New Lithium-Ion Batteries

[Jorma]

Hi T1 Terry,

what is the charge acceptance rate of LiFePO4 cells? If I keep the voltage limited up to 3.5 V/cell, will I ever see 3C currents (DOD 30-80%)?

With flooded cells or AGMs you never get so high charging currents with safe voltage, because of the lower acceptance rate.

Jorma

[noelex 77]

Originally Posted by T1 Terry

If you were to stick religiously to the 0.5C in either charge or discharge, stay between 70% DoD and 5% DoD (30% SOC and 95% SOC) you would probably be deciding which kid to leave them to in your will, eventually their capacity reduces but it is so slow after the 70% mark it would be hardly noticable. The Winston cells are rated to 5,000 cycles to 70% DoD, discharged to 70% and the recharged to 100% every day for close to 14 yrs.

T1 Terry

I have been using these batteries (mainly A123 cells) to power various small devices on board for many years. They are well charged with a good quality charger normally as single cells or with balance connections.
The cell life I am getting is nothing like the sort of cycles you are suggesting.
The RC people have also been using these cells they treat them hard but cell life is around 500 cycles.
The cells are also used by electric bike and car enthusiasts.
Can you give us some examples of users who have reported long cell life?

Sorry to be skeptical. I think Litium cells have a great future in boats, but my experience suggests many people are going to be disappointed by the cell life if they believe some of the extavagent claims.
Its easy for the manufacturers to provide a long warranty. If they get a significant number of claims in 4-5 years they close the business and start a new one.

[T1 Terry]

The A123 cells and other RC type stuff are for extremely high density charging/discharging, they will handle 10C or more but life expectancy is the trade off. there are a few early adopters on the DIY EV forum that have 5 plus years in an EV application but I don't have any personal contacts I can give you. Can't give you any for the Winston Battery company cells, they have only started production with the yttrium added to the make up for the last couple of yrs but they do make them for the Chinese military, not clever lieing to that mob so I assuming their specs are genuine. The life cycle testing is done by subjecting a series of 3 cells to 1,000 discharge cycles and measuring the loss of capacity and this fed into a computer progrm and it gives a projected cycle life, all battery manufacturers and infact all component manufacturers now use this system. i will see if I can find the PDF of the test regime these cells go through for the military, shooting holes in the cells with an AK47 is one of them :lol:

Hi T1 Terry,

what is the charge acceptance rate of LiFePO4 cells? If I keep the voltage limited up to 3.5 V/cell, will I ever see 3C currents (DOD 30-80%)?

With flooded cells or AGMs you never get so high charging currents with safe voltage, because of the lower acceptance rate.

Jorma

I have to honest, I don't know, I don't have a charger that will put out 3C to find out. I've fed 100 amps into a 90Ah 4 cell battery and the voltage remained low until nearly fully charged, I tried feeding 200amps in from a 15v battery but the cable started to smoe so I quite that test.
What size battery bank were you considering using, a 200Ah battery bank would require a 200 amp charger to even get to 1C, 600 amps for 3C, where would you find a 600amp charger?

T1 Terry

[Jorma]

Originally Posted by T1 Terry

I have to honest, I don't know, I don't have a charger that will put out 3C to find out. I've fed 100 amps into a 90Ah 4 cell battery and the voltage remained low until nearly fully charged, I tried feeding 200amps in from a 15v battery but the cable started to smoe so I quite that test.
What size battery bank were you considering using, a 200Ah battery bank would require a 200 amp charger to even get to 1C, 600 amps for 3C, where would you find a 600amp charger?

T1 Terry

Thanks again T1 Terry,

it seems 1 C is OK and probably even higher. At the moment I am just trying build an understanding of the LiFepo4 -thing - not being a professional myself.

I have a hunch that LiFePO batteries might change the way we organize our electric power production /use in the future once we learn about them and get to trust them (not being afraid of them "blowing up").

I have found interesting data on the EV forums like: Batteries and Charging - DIY Electric Car Forums

Jorma

[Jorma]

T1 Terry,

just one more thing:

Do you need to charge the LiFePO4 batteries to full every so often (like LA’s) or can you cycle between lower levels of SOC (like 40-80%) for extensive period for no harm done to the batteries?

Jorma

[Dockhead]

Is the charge curve similar to that of Lead Acid batteries? So the charge acceptance rate goes way down as the batteries approach a full charge?

[T1 Terry]

Originally Posted by Jorma

T1 Terry,

just one more thing:

Do you need to charge the LiFePO4 batteries to full every so often (like LA’s) or can you cycle between lower levels of SOC (like 40-80%) for extensive period for no harm done to the batteries?

Jorma

The only reason to charge to 100% is for a reference of where 100% is. state of charge meters tend to wander a bit, some even appear to have a built in loss factor to account for the rather inefficient lead acid batteries they were designed for. The fortunate thing is that these meters always read on the pessimistic side when it comes to Li batteries.
A test I did and am still in the processes of longer term testing was after a few weeks of cycling 200 plus Ah without returning to fully charged I brought all the cells up to 3.45v and held them there till the current flow stopped, the SOC reading was 98%. I conducted a heap discharge test to 2.8v per cell to see what the capacity was, just in case I'd actually lost 2% but I still recorded 367Ah out of a 360Ah pack, it was just a compounding error in the way the SOC meter works.
some claim fully charged is 3.6v per cell and 3.45v is only 98% charged but after repeated tests, there is no Ah capacity in the bit between 3.4v and 3.6v, much like the old lead acid batteries, you could get a terminal reading of 13.8v from a fully charged and disconnected battery but as soon as you put any load on the voltage was 12.8v, the other volt evaporated.

Is the charge curve similar to that of Lead Acid batteries? So the charge acceptance rate goes way down as the batteries approach a full charge?

Hi Dockhead,
The voltage curve for Lifep04 cells is very different to lead acid cells. Between 98% and 20% state of charge the voltage on a 4 cell 12v battery will be 13v to 13.3v unless you pull a big load but it will return to this voltage as soon as the load is removed. Here is a graph that represents roughly a 1C discharge test.
The second graph shows a recharge at 50 amps into a 90Ah battery while the inverter and my 2 x 250ltr fridges were still attached. Each line is a separate cell, 4 in series, you can see the free fall in cell voltage from 3.75v to 3.4v as soon as the charger was disconnected. The wave in the line is the load coming on from a fridge cutting in and then the solar recovering the 13.8v float, you can see a few deeper dips where both cut in at the same time.

T1 Terry

[OceanPlanet]

"State of charge meters tend to wander a bit, some even appear to have a built in loss factor to account for the rather inefficient lead acid batteries they were designed for. The fortunate thing is that these meters always read on the pessimistic side when it comes to Li batteries."

For those that don't already know, many monitors are programmable for CEF (Charge Efficiency Factor), Peukerts Exponent, etc. Which helps them be more accurate. However they can still drift off over time so it's good to go to 100% now & then with lithium to allow the monitor to sync.

I often tend to "widen" the voltage/current sync parameters so that the monitor syncs a bit early. As T1 says, the amount of extra energy actually stored by the last bit of voltage increase is negligible.

[FlyingCloud1937]

I still don't believe this technology is ready for prime time. It certainly is in BETA testing by the DIY community, with some success stories and failure stories.

Just remember system cost, also include capable charging system, and safety systems. The real MTF is only based on a computer algorithm. Remember when Gel and Agm's first hit the market? Many problems arose and I know that most if not all of the first to market batteries failed the manufactures claims.

How many of you have purchased CFL, CCFL, and LED lighting with manufacture claims of tens of thousands of hours lifetime, only to have to replace them in less then a thousand hrs? Those claims were based on a similar algorithm to guess the MTF rate.

If you think lead acid batteries are unforgiving of mistake and neglect, we haven't seen anything yet. I know Prius owners that are having to by battery packs that cost over 1/3 the price they paid for the car, in less then 2 years. I know dozens of owners that can't properly manage a well set-up lead acid bank, I sure wouldn't recommend these bats to those owners.

I haven't heard anyone speak to the Over Current Fault Protection required of these high discharge capable battery banks. A large 600 amp Gel bank requires a OCP of 10-20 times the amp hr size of the bank. I don't think the ABYC has even developed a standards for these bats installed to a yacht. How does this effect your Yacht Ins. policy? I'm only guessing but I wouldn't be surprised if OCP will require 30-40 times the amp hr size.

It will certainly require a voltage protection interface between NAV gear, and any other voltage sensitive electronics. This includes LED lighting, and Halogen lighting.

Don't even think about using welding cable for any of the high current cables!

To get max benefit of charge current acceptance rate of these batteries, is going to require a very expensive solution.

I would not install these bat banks to a yacht unless they were in their own fire proof enclosure. With a dedicated automatic fire suppression system rated to the potential and chemistry.

I have seen two boat fires this year caused by lead acid bat banks. One was right across the dock from my boat. The bat bank was installed less than a month, by a well known battery manufacture's own in-house installers. In my lifetime I have seen dozens of melted/exploded lead acid battery banks.

I look forward to the day these batteries are vetted and ready for prime-time...but that day isn't today, I doubt it will be this time next year.

It's fun to look at the amorous projections of how efficient/cheap these bats are at a per KW value...but none of the projections I read include the total system costs.

Just talking out loud...somebody show me the way.

Lloyd

[OceanPlanet]

Flying Cloud,

I'm glad to see someone bring up the fact that LA batts are involved with fires (somewhere on the planet) nearly every day.

Using the more comprehensive BMS systems (meaning dual pos buss, etc.) and LiFePo4 cells, it could be said that it is much safer than any LA house bank.

How many LA systems ever even look at individual cell voltage? Every 12V LA batt is several cells in series with no way to ever even see if they get out of balance. Only the LA systems using the big 2V cells could even have a way to monitor them but how many are doing it? Just about zero. And on those big boats everyone wonders why some cells burn out long before the others...

I do know of a hybrid propulsion engineering outfit that is developing cells modules and BMS system that will work for balancing big LA cells (since they were developing it for lithium anyway) realizing that big LA cells need balancing also, especially in high-load applications like propulsion.

Yes, the OCP, cabling, etc. must all be well though-out but that's true of any big LA system as well. And yes, the price of the entire "system" needs to be worked out and that certainly adds up. However to do a complete analysis, the reduced engine hours and fuel use should also be worked in; there is a lot to consider.

Lithium systems have gone around the world many times already, and several are going around right now. Fortunately the lessons of Lithium Cobalt have been learned (the hard way by some) and LiFePo4 has filled the gap and is proven (IMHO) as a safe(r?) alternative to LA. Albiet rather spendy up front.

[FlyingCloud1937]

A quick search turned this up in re ABYC. What about UL and Cg approvals?

Lloyd

[FlyingCloud1937]

This discussion is certainly worth the read

New Lithium Batteries - Page 2 - SailNet Community

Lloyd

[T1 Terry]

I don't think anyone in their right mind would use lithium polymer batteries when lithium iron batteries are so much safer and better suit the purpose. Lithium polymer is what the model plane people use, special bags to put them in case they explode or burst into flame. Lithium iron batteries don't do that, the Chinese manufactured prismatic cells are military spec tested to insane levels to prove they won't explode or catch fire. Don't make the mistake of comparing Lipo cells with Li cells, chalk and cheese. The worst thing an Li cell will do is vent gas similar to petrol fumes but far less dangerous than the fumes from lead acid batteries and a much smaller volume per cell. Abuse an Li cell and you will shorten it's life, but only the one cell, savagely over charge them and they inflate like a balloon and then vent out the cap, same if you reverse charge them but this can only happen in a long string high voltage pack like in an electric vehicle.
Personally, I see adding a BMS unit is adding a failure point, not a safe guard, they are as reliable as the toy you get in a Christmas cracker and have lead to far more battery failures than they have prevented. Long string high voltage battery packs may need them (jury is still out on the EV forums regarding that one) but in a 4 cell series pack? Waste of time and money. A simple cell logger from the hobby shop, I like the Junsi cell log 8, around $14 for a non data logging model and $28 for a data logger. These have an audible alarm for low and high cell voltage and an alarm port that can be used to drive a relay to shut down the charging system is a cell goes into high voltage. A few minutes maybe monthly is all that would be needed to balance any wayward cells but I haven't had to do that at all since I condition charged my battery pack and that was over 3 mths ago. my batteries work 24/7, over 200Ah flow in and out every 24hr period. They only need balance at the very top of the charge anyway so the 100% charge and balance can be done at the operators convenience. Even if a cell starts to fail for some reason it's only a loss of capacity, not a total failure unless the cell has been driven into a reverse charge condition, virtually impossible in a 4 series cell pack.
Don't get conned and ripped off buying stuff you don't need just because you don't realise you don't need it.

T1 Terry

[OceanPlanet]

Originally Posted by FlyingCloud1937

A quick search turned this up in re ABYC. What about UL and Cg approvals?

Lloyd

Yeah, I sat in on the early ABYC meetings on standards for OCP, AIC, etc. on lithium (and large AGM) banks.

Early suggested level for AIC rating (in lieu of a mfg recommendation) is 100 x the AH capacity of the bank.

Note: Re the Corvus stuff mention in that article...They seem to have been targeted more for higher-voltage propulsion applications. In fact, I'm delivering a 1080Ah x 24V house bank system next week to a client in BC that was looking at Corvus however it turned out that Corvus didn't yet have applicable BMS for the 24V house system.

[Jorma]

T1 Terry,

Still one for clarification of the charging curve:

If I get it right, one of the greatest things with LiFePO4 batteries is, that there will be no absorption phase of reduced charge acceptance as with LA’s when hitting SOC 80-85%. See the picture.

What is your experience? If you charge LiFePO4 cell with 1C current, when will it slow down and how much? At SOC 95% or 99%?

Jorma