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Old 13-09-2013, 06:44   #331
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Re: Lithium Batteries (for the rest of us)

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Originally Posted by goboatingnow View Post
WHat we must be very careful in evaluating LI large prismatics i.e. the

" dude my beer is cold the system works" pseudo science. ( with apologies to whoever said that type of thing).
I agree 100%. We do have folks stepping into this who simply want "drop-in" or "I want it to work with my existing stuff and do no more than drop in a box.". This does scare me for the dent that could hit their wallet.

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Originally Posted by goboatingnow View Post
Firstly we have very little reliable data on the life cycle of large prismatic Li formats, hell we are only building up data on small format Li as it is.

I agree 150% with that. The other wide spead uses thus far of prismatics have been in the EV world and that use, IMHO, may not translate well to deep cycling, off grid, fractional "C" use.

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Originally Posted by goboatingnow View Post
The EE industry is replete with Li issues, most of which resulted in unexpected premature cell death

heres a amatuer blog KA7OEI's blog: Problems with Lithium Iron Phosphate (LiFePO4) Batteries

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Originally Posted by goboatingnow View Post
etc etc

One only has to follow the progression in IC Li charge controllers to see the way the thinking has changed in a relatively short time.

It will be a sorry person , whose "beer' isnt "cold" in two years time and down a $5000 investment.
And I do believe we will be seeing those sorts of stories and LiFePO4 will take the bad rap not the improper use/charging.. This is why we charge then cease charging and cycle to 50% or 80% DOD before recharging. Our charge sources are only ever used to re-charge. Once charged, by my definition for our bank, charging is stopped and the bank cycled. It is very easy to do.



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Originally Posted by goboatingnow View Post
So lets review what the industry ( small Li charging) is saying and doing for best practice (its an area I actively design in). This is current best practice and of course you may not be able to implement that and the consequences may or may not be obvious .

Nor am I trying to frighten people off, I personally think Li is great . Ive just finished two designs with them in it.

So to summarise

1. Voltage stress is a key factor in determining reliable life and capacity , you pick you charge cut-off appropriately . HVC and LVC also are needed to avoid damage.
Yes everything I have read suggests the same.....


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Originally Posted by goboatingnow View Post
2. Float charging or maintenance charging is not regarded as a good idea, The theory seems to suggest that maintaining any electrical field , cause Ion movement and in effect "works the battery". Chargers should be disconnected after charge cutoff has been reached. Dont make the mistake of analysing Li in La(Pb) terms , very very different process at work.
I agree but I don't feel there has been enough long term testing of varying float voltages, on prismatics, to suggest what type of "cycle life hit" we would take. It would be nice to say floating reduces cycle life by 15% or 20% etc. and then folks could weight that against their wallet.


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Originally Posted by goboatingnow View Post
3. The charger reengagement point ( ie the voltage where the charger reconnects) seems to be a hotly debated point. Some bring the charger in at about 80% of cuttoff, others try to ensure the battery does a full or near full discharge.
For me this is easy. I re-engage at 80% DOD or 50% DOD or somewhere in-between. It is easy to do manually. Our battery monitor is re-set manually every time we reach 13.8V and ≤5A of charge current. Often the re-charge will coincide with when we know we will be running the motor so it can vary between 50% DOD and 80% DOD. We try not to re-charge when above 50% DOD.

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Originally Posted by goboatingnow View Post
4. "mini-cycles" causes problems as they use up the expected life cycles to some or greater extent. Mini cycles are typically caused in load sharing environments or where , the battery is effectively under constant demand and recharging occurs very regularly ( like in solar charging) .
This is why our solar is always in bulk and our battery charger is always in bulk.... They are cut off before they can load share and the battery cycled again.

Quote:
Originally Posted by goboatingnow View Post
5. Temperature plays and important part in Li life. extremes cause lower life, below freezing is very problematic
Unlike our old LA batts that were left on-board all winter, and actually benefited from the hibernation, our LiFePO4 pack will come off the boat. Taking it off the boat also allows for a lot more experimentation.

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Originally Posted by goboatingnow View Post
6. Load sharing causes mini cycles, which reduces life times, especially where high peak , short duration currents are being supplied by the battery in a load sharing situation. The battery should if possible be isolated from the power source in that the power source should not cause charging to occur.
Again this is what I have read, and it seems logical, but there is a real lack of data on prismatics and what the actual impact on cycle life would be. It would be nice to be able to quantify how this would impact the cells so as to make a wallet based decision. We have chosen the "safe" road based on this information and chosen not to load share but I am not so sure it absolutely can't or should not be done. I have not been able to dig up any really good cycling head to head testing data in a LS vs no LS A/B comparison.....


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Originally Posted by goboatingnow View Post
NOW, lets look at what we got in terms of existing boat charging sources and examine the issues

1. Smart LA orientated chargers, also used as a power source.

In my mind this is the biggest culprit as its often the source that is left active for long periods. Most people in marinas have teh battery on 24/7 with it supplying the boats loads in parallel to the battery.
We are on a mooring thus our shore charger is only ever used on the hard or when at a dock but the charge is monitored and terminated once full. We do have it programmed to enter a "turn off" voltage which is programmed below or close to resting voltage in-case I were to forget. I much prefer to manually use a bench top power supply but this obviously won't work on a boat.

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Originally Posted by goboatingnow View Post
Without modifications, a 3 stage charger is quite unsuited to Li charging.
Agree 100% and unfortunately many "smart" chargers can not be custom programmed.

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Originally Posted by goboatingnow View Post
Most chargers when the boat is being used are load sharing with typically more then float voltages being applied, this is causing mini cycles, we can only wait and see what effect it has on life cycles.
Yes it is a wait & see...


Quote:
Originally Posted by goboatingnow View Post
Ebaugh , I believe saw 15% reduction in capacity after 1 year, That if continued could change the cost equations.
Ebaugh did not have baseline from which to draw this conclusion. In science we don't operate that way. This is the sorts of data that can be easily misconstrued so I count his data set as a throw out. Still it won't stop folks from saying "Ebaugh had a 15% capacity reduction in 1 year." Accurate data, or flawed data? Flawed data set......

I do have numerous capacity baselines so I will be able to accurately compare cycle life over time. I wish everyone with LiFePO4 would get an accurate baseline but that is in the category of DREAM......

Quote:
Originally Posted by goboatingnow View Post
2.Solar

AGain this is a problematic method of charging Li, As my definition it tends to be connected for long periods, dropping in and out of the circuit. Theres no easy answer to solar and Li
For us solar charges, solar is disconnected. Simple stuff.

Quote:
Originally Posted by goboatingnow View Post
3. Genny, ALternators etc,

Much less of an issue as they tend to used solely as a recharger and then shut down. good match for Li. ( assuming cutoffs appropriate etc).
Because these banks charge so fast we actually found it necessary to install an alt cut switch to physically turn off engine charging. Bank hits 13.8V and less that or equal to 5A charging is cut off and the bank cycled.


Quote:
Originally Posted by goboatingnow View Post
Does that mean a system today with standard chargers, solars and Alernators can be made to work, yes, is it optimum , no , what will the effect be, Time will tell. ( but it might be an expensive lesson).
I agree and do think there will be some hard lessons, especially with the charging voltages I see people wanting to use. The Chinese spec sheets can be a tad bit misleading. Scary stuff after you've done hundreds of hours of testing on these banks and seen zero need to push voltages that high... IMHO, unlike cell phones and cordless tools etc., we do not need every last bit of capacity in these cells. It is very easy to give up a few Ah's and have significantly safer charging. The EV guys, and every other industry, seems to want every last ounce of capacity and insists on pushing up into the knee voltages. They claim it helps keep the cells in balance but my suspicion is because it forces the cells to shunt via a BMS. It is my suspicion that if we tested pushing to just below "chuck full", eg" 13.8V to 14.0V and stopped discharging at 80% DOD or 70% DOD we'd see the same or perhaps even better cycle life than continually pushing into the upper knee range? Problem is there is little to no data at frac "C" levels and only charging to below knee voltages. T1 Terry is well ahead of me and seems to be doing quite well. I am only at 168 cycles and aiming for 200 before December. That's a LOT of work.......


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Originally Posted by goboatingnow View Post
My own view , is that Li should be justified for its recharge,discharge , storage and use reasons, BUT not on life times. Justifying the cost because based on flimsy data that suggests you'll get 10 years or something , given our state of knowledge and the less then optimum usage environment is very silly

ie , dont justify Li on cost with the present state of knowledge.
I agree 1000%. I do not trust nor believe the Chinese cycle life data. I would be ecstatic if I could get 800 to 1000 cycles to 50% 50 80% DOD because at that point these batteries waste any LA.. The benefits for us are not in the cycle life, though I am curious. The benefits for us have been:

#1 Recharge Fast: All the way to 98% - 100% with a very short current taper.

#2
Weight: This means a full usable capacity of 78-80% of the capacity vs. about 30-35% with lead acid. We are not lugging around 70% of our battery bank as unusable dead lead weight... With our lead acid bank we were dragging around 140 +/- extra pounds of unusable lead capacity. With the LiFePO4 we carry only 26 pounds of unusable capacity.....

#3 Because of the almost non-existent Peukert effect our battery monitor never "drifts" it is also easier to manually re-synch because the bank gets back to 100% anytime we want it to...

#4 Zero Voltage Sag: The voltage sag is so non-existent at the loads we apply that it is basically zero. Our on board equipment loves it. Our Espar has never, ever run better, our 12V refrigeration is more efficient, our stereo plays louder and sounds better, our cabin fans move a LOT more air etc. etc. etc... Even during engine starting the battery bank barely even knows the starter motor is there.

#5 We gained storage space because the bank is so small and lightweight that we were able to fit it where no LA bank of that capacity would ever fit on our boat. We were able to do this without creating any port or starboard listing issues due to its light weigh.

#6 Cost: The cost for us was really not much more than doing a quality AGM bank. If one shops around these systems can be built fairly in-expensively and don't require a heck of a lot more than what a good AGM bank would in terms of alternator etc... The added expenses in a BMS or contactors etc. should be well exceeded in cycle life differences..

#7 Unlike LA No there is need to get the batteries back to 100% SOC.. This is REALLY nice...... We leave the boat at 50, 60, 70% SOC and don't have a care in the world....




I personally don't feel LiFePO4 is ready for DIY prime time. It does scare me that some don't want to take the time to study it so as to not negatively impact their wallet.

IMHO there WILL be failures. The ones who studied and listened to the available data the least will like scream the loudest that the technology "sucks"... Sad, but most like the way it will play out...

If my bank fails early I will be the first to admit it and will be the first to try and scientifically understand why. I went into this as an experiment first and foremost, and to share what I learn along the way. I document this so others can learn from my mistakes or successes. Hopefully it will be more success than failure but none of us can say with 100% certainty.
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Old 13-09-2013, 08:18   #332
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Re: Lithium Batteries (for the rest of us)

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... newbie...
newbie or not I like your style.
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Old 13-09-2013, 08:29   #333
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Originally Posted by Maine Sail View Post

Yes it is a wait & see...

Ebaugh did not have baseline from which to draw this conclusion. In science we don't operate that way. This is the sorts of data that can be easily misconstrued so I count his data set as a throw out. Still it won't stop folks from saying "Ebaugh had a 15% capacity reduction in 1 year." Accurate data, or flawed data? Flawed data set......

I do have numerous capacity baselines so I will be able to accurately compare cycle life over time. I wish everyone with LiFePO4 would get an accurate baseline but that is in the category of DREAM......

.
Great couple of posts by both Maine and Dave!

I agree the lack of baseline is very problematic. But I have confirmation of detailed testing on identical cells to mine when delivered new showing full capacity. So I believe it's reasonable to conclude I lost at least 10% in the first year.

It is flawed, but until you test your cells this winter, it's the only real life data available. And if floating or temperature is the culprit in my case, it will remain so until someone else steps up.....
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Old 13-09-2013, 08:32   #334
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Re: Lithium Batteries (for the rest of us)

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Great couple of posts by both Maine and Dave!

I agree the lack of baseline is very problematic. But I have confirmation of detailed testing on identical cells to mine when delivered new showing full capacity. So I believe it's reasonable to conclude I lost at least 10% in the first year.

It is flawed, but until you test your cells this winter, it's the only real life data available. And if floating or temperature is the culprit in my case, it will remain so until someone else steps up.....
How high are your battery temps?
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Old 13-09-2013, 09:08   #335
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Re: Lithium Batteries (for the rest of us)

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The chemistry was, and is; Nickel Iron (NiFe)
And a caustic electrolyte, nasty stuff mostly on a boat.
Quote: “Due to its high cost of manufacture, other types of rechargeable batteries have displaced the nickel-iron battery in most applications.”
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Old 13-09-2013, 09:53   #336
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Re: Lithium Batteries (for the rest of us)

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In science we don't operate that way.
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but until you test your cells this winter
So it makes me wonder how comparisons can be made between banks of different configuration and quality.

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My cells arrived today….
They are clearly not in "new" condition but quite good for the price.
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I just faced this problem with designing a 48 cell lithium array 12 cells in parallel, then 4 in series. I'm still not sure I have it right, so I keep reading.
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Old 13-09-2013, 11:03   #337
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Re: Lithium Batteries (for the rest of us)

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So it makes me wonder how comparisons can be made between banks of different configuration and quality.

If everyone were to get accurate baselines on their packs then yearly capacity testing then comparisons could "potentially" be made like for like. Of course treatment throughout life is the big unknown factor which really makes these comparisons impossible. Still it is impossible to say you had a 15% loss in one year without a baseline on the specific pack..

As of yet in the world of LA that has never happened so I don't expect it to here either...
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Old 13-09-2013, 11:27   #338
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Re: Lithium Batteries (for the rest of us)

I am still at a loss to understand where this mini cycling thing became an issue. As far as I can tell it is a non event, not that it doesn't happen, just that the battery doesn't seem to care.
Trying to use LA knowledge to understand Li behaviour doesn't make sense, there is no similarity in the way the two technologies work. Trying to compare small capacity cylindrical cells or other lithium chemical construction cells data is also meaningless. If you compared super capacitors to Li batteries you would be a lot closer to the mark, their make up is very similar, the difference is active material thickness but that's about it. Do you hear any panic about super capacitor mini cycling or any capacitor mini cycling for that matter.
The rules are the same basically as electrolytic capacitor, don't reverse charge them, don't exceed to safe working voltage, don't over heat them.
The last one is the most critical, don't over heat them, if you boil the electrolyte you loose the transfer medium.
Don't discharge or use Li cells until you have fully charged them, most certainly do not discharge them first to "bottom balance" you are asking for a short cycle life.
Li house batteries are not subjected to any of the conditions EV traction batteries are so there is no use in trying to use their cycle life figures to determine house battery cycle life figure. In fact, experienced EV people will tell you their tired EV battery are still in service as house batteries, many using them as solar bank charging stations for their EV.

Those that want to charge their cells to 3.6v or high each time, I hope they keep a good record for how long their batteries last, a comparison against 3.45v end of charging cycle life will be valuable information for future users.
My battery bank is now over 800 cycles, every one at least 30% DOD over night, often 70% DoD, around 8 100% DoD. 3 times down below 2.5v per cell, a few charges up around the 4v plus per cell as well, accidents happen. The pack has been float charged on solar since it was first assembled so mini cycling has occurred all it’s life.

As for capacity loss, specifications are required here, advertised capacity or actual capacity? At what discharge rate? My battery pack is a working battery pack, it doesn't live in a lab with flash equipment connected, it often experiences well over 200 amp discharge rates, it often experiences 125 amp to 150 amp charge rates, I gauge capacity used by reading Ah out, capacity replaced by Ah in, the discharge rates and charge rates are varied through out the cycle depending on what loads switch on. It relies on the sun coming out for recharging so it doesn’t get a recharge to 100% every cycle but a lot of the cycles are. In the new yr it will be up to it’s 1,000 cycles in service and I will do another capacity test then, each test so far has exceeded the advertised capacity.

T1 Terry
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Old 13-09-2013, 11:44   #339
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Re: Lithium Batteries (for the rest of us)

heres a amatuer blog KA7OEI's blog: Problems with Lithium Iron Phosphate (LiFePO4) Batteries

Interesting that the author pulled his own post regarding his findings of why he killed the battery pack early in it's cycle life. Cyclindrical cell and no cell voltage monitoring and over charging are the things I read in his first post.

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Old 13-09-2013, 12:05   #340
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Re: Lithium Batteries (for the rest of us)

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And a caustic electrolyte, nasty stuff mostly on a boat.
Quote: “Due to its high cost of manufacture, other types of rechargeable batteries have displaced the nickel-iron battery in most applications.”
If a battery needs to be replaced only every 20+ years, then who do you think that costs? IMHO I'd say the manufacturer.

As for caustic electrolyte, lead acid wasn't?
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Old 13-09-2013, 12:53   #341
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Re: Lithium Batteries (for the rest of us)

Bob-
"A fully charged LA 12 volt battery will show a voltage of 12.95 volts."
Forgive me but I've only seen 12.6 or 12.7 quoted as fully charged wet lead batteries. Who specs them at 12.95, fully charged but no showing a false surface charge?

It would also be interesting to compare and contrast the wealth of personal conclusions about "the right" voltage that have been given here, with "the right" voltage that the actual battery MAKERS give for the same brand and product. If they do not agree 100% then the question must be asked, why the folks who engineer the product don't know how to use it, or why they spec it differently from the way users are finding it to work best.

Considering that many 'typical' wet lead battery owners say four or five years is all you can ever expect, while others have said they're in their eighth or tenth year with no problems...I think we can expect to see a similar 2x variation based on "invisible" differences in Li battery user habits as well.

Of course if someone were to suggest to someone that they ship a pallet of Li batteries down to a charter fleet...in three or four years we'd have some meaningful numbers and they would have a great sales point. Or not.
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Old 13-09-2013, 14:23   #342
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How high are your battery temps?
The text below summarizes the operating environment for the one year of operation.

The boat spent roughly 1/2 time at dock and 1/2 time at anchor. At anchor, the
batteries were cycled 2x per day between 50% and 95% SOC. Average
cycle was about 30% of capacity. Normal charge .15C to 3.45V and
normal discharge .02C. At dock, the cells were held at a constant
voltage at 3.35V, with the charger absorbing loads.

Underway, the ambient cell temperature in the engine room was 45
degrees C. At anchor or dock about 35C. Days underway is 1 in 4
days, but most days underway are only 4-8 hours. Underway, the cells
were maintained at 3.33V by the engine alternator.

I cut and pasted that, and will expand the temp part and use F versus C. At anchor or the marina, the temps run about 92-98F. The generator raises the temp over a couple hours to maybe 102F, when running to charge at anchor. Underway, the temp slowly rises to 118-119F over about a 12-15 hour period, and then levels off. The readings match my IR gun, and are taken by the BMS boards on the cells in the middle of the pack.

We only ran the boat 19-20 days of the year long enough to see the 118F, between Grenada to Bonaire, Aruba to Colombia, Colombia to Panama, Panama to San Andres, San Andres to Honduras, Honduras to Mexico and finally Mexico to Ft Myers. Most of the other running days were shorter, mostly in the San Blas where we moved every couple of days, but only an hour or two. The ER is sort of a heat sink. There is usually 400-500 gallons of diesel, and 300 gallons of water there, so it takes quite a while to heat up. But it also takes quite awhile to cool off.

All the battery temps observed were a result of ambient temp in the engine room, not charge or discharge.
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Old 13-09-2013, 17:09   #343
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T1 Terry. I don't think you'll find much disagreement between us. But mini cycles , ie short discharge followed by recharge has been discussed quite significantly in research papers. Floating has long been warned arsonist for Li and most charging ICs don't implement it as a result.

I don't see any science that indicates that large prismatics behave in any way different to there smaller brethren. All the data suggests they are identical in base characteristics.

We will have to wait and see.

Dave
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Old 13-09-2013, 17:46   #344
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Re: Lithium Batteries (for the rest of us)

ebaugh-
"Underway, the temp slowly rises to 118-119F " Isn't 113F or 45C usually given as the maximum safe temperature to charge lithium batteries? Cutting it close?
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Old 13-09-2013, 19:25   #345
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ebaugh-
"Underway, the temp slowly rises to 118-119F " Isn't 113F or 45C usually given as the maximum safe temperature to charge lithium batteries? Cutting it close?
Good question, I need to think about this some more.....

On the Chinese website for the manufacturer of my cells, 45 degrees C is the max charging temp and 65 degrees C for discharging. Storage spec is 45C. I don't "charge" underway. My alternators are set to a max of 3.33V per cell, and by the time we reach 118F, they are certainly "floating". In my setup, even at start up on partially discharged cells, the charge rate is less than 60A by design on a 1200Ah bank. Normally 40A or less.

Close yes, within spec, probably. If "floating" is considered not charging, a central discussion topic. Never less, I'm thinking maybe I should isolate them for long trips at mid charge. Full charge and high temps is a proven aging factor for the chemistry even in storage. 113F is 45C and I don't know many engine rooms in the tropics that can hold 113F or less underway. Perhaps the cells should be situated outside the engine room?
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