LFP FLA hybrid

[Delfin]

I am having trouble understanding the advantages of this arrangement. It seems like a solution in search of a problem, although I guess it has the advantage of reducing the spend on Lithium at the cost of continuing to maintain a large LA bank.

I must be missing something on the advantages of the hybrid approach, but it seems to me that a far simpler system is just to install the LFP bank, use it for every load since it's far superior to LA in terms of stability of voltage, then use an existing LA starter bank as the charging destination when the LFP bank is full while cruising, or when sitting at the dock on shore power. Which bank is being used when is managed through a relatively inexpensive Blue Seas ACR switch.

Granted, there are differences between the charging profiles of the two chemistries, with a longer absorption time and higher float voltage for the LA, but as a practical matter I am not sure that matters in real world usage. I've installed a Balmar Smart Gauge on the LA bank on my boat to see what the SoC is on that starter bank after using both banks as described, and if it indicates chronic undercharging of the LA bank, simply flipping the ACR to manual combine at anchorage will top up the LA bank to around 26.5 volts or so, which on a 24 v LA battery is pretty full. Or, since I never float the LFP bank anyway, I may adjust the float on charging sources up to the LA preference of 27 v or so. Either way, this has worked well for the last two years of cruising and doesn't seem to be hurting the LA bank since when I temporarily adjust the charger to LA settings at the dock with the LFP bank offline, the LA bank doesn't act like it is undercharged since it doesn't accept more than a few amps for a short period of time before dropping to a CAR <2% of capacity.

[Dockhead]

Originally Posted by Delfin

I am having trouble understanding the advantages of this arrangement. It seems like a solution in search of a problem, although I guess it has the advantage of reducing the spend on Lithium at the cost of continuing to maintain a large LA bank.

I must be missing something on the advantages of the hybrid approach, but it seems to me that a far simpler system is just to install the LFP bank, use it for every load since it's far superior to LA in terms of stability of voltage, then use an existing LA starter bank as the charging destination when the LFP bank is full while cruising, or when sitting at the dock on shore power. Which bank is being used when is managed through a relatively inexpensive Blue Seas ACR switch.

Granted, there are differences between the charging profiles of the two chemistries, with a longer absorption time and higher float voltage for the LA, but as a practical matter I am not sure that matters in real world usage. I've installed a Balmar Smart Gauge on the LA bank on my boat to see what the SoC is on that starter bank after using both banks as described, and if it indicates chronic undercharging of the LA bank, simply flipping the ACR to manual combine at anchorage will top up the LA bank to around 26.5 volts or so, which on a 24 v LA battery is pretty full. Or, since I never float the LFP bank anyway, I may adjust the float on charging sources up to the LA preference of 27 v or so. Either way, this has worked well for the last two years of cruising and doesn't seem to be hurting the LA bank since when I temporarily adjust the charger to LA settings at the dock with the LFP bank offline, the LA bank doesn't act like it is undercharged since it doesn't accept more than a few amps for a short period of time before dropping to a CAR <2% of capacity.

Well, this will certainly not be a solution for everyone.


It has a few advantages though:


1. You can increase the capacity of the system with lead used as cheap "hamburger helper", if you like. The lead will live long and healthy, reducing cycle cost, possibly drastically, since you will always be able to get a proper finishing charge on it.


2. You have uninterruptable backup power in case the lithium BMS makes a decision to open the LVC contactors.


3. In some installations (not the one I am working on, unfortunately) the lead can be used to protect the alternator in case of a HVC event.





In my particular probably unusual case, my boat was originally built with separate technical and house banks, so a hybrid bank would be an easy installation.



But -- dual lithium banks would have advantage number 2, and the cost per kW/h cycled might still be less for lithium, even compared to ideally maintained lead. So -- I'm not saying that this absolutely makes sense for everyone. It certainly may not make sense for many.

[john61ct]

Looking only at the ability to "finish the long tail" from LFP to lead.

Basically replaces the need to install solar if that was your main reason for needing to.

Can apply to where the large Main bank is lead, and a smaller Reserve is LFP.

Or the other way around, or both used as alternating House1 & House2.

Or even if just one LFP House plus lead Starter(s).

Obviously the lead batts being expensive is what increases the motivation.

[Delfin]

Originally Posted by Dockhead

Well, this will certainly not be a solution for everyone.

Thanks, that helps and I think I am starting to get the picture. Seems like the solution is predicated on using the least expensive wet cells you can get. Just based on my own experience and no other expertise, I would make the following comments:

Originally Posted by Dockhead

1. You can increase the capacity of the system with lead used as cheap "hamburger helper", if you like. The lead will live long and healthy, reducing cycle cost, possibly drastically, since you will always be able to get a proper finishing charge on it.

Makes sense, although the simplicity of not fussing with wet cells has a certain appeal....

Originally Posted by Dockhead

2. You have uninterruptable backup power in case the lithium BMS makes a decision to open the LVC contactors.

With my system, I have 100 Ah of backup from the starter bank, plus the genset. Not sure how compelling this advantage is.

Originally Posted by Dockhead

3. In some installations (not the one I am working on, unfortunately) the lead can be used to protect the alternator in case of a HVC event.

You can accomplish the same thing using Li as House and LA as starter through an ACR, as I do. Plus, the BMS provides that protection as a backup in any case.

Originally Posted by Dockhead

In my particular probably unusual case, my boat was originally built with separate technical and house banks, so a hybrid bank would be an easy installation.

Understood. I have never heard of a setup like yours, but if you have it, splitting battery chemistries between busses is certainly doable. In my case, most of my loads involve some kind of a motor, or contain PCBs and for those, Lithium is much better due to stable, higher voltages throughout the discharge curve, even at temporary higher rates of discharge. I mentioned it elsewhere, but I had to spend $3,500 repairing a Kabola boiler when the PCB burned out due to dc voltage drop when using AGMs. That wouldn't have happened with Li.

Originally Posted by Dockhead

But -- dual lithium banks would have advantage number 2, and the cost per kW/h cycled might still be less for lithium, even compared to ideally maintained lead. So -- I'm not saying that this absolutely makes sense for everyone. It certainly may not make sense for many.

Agreed. But I do now see the point of using Lithium's ability to suck up current without taper providing the taper charge that keeps LA healthy. That said, it does seem a bit like buying a Ferrari so you can use it to tow your Borgward up steep hills.

[Dockhead]

Originally Posted by Delfin

Thanks, that helps and I think I am starting to get the picture. Seems like the solution is predicated on using the least expensive wet cells you can get. Just based on my own experience and no other expertise, I would make the following comments:


Makes sense, although the simplicity of not fussing with wet cells has a certain appeal....


With my system, I have 100 Ah of backup from the starter bank, plus the genset. Not sure how compelling this advantage is.


You can accomplish the same thing using Li as House and LA as starter through an ACR, as I do. Plus, the BMS provides that protection as a backup in any case.


Understood. I have never heard of a setup like yours, but if you have it, splitting battery chemistries between busses is certainly doable. In my case, most of my loads involve some kind of a motor, or contain PCBs and for those, Lithium is much better due to stable, higher voltages throughout the discharge curve, even at temporary higher rates of discharge. I mentioned it elsewhere, but I had to spend $3,500 repairing a Kabola boiler when the PCB burned out due to dc voltage drop when using AGMs. That wouldn't have happened with Li.

Agreed. But I do now see the point of using Lithium's ability to suck up current without taper providing the taper charge that keeps LA healthy. That said, it does seem a bit like buying a Ferrari so you can use it to tow your Borgward up steep hills.

Hey, the Borgward was a fabulous car. My stepfather had one. Fine German engineering not obviously worse than Ferraris of the same era.

[john61ct]

I'm not at all pushing the idea for those with more conventional ways to get their big expensive lead bank to 100% Full on a regular basis.

Nor suitable for those ready & willing to fully convert to LFP.

But it is an added value for those with chronic PSOC problems, and also interested in dipping their toe into playing around with LFP.

[four winds]

Originally Posted by Dockhead

I'm bringing this discussion out of the "Depth of Discharge Myth?" thread and into here.

I'm still daydreaming about this. Thanks for pushing it along.

You said, "The simplest way to do this on a small boat would be to create a small lithium bank which is not connected to any load except the B2B charger and which is used exclusively for topping off the lead bank and passing power through the lead system."

Ok, the backwards plan I had is shelved for now. If the concept results in a lead bank that is back to 100% daily or so, most of then the concerns I had wouldn't exist anyway.

As I said elsewhere, this interests me because it may suit this scenario....... Small boat vagabond coastal sailor on the hook 365- NO solar (ever)- no genset- no windgen- a relatively small 100a alternator,---and no hope of being able to care for the lead bank properly. Sailing, not motoring, or at anchor.

Enter the lithium lead hybrid solution. Any deficit in Ahr replenishment eventually shows up in the Li bank, not the lead bank, which it tolerates better than the lead bank. The lead bank happily spends more time at a higher SOC. When the engine is used to recharge the Li bank accepts it more readily and minimizes runtime. The Li bank continues to pamper lead bank.

I think it's possible the common smallish boat 440 Ahr bank, typically with solar and a Honda gen (a manageable solution), could be instead a split 200Ahr Li / 220Ahr lead bank and a good alternator. It might also be a manageable solution. Without solar. And stand just as good a chance at battery longevity perhaps.

Without all that hardware on the back porch the sailing experience is better to me.

What's funny is all this so I can have at all times a cold drink in the fridge and live on the hook. (GREGREGS rule #5). And sail with a wide open singlehanders cockpit.

[rgleason]

Dockhead wrote:

You said, "The simplest way to do this on a small boat would be to create a small lithium bank which is not connected to any load except the B2B charger and which is used exclusively for topping off the lead bank and passing power through the lead system."

4 Winds wrote:

As I said elsewhere, this interests me because it may suit this scenario....... Small boat vagabond coastal sailor on the hook 365- NO solar (ever)- no genset- no windgen- a relatively small 100a alternator,---and no hope of being able to care for the lead bank properly. Sailing, not motoring, or at anchor.

Enter the lithium lead hybrid solution. Any deficit in Ahr replenishment eventually shows up in the Li bank, not the lead bank, which it tolerates better than the lead bank. The lead bank happily spends more time at a higher SOC. When the engine is used to recharge the Li bank accepts it more readily and minimizes runtime. The Li bank continues to pamper lead bank.

I think it's possible the common smallish boat 440 Ahr bank, typically with solar and a Honda gen (a manageable solution), could be instead a split 200Ahr Li / 220Ahr lead bank and a good alternator. It might also be a manageable solution. Without solar. And stand just as good a chance at battery longevity perhaps.

I really like this idea. I would not purchase a Sterling Pro Ultra Charger 40a but get:
1. Sterling Pro Ultra battery to battery charger. 10a-20a ? Which would actually be used at every charging!
2. Small Lithium Battery 100ah and BMS
3. Existing house bank 225ah
4. Charge both Lithium and FLA Bank batteries with a good 120amp alternator derated to 80a at to whatever voltage works for both battery types in bulk.
5. Back off on alternator as needed using Small Engine mode or whatever is needed or shut off the engine.
6. Let the Sterling Pro BB complete the absorption stage at 14.4v (6.25a -2.25a) for however many hours are needed.
7. Let the Sterling Pro BB "Float" the FLA at 13.8v using the Lithium battery.


dockhead

The simplest way to do this on a small boat would be to create a small lithium bank which is not connected to any load except the B2B charger and which is used exclusively for topping off the lead bank and passing power through the lead system.

FLA 225ah 80-100%SOC = .2C = 44ah at CEF .85%? = 51ah
Li 100ah Say they are 90% full, 100amp-51ah=49ah

The Sterling B2B charger may have some inefficiencies too.
The Lithionics website and Sterling website have Lithium batteries and Battery Management Systems all designed and ready.
This could be joined by some small solar panels as well.
The lithium battery could act as the reserve battery as well.

What would the 60a-100a Lithium battery & BMS cost?
Could I get away with a 10a or 20a B2B charger?

Maybe Dockhead is suggesting to connect the alt directly to the Lithium Battery and have the B2B output connected to the FLA bank.

[Dockhead]

Originally Posted by rgleason

. . . Maybe Dockhead is suggesting to connect the alt directly to the Lithium Battery and have the B2B output connected to the FLA bank.

Yes, that's what I was suggesting. It goes without saying that there should be an appropriate HVC between the alternator and the batteries, and the alternator should be correctly regulated for lithium. There is an issue with protecting the alternator diodes in case of a HVC event.

[rgleason]

Dockhead:
"appropriate HVC between the alternator and the batteries"

What is HVC?
What type of lithium builtin BMC battery would be appropriate? They appear to be pretty expensive.
Would 100ah Lithium work with 225ah FLA?
Could the 100ah Lithium be reduced to 60ah?
Should the BMC be built in?

The alternator should be well ventilated to prevent overheating, and oversized (amperage) with belt program set appropriately, ready to provide longer -term power at higher amps which would be dependent on the size and type of lithium battery and the load of the Sterling Pro Ultra B2B charging the FLA batteries. It is likely that the engine/alt charging times will also be reduced.

[Dockhead]

Originally Posted by rgleason

Dockhead:
"appropriate HVC between the alternator and the batteries"

What is HVC?
What type of lithium builtin BMC battery would be appropriate? They appear to be pretty expensive.
Would 100ah Lithium work with 225ah FLA?
Could the 100ah Lithium be reduced to 60ah?
Should the BMC be built in?

The alternator should be well ventilated to prevent overheating, and oversized (amperage) with belt program set appropriately, ready to provide longer -term power at higher amps which would be dependent on the size and type of lithium battery and the load of the Sterling Pro Ultra B2B charging the FLA batteries. It is likely that the engine/alt charging times will also be reduced.

HVC is High Voltage Cutoff. Yes, it's controlled by the BMC. It disconnects charging sources as a last ditch protection against overcharging, which destroys lithium.


As to sizing -- there's no bright line. But I think you would want the lithium to be at least 30% the nominal size of the lead so that there is plenty of capacity to get the lead from 80% or whenever you shut off bulk charging, to 100%. 30% not 20% because of inefficiency during this stage. Better 40% or 50%.


You are asking me for advice, but let me say again that I am myself only dreaming about this -- never tried it. So these are just ideas so far.

[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.

[Dockhead]

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.

I think this is an entirely valid point of view, well expressed. I'm not sure it decides the matter a priori, but all of these are important things to think about.



For my particular case, I could have TWO lithium banks in the spaces designed in my boat for the two lead banks, instead of keeping one of them in lead. One cool thing about lithium is that with almost no Peukert, there isn't the same kind of demand to combine all battery capacity into a single bank, like with lead.



But this wouldn't be much if any less complexity than a hybrid bank.

[CatNewBee]

Two independent LFP batteries is also a complex thing.

In general there a re two approaches.

One is to create 2 encapsulated systems, each with its own BMS, and a dedicated solenoid that handles both charging and discharging. (OVP / UVP) for each battery. Then run them either always in parallel or alternate them during discharge by a controller / combing them when charging and on heavy loads.

There are such systems for FLA batteries, you need something similar for higher amps: (NDS iManager)

Another option is to do it manually having one bank in stand-by and the other active and switching between them. Then you have some redundancy and spare capacity to switch to.

The second option is more complex by separating charge buses and discharge buses for both batteries by using high current semiconductors as battery separators / combiners. Both batteries will then be independent and separated - no cross currents, but act as one all the time.

There is one issue to be additionally addressed: Usage of combi-units like a Victron Quattro Inverter / Charger. There is no separation between charge and load bus when using that unit, so you may either accept that fact or do some custom programming using the relays to switch the unit between charge bus when the charger is running and the discharge bus, when the inverter is running. It is doable, but requires some more solenoids.

You have in general the same issue with a single bank and combi devices too when you want bus separation. I have solved it by other means controlling the Victron separately by signals from the BMS and giving it a third independent bus with a solenoid. This setup would not work in a two battery scenario, it would shortcut the buses.

[Dockhead]

Originally Posted by CatNewBee

Two independent LFP batteries is also a complex thing.

In general there a re two approaches.

One is to create 2 encapsulated systems, each with its own BMS, and a dedicated solenoid that handles both charging and discharging. (OVP / UVP) for each battery. Then run them either always in parallel or alternate them during discharge by a controller / combing them when charging and on heavy loads.

There are such systems for FLA batteries, you need something similar for higher amps: (NDS iManager)

Another option is to do it manually having one bank in stand-by and the other active and switching between them. Then you have some redundancy and spare capacity to switch to.

The second option is more complex by separating charge buses and discharge buses for both batteries by using high current semiconductors as battery separators / combiners. Both batteries will then be independent and separated - no cross currents, but act as one all the time.

I really appreciate that you have done a lot of work and a lot of engineering on this. I really hope you will continue to share with us all the knowledge that you have gained.


If I had two lithium banks, I would want them to be entirely independent and redundant, each with its own BMS and charging system, used in turn by switching back and forth. The purpose of this would be to gain redundancy and backup. I would not see any point to the other configuration you mentioned.



Who was it -- MaineSail? -- who said we have to completely put behind us all the habits of thought we got from lead. Here is a great case of this.


You just DON'T DO that with lead -- switch back and forth between two possibly partially charged banks. But lithium JUST DOESN'T CARE. It's like having two fuel tanks.


I would not be considering this at all but for the basic architecture of my boat's power system, which has two basically separate electrical systems -- one for house loads, and one for technical loads, each with its own battery bank. The electrical system of my boat is really beautifully designed and executed -- best I've ever seen on a boat -- and I have always tried to preserve it as much as possible. I screwed it up in some respects by combining the two lead banks years ago, and one strong appeal of changing the battery system now is to restore to some extent the original architecture of the system.