Depth of Discharge Myth?

[evm1024]

So the conclusion of this thread is that the depth of discharge myth is not a myth for FLA and lead acid in general. Also that PSOC is a real problem in terms of lost capacity and thus cycle count. And that when you combine DOD below 50% and PSOC you end up with LA batteries that die (20% capacity loss) in as low as 30 cycles in some cases.

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I would suggest that we cannot consider any AH below the 50% SOC as a reserve because of the damage it does to the cycle count of the battery. Thus the term Dead Lead has meaning. We could consider it an emergency reserve but not a reserve.

As an example my car has a reserve. If I am careless I might run the tank down and the reserve light will come on. Using the gas in the "reserve" does no harm to my engine.

However, if I run the car out of gas and then put a gallon of white gas (Colman stove fuel) in the tank the car will run. It will get me out of the mountains and to a fill up station (hopefully). It will sputter and ping and run quite poorly. And do damage to the engine due to preignition etc. Something you would do only in an emergency. (I've actually done this. The stove fuel got me out of the mountains and saved me from a long walk)

So the premise is simply that AH below 50% in LA batteries are emergency reserve where you trade safety for longevity.

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Using the numbers from the cycle count charts I showed that LiFePO4 was much more cost effective than LA in a prior post.

Of course those cycle count graphs are suspect with real world cycle counts many time less than indicated. A question is "does the cycle count for FLA decrease more (in terms of %) than LiFePO4 or do the both decrease in the real world in equal percentages or does LiFePO4 cycle counts decrease at a rate greater than FLA.

In the case of FLA decreases at a greater or equal rate then the advantage goes to LiFePO4 in terms of cost effectiveness.

I would suggest that due to the difficulty in getting FLA to 100% SOC (damn that low acceptance rate at rising SOC and long tail times) that is is more likely that FLA will spend a lot of its time in PSOC and thus the cycle count will suffer (putting LiFePO4 further ahead).

Also, if you want to stay our of the 50% or less SOC region you will need to size your FLA bank to handle your peak usage (not your average). This leads to larger FLA banks (and even more FLA if you have large power needs).

Larger FLA banks lead to more difficulties in reaching 100% SOC. At some point the amount of solar/wind needed to just does not scale and thus you end up with the requirement to run a generator. And even with a generator you are often PSOC.

It is a downward spiral. And as Dockhead and others have noted they do not get anywhere near the life from FLA as expected.

Enter LiFePO4 - given the actual lifetimes of FLA systems in real world cruising LiFePO4 had a lower lifetime cost than FLA. Has a better quality of life nearing the end of the LiFePO4 banks life (how much dread do you feel inthe last year of a FLA banks life?).

All in all for many a much better power source....

[ramblinrod]

Originally Posted by evm1024

Rod, You have not confirmed your number of LiFePO4 intalls.

Yes, actually I have stated my experience with Lithium base batteries.

All of my portable tools are L-ion, as is the back up start battery on my personal boat. With countless reviews of customer battery and charging system needs, I have yet to encounter one who could justify the cost, after the facts were provided, regarding real world performance and risk.

And I have stated my credentials of continuos education and career positions in combination with my 40 years experience of design, develop, test, production, quality control, installation, troubleshooting, and repair of electrical, electronic, and electro-mechanical systems so compicated it would likely make your head spin.

I ask again, really simple question, “What LFP battery and BMS system do you have your experience with?

Bonus round, “What is the size of your customer install base, using the same product (excluding boats you have owned, modified the electrical, and then sold?

E

[a64pilot]

Originally Posted by rgleason

Great tests and info. Are these correct?
A64pilot - T-105 gc2?
Leaseonlife - Deka gc2?
Newhaul - Li?

Two observations:
How do yet adjust Genasun GV-10 pb couldn't find instructions?
This problem getting to 100SOC suggests that smaller size banks might be better, that solar size and adjustible solar controllers are essential, and that Firefly batteries might be a reasonable choice.

What solar controllers are adjustible?

Dear wife thinks I'm obsessed about soc and batts -' just get new when needed. Shes sick of it.

Lifeline GPL-4CT

[evm1024]

Originally Posted by ramblinrod

Yes, actually I have stated my experience with Lithium base batteries.

All of my portable tools are L-ion, as is the back up start battery on my personal boat. With countless reviews of customer battery and charging system needs, I have yet to encounter one who could justify the cost, after the facts were provided, regarding real world performance and risk.

And I have stated my credentials of continuos education and career positions in combination with my 40 years experience of design, develop, test, production, quality control, installation, troubleshooting, and repair of electrical, electronic, and electro-mechanical systems so compicated it would likely make your head spin.

I ask again, really simple question, “What LFP battery and BMS system do you have your experience with?

Bonus round, “What is the size of your customer install base, using the same product (excluding boats you have owned, modified the electrical, and then sold?

E

Actually you have not. You have stated that you have tools etc but not actually come out and stated that you have 0 LiFePO4 installs and 0 LiFePO4 systems that you work on.

It is simple evasion.

As to my experience I have stated clearly that I have exactly 1 install and that is on my boat. I have 0 installs on customers boats (the same as you).

So rather than evading and inflating your (limited) experience do be accurate.

Rod it is rather simple. Rather than dancing just stop moving and state "I have no LiFePO4 installs and 0 of my customers have LiFePO4 systems that I work on".

Of course if any of those 2 numbers are not 0 the put the accurate number in its place. Just stop dancing and be honest.

[ramblinrod]

Originally Posted by evm1024

How does your experience compare to Bonneville's power grid? I've done a "little" work for BPA. I might have seen something a little complicated.

But I am sure that my (ahem) is much smaller than yours.

I have no idea how my experience compares to yours.

I have done some pretty cool stuff and have been known to “geek out” on technology now and again.

The point is, I have more than adequate credentials to analyse the validity of a Marine battery technology.

The one thing I don’t do is experiment on customer boats.

[john61ct]

You **can** use the higher DoD% ranges as reserve capacity.

There is no black and white magic about 50%.

If you usually stay well above that point, **very occasional** dropping below 80% SoC will not significantly reduce lifetime.

As long as the bank doesn't sit there long, and not coupled with PSOC abuse.

If you usually stay above 20-30% DoD, then you can afford to "go low" a bit more often.

There are no hard rules with firm numbers.

Use common sense based on your knowledge and accurate as possible SoC guesstimating gear.

[evm1024]

Originally Posted by ramblinrod

I have no idea how my experience compares to yours.

I have done some pretty cool stuff and have been known to “geek out” on technology now and again.

The point is, I have more than adequate credentials to analyse the validity of a Marine battery technology.

The one thing I don’t do is experiment on customer boats.

I am quite sure that you have a rich and rewarding career life. And that you know a lot about many things. And that you have strong opinions.

It appears that there are 2 things that you do not do - Experiment and answer direct questions.

Rather than saying you do not experiment on customers boats you could say that you have zero installs and that you consider installing (oh say Victron's) LiFePO4 systems to be experimenting on customers boats.

But it appears that you cannot admit to zero installs directly and that your evaluations are based on reading not direct experience.

I'm not trying to push you too hard here. I just get confused when you evade direct questions and imply the answer.

As I said you do have quite a lot of experience, just not with LiFePO4 installs it appears.

[newhaul]

Originally Posted by ramblinrod

The one thing I don’t do is experiment on customer boats.

on this we are in agreement hence I did installs and experimenting on my own first.
And just to answer the unasked ( perhaps it has been asked ) No I don't count my personal vessels in my install numbers.

[evm1024]

Originally Posted by john61ct

You **can** use the higher DoD% ranges as reserve capacity.

There is no black and white magic about 50%.

If you usually stay well above that point, **very occasional** dropping below 80% SoC will not significantly reduce lifetime.

As long as the bank doesn't sit there long, and not coupled with PSOC abuse.

If you usually stay above 20-30% DoD, then you can afford to "go low" a bit more often.

There are no hard rules with firm numbers.

Use common sense based on your knowledge and accurate as possible SoC guesstimating gear.

I completely agree. If you base your FLA bank size to hit 80% SOC or lower but above 50% then you have a reserve from 80% to 50%. And you cna expect good performance.

And as you noted the 50% mark is just convention and not a hard and fast rule. Gosh, With batteries and boats that really are no hard and fast rules.


I've been boating for 45 years or so (got a Ranger 20 in my teens) and had FLA the whole time up until I put LiFePO4 in 2014. No way would I go back to LA. Just too many down sides that I learned to live with and compensate for over the years.

I know for example that my LiFePO4 house bank (after 3 days use without charging) will spin my starter (with a shorted field coil) and start the diesel where the dedicated AGM start battery (at or near 100% SOC) just caused the started to click.

That is current!

[Dockhead]

Originally Posted by john61ct

You **can** use the higher DoD% ranges as reserve capacity.

There is no black and white magic about 50%.

If you usually stay well above that point, **very occasional** dropping below 80% SoC will not significantly reduce lifetime.

As long as the bank doesn't sit there long, and not coupled with PSOC abuse.

If you usually stay above 20-30% DoD, then you can afford to "go low" a bit more often.

There are no hard rules with firm numbers.

Use common sense based on your knowledge and accurate as possible SoC guesstimating gear.

Sure. The normally unusable bottom half of the capacity of a lead bank certainly can be used as an emergency reserve. But the value of that will vary greatly between different cruisers. And I doubt that ANYONE needs as much as 50%. Does anyone advise not letting the fuel in your car go below 50%? Of course not.

Someone who might need a bigger reserve might be someone with solar only. But for someone with multiple ic charging sources and separate starting banks - like me - you would gladly forget about the reserve and use nearly all of your battery capacity, if you could.

[evm1024]

Originally Posted by Dockhead

Sure. The normally unusable bottom half of the capacity of a lead bank certainly can be used as an emergency reserve. But the value of that will vary greatly between different cruisers. And I doubt that ANYONE needs as much as 50%. Does anyone advise not letting the fuel in your car go below 50%? Of course not.

Someone who might need a bigger reserve might be someone with solar only. But for someone with multiple ic charging sources and separate starting banks - like me - you would gladly forget about the reserve and use nearly all of your battery capacity, if you could.

Did someone say LiFePO4?

[Dockhead]

Originally Posted by evm1024

Did someone say LiFePO4?

. ,.

[ramblinrod]

Originally Posted by evm1024

Actually you have not. You have stated that you have tools etc but not actually come out and stated that you have 0 LiFePO4 installs and 0 LiFePO4 systems that you work on.

It is simple evasion.

As to my experience I have stated clearly that I have exactly 1 install and that is on my boat. I have 0 installs on customers boats (the same as you).

So rather than evading and inflating your (limited) experience do be accurate.

Rod it is rather simple. Rather than dancing just stop moving and state "I have no LiFePO4 installs and 0 of my customers have LiFePO4 systems that I work on".

Of course if any of those 2 numbers are not 0 the put the accurate number in its place. Just stop dancing and be honest.

I was honest, I have lots of experience consulting, designing, installing, and troubleshooting FLA based battery systems.

I have ample credentials to research and evaluate any battery technology.

I have yet to encounter a customer who has approved an LFP system, after I honestly explained the pros, cons, risks, and real rewards likely to be gained.

My customer base is mostly 30 to 45 foot sailboats in the $10K to $300K FMV range.

I have encountered owners of LFP systems. Some are happy, some are upset and have already converted back to FLA. Many have lost the honeymoon elation after about a year, encountering cruisers like my customers in an anchorage, who rarely have to run ICE chargers, and don’t need to figure out how to add even more capacity to cover AC, because of the heat generated in the cabin.

[newhaul]

Originally Posted by Dockhead

Sure. The normally unusable bottom half of the capacity of a lead bank certainly can be used as an emergency reserve. But the value of that will vary greatly between different cruisers. And I doubt that ANYONE needs as much as 50%. Does anyone advise not letting the fuel in your car go below 50%? Of course not.

actually my grandfather used to say just that.
He would say " in my experience its much easier to keep the top half full than fill from the bottom." Sadly he passed while I was overseas .

[conachair]

Complete guess and only half joking, a graph of boat owners against battery lifespan would show a sharp increase in lifespan for owners who frequent the web because of threads like this one, knowledge of how to get a longer happier battery life really must have increased substantially in the past 5/10 years. Well done for those in the know for posting and to google for coming up with the interesting links

May you all be back to full every discharge