Practical Questions about LiFePo4 Power Systems

[Dockhead]

Originally Posted by daletournier

The point I was trying to make is, how much do you gain in real life by going the lithium way? I used my own experience as an example, on paper I could see all these wonderful advantages BUT the longer I thought about it the more I realised it wouldn't change or improve my cruising at all, or at least very little.

Catnewbee determined it would and did improve his cruising considerably.

You have all the information you could possibly want regarding this subject, only you can decide if or how much of an improvement it will make to your cruising life and if that improvement is worth the cost and energy of instalation.
No wrong decision here, just cost VS returns.

Well, naturally. This is the question.


I'm not asking for anyone to tell me the answer -- I'm trying to build up the basis of technical knowledge which I will need to answer it myself.


As to improving cruising life -- it's simple. My lead-acid bank irritated me this summer, demanding more attention and far more generator time, than I thought was appropriate, running down too quickly and too often. That's all. I'm exploring whether my cruising life, on my boat and according to my own use pattern, might be improved with lithium to the extent that it's worth the expense and trouble. The jury is still out.




But another aspect of it is that it is INTERESTING. It's not like I have loads of free time and am looking for more and more projects (God forbid), but I would ENJOY engineering and implementing a system like this, and it would give me pleasure if it worked well. Cruising is a hobby, after all. This by itself is of course not a reason to make the switch, but it adds a little something to the scales on that side.

[john61ct]

Originally Posted by daletournier

I suppose my point is, how much improvement, how much extra happiness do you get for the money and energy spent? Law of diminishing returns.

Boats that can't fit or carry that much lead.

PSOC abuse leading to fast death, or desire for no solar.

Need to keep voltage higher under heavy loads.

Are the three more compelling reasons.

Otherwise just a preference.

[john61ct]

Originally Posted by senormechanico

That's why I don't have a LVD.

that does not compute for me, I prefer to prevent damaging the bank, and can't rely on my watching an SoC meter myself manually.

[Dockhead]

Originally Posted by john61ct

In that case I'd put all charge sources especially the alt to the Main/House lead bank. Regular ACRs to Starters, any other lead banks.

One Sterling B2B, big as possible, to feed Reserve LFP at perfectionist setpoints, BMS protected as you like.

A second, smaller B2B to go the other way, keep the lead bank "long tail" charging from LFP once the primary charge sources are shut down. Of course only if needed, haven't been getting to 100% for a few days.

Or old school solution, cheap lead replaced more often, if that makes more sense for you.

OK, I'm starting to get my head around this, and I like it. Not so much because it's the supremely elegant architecture for a hybrid lead/lithium power system, but because it might just fit into my boat using 90% of the original and beautiful power system.


So the idea would be to make the lead bank the primary power supply for house loads (inverter and technical loads, however, connected directly to lithium). So the whole system goes back to its original configuration, except:




1. Separate AC battery charger for the lead.


2. Victron inverter/charger connected to the lithium.



3. A new path for charging lead from lithium (and charge sources connected to lithium) is created via a Sterling B2B charger.


This will allow the house loads to be practically run from the lithium as the B2B charger is acting as a power supply -- as if I were on shore power. if the lithium runs out or gets disconnected or gets shut down by me, the lead just takes over, just as it would, if I had disconnected shore power or shore power had failed. Otherwise, the entire system is working just like when my boat was built, with one bank attached to the technical loads, and the other bank attached to the house loads. So far so good!



That leaves the alternator, again as the only problem. I don't think it would be possible to connect it to the lead, with a second B2B charger on it -- there would be conflict with the other one which would not be able to sense which way the power is flowing from the voltages. I think the alternator needs to be connected to the lithium, from where it will power the lead via the B2B charger. Then it just needs some kind of dump load on it, perhaps via the existing diode splitter, or maybe protection can be provided in some other way (flyback diode?). Or maybe really just cutting the field current is enough, with a small delay in the LVC relay. I guess I'm going to need a proper EE for this part.



This is very elegant, I think, and would not require any expensive reconfiguration of my existing electrical system, since it builds so much on the existing architecture.




Another significant plus is that the lead will not just be sitting there waiting to be used as reserve power -- its capacity can be used fully, and with an ideal usage regime using the lithium bank to do the tail charge up to 100% every time it's cycled. I believe this will allow reduction of the size and therefore cost of the lithium bank. This is very good.

[daletournier]

Originally Posted by john61ct

Boats that can't fit or carry that much lead.

PSOC abuse leading to fast death, or desire for no solar.

Need to keep voltage higher under heavy loads.

Are the three more compelling reasons.

Otherwise just a preference.

I agree, regarding boats that can't carry sufficient fla.

From what I see in the cruising world most banks suffer from PSOC, many suffer due to lack of knowledge not due to lack of charging options. That lack of knowledge regarding basics of fla isn't likely to improve with the step up to liFepo4 although one may suggest a greater understanding is required.

That said I see many banks of fla lasting years even though they live permanently in a PSOC and in recent times I seem to be coming across more LiFepo4 setups with owners that have little understanding of their setups yet are having no problems. This suggests to me we maybe all a little anal here when it comes to battery management? .. Lol.

One thing that I'm not convinced about yet is the number of life cycles claimed by Lifepo providers. Are there enough of them out there in the cruising world and for a long enough time yet to know these claims to be true?

[LifePart2]

When I installed our lithium house bank 3 years ago I found the advice out on the net to be very confusing.

Eventually I figured out that it was actually very simple, once one accepted that we are on cruising boats and not radio controlled airplanes or electric cars.

And so I wrote an ebook on How to Install and Maintain your Lithium House Bank. It is offered here, free of charge, with no warranties of any kind. I hope you find it useful.

[newhaul]

Originally Posted by LifePart2

When I installed our lithium house bank 3 years ago I found the advice out on the net to be very confusing.

Eventually I figured out that it was actually very simple, once one accepted that we are on cruising boats and not radio controlled airplanes or electric cars.

And so I wrote an ebook on How to Install and Maintain your Lithium House Bank. It is offered here, free of charge, with no warranties of any kind. I hope you find it useful.

thank you noel.

[Dockhead]

Latest thinking.

[curtis742]

It would seem to me these issues could be resolved by running all charge sources through charge controllers. One set for lfpo the other set for fla.

[CatNewBee]

Originally Posted by daletournier

The point I was trying to make is, how much do you gain in real life by going the lithium way? I used my own experience as an example, on paper I could see all these wonderful advantages BUT the longer I thought about it the more I realised it wouldn't change or improve my cruising at all, or at least very little.

Catnewbee determined it would and did improve his cruising considerably.

You have all the information you could possibly want regarding this subject, only you can decide if or how much of an improvement it will make to your cruising life and if that improvement is worth the cost and energy of instalation.
No wrong decision here, just cost VS returns.

For me it was comfort. Nor looking for propane refill, differend adapters, bottles in differend countries etc. Energy is just there when needed, no genny hours. And if ever, 2 ..3 hours genny time would recharge the 1000Ah battery from empty to full. Even electric heating and A/C is an option.

But I do recon, there are people striving for the simple life, making fire with two dry sticks and eating raw fish (sushi) ;-).
They web their fabric for the clothes themselves and wash them in the river. That is O.K.... but not my life style.

[john61ct]

Originally Posted by Dockhead

OK, I'm starting to get my head around this, and I like it.

Great, and of course some more food for thought.

> So the idea would be to make the lead bank the primary power supply for house loads (inverter and technical loads, however, connected directly to lithium).

I would make the lead the only bank to get primary charge sources. The only LFP charging is via a big B2B.

The problem with Kombi inverter chargers and LFP is not possible to isolate from Loads (LVD) separately from Charging (HVD). That is usually done with separate busses for LFP.

Loads can be switched between banks as desired by grouping into circuits (IMO by importance) and A/B switches.

> This will allow the house loads to be practically run from the lithium as the B2B charger is acting as a power supply -- as if I were on shore power.

Thus the Victron Kombi can be on the lead bank?


> That leaves the alternator, again as the only problem. I don't think it would be possible to connect it to the lead, with a second B2B charger on it -- there would be conflict with the other one which would not be able to sense which way the power is flowing from the voltages.

I see the routine high-amp charging from (all) primary charge sources going through the lead and big-B2B to LFP. Remember the LFP high CAR will mean you will stop its charging much more quickly than the lead bank.

As long as there is an active charge source, the lead will not need the small-B2B.

Only if all primary sources are inactive, and lead bank not yet Full, will you turn on the small-B2B.

And that may only be a few times per month. Even if you never get to Full without it, no more than 2-3 times a week.

[john61ct]

Originally Posted by daletournier

From what I see in the cruising world most banks suffer from PSOC, many suffer due to lack of knowledge not due to lack of charging options. That lack of knowledge regarding basics of fla isn't likely to improve with the step up to liFepo4 although one may suggest a greater understanding is required.

Totally different topic domain. Those well versed in lead bank management need to **unlearn** a lot of ingrained assumptions and thought habits.

> That said I see many banks of fla lasting years even though they live permanently in a PSOC

Years is not a high bar, as in 3-5. 8-15 takes better care. Assuming good quality of course.

> LiFepo4 setups with owners that have little understanding of their setups yet are having no problems.

Again, just getting 7-9 years should be pretty guaranteed with a packaged system, barring accidents.

Doing it yourself from bare prismatics + DIY protections takes a much higher level of knowledge and care.

Getting to 15-20+ years means going **against** vendor recommendations, their predicted lifespans are **way** too low, longer is not in their interests.

[mbartosch]

Originally Posted by john61ct

The problem with Kombi inverter chargers and LFP is not possible to isolate from Loads (LVD) separately from Charging (HVD). That is usually done with separate busses for LFP.

Connect the 12 V leg of the Charger/Inverter to the load bus (LVC). The shore power AC line is routed through a Normally Closed relay which gets triggered by the BMS HVC. Problem solved.

[missourisailor]

Originally Posted by mbartosch

Connect the 12 V leg of the Charger/Inverter to the load bus (LVC). The shore power AC line is routed through a Normally Closed relay which gets triggered by the BMS HVC. Problem solved.

Doable, but there are some consideration that must be taken into account.

First, as most Combo units are pass through, when you open the shore power leg because of an OV event, you also will lose all AC (alternating current not air conditioning) on the boat. Unless the inverter switch is on. Which now means that all AC power is coming from the batteries through the inverter.
Which is not really a bad thing unless you have a high amperage load operating. Like a water heater. Which can drain the bank pretty quick. Once again, not a major deal if you are aware what is happening. And can shut things down.
But if you are away from the boat, you may come back to a ruined bank.

The way around this is to leave the inverter off when not in use. With the knowledge that in case of an OV event, you will also lose the whole AC buss.

Second, a lot if not most combo units don’t even have LiFePo settings. Quite a few don’t even have “true” custom settings. So getting the proper charge profile can be problem matic.

What you propose is more than doable, but to be honest most DIY’ers need to change out everything any how. So it is just easier to buy separates.