rather a point for discussion. If they get way out of balance, and when you finally bring them to a high enough voltage to balance, it takes weeks to bring them back into balance, is that the only downside?

[wholybee]

Originally Posted by sailingharry

Quite a bit of discussion about balance. I get the balancing is important, as it allows you to uniformly bring all cells to full charge so that you can then uniformly discharge them to a nearly uniform bottom of charge. The closer they are to balance, the more available power. I'm not disputing the value.

But a comment upthread about leaving them in storage for a lengthy period of time, where there is no opportunity for balancing, got me wondering. Is there a fundamental problem with being out of balance? If you run your cells say 60 to 80% for months or years on end and they get significantly out of balance, is that inherently bad? I don't know if this question has a real world application, but rather a point for discussion. If they get way out of balance, and when you finally bring them to a high enough voltage to balance, it takes weeks to bring them back into balance, is that the only downside?

As long as something prevents overcharge/discharge of a single cell then no. But there can be consequences. You introduce the possibility that you will have a BMS disconnect which can damage equipment. And especially with drop ins you might have an impossible time getting them into balance. Not just because of the length of time, but because the BMS will cut off charging when one cell gets too high, but before balancing has actually started. There are ways to combat that, but it's a hassle.

But in general, there is no problem with cells slightly out of balance. Also, cells in good condition should stay pretty close for a few months with no balancing at all. That is why such small passive balancers on many BMS's are actually fine. The amount of balancing needed weekly is minuscule.

[hjohnson]

Originally Posted by wholybee

As long as something prevents overcharge/discharge of a single cell then no. But there can be consequences. You introduce the possibility that you will have a BMS disconnect which can damage equipment. And especially with drop ins you might have an impossible time getting them into balance. Not just because of the length of time, but because the BMS will cut off charging when one cell gets too high, but before balancing has actually started. There are ways to combat that, but it's a hassle.

But in general, there is no problem with cells slightly out of balance. Also, cells in good condition should stay pretty close for a few months with no balancing at all. That is why such small passive balancers on many BMS's are actually fine. The amount of balancing needed weekly is minuscule.

That’s what I like about having my BMS in control of all the charging sources. If the cells ever do get out of balance, it just dials back the charging to 2A, and lets its internal balancer do its thing to bring the batteries back in line. It also follows a more intelligent charging setup, where in day to day operation, the system operates down in the flat part of the curve. But if I deeply discharge, or its been over a week, it will change the limits to 3.65vpc, and let it charge back up again to check balance (and rebalance if needed) before going back to 3.45vpc.

[sailorboy1]

you guys made it sound hard!

[sv_isara]

Originally Posted by sailingharry

Quite a bit of discussion about balance. I get the balancing is important, as it allows you to uniformly bring all cells to full charge so that you can then uniformly discharge them to a nearly uniform bottom of charge. The closer they are to balance, the more available power. I'm not disputing the value.

But a comment upthread about leaving them in storage for a lengthy period of time, where there is no opportunity for balancing, got me wondering. Is there a fundamental problem with being out of balance? If you run your cells say 60 to 80% for months or years on end and they get significantly out of balance, is that inherently bad? I don't know if this question has a real world application, but rather a point for discussion. If they get way out of balance, and when you finally bring them to a high enough voltage to balance, it takes weeks to bring them back into balance, is that the only downside?

It depends on how out of balance. If the difference is small, sure no problem. But your question is inclusive of the situation that I have seen happen to thousands of batteries regarding a specific single cell, short and long term:

Short term, a low or high cell would be cycling at an improper or less ideal voltage. Ie, being over discharged, and then not fully charged, and vice versa. For a single battery, you'll often see the low cell practically inducing a high voltage in the lowest resistant cell - as a charger forces the battery to 14v for example, 4 cells could look like: 3.5v, 3.5v, 3v, 4v.

Long term: potential could be that the differential above and thus improper charge voltage increases causing capacity loss and bms actions etc.

Not saying the above will happen for sure or even that it's very common, just that this is a very common failure mode that I have seen in the field working for years as a LiFe battery tech.