LFP FLA hybrid

[Dockhead]

Originally Posted by john61ct

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.

Combining the banks would defeat a main system architectural feature of such a system.


But I think there is far less need for this with lithium, considering the near absence of Peukert and total absence of a need for a finishing charge.

[rgleason]

Tanglewood
What is "Most cell specs allow for 2C discharge, " this? Unheard of.

[Dockhead]

By the way, does anyone know whether you can still switch on and off, individual Victron Multipluses, individually, when they are ganged together?


If I did do dual lithium, I would add not an additional charger only, but an additional charger/inverter, provided I could choose "either" as well as both, depending on the SOC of the individual banks.


Also, to gang them together, do they need to be identical models?

[john61ct]

Originally Posted by Dockhead

Combining the banks would defeat a main system architectural feature of such a system.


But I think there is far less need for this with lithium, considering the near absence of Peukert and total absence of a need for a finishing charge.

I meant only while drawing C+ loads like your bow thrusters.

1-2-B switch for load direct.

So isolated from each other 99% of the time

Possibly for high-amp charging as well if you didn't use a 500A ACR to routinely automate that.

[rgleason]

John, when I write FLA I mean floodedleadacid batteries, nothing more. Trojan T -105. I've had Gel and AGM but when talking about voltages etc I stick to fla right now.

[tanglewood]

Originally Posted by Dockhead

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.

My thinking so far is to just parallel the two LFP banks. So the load side of the disconnect relay is tied together. Charging and loads are all common to which ever banks are on line, and the emergency battery disconnect relay determines if the bank is on line. So the only time a bank drops out is if its BMS panics and pulls it off line.


This makes for a simple setup utilizing the existing BMS capabilities. The down side is that if one bank does drop out, it can then be an exercise to get is recharged in sync (i.e. re-balanced) with the other bank. So those darn trade-offs keep popping up again.

[john61ct]

Originally Posted by rgleason

Tanglewood
What is "Most cell specs allow for 2C discharge, " this? Unheard of.

No that is normal.

Again, not drop-ins where a cheap BMS gets in the way.

Direct access to and from the prismatic cells themselves.

[john61ct]

Originally Posted by rgleason

John, when I write FLA I mean flooded lead acid batteries, nothing more.

Yes that is the canonical meaning.

Your confusion above I thought was maybe due to the use of "LA", which just means lead in general.

[john61ct]

Originally Posted by tanglewood

The down side is that if one bank does drop out, it can then be an exercise to get is recharged in sync (i.e. re-balanced) with the other bank.

Unlike series strings, I believe paralleled banks should naturally self-balance.

Robust inter-block connections should handle high current between full and empty blocks, maybe test to see if an over-temp timed cutoff would be called for.

[ramblinrod]

Originally Posted by john61ct

A fully setpoint adjustable B2B DCDC charger will convert any primary source feeding your FLA bank to exactly what you want your LFP bank to receive.

If anyone knows one besides Sterling's let me know.

Much better solution than doubling up on separate mains / solar / alt+VR setups.

I concur.

This eliminates the possible equipment damaging transients that can occur when a BMS LVD and HVC activates.

It will also prevent alternator rectifier failure from sudden open circuit on LVD activation.

[tanglewood]

Originally Posted by rgleason

Tanglewood
What is "Most cell specs allow for 2C discharge, " this? Unheard of.

Just read CALB and/or Winston's cell spec sheets. Also the more packaged offerings from Victron, Mastervolt, Lithionics, Relion, etc., some of which I know are built around those cells, and others I expect are too.

[tanglewood]

Originally Posted by john61ct

Unlike series strings, I believe paralleled banks should naturally self-balance.

Robust inter-block connections should handle high current between full and empty blocks, maybe test to see if an over-temp timed cutoff would be called for.

Yes, good point. I forgot about that. In fact, somewhere I found a research paper where someone explored the cross-charging currents and the time to achieve balance between cells (he was looking at cells in parallel, not series strings, but I think the principals should still hold). There was a lot less current, and it took a lot less time to balance than one might intuit. Now if I could only figure out where I found that paper.......

[Delfin]

Originally Posted by 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.

Not so sure about #1 above. My experience is that there is no tail at all for LFP. I've posted this before, but the below illustrates the point. Besides, LFP doesn't have PSoC issues, so even if there were a long taper to reach full charge (and there isn't), it wouldn't matter.

On number 2, again, my experience is that the conversion to LFP was seamless. The only sense wire I added was to disconnect the alternator if the BMS hits a high voltage target that indicates the system is in run away mode.

On number 3, well, testify brother. You are right there, especially if you buy one of the integrated systems rather than rolling your own.

[ramblinrod]

Originally Posted by Dockhead

So, in response to Four Winds:


I think that something like this might actually make a great deal of sense even on a small boat and on a limited budget.


I think the idea of a hybrid lithium-lead bank is very powerful and might be applicable to a wide variety of use cases.


First of all, for you to advance your thinking on this, you need to read carefully the manual for the Sterling B2B charger and get a thorough understanding of how it works. Here: https://sterling-power.com/products/...rip-proof-ip21



It is most certainly not a combiner. It is a full fledged battery charger which creates its own charging profile. It is merely powered by DC; the charging profile has nothing to do with what is going on on the supply side. This is really cool and key to an application like this, because it means you can regulate the alternator (or other chargers, too) to suit the primary bank exactly, and then charge the secondary bank with its own completely different profile.





I would definitely put the alternator on the lithium bank, for the reasons I mentioned in the last post. If the lithium bank goes down, your loads will continue to be powered by the lead bank, and you can manually override the B2B charger to force it to work with no primary battery attached (Sterling calls the primary battery the "output battery"), passing alternator power on to it.


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.


If the lithium is quite small in relation to the lead bank size, I think you could then go back to connecting the alternator to the lead bank, but then you would need TWO B2B chargers (£££), and you would need to construct a way to switch them over so they're not connected at the same time. But, you would gain a great deal of simplicity and simplicity in operation. You would just need to manually switch back and forth between charging the lithium and using power from the lithium.

Danger Will Robinson....

If you connect high current charging sources to a Lithium bank directly, when you hit HVD it can induce equipment damaging transients through all devices connected (think nav electronics and refrigerant compressor modules).

Additionally, when LFP HVD activates your alternator could be facing "open circuit" and take out the rectifier diodes.

[john61ct]

Originally Posted by ramblinrod

This eliminates the possible equipment damaging transients that can occur when a BMS LVD and HVC activates.

It will also prevent alternator rectifier failure from sudden open circuit on LVD activation.

Yes to the latter, no to the former.