Depth of Discharge Myth?

[a64pilot]

Originally Posted by Dockhead

You will need some kind of battery in the system to use alternator power to keep your systems on.








It's a valid point, and to my mind and for my use case a major disadvantage of lithium -- I mean the complexity of having another battery or another bank as backup or at least dump load.


I don't know what is the relevance of the freezer remark, however. I never leave refrigeration running when I'm off the boat for more than overnight in any case, which means I throw out tons of food. I was always afraid someone might kick the shorepower plug out and the reefers would kill my batteries. If they are being run off lithium with a LVC perhaps it could be worth the risk from time to time -- you risk the stink, but not ruining batteries. A backup bank would be useless in this case and irrelevant -- would just delay the inevitable by another day or whatever.



Same thing with bilge pumps -- there is no reason to set up the bilge pumps to be able to kill your batteries. If you have a leak with no one aboard, either someone will notice and do something, or if they don't, the batteries will die and your boat will sink. A few hours plus or minus is not going to make any difference. Even with uninterrupted shore power -- the pumps will clog or burn up and your boat will sink. This is why I NEVER leave the boat even overnight without closing all my through hulls.

That is a difference in our use.
First, I often have hundreds of dollars in frozen steaks etc on board at a time, my freezer is 7 cu Ft, a 55 gl drum is 7.35 cu Ft. My fridge is the same, and if I’m going somewhere the plan is to also have the Engel full of frozen food. I like having months of food on board.
We stay aboard now, hopefully full time, although I learned last year that you can be eating breakfast one day, leave in an hour and not return for months, Boat on a mooring. Stuff that you don’t like, and can not control, happens.
However with a kilowatt of Solar, it ought to keep the bank topped up and run a fridge and pump for a long time. It did anyway.
So I may not plan on leaving the boat for extended intervals, but it can happen. When we left last Jan, we were supposed to be back in 48 hours, instead it was months.

So I think leaving the LFP bank at 50% and disconnected is a smart move, but that requires a separate lead bank, with separate charge sources, or a way to change over charge sources from one bank to the next, that could easily be done with 1,2 all switches of course, just more items.

[Dockhead]

Originally Posted by Kenomac

How many through hull fittings do you have? How long does it take to do all that?

17.


I give myself an hour to flush the toilets through with fresh water and then close all the sea cocks throughout the boat.


It's a pleasant routine which has the additional benefit of exercising the sea cocks -- they will jam up if you don't use them regularly.

[Dockhead]

Originally Posted by a64pilot

That is a difference in our use.
First, I often have hundreds of dollars in frozen steaks etc on board at a time, my freezer is 7 cu Ft, a 55 gl drum is 7.35 cu Ft. My fridge is the same, and if I’m going somewhere the plan is to also have the Engel full of frozen food. I like having months of food on board.
We stay aboard now, hopefully full time, although I learned last year that you can be eating breakfast one day, leave in an hour and not return for months, Boat on a mooring. Stuff that you don’t like, and can not control, happens.
However with a kilowatt of Solar, it ought to keep the bank topped up and run a fridge and pump for a long time. It did anyway.
So I may not plan on leaving the boat for extended intervals, but it can happen. When we left last Jan, we were supposed to be back in 48 hours, instead it was months.

So I think leaving the LFP bank at 50% and disconnected is a smart move, but that requires a separate lead bank, with separate charge sources, or a way to change over charge sources from one bank to the next, that could easily be done with 1,2 all switches of course, just more items.

OK, that makes sense. Different use case.


But why do you need the backup bank? I don't think you do, just to keep the freezer running. Either your solar is covering the consumption, or it's not. If it doesn't, then an extra bank is not going to help you really -- just delay the stink by a day or two. And the extra bank won't do a damned thing that a slightly bigger lithium bank wouldn't do. So this is not an argument for a backup lead bank.

[Dockhead]

Originally Posted by john61ct

I have not seen anyone advocate for a single LFP bank only, no lead on the boat.

My Main / Reserve design, as opposed to House / Starter, adds no extra bank, little extra complexity.

Without an LVD the power's gone anyway, just a bit later and after the bank's been damaged.

LVDs are used more (not exclusively) with LFP because the damage from going dead flat is catastrophic and the up-front investment is higher.

Situational awareness wrt your banks' SoH and SoC on an ongoing basis is required no matter what chemistry they are. **No Surprises** a critical operational goal of the overall design, not just physical infrastructure, but checklisted and scheduled inspection, testing, maintenance, and proactive replacement protocols.

Finally, for me, anyone whose setup requires working electricity for their survival, is not doing it right.

This is a very interesting and insightful post.


I agree that if we were managing our lead banks correctly, we would be doing the same things with them we do with lithium -- we would use BMS.


I only disagree with the last paragraph. Many boats will make electrical power mission critical, consciously. For example: I cover too much difference in my annual summer cruises to possibly keep paper charts of everything on board (as it is, I have a significant fraction of a ton of paper charts, stuffed under every bunk). So I use electronic charting. And on top of that: I could hardly lift my anchor and ground tackle (weighing almost half a tonne between them) without the electric windlass. Making electrical power fail safe with multiple backups is not an overwhelmingly difficult thing.

[a64pilot]

Originally Posted by Dockhead

OK, that makes sense. Different use case.


But why do you need the backup bank? I don't think you do, just to keep the freezer running. Either your solar is covering the consumption, or it's not. If it doesn't, then an extra bank is not going to help you really -- just delay the stink by a day or two. And the extra bank won't do a damned thing that a slightly bigger lithium bank wouldn't do. So this is not an argument for a backup lead bank.

Primarily because Maine Sail recommended you to not leave an LFP bank connected when on a mooring and your away, presumably because an LFP bank is not a set and forget thing, it needs not be left to fend for itself, apparently.
He recommended a second lead bank if you leave it on a mooring.
So I’m just going off of his recommendation, cause I have no experience myself, it’s all theory to me.

[kmacdonald]

The DOD myth is NOT resolved. There are too many people discharging well below 50% and are quite happy with their battery longevity. There are just too many variables to pick a "best" battery type or usage profile for everyone. Everyone's mileage will vary.
Shorter run times of ICE will be the biggest advantage of LiFePO4 for some people and the cost savings could be enormous.

How are you guys with LiFePO4 determine when they are fully charged and how are all of the charging sources being turned off when they are full?

[Dockhead]

Originally Posted by a64pilot

Primarily because Maine Sail recommended you to not leave an LFP bank connected when on a mooring and your away, presumably because an LFP bank is not a set and forget thing, it needs not be left to fend for itself, apparently.
He recommended a second lead bank if you leave it on a mooring.
So I’m just going off of his recommendation, cause I have no experience myself, it’s all theory to me.

I would give a lot of weight to MaineSail's recommendation. Would be nice to know his reasoning, however.

[newhaul]

Originally Posted by a64pilot

Primarily because Maine Sail recommended you to not leave an LFP bank connected when on a mooring and your away, presumably because an LFP bank is not a set and forget thing, it needs not be left to fend for itself, apparently.
He recommended a second lead bank if you leave it on a mooring.
So I’m just going off of his recommendation, cause I have no experience myself, it’s all theory to me.

not 100% sure but I have a suspicion that mainesail is referring to leaving an Lfp for long periods with no usage . If you are maintaining a refrigerator on the boat then you are using the bank not just storing it .

[newhaul]

Originally Posted by kmacdonald

The DOD myth is NOT resolved. There are too many people discharging well below 50% and are quite happy with their battery longevity. There are just too many variables to pick a "best" battery type or usage profile for everyone. Everyone's mileage will vary.
Shorter run times of ICE will be the biggest advantage of LiFePO4 for some people and the cost savings could be enormous.

How are you guys with LiFePO4 determine when they are fully charged and how are all of the charging sources being turned off when they are full?

still learning but I set my solar controller to stop charging when the Lfp bank is about 90% charged.
That's what I set to on customers boats as well.

[evm1024]

Originally Posted by kmacdonald

The DOD myth is NOT resolved. There are too many people discharging well below 50% and are quite happy with their battery longevity. There are just too many variables to pick a "best" battery type or usage profile for everyone. Everyone's mileage will vary.
Shorter run times of ICE will be the biggest advantage of LiFePO4 for some people and the cost savings could be enormous.

How are you guys with LiFePO4 determine when they are fully charged and how are all of the charging sources being turned off when they are full?

I've always found the attached graph interesting to study.

What we do know is that LiFePO4 cells will continue to transport/transform Lithium so long as a charge voltage is connected (there is no safe trickle charging)

We know from the graphs that charging to 3.3 VPC gives us roughly 25% of the charge as charging to 3.4 VPC.

It also shows us that there is little difference between 3.5 and 3.7 VPC in terms of AH of charge.

Charging to 3.45 VPC (13.8 volts) has been stated as a good charging voltage. We do not know where it falls between 3.4 and 3.5 VPC in terms of capacity but we do know that going above 3.5 VPC (14.0 volts) does not really buy us any more capacity.

What would be interesting (the data must be out there) is to see a set of graphs showing AH removed based on time at the target VPC.

That would show us when we know that we are fully charged.

So AH available with 0 time at 3.45 VPC, the same doe AH removed for 5 minutes, 10 minutes and so on. In other words, vary the tail time.

[evm1024]

The abstracts to the papers that show overcharge and over discharge failures for LiFePO4 (that I posted in another thread) indicate that the growth of Iron and Lithium dendrites were the primary causes of failure.

What I did not get out of the abstract (I do not have the full papers) was the time frame for the growth of those dendrites.

My thinking is that in the event of an over discharge of a LiFePO4 bank the total failure of the bank may take some time. Minutes? Hours? Days? How long would it take for the bank to go to 0 volts and would any charging be possible after such an over discharge?

A failed bank is a bank that only has 80% of its sticker capacity available (after a full charge) as a standard.

[kmacdonald]

Are all your charge sources able to be programmed to charge to 13.8 volts (or other programmable voltage) and shut off at a programmable tail current?

When I say charge sources, I mean alternator, solar, wind, and shore power charger. Make and model please.

[kmacdonald]

Originally Posted by kmacdonald

Are all your charge sources able to be programmed to charge to 13.8 volts (or other programmable voltage) and shut off at a programmable tail current?

When I say charge sources, I mean alternator, solar, wind, and shore power charger. Make and model please.

I didn't think they existed. Same problem with LA chargers and bulk charging. LiFePO4 installations still require user intervention and therefore the possibility of human error.
Who makes the best LiFePO4 cells?

[newhaul]

Originally Posted by kmacdonald

Are all your charge sources able to be programmed to charge to 13.8 volts (or other programmable voltage) and shut off at a programmable tail current?

When I say charge sources, I mean alternator, solar, wind, and shore power charger. Make and model please.

ok for my case its solar charging via a P30L fully programmable PWM controller , as to my wind its an old airx400 with adjustable internal regulator from 13.1 volts to 17.0 volts
Factory set to 14.1 volts no alternator and as of this time no shore charger for the Lfp bank.

[kmacdonald]

Originally Posted by newhaul

ok for my case its solar charging via a P30L fully programmable PWM controller , as to my wind its an old airx400 with adjustable internal regulator from 13.1 volts to 17.0 volts
Factory set to 14.1 volts no alternator and as of this time no shore charger for the Lfp bank.

Can they be programmed to shut off at a specified tail current?