Quote:
Originally Posted by goboatingnow
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).
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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.
Quote:
Originally Posted by goboatingnow
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.
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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.
Quote:
Originally Posted by goboatingnow
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Quote:
Originally Posted by goboatingnow
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.
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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.
Quote:
Originally Posted by goboatingnow
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.
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Yes everything I have read suggests the same.....
Quote:
Originally Posted by goboatingnow
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.
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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.
Quote:
Originally Posted by goboatingnow
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.
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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.
Quote:
Originally Posted by goboatingnow
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) .
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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
5. Temperature plays and important part in Li life. extremes cause lower life, below freezing is very problematic
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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.
Quote:
Originally Posted by goboatingnow
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.
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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.....
Quote:
Originally Posted by goboatingnow
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.
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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.
Quote:
Originally Posted by goboatingnow
Without modifications, a 3 stage charger is quite unsuited to Li charging.
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Agree 100% and unfortunately many "smart" chargers can not be custom programmed.
Quote:
Originally Posted by goboatingnow
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.
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Yes it is a wait & see...
Quote:
Originally Posted by goboatingnow
Ebaugh , I believe saw 15% reduction in capacity after 1 year, That if continued could change the cost equations.
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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
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
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For us solar charges, solar is disconnected. Simple stuff.
Quote:
Originally Posted by goboatingnow
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).
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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
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).
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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.......
Quote:
Originally Posted by goboatingnow
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.
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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.