200a Portable Lifepo + BMS + Balancing

[rgleason]

Tanglewood,
You raise a great point I had forgotten, about "Float" and a clearer definition of what is meant. Perhaps

1. "Battery Charging Float" as is used in FLA external 3 step chargers which keep voltage level elevated a little to "finish" charging the FLA over a long period of time.
2. "House Loads Float" to carry only house loads and not add any flioat charge to the battery.

Of course, I would like to have capability in #2. It might be useful, particularly at a dock with a 120vac charger. The charger regulator would have to sense voltage & amps depletion at the shunt and increase charge to match it and make it 0.

Does such a charger exist?

While on board and using equipment, when the eng is on, alternator charging is available for charging up lifepo4. When the lifepo4 reaches 3.44vpc which is fully charged the, alternator should stop charging altogether, unless it is able to sense and adjust its charging to balance out house loads?

Does such a regulator exist?

Of course I want to be able to run the alternator to balance out (zero out) refridge, nav, radar, house loads, while not overcharging the lifepo4!

Is this possible?

Of course when eng/alt is not running, house loads are carried by lifepo4 bank.

[rgleason]

Tanglewood wrote:

You could certainly do it this way, but a question...

When on shore power, and your LFP is charged and the BB charger is shut off, what powers your onboard loads? Unless you switch the loads from the LFP to LA, you will be needlessly cycling the LFP when shore power is right there for the taking. And if you switch the loads, will it be manually controlled? Automatically controlled and by what? Will the switch over be transparent to loads so everything on the boat doesn't blink and computers and other systems restart? What happens if shore power is lost? How does the switching and charging respond?

And one thing I have found in this whole LFP exploration is that you need to be really careful to understand what someone is saying. There have been a number of threads demonstrating how the same term means different things to different people. The "Float" thread that I started is an example.

A bunch of people defined "float" in the context we know it from LA land, namely an elevated voltage that yields a continuous trickle charge current. It's well established and demonstrated that continuous charge current is damaging to an LFP cell once it reached full charge. So in that context, the "no float" mantra is correct.

But others define float as the stage/behavior of a charger after charge is complete. And with an adjustable voltage, that stage can serve to carry loads, and NOT provide any ongoing charge current to the batteries. It's just about setting the voltage correctly.

So going back to your quote:

"The only float paper I have was using Mn doped LiFePO4 cells and in 24 months cells floated maintained at 100% SOC and at 25ºC lost 30% of their capacity, without any cycling. What we do know is that storing these batteries at 100% SOC resting voltage (not even charging) can lead to capacity loss and is advised against by every LFP cell maker I know of."

1) We already know that 2 year storage at 100% SOC will cause capacity loss. So there is no way to separate that out from the effects of "float".

2) We don't know what "float" was in this context, and would have to read the paper to see. If it was a continued charge current, then yes, that would be bad.

========
I don't have answers yet for all your good questions. I am trying to figure this out.

The boat is on a mooring and rarely sees shore power, as I believe was stated in OP.
Definitions needed good point.

"Battery Charge Float" as in FLA charge routine. BCFloat

"House Load Float" to cover only house loads. HLFloat.

Of course I want to cover house loads whenever possible This could be done through sensing at the shunt, but no regulator, solar mppt regulator or shorepower regulator that I know of approaches that sophistication.

If you know of such equipment please advise. It needs to control the charge souces variably to make up for house loads - refridge, nav, chartplotter, radar, etc. So that the LiFePo4 is not charged after reaching 3.45vpc

I am not sure I need fancy switching at the charge bus with our use. When at the dock the charger would be used. When cruising the alternator would be used.
Initially intend to have small (2) 57watt solarpv on the dodger. These will not be permitted to charge the lifepo4 while on the mooring. I think they would be most appropriately connected to the start bank FLA anyway and not worth using for the LiFePo4 House bank unless cruising and in use.

This is a small boat and if it can be simple it would be much better.

Thankyou for asking these questions!

I agree the white paper needs to be read in context to check, but Float is likely BCFloat.

[CGirvan]

Originally Posted by hellosailor

"My expected use would be a 300 ah LFP house bank charged primarily by solar. I would also like to have a 100 ah portable LFP pack for the dinghy"

Run the numbers.
If we rashly assume that you intend to use that 300ah main bank to a 33% discharge and will be using and replacing 100 ah in a normal day...you will need a solar array that is rated at 20A output at a nominal 14.4 volts to put the charge back in. (That's based on the fact that a solar panel will basically put out the equivalent of five hours at full rated power, in a real day, summer or winter wherever all averaged out.)
So do you have room for, and have you planned on, something like 300 watts of solar panels? Clear of all shadowing?
Or whatever your situation calls for? If you're planning to use more than 100 ah per day, you'll need even more panels. That starts to mean a bigger boat at a certain point.

Same thing for the dingy. If you have a 100 ah battery on board, and plan to get any reasonable charing out of a solar panel you're going to need an awful lot of panel.

Just wondering, have you planned this all the way through?

In the planning or at least thinking about and research phase.


300 watts is about what I was thinking for the boat but it definitely wouldn't all be shadeless.
I was thinking that the electric outboard wouldn't need 100 ah but the Hookah would, but only on occasion and not every day. So the power used from the portable pack would differ daily.



I agree the electrical system on a boat is a bit of a balancing act with power in vs power out.
My question was more about the physical charging layout rather than where the power was coming from.


The question is how would you go about charging a portable LFP pack on a boat at anchor away from shorepower.


Again thanks for your comments

[tanglewood]

Originally Posted by rgleason

Tanglewood,
You raise a great point I had forgotten, about "Float" and a clearer definition of what is meant. Perhaps

1. "Battery Charging Float" as is used in FLA external 3 step chargers which keep voltage level elevated a little to "finish" charging the FLA over a long period of time.
2. "House Loads Float" to carry only house loads and not add any flioat charge to the battery.

Of course, I would like to have capability in #2. It might be useful, particularly at a dock with a 120vac charger. The charger regulator would have to sense voltage & amps depletion at the shunt and increase charge to match it and make it 0.

Does such a charger exist?

While on board and using equipment, when the eng is on, alternator charging is available for charging up lifepo4. When the lifepo4 reaches 3.44vpc which is fully charged the, alternator should stop charging altogether, unless it is able to sense and adjust its charging to balance out house loads?

Does such a regulator exist?

Of course I want to be able to run the alternator to balance out (zero out) refridge, nav, radar, house loads, while not overcharging the lifepo4!

Is this possible?

Of course when eng/alt is not running, house loads are carried by lifepo4 bank.

Yes to all the above. Just set the float voltage to the battery's resting voltage. Load will then be served by both the battery and charger. As the battery voltage drops, the charger will carry more and more of the load. No special controls are required. This, BTW, is how Victron runs all their LFP products.


The challenge is that the LFP battery voltage doesn't vary a lot, so there is a certain amount of slop around the exact SOC that the battery will settle into where it's no longer carrying much, if any load vs the charger. But you should be able to hit a range without too much trouble.

[rgleason]

Tanglewood:

Yes to all the above. Just set the float voltage to the battery's resting voltage. Load will then be served by both the battery and charger. As the battery voltage drops, the charger will carry more and more of the load. No special controls are required. This, BTW, is how Victron runs all their LFP products.

The challenge is that the LFP battery voltage doesn't vary a lot, so there is a certain amount of slop around the exact SOC that the battery will settle into where it's no longer carrying much, if any load vs the charger. But you should be able to hit a range without too much trouble.

This would be awesome. Never understood that approach until now. What voltage would you suggest? What do you use?
I think MaineSail would rather not have it floated, and certainly not at 13.8v. I think he would prefer discharge of the battery and then recharge, but could this be done at some lower SoC?

I can understand the voltage does not change much thus there is some slop. Does this situation create additional cycling on a smaller scale, I wonder, and does it really affect the overall cycles in the battery, I also wonder.


MaineSail has a totally different belief. I will try to find the link.

[rgleason]

Search for "Float Charging" here

....Floating LFP is a complex subject and I will touch more on this later. Bottom line is to avoid floating LFP banks if you can. Some have argued that a float voltage of 3.35VPC or lower (13.4V for a 12V nominal bank) is not badly damaging. I would simply counter that with we don’t have enough data to confirm that. T

Can you float at 3.35VPC or lower? Sure, you can do what ever you want to, but we don’t really know the long term affects

Then search for: "JUST SAY NO TO FLOAT CHARGING!!!!"
and see what he says.


I wonder if he is using "Float" as in Battery Charging Float rather than House Load Float?


He does use the term "Float Charging"


Just say no to float charging:

Please, please, please stop asking if it is okay to float your LiFePO4 batteries. The answer is still going to be NO. If you want to continually float your LFP bank you bought them for the wrong reason. These batteries LOVE TO CYCLE. They hate being at 100% SOC and even the mere act of storing them at 100% SOC, as we need to do with lead acid, is damaging to their life span. Adding a slight over voltage, above cell resting voltage, is even WORSE for them. DO NOT FLOAT LFP.
If you are in a situation where charge equipment can’t be turned off and would necessitate floating the LFP bank, you need to wire in a cross-over lead acid battery to handle shore-side or unattended duration’s of alternative energy charging. For dock side or unattended uses you need to be able to discharge the LFP to 50-60% SOC and TAKE IT OFF-LINE while allowing the small lead acid bank to run DC system loads along with the shore side charger or alternative energy systems

[john61ct]

I am not dogmatic about it.

Some people are "certain" a low enough Float V say below 3.3Vpc, that no current is flowing into the bank, will not effect longevity, and

find keeping LFP online with a load carrying Float,

simpler and practical.

I say fine, long as they do so fully informed, not just based on lead thinking.

For my banks, I won't float unless that really compromises other design goals.

[nebster]

Originally Posted by rgleason

I can understand the voltage does not change much thus there is some slop. Does this situation create additional cycling on a smaller scale, I wonder, and does it really affect the overall cycles in the battery, I also wonder.

It is true that the regulation around the float voltage subjects the battery to very small amounts of very slight charging and discharging. (Even one or two degrees of ambient temperature change alters the voltage slightly, and for example my pack always seems to have a couple of watts going one way or the other.) And it is a fair -- and I believe open -- question as to how much this impacts lifetime performance.

Some of us are speculating that that tiny fluctuation is immaterial. I think there are some good reasons to argue for that, but then the reality is that we are unlikely to find any scientific inquiry on this question in the future. Such an experiment would no doubt be very long, quite expensive, and very boring to conduct.

On the other hand, having the battery always there to backstop flaky shore power is a huge and immediate benefit for those of us using hybrid inverters and spending substantial time living in our vessels.

It's probably worth the (small) gamble for many. But, putting the pack offline is even more conservative.

[john61ct]

A very balanced statement of the issue, thanks.

After some more googling I will say, paralleling **single cells** to reach higher AH capacities apparently may not create the same imbalance risks as paralleling strings.

The 3-4 max guideline for the latter is just that, and just like "50% DoD" or "1% voltage drop" can be 'violated' by a knowledgeable designer / builder aware of the issues if needed.

In this case maybe scaling back frequency of checking for imbalances a bit more slowly, e.g. quarterly rather than every six months after the first few years.

But for me, I see no reason to go more than a pair of strings, with each comprised of paralleled 180AH cells can build some pretty darn big banks.

[tanglewood]

Originally Posted by rgleason

Tanglewood:


This would be awesome. Never understood that approach until now. What voltage would you suggest? What do you use?
I think MaineSail would rather not have it floated, and certainly not at 13.8v. I think he would prefer discharge of the battery and then recharge, but could this be done at some lower SoC?

I can understand the voltage does not change much thus there is some slop. Does this situation create additional cycling on a smaller scale, I wonder, and does it really affect the overall cycles in the battery, I also wonder.


MaineSail has a totally different belief. I will try to find the link.

I am still building my bank, but am thinking 3.30 to 3.35 vpc. If I recall correctly, Victron recommends 3.35 vpc.

[rgleason]

Would this then be a safe/good HouseLoadFloat value, provided it did not add any amps to the LiFePo4 bank.

The other suggestion is to set the value at the present "Resting voltage value"

Don't know which is better, but I think either one would be fine.

Would this then be used to program the shore charger and the solar controller when the boat is on the mooring?

Or could I program the solar controller when on a mooring to a voltage that would charge the batteries up to 60% SoC (whatever that cell voltage/12v nominal is) and then STOP with no float?

So that when we return to the boat we just have 40% SoC to recharge, which would mean less engine run time.

Then when cruising, we could set the voltage higher perhaps, to 3.4vpc / 13.2v perhaps to more fully utilize solarPV?

It becomes clear then that we need an easy way to save these settings and to change them for each particular use without having to undo things or crawl into lockers.

Tanglewood wrote:
I am still building my bank, but am thinking 3.30 to 3.35 vpc. If I recall correctly, Victron recommends 3.35 vpc.

[rgleason]

John thanks for the clarification in the other thread.

There are some 2"x7"x7" 90ah LiFePo4 available, pretty inexpensive, which would fit under the cabin seat in drawer space. I drew a 3P4S system (it is mislabeled in the image) and would like to know if what I've shown is correct.

http://www.cruisersforum.com/forums/...d.php?t=203411

Do the series connections in cable have to be the same length? -I don't think so. Would these stay balenced?

This is just a trial balloon at this point.

[john61ct]

Originally Posted by rgleason

It seems to me this is what a good BMS should be responsible for, keeping the cells top or bottom balanced.

Often BMSs include a "live balancing" functionality, but usually kicks in at voltages I would not approach in normal cycling.

I see BMS functionality as being last-ditch protective in nature.

If there were "a BMS" with an open hardware approach, fully adjustable and available at reasonable cost, and it happened to also control charge sources I'd be open to looking at it.

But at this stage of development I won't hold my breath, and by buying good cells new and avoiding the shoulders, re-balancing may be at most an annual maintenance routine.

[skippermdj]

Has anyone had experience with either the Orion BMS Jr. or BMS123 (from the Czech Republic) systems for their LiFePO4 house bank? Other BMS recommendations?



I built a 300ah 3P4S system two seasons ago with the Housepower BMS and a dozen Calb CA100s. Sterling smart charger and Balmar 614 regulator configured per info published by MainSail and Stan Honey - a huge help, BTW, so many thanks to both of them. Now seems like a good time to upgrade, but not much info that I can find on alternatives.


Thanks in advance!

[CharlieJ]

skippermdj #149: The Orion JR is a solid, feature rich unit. The learning curve is a bit long but not insurmountable and the tech support from Ewert Engineering has always been superb.
To learn all of the features in the Orion JR I recommend that you purchase some small LFP cells and set them up on a work bench. Connect a battery supply and a load with the BMS and learn the system.