Depth of Discharge Myth?

[four winds]

Thanks Dockhead. I hear you and understand your input. Obviously when you mentioned the hybrid banks idea it got me thinking. Though I missed the diagram you posted. It did occur to me I might be able to extrapolate your notes down from "mega yacht" to "garbage scow" status for my needs. A little hyperbole, not much. The other thing is you are gonna do it and I'm just thinking for fun.

Keeping the lead bank topped off, as a starting/light loads/reserve bank appeals. Lasts long time and there when you need it. Like when the finicky Li bank goes down.

Letting the Li bank handle the heavier loads and being less concerned with the SOC being low for a while appeals.

And in both cases promote longevity of the banks.

About the B2B, I have a knowledge vacuum there. Sounds like it's smarter than I thought, more than a charge combiner relay. I considered it to be operated manually, turned on to charge the Li bank (in my case) when needed and chosen by the operator.

Why the alt going to the lead bank in my case? To ensure the lead (reserve) bank is almost always full. And because I don't fully trust my experimental, finicky Li bank, bless its heart. And maybe no LVC induced alt failure, too, or the need for more hardware.

So the lead bank has priority. The B2B stays off til I say so. And I keep the banks and alt charge wire on the 1-2 switch as well. So I could direct alt charge to the Li bank as a back up.

Add a few of those cheap volt/amp meters here and there, and be my own BMS. I'm always on the boat. I'd just have to be vigilant when charging the Li bank at a time of my choosing. That time would be when the lead bank is "full" and the alt output goes to the Li bank via the B2B.

If I'm away from the boat for a few days the lead bank will take care of bilge and anchor light. And the Li bank would be off.


About the B2B again. Let's say the alt goes to the Li bank and B2B to the lead bank. When the Li bank is "full" does the B2B stop all charging to the Li bank and send everything to the lead bank?

In my "backwards" scenario I assumed the B2B would send most of the charge to the Li bank while maintaining absorption or float on the "full" lead bank.

[kmacdonald]

Originally Posted by Dockhead

Again, the false dichotomy between more solar vs. lithium. This sentence is nonsensical. More solar will reduce running engines, with or without lead. There is no scenario where lead batteries vs. lithium will reduce engine running time so a desire to run engines less is simply NOT an argument for lead batteries - it's an argument for more solar.




And for anyone who CAN'T add more solar (or have any solar at all, or doesn't want to), then lithium, not lead, is the way to reduce engine run time.


Lithium reduces engine run time in two powerful ways:


1. You don't run any engine to put on a finish charge, a matter of life and death for lead, but which lithium does not require or even want.


2. You can add more charging capacity (bigger alternator, bigger AC chargers) to take advantage of lithium's much greater acceptance rate.




Why is this something to argue about? I don't understand -- these are clear and obvious facts, and based on them, and others, some people will make one choice and others will make a different choice. I really don't understand why that bothers anyone, unless arguing itself is a kind of sport.

EXACTLY.

[four winds]

Originally Posted by Dockhead

No, this is not necessary. It's unlikely to even be possible, unless the lithium bank is very small, considering the very high maximum acceptance rate of lithium (several x of C, at least).





The bank which is being charged by the B2B charger (let's call it the "secondary bank") will have priority, because the B2B charger acts as a load. The other bank (the "primary bank", the one directly connected to the alternator) will get charged only to the extent that the load produced by the B2B charger is small enough as a percentage of alternator capacity that the voltage can rise to the level where the primary bank can accept current.



So you can use any size alternator with any combination of banks -- no problem.


But you don't want the primary bank to be the lead one -- this could greatly increase the time required to achieve full charge on both banks. Because the lithium will get priority, then only after the lithium is charged will the lead bank start its whole charging cycle beginning with bulk.


Also, you would limit the charging of the lithium to the maximum capacity of the B2B charger and lose the benefit of getting full output into the lithium, in case the alternator is bigger than the largest B2B charger.




In all of this keep in mind that lithium melts alternators which are not designed for bulk power production and/or which are not derated, and all the more in a configuration like this. I think the Balmar Belt Saver function will be essential for this kind of bank, and I also think that such a bank makes little sense if you don't have or can't fit a large frame alternator (or at least one of those souped up Grasser jobs like MaineSail uses on his own boat).

Thanks for taking the time, much appreciated.

For this thought exercise I was trying to figure out how complex an alternator setup would be needed and an idea for the overall complexity in terms of hardware, with an eye to manual supervision of the system and simplicity. And "cheaper".

Thanks again. Plenty of time to figure it out for me. Several years.

[Dockhead]

Originally Posted by four winds

Thanks Dockhead. I hear you and understand your input. Obviously when you mentioned the hybrid banks idea it got me thinking. Though I missed the diagram you posted. It did occur to me I might be able to extrapolate your notes down from "mega yacht" to "garbage scow" status for my needs. A little hyperbole, not much. The other thing is you are gonna do it and I'm just thinking for fun.

Keeping the lead bank topped off, as a starting/light loads/reserve bank appeals. Lasts long time and there when you need it. Like when the finicky Li bank goes down.

Letting the Li bank handle the heavier loads and being less concerned with the SOC being low for a while appeals.

And in both cases promote longevity of the banks.

About the B2B, I have a knowledge vacuum there. Sounds like it's smarter than I thought, more than a charge combiner relay. I considered it to be operated manually, turned on to charge the Li bank (in my case) when needed and chosen by the operator.

Why the alt going to the lead bank in my case? To ensure the lead (reserve) bank is almost always full. And because I don't fully trust my experimental, finicky Li bank, bless its heart. And maybe no LVC induced alt failure, too, or the need for more hardware.

So the lead bank has priority. The B2B stays off til I say so. And I keep the banks and alt charge wire on the 1-2 switch as well. So I could direct alt charge to the Li bank as a back up.

Add a few of those cheap volt/amp meters here and there, and be my own BMS. I'm always on the boat. I'd just have to be vigilant when charging the Li bank at a time of my choosing. That time would be when the lead bank is "full" and the alt output goes to the Li bank via the B2B.

If I'm away from the boat for a few days the lead bank will take care of bilge and anchor light. And the Li bank would be off.


About the B2B again. Let's say the alt goes to the Li bank and B2B to the lead bank. When the Li bank is "full" does the B2B stop all charging to the Li bank and send everything to the lead bank?

In my "backwards" scenario I assumed the B2B would send most of the charge to the Li bank while maintaining absorption or float on the "full" lead bank.

I think this is a really interesting and enjoyable discussion, but why don't we move it to a more appropriate thread?


I've quoted your post here: http://www.cruisersforum.com/forums/...ml#post2715851

[john61ct]

Originally Posted by Dockhead

No, this is not necessary.

Some strange quoting going on, little arrow?

Quote cited to me by mistake

[ramblinrod]

Originally Posted by evm1024

What is clear is that the model predicts (at least in this stage) that FLA will be in PSOC most of the time and is likely to have significant lifespan reductions.

You need to be more careful about FLA harm claims.

PSOC down to 80% over 9 hours (sunset to sunrise), followed by a full charge to 100% via wind and solar over the course of the day does not harm FLA batteries at all. Its just normal wear and tear, 6 years life expectancy in normal use, good maintenance and monitoring.

PSOC down to 50% every second day over 9 hours, followed by a full charge to 100% via sun and wind, may reduce life expectancy to 5 years.

As above but with occasional foray (once every 2 weeks) down to 30% PSOC, with full recharge by end of day via 1 hour alternator, wind and sun, may reduce life expectancy by to 4 years.

Plus the other advantages of the LifePO4 bank are there as well. Expensive in the short term but frugal in the long term.

Again you have to be very careful here. If one trashes the LFP bank due to system problems, that is not frugal. If one sells the boat before payback (could be as high as 10 years) that is not frugal.

From a normal equipment investment standpoint, if one is not going to hot break even in 4 years, the cost and risk is too high that it simply won't happen, and the money is better invested elsewhere.

Imagine getting up in the morning and seeing that your bank is sitting at 30% and NOT having a heart attack.

I don't have to imagine in it. I never see 30% on our FLA bank in the morning. Under pretty much worst conditions (max load and no sun at all), I wake up in the morning (from 100%) with about 60% SOC. No heart attack. If the forecast and sky dictates good sun, there is nothing to do. If the forecast and sky dictates no or little sun, I start the alternator for an hour and tell the wife she'll have hot water for a shower. Life is pretty good.

You know that with LiFePO4 the bank is fine and able to produce full amperage without breaking a sweat. And that solar or an alternator run later in the day will bring the bank up in SOC.

For me this is priceless.

But if one has the load vs charging ratios with FLA I recommend, there would be little to no difference, except ICE charging is not required for all charging. Drinks are cold, ice is hard, and for 5 mornings out of 7, the cabin is cool, there is no diesel exhaust swirling back into the cabin, and it is peaceful and quiet.

For me, this is priceless and switching to LFP from FLA is worthless.

So replace the inexpensive, purchase anywhere, no shipping FLA bank every 4 - 6 years, instead of having a nervous breakdown worrying that one wrong move to destroy the entire expensive LFP bank that will take 2 months and your left arm to ship to your location.

It's all about perspective. Do you wanna try to look cool as an LFP early adopter, or do you wanna actually be cool staying with FLA and incorporating wind/sun until LFP price fall to make them financially justifiable.

I guess it really is a matter of personal preference, like blondes, brunettes, and redheads.

(I kinda like them all, but try to stay away from the high cost ones.) ;-)

[Dockhead]

Originally Posted by john61ct

Some strange quoting going on, little arrow?

Quote cited to me by mistake

Sorry about that -- don't know how that happened.

[Dockhead]

Originally Posted by ramblinrod

. . Do you wanna try to look cool as an LFP early adopter, or do you wanna actually be cool staying with FLA and incorporating wind/sun until LFP price fall to make them financially justifiable.. . .

Those are not the only two choices!

[ramblinrod]

Originally Posted by four winds

Thanks for the reply John (and others). I think you do understand what I'm wondering about. I'd like to ask different question, or in a different way at least.

Let's say the Li is accepting (wanting) 70a from the dcdc charger, getting it from the FLA bank. And the FLA bank is accepting (wanting) 60a at the same time. Would the system be requiring 130a total from the alternator?

If so....... let's say the alternator will do 90a continuous without melting down. ok... I visualize the Li bank getting it needs filled at 70a. Because the lead bank will give it up without hesitation. But the lead bank state of charge is dropping, needing 60a, but only 30a left for the alt to give.

If that is bad, then is it possible a hybrid Li/FLA system, with alt only charging, must be able to support charging at max combined acceptance of both banks?

If I understand you correctly, having an LFP bank in parallel with FLA, both being partially discharged, and connected to one charge source, with output limited to less than total load...

The bank with the lower internal resistance will receive more current. As it charges the internal resistance will increase and more current will be available for the other battery.

In general, LFP banks have less internal resistance than FLA banks. So the majority of the current would go the LFP until very nearly full, and then current would increase to the FLA bank.

If desired to divert more current to the FLA bank first, then one could manually or automatically divert more current to the FLA bank until the acceptance fell below the charge source limit, and then start diverting current to the LFP bank. This would have the effect of reducing the overall time to get the entire battery capacity full, but the increased complexity wouldn't likely be worth the limited benefit.

[john61ct]

Originally Posted by ramblinrod

PSOC down to 80% over 9 hours (sunset to sunrise), followed by a full charge to 100% via wind and solar over the course of the day does not harm FLA batteries at all. Its just normal wear and tear, 6 years life expectancy in normal use, good maintenance and monitoring.

PSOC down to 50% every second day over 9 hours, followed by a full charge to 100% via sun and wind, may reduce life expectancy to 5 years

> down to 30% PSOC

That is not what PSOC means. The term has nothing to do with DOD.

Better quality true deep cycle FLA, well coddled - and that includes keeping avg DoD shallow - can last 10 even 13 years, even when proactively replacing at 70-80% SoH rather than the usual bank EOL = failure.

> LFP price fall

Not going to happen.

[Dockhead]

Originally Posted by john61ct

. . .
> LFP price fall

Not going to happen.

Indeed. We can always hope, but there is no good reason to expect the prices for LiFePo4 cells to come down significantly, any time soon. They are very complex to manufacture, involving nanotechnology, far more complex than manufacturing lead batteries, and manufacturing capacity is concentrated in two or three companies in one country. Demand grows by leaps and bounds. The pricing is already right -- significantly cheaper than lead batteries already, for any user that cycles enough to use the long cycle life.



I only hope that prices don't INCREASE.

[ramblinrod]

Originally Posted by Dockhead

Again, the false dichotomy between more solar vs. lithium. This sentence is nonsensical. More solar will reduce running engines, with or without lead. There is no scenario where lead batteries vs. lithium will reduce engine running time so a desire to run engines less is simply NOT an argument for lead batteries - it's an argument for more solar.

Because in the real world I live in every day, most boaters have a finite budget for boat mods and improvements, and demand good value for money spent.

For a boat that has 100 A-hr avg. daily consumption and 300 A-hr FLA batteries that are being killed prematurely due to chronic undercharging by ICE connected 80 A alternator running 2.5 hours per day between 83% to 50%, there are various solutions to consider (including but not limited to...)

Option A) Add 200 W solar and 200 W wind generator. Initial Cost = ~$800 to $3000 DIY depending on mounting and product quality at $20/hr personal time value.

Benefits over original system:

1. Double FLA battery life (average)

2. Eliminate smelly, noisy, cabin heating ICE charging most if not all days.

3. Minimal risk

4. Lower initial cost.

5. Immediate payback. Financing cost is covered by fuel and diesel engine overhaul delay savings.

6. Silent or virtually silent (most days).

7. Zero diesel smell and possible CO poisoning (most days).

8. Zero cabin heating (most days).

Cons (compared to option B):

1. FLA Battery replacement every 4-8 years depending on use patterns.

Option B) Change FLA to LFP, add BMS, and change all vessel charging and battery combining systems to suit. Cost = ~$3000 to 6000 at $20/hr personal time value.

Benefits over original system:

1. ICE charging run time reduced from 2.5 hours to 1.5 hours every day. (If one implements a significantly larger ICE charging system, run time could be reduced further for a significant additional cost.)

2. Increased battery life expectancy (about 10 years, my estimate).

Cons (compared to option A):

1. Smelly, noisy, cabin heating ICE charging reduced but not eliminated most days compared to FLA

3. Moderate risk

4. Higher initial cost.

5. Limited if any payback. (Vessel may be sold before break even point).

6. Noisy every day.

7. Smelly and possible CO poisoning every day.

8. Cabin heating every day.

And for anyone who CAN'T add more solar (or have any solar at all, or doesn't want to), then lithium, not lead, is the way to reduce engine run time.

In all my years reviewing vessel electrical systems, I have yet to find anyone who "CAN'T" add solar or wind.

Even for my own very traditional vessel, I had a very hard time with the thought of adding solar, from an aesthetic point of view. On completion, I love the look of my hard bimini with solar, because I know what it means to my comfort swinging at anchor. Going to weather, it may knock 1/10th knot off my boat speed. I'm OK with that.

Why is this something to argue about?

You tell me.

Your posts are arguments for FLA to LFP transition.

My arguments are against.

I guess we are both defending our opposing positions.

I really don't understand why that bothers anyone, unless arguing itself is a kind of sport.

I do every thing I can to help the boating community (through CF) obtain all of the facts, rather than one-sided arguments from those attempting to bully (not you) their position, by posting incomplete information.

Frankly, when one looks at the big picture and all the facts, taking an existing system and adding appropriate amount of FLA with ICE and WIND will beat LFP with more ICE, just about every time from every aspect but a "look at me, I'm an early adopter" point of view.

[Dockhead]

Originally Posted by ramblinrod

Because in the real world I live in every day, most boaters have a finite budget for boat mods and improvements, and demand good value for money spent.. . .

We understood your argument, which makes sense for some.


But don't say -- "choose lead in order to reduce ICE charging". This is simply silly. Say rather "spend your money on more solar rather than better batteries". That's an argument which is coherent, and will make sense for many people.




Also it is manipulative and incorrect to say: "Either be sensible and do it my way (use lead), or be a show off early adopter and waste your money." This is borderline trolling, actually. An incorrect representation of a much more complicated question. There are more choices than these two.




Your ideas are based on a narrow sample of weekend-use lake boats, operated by people lacking any technical knowledge or ability. Your advice is excellent -- for this particular group. But these folks, your customers, are NOT "average cruisers", around here. The world is a wide place, and there are other styles of cruising, than this one. There is no such thing as the "average cruising boat", the way you keep insisting on.

Originally Posted by ramblinrod

Your posts are arguments for FLA to LFP transition.

My arguments are against.

I guess we are both defending our opposing positions.

Just to be clear -- I am not arguing "for FLA to LFP transition." I don't have a belief, that one technology is better than the other, for everyone or even most people.



It's not a contest between this argument vs. that argument. There are good arguments for both systems, for different uses. I think I've always said that.

[kmacdonald]

Originally Posted by Dockhead

Indeed. We can always hope, but there is no good reason to expect the prices for LiFePo4 cells to come down significantly, any time soon. They are very complex to manufacture, involving nanotechnology, far more complex than manufacturing lead batteries, and manufacturing capacity is concentrated in two or three companies in one country. Demand grows by leaps and bounds. The pricing is already right -- significantly cheaper than lead batteries already, for any user that cycles enough to use the long cycle life.



I only hope that prices don't INCREASE.

That's true. The lithium batters i bought four years ago are the same price or more today. They haven't come down in price.
As with most things, the best choice in batteries will need to be determined on a case by case basis. There are too many variables and use patterns to yield a single solution for everyone.

[evm1024]

PSOC is really just not fully charging the bank before then next load draw down starts. (Hows that for a working definition?)

To quote from some paper with the bolding mine:

Manufacturers usually state for lead-acid batteries, that after a discharge and prior to next use, a battery must first be fully recharged (notice that this may take up to 16 hours). Specifications for battery life and cycles assume that the above condition is met (although it is not stated clearly).

My model run indicated that the FLA bank rarely reached 100% SOC even with the model not taking low acceptance of FLA at high SOC into account. And that the FLA never ever in the 50 days of the run had more than an hour or 2 at 100% SOC let alone the up to 16 hours required.

The model lets me infer that cruisers who have a bank like the on modeled will be PSOC every day and that they have other ways to get to 100% SOC and stay there for extended time (Shore power sounds likely).