LFP FLA hybrid

[john61ct]

Originally Posted by evm1024

We are having a good conversation with a relatively high signal to noise ratio.

Trying to anyway 8-).

Dockhead, your issue with charge efficiency is certainly valid, in theory and on paper.

However I think experiment / prototyping projects are IRL well worth trying.

The high-amp ICE-to-LFP charging piece is so quick and effortless, so plentiful almost free energy input, seems academic IMO to be so concerned about what may prove in practice minor wastages.

Obviously I'm talking about scenarios where the owner wants to reduce ICE runtime.

If you are running those sources 8 hours a day anyway, then yes scrap the idea completely unnecessary.

If just a little solar is enough for the long tail ditto.

But just accepting PSOC murder, or running big ICEs to push tiny currents for many hours, neither seems acceptable

To me

[john61ct]

Constructive tangents are a wonderful added-value, often the best source of increasing knowledge overall.

Only the OP should police their thread, except when egregious time wasters try to subvert the group's intended discussion flow with unproductive trolling.

[CatNewBee]

Originally Posted by evm1024

In my case that small lead bank is the start battery (and actually the windless battery). Along with a single larger LiFePO4 main bank.

I'll be starting a new thread on where I am going with mine RSN (real soon now).

Till then carry on, We are having a good conversation with a relatively high signal to noise ratio.

This is the optimal dessign, because small cheap FLA start batteries are used exactly for what they are designed for, to start an engine and get quickly re-charged by the alternator, with very little discharge and staying all the time at 100% SOC. That is, what lead technology was developed to do. Small, light and powerful batteries for cranking a starter for a few seconds. AGM's are best at it. While it is possible to use LFP here too, it makes very little sense to do so - except you are very weight sensitive.

On the other side - high capacity deep discharge deep cycle batteries with little voltage drop and high efficiency, insentive to partial charging / discharging and sulphation - that is the playground of LFP.

If you use inverter on regular base to power high-demand loads, you'll wreck any FLA very soon, but a LFP will be happy about such abuse. The main reasons for migration are thise use pattern: propulsion (main power train, bow trusters etc.), diving compressors, water maker, electric galley, A/C, electric winches, windlasses, electro-hydraulic autopilots, washing machines and dish washers, large fridges and freezers, efficient use of renewable energy and enjoing silence in remote anchorages without the need to run generators.

[Dockhead]

Originally Posted by evm1024

In my case that small lead bank is the start battery (and actually the windless battery). Along with a single larger LiFePO4 main bank.

I'll be starting a new thread on where I am going with mine RSN (real soon now).

Till then carry on, We are having a good conversation with a relatively high signal to noise ratio.

OK, but I don't think that connecting a starting battery into the system is actually a hybrid bank along the lines that the OP and others have been discussing it.


Do you use the starting battery to provide backup power to any systems (which ones?). Or just as a "dump load"?

[CatNewBee]

Originally Posted by Dockhead

OK, but I don't think that connecting a starting battery into the system is actually a hybrid bank along the lines that the OP and others have been discussing it.


Do you use the starting battery to provide backup power to any systems (which ones?). Or just as a "dump load"?

The silliness of a hybrid approach was sorted out on the first few postings in this tread. After 200+ comments we have pictured potential pitfalls or solutions to problems that simply would not occur if you use a plain design and not mix-up FLA with LFP.

But back to your question and sorry that it does not relate to the original proposal of the hybrid system of the tread starter.

I have had 3 start batteries, one per engine and one for the generator, the last was removed after dead and now the genny is started by the port engine start battery.

There is a "hybrid" thing as far as the startbatteries are charged by the alternators along with the LFP, the battery monitor is connecting and disconnencting legacy charge sources, the start batteries and the LFP are also charged by shore power chargers considered "legacy chargers" with separate outputs, and the start FLA batteries can be charged by this chargers by the house bank using the inverter and the shore power chargers if necessary to top them off.

Now to the redundancy discussion.

There ts a power transfer switch that allows to jump-start either engine by combining both independent start batteries in case one of them fails unexpectedly.

With a small change in wiring (one bridge or a battery selector switch) it is possible to:
- use the house battery to start engines and generator
- use the combined start batteries to emergency power on-board electronics when the house bank fails unexpectedly and un-recoverably - of course with only emergency power for few vital systems like navigation, communication and bilge pumps.


It is not intended to use LFP to regulary top up FLA, but to do it when necessary - e.g. once a month, when not using the engines for a long time either while sailing or anchoring somewhere without shore power.

[rom]

Originally Posted by CatNewBee

This is the optimal dessign, because small cheap FLA start batteries are used exactly for what they are designed for, to start an engine and get quickly re-charged by the alternator, with very little discharge and staying all the time at 100% SOC. That is, what lead technology was developed to do. Small, light and powerful batteries for cranking a starter for a few seconds. AGM's are best at it. While it is possible to use LFP here too, it makes very little sense to do so - except you are very weight sensitive.

On the other side - high capacity deep discharge deep cycle batteries with little voltage drop and high efficiency, insentive to partial charging / discharging and sulphation - that is the playground of LFP.

If you use inverter on regular base to power high-demand loads, you'll wreck any FLA very soon, but a LFP will be happy about such abuse. The main reasons for migration are thise use pattern: propulsion (main power train, bow trusters etc.), diving compressors, water maker, electric galley, A/C, electric winches, windlasses, electro-hydraulic autopilots, washing machines and dish washers, large fridges and freezers, efficient use of renewable energy and enjoing silence in remote anchorages without the need to run generators.

In your opinion. Not mine. You described your Lagoon electrical system in a later post, this is a complete nightmare. My opinion is everything should directly connected to the house batt. Add to that a safety batt connected to the system through a 1/2/both/off switch, job done.



And now if that safety batt is LFP, you just need to make sure every now and then it is properly sitting at 50% SOC.

[CatNewBee]

Originally Posted by rom

In your opinion. Not mine. You described your Lagoon electrical system in a later post, this is a complete nightmare. My opinion is everything should directly connected to the house batt. Add to that a safety batt connected to the system through a 1/2/both/off switch, job done.



And now if that safety batt is LFP, you just need to make sure every now and then it is properly sitting at 50% SOC.

Well, yes, but is is waste of capacity and money if you just keep a LFP at 50% SOC and not using it for 20 years (MTBF of a LFP bank)

[rom]

Originally Posted by CatNewBee

Well, yes, but is is waste of capacity and money if you just keep a LFP at 50% SOC and not using it for 20 years (MTBF of a LFP bank)

About 200 EUR for 40Ah@12V. That should be way less than your 2 start batteries, switches, diode splitters and cables. Isn't it ?

[CatNewBee]

Originally Posted by rom

About 200 EUR for 40Ah@12V. That should be way less than your 2 start batteries, switches, diode splitters and cables. Isn't it ?

Well, NO. They were there already installed and operational when I bought the boat. I will use them as-is until they die.

But if I have to built something with no legacy-conditions, probably I would consider a single start battery for both engines - and maybe even a cheap deplorable 40Ah LFP drop-in 12V block without a BMS for the job, yes.

I doubt, it would be sufficient as a back-up system in case the main bank fails - especially if held all the time at the suggested 50% SOC.

[Dockhead]

Originally Posted by CatNewBee

Well, NO. They were there already installed and operational when I bought the boat. I will use them as-is until they die.

But if I have to built something with no legacy-conditions, probably I would consider a single start battery for both engines - and maybe even a cheap deplorable 40Ah LFP drop-in 12V block without a BMS for the job, yes.

I doubt, it would be sufficient as a back-up system in case the main bank fails - especially if held all the time at the suggested 50% SOC.

OK, so here's a directly relevant question for everyone thinking about hybrid - do we think we NEED emergency backup?

The answer to this may vary according to use case, of course. I was a couple hundred miles above the Arctic Circle thus summer.

[Dockhead]

Originally Posted by CatNewBee

The silliness of a hybrid approach was sorted out on the first few postings in this tread. After 200+ comments we have pictured potential pitfalls or solutions to problems that simply would not occur if you use a plain design and not mix-up FLA with LFP.

But back to your question and sorry that it does not relate to the original proposal of the hybrid system of the tread starter.

I have had 3 start batteries, one per engine and one for the generator, the last was removed after dead and now the genny is started by the port engine start battery.

There is a "hybrid" thing as far as the startbatteries are charged by the alternators along with the LFP, the battery monitor is connecting and disconnencting legacy charge sources, the start batteries and the LFP are also charged by shore power chargers considered "legacy chargers" with separate outputs, and the start FLA batteries can be charged by this chargers by the house bank using the inverter and the shore power chargers if necessary to top them off.

Now to the redundancy discussion.

There ts a power transfer switch that allows to jump-start either engine by combining both independent start batteries in case one of them fails unexpectedly.

With a small change in wiring (one bridge or a battery selector switch) it is possible to:
- use the house battery to start engines and generator
- use the combined start batteries to emergency power on-board electronics when the house bank fails unexpectedly and un-recoverably - of course with only emergency power for few vital systems like navigation, communication and bilge pumps.


It is not intended to use LFP to regulary top up FLA, but to do it when necessary - e.g. once a month, when not using the engines for a long time either while sailing or anchoring somewhere without shore power.

I'm not sure if I agree with you about the "silliness" of hybrid lead-lithium power. Although this issue of charge efficiency during the finish charge has dealt a blow to my thinking about this, there are still some possible benefits to this kind of arrangement.


One big one (possible benefit) is to simply provide some kind of backup power without intending to regularly use the lead bank. Lead is still a very viable technology for backup power, as evidenced by the prevalence of lead batteries in industrial and telecomms backup power systems.


I see that some of you guys who have already implemented lithium power are not bothering with any kind of backup power, and maybe I'm being paranoid thinking many of us need it.


On my boat, I have two large truck batteries used to start the main engine and generator, respectively. These could be wired together to provide enough 24v power to run my lighting, navigation gear and radios, and probably other stuff too, and these batteries can be charged by either of two 12v charging systems which are entirely separated from the main power system. Maybe that's enough, and maybe the OP and others can do it like that, too. I don't know.




By the way, the very poor charge efficiency of lead during the finish charge is a drawback of lead batteries which affects not only this question. As we heard from the OP -- this reduces the efficiency of solar power, too. It's obvious that generator and alternator charging is made much more efficient with lithium, but solar benefits also from not having to waste energy heating up the batteries for hours during the finishing charge. This energy can be just directly stored by lithium and used later. You will not care about this only if you have a big surplus of solar power, such that you don't really have anything better to do with the power you produce.

[john61ct]

Still better that all current goes into the bank, then switched to the "surplus loads"

Rather than the hours of crossover as amps acceptance reduces,

you don't want loads to take too much and interfere with the charging

[Delfin]

Originally Posted by Dockhead

OK, so here's a directly relevant question for everyone thinking about hybrid - do we think we NEED emergency backup?

The answer to this may vary according to use case, of course. I was a couple hundred miles above the Arctic Circle thus summer.

You mean like start the genset?

[Delfin]

Originally Posted by Dockhead

Borgward is a MUCH better engineered vehicle than a Corvette!




I think though that I have come up with the biggest argument of all against any kind of hybrid bank. It's a big one and maybe takes this off the table for me.



And this is something like your own point, actually.


That is the CHARGE EFFICIENCY during the finish charge of the lead.


A main premise of the hybrid bank is that you can use the high acceptance rate of the lithium and indifference to PSOC to give the lead part of your bank an ideal finish charge every cycle.


So one variant of the hybrid bank is a lead-centric one where the lead is as large as possible (say 450 amp/hours * 24v in my case) and the lithium then needs to be only big enough to put on a finishing charge and support house loads during the finishing charge process -- say 100 amp/hours.


But wait a minute --you can't just take the nominal volume of the finishing charge -- say 15% * 450 amp/hours. AFAIU, charge efficiency goes down to something like 50% during this stage. So it's actually going to take you not 70 amp/hours but 140 amp/hours of energy to put the finishing charge on a 450 amp/hours lead bank -- bah!



So for such a lead bank, you will be using a nearly 200 amp/hour lithium bank to do nothing but heat up your lead bank while it's getting it's stupid finishing charge.


This is a stupid use of this beautiful technology!!


This is less of a problem if the lead bank is relatively smaller and the lithium relatively larger, and becomes dramatically less of a problem as these proportions change.


I think this invalidates the idea of using a relatively small lithium bank for a finishing charge of a relatively large lead bank.


Query whether a relatively small lead bank does enough of anything useful to be worth messing with.



So that brings me back to dual lithium banks, or just a massive lead bank made up of lead batteries which are reasonably tolerant of PSOC cycling, like those Trojan L16's.



Or a relatively small lead bank to do nothing but provide backup power in case of some kind of fault in the lithium system. I would have to compare the cost, but in this configuration the lead doesn't really provide any daily usable power, or very little. This probably doesn't make any sense compared to dual ilthium, where you get the redundancy but all of the power is usable on a daily basis.



That means the combined size of the dual lithium banks can be about the same as the single lithium you would need in the hybrid bank. There is not much cost difference (one extra BMS, one extra battery monitor, one set of controls, basically), and not really any disadvantage in functionality given the absence with lithium of those reasons we have for lead, to avoid splitting up banks.


A small lead backup bank could make sense if we analyze the cost of it, including any extra equipment we have to buy, as if the capacity of the lead adds nothing to the system, but all this cost is less than the cost of the extra gear needed to split the lithium bank up. Another consideration might be whether this would be simpler to operate -- so no switching back and forth between different banks, for example.


But to my mind, this is a huge hit against the hybrid idea.

I believe I suggested, lo these many posts ago, that the size of the LFP bank to do what was expected of it in the envisioned hybrid configuration was a great deal larger than folks were suggesting. I should have been more explicit why, but your explanation is a good one.

[CatNewBee]

FLA as always charged backup is for me personaly a no-go. I have used smaller inline UPS for years for my servers and other gear, they use AGM batteries inside, always on, and stay charged. Everey 2nd year there is a power outage and guess what happens, systems crash, because the batteries fail. overcharged and dried out.

It is not a good idea to just keep FLA on float all the time.