LFP FLA hybrid

[Dockhead]

Originally Posted by tanglewood

I see this as one of the big downsides to swapping in an LA battery when the LFP is full. You now have limited power for thrusters, large inverter loads, and inverter features like power assist from batteries when on shore or generator.

Well, my proposal is not to "swap in" the lead bank.


All the heavy loads in my hypothetical installation would be connected to the lithium bank.


But as John observed, once the SOC drops below the hysteresis point, or if there is enough voltage sag, the alternator will be re-connected to the lithium bank. I think this should work if the control system works.

[Dockhead]

Originally Posted by john61ct

Why not start a new thread?

#1 introduce the new Sterling gadget, link to the docs and explain its purpose how it works.

Charles sometimes creates Solutions in search of an actual Problem.

This will force you to really figure it out, "if you want to learn teach".

Once it seems we all are au fait with it, after any relevant discussion / debate has settled down (hopefully ignoring any trolls that may appear)

then #2 let's break down how it may fit into your use case, up to you in that thread or (IMO best to) link to a new one

Good idea!


Et voila:


Sterling "Alternator Lineariser" - Cruisers & Sailing Forums

[john61ct]

I claim no authority, just making suggestions and requests, doing my best to help the community as a whole.

[tanglewood]

Originally Posted by Dockhead

Well, my proposal is not to "swap in" the lead bank.


All the heavy loads in my hypothetical installation would be connected to the lithium bank.


But as John observed, once the SOC drops below the hysteresis point, or if there is enough voltage sag, the alternator will be re-connected to the lithium bank. I think this should work if the control system works.

Got it. I was thinking of Delfin’s system which is another hybrid variation.

[Dockhead]

Originally Posted by tanglewood

Got it. I was thinking of Delfin’s system which is another hybrid variation.

Sure.


The idea for mine looks something like this:

[rgleason]

Here are some nicely done LiFePo Design Diagrams

[Delfin]

Originally Posted by tanglewood

Got it. I was thinking of Delfin’s system which is another hybrid variation.

I have hydraulic thrusters, so avoid the big load they would place on the starter bank when I reach the dock after the LFP bank has been taken off line after charging. In my setup, if I had electric thrusters it would require additional wiring.

You would know better than I, but would it not be possible to trigger the BMS back on from a switch in the pilot house to bring the LFP bank online when you want the extra oomph?

[Delfin]

Originally Posted by Dockhead

Sure.


The idea for mine looks something like this:


Attachment 177322

Given the different busses you have for technical and house loads, that seems like a workable solution. The BMS would provide the LVC and HVC switch noted.

Absent dual busses, I'm still visualizing a corvette towing your Father-in-Law's Borgward up a steep hill.....

[ramblinrod]

Originally Posted by Dockhead

Sure.


The idea for mine looks something like this:


Attachment 177322

Need to protect the alternator from a disconnect with the LFP bank.

[Dockhead]

Originally Posted by ramblinrod

Need to protect the alternator from a disconnect with the LFP bank.

You are not paying attention. Read back through the thread and you will see that this is discussed in detail.

[john61ct]

I * think we should spend a lot of time and energy arguing about what we should be arguing about.

* do not

[ramblinrod]

Originally Posted by Dockhead

You are not paying attention. Read back through the thread and you will see that this is discussed in detail.

I was paying attention to the diagram posted. Not shown.

BTW, this thread is supposed to be about commenting on the OPs FLA/LFP design.

Who’s not paying attention?

[Dockhead]

Originally Posted by Delfin

Given the different busses you have for technical and house loads, that seems like a workable solution. The BMS would provide the LVC and HVC switch noted.

Absent dual busses, I'm still visualizing a corvette towing your Father-in-Law's Borgward up a steep hill.....

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.

[Dockhead]

Originally Posted by ramblinrod

I was paying attention to the diagram posted. Not shown.

BTW, this thread is supposed to be about commenting on the OPs FLA/LFP design.

Who’s not paying attention?

This thread is not about the OP's design. It is about hybrid banks in general.


All the drawings are schematic and not every design feature is shown. Alternator protection -- a trivial issue -- is extensively discussed. We even started a separate thread on the Sterling device which would be the best candidate for dealing with this and another design problem.


Really, if you want to actually participate in the discussion rather than just disrupt it for the sake of propagandizing for your own single solution to all power system tasks, please read before posting.

[evm1024]

Originally Posted by Dockhead

SNIP

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.

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.