LFP FLA hybrid

[CatNewBee]

Completely independent circuits is very appealing, you'll need probably different capacities too, technical loads are far less demanding then house loads.

[CatNewBee]

This is a schematic on how to run independent totaly isolated batteries on separated buses for charging and discharging, also having a bypass for using charge energy directly on the loads and separating combi devices.

[Delfin]

Originally Posted by CatNewBee

In theory it looks appealing, but I would opt for a clean transition to LFP or sticking with FLA and making some marginal improvements on the monitoring and charging - e.g. by adding some solar and a good controller.

Instead of throwing money to extend the life of an old technology,
I would rather spent it on capacity of the new LFP bank.

Otherwise you have to deal with a quite complex system, 2 incompatible charging technologies and threshold settings, lots of monitoring and devices in between (b2b charger to pump the power in both directions), combined with power losses on the transformation and on the FLA battery power acceptance.

It is simply not worth the headache.

From an engineering point of view it is doable, but inefficient - from a economical point of view it is a significant investment with little benefits - you still will have to replace your FLA from time to time because of their poor life expectancy, you will not leverage fully the advantages / life expectancy of a LFP bank, because you will have to invest again in FLA at some point. From the usage point of view, you have more complexity and potential failing devices to monitor, also the user experience will not be the same as with a larger capacity LFP - so you will have some improvements - you have the advantages of both worlds - but also the problems of both worlds - so something between win/win and lose/lose.

Tend to agree. To use a Lithium battery to top off a LA bank means the Li bank needs to be large enough to provide the last 20% of capacity to the LA batteries, plus house loads during that process. Seems like if you just doubled, or maybe a bit more, the size of the Li bank you don't need the LA bank for house loads at all. Simpler is sometimes better...

[rgleason]

CatNewbee:

In theory it looks appealing, but I would opt for a clean transition to LFP or sticking with FLA and making some marginal improvements on the monitoring and charging - e.g. by adding some solar and a good controller.

Instead of throwing money to extend the life of an old technology,
I would rather spent it on capacity of the new LFP bank.

It is simply not worth the headache.

Delfin:

To use a Lithium battery to top off a LA bank means the Li bank needs to be large enough to provide the last 20% of capacity to the LA batteries, plus house loads during that process. Seems like if you just doubled, or maybe a bit more, the size of the Li bank you don't need the LA bank for house loads at all. Simpler is sometimes better...

Hybrid System

FLA 225ah - Existing, Replace every 6-8 years.

LA 45ah (.2C) or 66ah (.3C) 1 x $800-1000
Sterling Pro Ultra B2B $350 + wiring.
Change settings of charger appropriately.

LA System
LA 160 ah with built in BMS under/over voltage limits. 2 x $1000 = $2000
Would still get a shore charger probably.$350

I knew the argument for a full LA system would be made and the argument for simplicty is rational. I am still not so sure there are are not good reasons to go with a hybrid system:The Lithium battery type seems solve the 100%SOC issue for FLA.

1. The high Lithium battery acceptance rate can be used to shorten charging time, with long times at high amps, but shorter periods, which supports greater sailing rather than motoring.
2. The FLA batteries as "House Bank" provide an inexpensive, known and common battery type that now has a much better chance of lasting for 6-8 years, providing the source for the house loads.
3. The Lithium Battery would become the "Charging & Reserve Bank" acting also acting as "Emergency" in the event the House Bank is discharged or fails.
4. The overall system might be very efficient and effective.
5. Solar PV would not have to be as large or maybe is not really necessary because the Alternator is used for the most part.
6. The thing that might put this system in the trash is:

* How often would the LA batteries have to be brought up to 100%?
* How long would that take for a small LA?
* What is the LA typical:
- Max Discharge level C
- Bulk level C -max absorption amps & voltage level.
- Absorption level C -CV? amp ranges, trailing amps?
- Float level C & voltage?

[john61ct]

Originally Posted by rgleason

Solar PV would not have to be as large or maybe is not really necessary because the Alternator is used for the most part.

IF ICE was running 2-3 hours a day anyway then yes no solar needed, if that is a preference.

> How often would the LA batteries have to be brought up to 100%?

2-3 times a week minimum, more the better. Except for Firefly but pricey.

> How long would that take for a small LA?

Doesn't matter, ICE for 2-3 hours, rest handled by the LFP.

AGM high CAR helps reduce ICE runtime, get to 85-90% quicker.

[rgleason]

Victron Lithium 90ah battery with built in BMS $1,125
An external BMS and other equipment will be needed too with this battery.

Link with full datasheet


Charge between 14-15v 14.5v recommended, at 100a, can accept 500a
70% DoD 2500 cycles

80% DoD 3000 cycles
50% DoD 5000 cycles
Does not like cold. Do not leave in boat in freezing weather.
"A LFP battery does not need to be fully charged. Service life even slightly improves in case of partial charge instead of a full charge. This is a major advantage of LFP compared to lead-acid."
LFP is 90% efficient at high states of charge, unlike FLA

[rgleason]

Thanks John,

> How often would the LA batteries have to be brought up to 100%?
2-3 times a week minimum, more the better.

That is just as bad as FLA!!!
Do they get there any faster?
Say for a 90ah battery using a 120ah Alternator with belt management output easily 80ah recharging 60ah to 100%SOC?
Do we still have all the same problems determining when the batterys are full?
IE Measure trailing amps with a clampon meter still?

It seems like Victron Datasheet says:
"A LFP battery does not need to be fully charged. Service life even slightly improves in case of partial charge instead of a full charge. This is a major advantage of LFP compared to lead-acid."

They don't mention the need to get to 100%SOC.

2-3 hours of ICE is not really the idea I had in mind, perhaps 2 hrs, but not 3....

[john61ct]

Originally Posted by rgleason

That is just as bad as FLA!!!

FLA are LA.

If you mean a particular type, specify it, e.g. GEL or AGM or?

Size does not make much difference, nor so much DoD once past 30%, the long tail's always there, last 5% can take 3+ hours.

Why this LFP idea as alternative to solar, low amps makes ICE crazy for getting to 100%.

> Measure trailing amps with a clampon meter still?

With any lead yes.

Why were you thinking anything different? So confused. . .

Unless it's you, LA is lead.

LFP has none of these issues.

> 2-3 hours of ICE is not really the idea I had in mind, perhaps 2 hrs, but not 3

Well depends on amps of the charge source, vs

getting lead to what 85-90%, if tgat is a big bank can't leave too many AH for the LFP to transfer

plus getting LFP to Full, so it can charge the lead.

Remember this whole concept is a whacko thought experiment, no one is suggesting actually doing it for a production setup.

[tanglewood]

I think there are only two reasons to have LFP and LA interact in a power system.


One is because you can't sufficiently control the charging sources for proper LFP charging. For example, fixed voltage alternator regulators, and devices that can't be turned off gracefully and threaten to create voltage spikes of one sort or another.


The other is as a back up in case the LFP battery system craps out. There is a lot more stuff that needs to work to keep an LFP system on line. BMS devices need to operate correctly, as do chargers, and communications between BMS and chargers. And of course the cells need to work. Failure of any of these can lead to a protective shutdown, even though the battery cells themselves might be just fine and have plenty of power available.


One challenge with retrofitting an existing boat is figuring out the best path from here (LA) to there (LFP). I think it's intermediate steps that lead one to consider interactive LFP and LA.


If step back and sketch out where you would like to end up, I think the preferred design is one with proper control of all the charging sources. So no interactive LA/LFP for that. And the preferred backup strategy is a dual LFP bank so that any component failure can be survived using the other battery system until repairs can be made.


I suspect that going straight to the final design is probably easier in the end than an intermediate LA/LFP hybrid, but that's just me.

[Dockhead]

Originally Posted by tanglewood

I think there are only two reasons to have LFP and LA interact in a power system.


One is because you can't sufficiently control the charging sources for proper LFP charging. For example, fixed voltage alternator regulators, and devices that can't be turned off gracefully and threaten to create voltage spikes of one sort or another.


The other is as a back up in case the LFP battery system craps out. There is a lot more stuff that needs to work to keep an LFP system on line. BMS devices need to operate correctly, as do chargers, and communications between BMS and chargers. And of course the cells need to work. Failure of any of these can lead to a protective shutdown, even though the battery cells themselves might be just fine and have plenty of power available.


One challenge with retrofitting an existing boat is figuring out the best path from here (LA) to there (LFP). I think it's intermediate steps that lead one to consider interactive LFP and LA.


If step back and sketch out where you would like to end up, I think the preferred design is one with proper control of all the charging sources. So no interactive LA/LFP for that. And the preferred backup strategy is a dual LFP bank so that any component failure can be survived using the other battery system until repairs can be made.


I suspect that going straight to the final design is probably easier in the end than an intermediate LA/LFP hybrid, but that's just me.

I think there's a lot of sound reasoning here -- thanks for thinking about it and posting.


But I think besides the factor suggested here, you have to consider the individual boat and its individual configuration.


For my particular case -- dual LFP banks might work. I doubt that this would be simpler -- for my particular case -- than a hybrid bank. Whether it would be BETTER is hard to say -- maybe.


Dual identical anything can be good for any complex system on board -- because it makes it easier to carry spares and also the knowledge needed to get the systems going.



I guess in my case I could put one lithium bank in each battery box, add another charger/inverter, then add a B2B charger to share the technical bank's charge with the house bank.


I don't know how the alternator would be connected -- possibly both banks can be charged at the same time via the diode splitter, then you just disconnect one of them when you need to -- something you can't do well with lead because of the charge profile. Alternatively, alternator charge could be shared via the B2B charger.



Add a large separate charger for the second lithium bank.


Might be ok, but hard to see a big advantage over hybrid, which has one big advantage of having the greater fault tolerance of the lead as a robust backup.

[tanglewood]

Speaking of dual LFP battery banks for redundancy, I think there is a battery bank sizing consideration.


I've been off reading research papers on the aging effects on LFP of various charging excesses, temperature excesses, storage methods, etc. This was prompted by my own question in another thread about what's behind the various operational rule that we throw around, and what the actual failure mechanisms are in LFP batteries. It's been very interesting, but not the subject of this post...


What I have learned is that there are concrete degradation processes that start to take place when you charge an LFP cell with too much current (you start to get irreversible lithium plating on one of the poles (can't recall which). And similar damage, though a different mechanism, if you discharge too quickly. This is what's behind the max and recommended charge and discharge rates.


Bringing this back around, if you split your battery bank, each is now half the capacity, and can only support half the charge and discharge rates. Most cell specs allow for 2C discharge, but if you have heavy inverter loads, this might start to be an issue. And for charging most recommend 0.25C to 0.3C for "normal" charging, and 1C as the max for a fast charge. Some boats have a lot of charging capacity, and this might become an issue too.


Presumably under normal operation you would run the banks in parallel, so one strategy to deal with this would be to limit loans and charging only when operating on a single bank, and that might be the best approach. But one way or another, it all needs to be considered in a power system design.

[rgleason]

It certainly is a thought experiment, but useful.
1. With LFP there is still a long tail, solar is still needed.
2. LFP adds complexity and all controls and sensing wires must work or it just shuts down, requiring backup. -how frequent?
3. LFP is significantly more expensive.

I guess I am sticking with FLA or is it LA? GC2 acid batts, with Firefly in the future. Definitely solar too.

Thanks for all the time ideas/ considerations.

[Dockhead]

Originally Posted by tanglewood

Speaking of dual LFP battery banks for redundancy, I think there is a battery bank sizing consideration.


I've been off reading research papers on the aging effects on LFP of various charging excesses, temperature excesses, storage methods, etc. This was prompted by my own question in another thread about what's behind the various operational rule that we throw around, and what the actual failure mechanisms are in LFP batteries. It's been very interesting, but not the subject of this post...


What I have learned is that there are concrete degradation processes that start to take place when you charge an LFP cell with too much current (you start to get irreversible lithium plating on one of the poles (can't recall which). And similar damage, though a different mechanism, if you discharge too quickly. This is what's behind the max and recommended charge and discharge rates.


Bringing this back around, if you split your battery bank, each is now half the capacity, and can only support half the charge and discharge rates. Most cell specs allow for 2C discharge, but if you have heavy inverter loads, this might start to be an issue. And for charging most recommend 0.25C to 0.3C for "normal" charging, and 1C as the max for a fast charge. Some boats have a lot of charging capacity, and this might become an issue too.


Presumably under normal operation you would run the banks in parallel, so one strategy to deal with this would be to limit loans and charging only when operating on a single bank, and that might be the best approach. But one way or another, it all needs to be considered in a power system design.

Interesting question!


My bow thruster can draw about 8kW @ 24v or 25v -- about 320 amps or about 1.5C of one bank, if I went to dual banks. Would that be a problem, do you think, running off half the lithium? Normally it would be less than that since the engine will be running and the alternator will be supplying at least 2kW of the needed power.


70 amps (existing Victron Multiplus) would be about 0.3C


110 amps (alternator) would be about 0.5C


It is possible to use both at the same time (generator running), which would be a 0.8C "fast charge" on one bank.

[john61ct]

Originally Posted by rgleason

With LFP there is still a long tail, solar is still needed.

False.

I clearly stated the opposite, many times, not sure where you got that idea, unless you thought LA means LFP or something.

> LFP adds complexity and all controls and sensing wires must work or it just shuts down, requiring backup.

The shutting down when BMS fails is a feature, otherwise may wreck the bank.

In a well designed system, will happen less often than FLA banks need replacing.

> FLA or is it LA

All lead can be called LA, best IMO to just use "lead".

Flooded, AGM and GEL are the main types of lead used for deep cycling. Firefly are a unique type of AGM.

[john61ct]

Originally Posted by Dockhead

My bow thruster can draw about 8kW @ 24v or 25v -- about 320 amps or about 1.5C of one bank, if I went to dual banks. Would that be a problem, do you think, running off half the lithium? Normally it would be less than that since the engine will be running and the alternator will be supplying at least 2kW of the needed power.

With charge sources supporting, should be fine but better to reduce C rate by combining banks.

The rest I would not worry at all, far below routine EV usage rates.

Same with charging, up to 1C long as robust infrastructure and temp protection.

Talking about cells, not BMS limitations.