kurt,
thanks for all your pictures and explanations. would you mind telling us how you are manually "equalizing" the cells of your lifepo4 battery?
i have a similar setup like yours bought from the same seller, although the blue evpower box has different disconnect relays at the bottom. i prefer not going past 56volts for the equalizing to take effect on the little circuit boards.
thanks in advance
greetings urs
To avoid having to spend long periods at 3.6v and above (could be as high as 3.8v) using the built in shunts on the boards. I just charge to 3.6v x the number of cells 57.6v for me (I set it up as a manual EQ in the classic) then I stick by the bank with a good acurate digital MM and keep tabs on the cells as the rise in voltage . If I see any cells that are lagging behind the others. For example 15 of them are at 3.58v and one is at 3.52v. I will boost charge the low cell with a 10A single cell charger. (just a little hobby charge designed for RC cars) I set it for one cell 3.6v and about 5A and within 10 - 15 min I can have all the cells within a few MV of each other. (within 15mv at 3.6v I call it a day) No need to be pedantic about a few MV.
I haven't had it yet ( usually just one or two low) but if I had a high cell that got to 3.6v well befor the others the shunt on the boards would start to bleed off the current by its self. Just using the single cell top up charger speeds up the presses rather than it taking hrs for a low cell to catch up the the others.
The chargers can be had for about $30 - $50 from places like hobby king online. (handy for other jobs to as they charge lead acid, NMH,Lipo,Lifepo4 fully programmable. They also discharge and balance up to 8 cells at a time.Handy tool to have in the shed. You power them from another 12v battery or a 12v power supply (just make sure the power supply used is isolated if your charging the very same battery that is powering the external charger) As in its charging its self :)
I have scheduled the balance to be done every 3 months on my calendar I'm sure you could stretch it out longer but nice to keep tabs on it 4 times a year.
Kurt
thanks kurt,
i appreciate your help and experience. i will give your instructions a try.
the 12v system about 1mV max difference per cell at 13.5V
however the 48v system is a different kettle of fish. there is about 10mV at 53.4V. but much higher at the 58v level: 0,2V. probably the circuit boards might have influenced that voltage reading. there seems to be 2 kinds of cells, low ones and high ones and not much in between.
this was the first time i looked at the voltages of the 48v battery bank as it is fairly new and only slightly used yet. 600w panels hooked up. once that NSW 60 cents gross feed in tariff ends i will switch over to fully use the 48v battery bank and probably go off the grid altogether
using a separate power source to do the top up charging is an important point.
thanks again
greetings urs
Quotei appreciate your help and experience. i will give your instructions a try.
the 12v system about 1mV max difference per cell at 13.5V
however the 48v system is a different kettle of fish. there is about 10mV at 53.4V. but much higher at the 58v level: 0,2V. probably the circuit boards might have influenced that voltage reading. there seems to be 2 kinds of cells, low ones and high ones and not much in between.
Just want to make sure your reading your MM correctly
one MV is 0.001v
you will never get things that tight (particularly at the top of charge) and there is no point in doing so even if you could.
Ignore the imbalance in the middle of the SOC as this will never show anything they always read the same voltage out of the upper and lower knee.
0.2v is 200mv that's worth leveling out that's starting to represent some capacity imbalance between cells. You will get a feel for what it represents in AH or mah as you top up or discharge cells to level it all out.
Only the discrepancy at the the 58v mark count. within 10 - 20 mv you my as well call it quits until next time rather than chasing your tail as your only balancing to try and keep tabs on it befor it gets out of hand....enough to reduce your usable capacity.
I don't understand what kind of lithium balancing you are doing ? It does not sound like bottom balancing . Top balancing ?
Larry
Ballancing at the top.
Ballancing at the bottom is hardly practical in a offgrid system that's powering live loads at the time.
Ballancing = ironing out any small SOC differences between individual cells. The unbalance only becomes a problem when ...if it becomes so great that one cell reaches a low SOC or high SOC well befor the others. Effectively reducing the usable capacity scope of the bank.
Even ballancing every 3 months or so I only see very small discrepancies. In the order of 800mah or so on a 400 ah bank. So perhaps 3.2ah over a year.I still like to trim them all up regularly as it's a quick job and potentially catches out something odd that could have hapend.
Kurt
Hi Kurt,
Sorry for off topic , lol.
Easter is all good. Mate we have spare beds in the the house, lol.
Not cold at that time so whatever floats your boat ;)
I will have a fugitsu (split system) 3.5 kw inverter A/c from bundy by then.
Bring your bow as Doug will appreciate dragging you around after rabbits. :o
Give me a ring or I will ring you closer to time.
Russ
Just Having a gander at the the WA ev power site.
Quote from: offgridQLD on February 23, 2016, 03:40:11 PM
Ballancing at the top.
Ballancing at the bottom is hardly practical in a offgrid system that's powering live loads at the time.
Kurt
I don't understand why bottom balancing would be any different when running live loads ?
Larry
because the battery is empty and you won't do much running of "live loads" then.
+ we try the batteries to be charged as much as possible.
I don't want my cells at 2.5v volts what ever voltage your taking them down to when bottom balancing. Particualy when a 5kw+ load comes on from the house when they are down there. For one the inverter would most likely drop out on LVD . Then I a have a bank thats most likely at 10% or less SOC and I have a house , workshop and electric car to run and a bank at 10% SOC ...great!
In a stationary storage situation...particularly one where you have a big PV array ample battery capacity and located in a area with lots of sun all year. The likelihood of a High voltage ...top of the SOc curve imbalance event is much more likely than a low SOC situation. As in. I have never seen my 400ah bank below 300AH remaining capacity . I never see the bottom area so why make the cells balanced at the bottom. A area they will never see.
In a electric car where you want to suck every last Ah you can from the bank to get the most usable range its not uncommon to be lurking in the lower 10 - 20% of the SOC you might be concerned with how the cells are balanced at the bottom.....and really only if you don't have a LVD on each cell.
Again having a bank that's not balanced isn't a big issue if you have LVD and HVD at cell level. The worst that can happen is you will trigger the LVD or HVD befor you were expecting it due to the weekest link or cell that triggers it 1st. Effective reducing your usable capacity scope.
In my case I would probably need a cell to be a massive 100 150ah out of balance befor I would notice it triggering a LVD or HVD. I have had reports from other offgrid systems where they are working there pack very hard over the full capacity and went for a very long period without any balancing at all. The result they had to trim about 30ah back into a 400ah bank when they did get around to doing a balance.The outcome. They decided to perhaps balance a tad more regularly.
As mentioned I'm trimming under 1Ah pr 3 months on a 400ah bank. Hardly even worth bothering with really but i do it anyhow to keep trimming job quick and regular chance to glance over the bank for other issues. More or less a reason to hang out in the Air conditioned power room and play with everything ;D
Some of it is luck with how well matched the cells are that you ended up with also there can my very small differences in the tiny load that the cell level boards apply to each cell. How hard your working the bank will have some effect on how often and how much balancing you might want to do.
Kurt
i balanced the 48V/400A/h lifepo4 battery:
as mentioned earlier the last time i balanced with the small circuit boards from evpower, i left off at 200mV max difference between the lowest and highest cell.
this time heeding Kurt's advice i helped bringing up the 4 lower cells with an external isolated power source. they came up relatively quickly. but it is a bit like chasing bits of paper in the wind. you bring them 4 up, some others go down. (the overall voltage of 57.4 volts stays the same of course, so other cells have to go down, not evenly though.) the little balancing circuit boards probably do their bit in addition as well. and like Kurt mentioned there is not that much energy in the lift up. anyway the max difference is brought down to 45mV. so this is much better.
as for the 12V/300A/h small lifepo4 battery, the max difference is 16mV at 14.4 Volts. this has been running for a year and so 50 to 60% SOC every day.
so i am much happier with the 45mV than the 200mV. makes for easier sleeping at night. heheheh
greetings and thanks for that professional advice, Kurt
urs
I thought bottom balancing was just where you start them off initially - so after that you use the Whizbang to tell when they are full enough at about 90 % or so and let that terminate absorb and go into float . All the other loads during the daytime when the sun is out would just be available to the loads as usual.
I just got some 100 AH Calb but haven't started using them yet. So that is why I am trying to understand the different lithium charging philosophies
Larry
there seem to be two ideologies: the bottom and the top balancers.
like kurt already said, the bottom balancing is mostly used in car batteries. you do it once at the beginning of installation. the reason behind that is that when you deplete the battery to almost zero, all the cells are still delivering current. and not one or some going under the dangerous destructive voltage, whilst the overall voltage is still ok. (they have many more cells than house batteries)
however batteries running the electricity in houses spend a lot of time at the top voltage. many systems go into float in the morning. so you do not want to just charge them only 90%. i don't think there is a provision for the whizzbang jr to go into float at 90%. you would have to change absorption and float voltages to get an approximation of 90%. (but the way we charge them might be only 90% for all i know)
so here in australia the company evpower sells battery packs including all the bms (battery management system) and bcu (battery control unit). this disconnects the battery when one cell goes over- or under voltage, low or high voltage disconnect. over current. etc. the little circuit boards on the battery also do balancing at the high end of voltage. unfortunately this is at a voltage we try to avoid for reasons of longevity of our investment. so in my case absorb is 3.5V, but the bms kicks in at 3.6v . so what i have done with the small 12v system, charge it once a month with 3.65v absorb. and measure the cells with the voltmeter. to see they are reasonably close together. (the multimeter i use measures down to 1mV)
my 48v system is fairly new, has for the time being only light use and it was the first time i balanced the cells. so that's why i had 200mV difference between the highest and lowest cell. that why i asked kurt how he does his cell balancing, because i did not like the battery being in that 3.65v area for a longish time.
a cell unbalance seems to work accumulative. every cycle it gets a bit worse. but we think it might take a long time to get into danger zone.
basically we take care of hour investment and want it to last for the longest possible time. that is the reason we check them periodically and install air conditioners. most of the time we have the free electricity to run the air conditioner anyway. the weather is usually hot when the sun shines.
and all with the lifepo4's is a bit new. basically we learn of other people"s mistake. the chinese manufacturers are not really interested in experimenting how to charg them. (they leave that to us the users) and they do not greatly appreciate advice. i think it has something to do with their ideology of loosing face.
so that is the reason why there are so many threads of how to balance and charge lifepo4 batteries. also the manufacturers specification might not necessarily be the best.
ok, hopes helps a bit for future lifepo4 users
urs
Quote from: offgridQLD on February 23, 2016, 03:40:11 PM
Ballancing at the top.
Ballancing at the bottom is hardly practical in a offgrid system that's powering live loads at the time.......
I'll disagree.
Top Balance = Charging cells to the top 90% of allowable long term float voltage, and generally relies on "Balance Boards" to bleed off the lower capacity cells that charge up quicker to full. But a 2A balance board really will do nothing with a 40A charger, still 38A going into the full cell.
So the lower capacity cells are bumping the Full limit often.
Then at discharge, those low cap cells reach the 80% discharged point and start sliding down the voltage knee way before the better cells hit the knee. If you don't have generous LVD set, you risk reverse charging a cell and destroying it.
Bottom Balance = bleeding each cell down to it's 80% discharged point and then while recharging, the Controller can sense the top end at 90% full, before the knee starts and terminate charge.
I guess it's the devil you trust vs the unknown. Top: I distrust 15+ little balance boards to work properly for as long as the batteries are expected (hoped) to last. if one fails, or a single cell hits the knee and reverses, it's spending time.
Bottom: The fail points are the inverter's LVD setting and the charge controllers Hi Volt disconnect. But you save 15+ balance boards and their wires from being added to the failure route.
in god we trust
do you trust the electronics of the solar charger?
do you trusts the electronics of an inverter?
do you trust the electronics of a smoke detector? (or not having one because it might fail?)
during absorb the voltage is fixed. so as your 40amp charger approaches full charge the current bleeds off to the programmed end amps. depending on the size of your bank (400ah = 8amps)
so is it possible your mathematics are flawed?
This overhead pic gives some better Idea of how the PV is facing and distance. (southern hemisphere to ;)) Guessing it was taken about 1:00pm or so by the shadows but just a guess.
(https://farm2.staticflickr.com/1654/25265677525_c25fb3ef07.jpg)
Kurt
Hmm.... I'm kind of over worrying about what others want to do with there own lithium cells. Mine power my house 24/7 and are fine. I treat them as I have many other smaller lifpo4 cells from EV projects that are going on 8 years old and are still all considered healthy So I'm happy with how I am managing them.
I don't fully charge my cells I have a conservation upper limit. As mentioned absorb voltage set points and a CC with tapering current I'm lucky to have 1 or 2 amps going into my bank for a cell level board to deal with. Again I don't use the boards to balance.
You don't need to be balancing all the time a little bit if trimming by hand one or two times a year works. Not worth getting carried away over.
You always have to use some electronics to call the shots. Inverter LVD, charge controller set points, External contractors LVD, HVD. you name it there isn't a situation where a cell can be connected to a charger or a load without having some kind of electronics to keep things under control. Electronics are way more reliable than trusting a human to to it all the time.
Yes I intervene on my automated system to make it work more in the scope I like to work my bank (I could have the set points adjusted down a little on the cell boards to meet my liking) but even as is if I got run over by a bus then the electronics have my back.
As it is its kind of like having a overload breaker on a electric chop saw if you stall the motor it will cut the power befror it burns out. Though how I am operating now it taking my finger off the trigger when I first hear the motor load up to much. So solving issues befor they come up by human intervention. But if I got lazy or was distracted the overload breaker has by back.
How often do you run your bank all the way down to the bottom knee to check its still in balance at the bottom? and when you do do you have to shut your house system (inverter) down while doing so? I would say you have to be down a lot more that 80 discharged to bottom balance. At 20% SOC your voltage is still in the stiff flat section of the voltage curve.
Kurt
i just added voltmeters to each individual cell in the 12V system
intend to add it to the 48v system too
For some reason the 4 red meters reminds me of the dash of the car in back to the future :)
(http://images.techhive.com/images/article/2015/10/back2future-2-100620010-orig.jpg)
Kurt
Theres electronics and then theres electronics. Do i trust chinese made inverters, no i dont. Do i trust unbranded dinky, unprotected, balance boards that defy all the conventional wisdome about cable protection and fusing, not even close. Do i trust quality top of the line gear with a long industry track record, and independent third party certification testing, of course i do. Of the 10s of thousands of Midnite charge controllers ever produced, theres only been a single instance to my knowledge of one failing short circuit. So until a BMS is made by someone of midnites calibre, count me out.
My cells boards are from a local Australian company and have been in operation for years in many aplications. Not a chinese rubbish ebay thing.
that said yes there are some things that are not ideal that given the chance I would change about them.
Two friends of mine have designed and built there own BMS and cell boards that use fiber optic cable for the interconnects between boards. So no issue with high shorts or the like.
They used fiber optics as they were building the BMS and cells boards for a 720v DC home built electric car with over 218 cells to balance and monitor. They are now marketing it for stationary storage applications. If I hadn't already purchased my unit I would have gone with it. It ticks all the boxes that I dot like about my unit.
Kurt
Kurt, I just get a time out error from GitHub.io ???
Quote from: offgridQLD on February 27, 2016, 07:02:36 PM
My cells boards are from a local Australian company and have been in operation for years in many aplications. Not a chinese rubbish ebay thing.
that said yes there are some things that are not ideal that given the chance I would change about them.
Two friends of mine have designed and built there own BMS and cell boards that use fiber optic cable for the interconnects between boards. So no issue with high shorts or the like.
They used fiber optics as they were building the BMS and cells boards for a 720v DC home built electric car with over 218 cells to balance and monitor. They are now marketing it for stationary storage applications. If I hadn't already purchased my unit I would have gone with it. It ticks all the boxes that I dot like about my unit.
http://dkeenan7.github.io/LyteFyba/ (ftp://dkeenan7.github.io/LyteFyba/)
Kurt
Quote from: Westbranch on February 27, 2016, 07:08:07 PM
Kurt, I just get a time out error from GitHub.io ???
me also? ???
Quote from: offgridQLD on February 27, 2016, 07:11:25 PM
Try this link then its there forum thread on the BMS http://forums.aeva.asn.au/weber-coulombs-lytefyba-bms_topic4302.html (ftp://forums.aeva.asn.au/weber-coulombs-lytefyba-bms_topic4302.html)
Kurt
nada, hmm not getting threw.
walt
Quote from: offgridQLD on February 27, 2016, 07:13:59 PM
Not sure whats going on I cant seem to link to it. I can see the page but if I link to it on this forum it wont work.
Kurt
At least you tried. ;)
Walt
Try typing in LyteFyba bms into google
Kurt
Quote from: offgridQLD on February 27, 2016, 07:17:39 PM
Try typing in LyteFyba bms into google
Kurt
score! thank you Kurt, ill read into it! ;D
Walt
Ok I think this thread has drifted way off topic and is being moderated.
Kurt
the second link wanted a username and P/W..
third one is all up to date..
tks
Quote from: offgridQLD on February 27, 2016, 07:11:25 PM
Try this link then its there forum thread on the BMS http://forums.aeva.asn.au/weber-coulombs-lytefyba-bms_topic4302.html (ftp://forums.aeva.asn.au/weber-coulombs-lytefyba-bms_topic4302.html)
Kurt
No permission to view
Just type in LyteFyba bms into google and you can find it.
Links are being moderated I think or something like that . I have removed the other posts with broken links.
Kurt
The idea of Bottom Balancing isn't simply for Electric cars. You all are correct that a house battery tends to remain in the upper voltages, however that is moot to the idea of a balanced system. One balances cells amongst themselves because of rare instances when you accidently fall into the extremes.
Bottom Balancing is a one time off thing. You bring them all down to the same level at the bottom and then charge them all up together until they hit a voltage that all of them can use without deviation. If they deviate slightly at the top it doesn't matter.
You wouldn't push your cells to use 100% of their top end anyway. No cell is ever going to be exact as the others regardless of batch. One will be 100aH, one will be 101aH. One could be 110aH. The only capacity you have available to use is the least capacity cell.
As you shouldn't be programming your Classics to have your batteries at such high voltage (There really isn't much useful capacity between 3.5vpc and 3.6vpc) the danger is if your system doesn't shut down in a low voltage state.
If you are waiting until your inverter kicks off for lithiums (and you havent changed the setpoints specific in the inverter for lithiums) you will find that one of your cells is going to be close to 2v while the others are near 3. That is the point of Bottom Balancing. When it matters, you do not have 15 cells at 3v trying to kill the smallest capacitance cell to below 2v. If they all remain at the same voltage at 0% then no harm - no foul.
PC Boards fail all the time. So do alarms. I simply do no trust $30 boards running all over the place to give me insurance.
Side note: those little boards each draw mA. If I leave my system, I can hit the giant breaker and kill the entire pack. Come back months later to a bank that was just as full as I left it (Lithiums have no self-discharge mechanism) however, if I have a ton of BMS wires all over the place, they will kill that pack through small loads while I am gone.
- Cloud.
At the end of the day it is everyones choice. I choose no on bms in an off-grid setting. (3 yrs full time living)
Cniemand,
i follow your logic. and we all agree when all the cells have a very close capacity and work 100%, then there is no balancing to do.
as some of us do top balancing we are very aware how far apart the voltages of the individual cells at the top end are. could you do as all a favour and measure your individual cells just before your charging goes into float? (you might have to hold the voltage there and disconnect the inverter etc to have a stable total voltage)
this is absolutely not to criticize you at all. it is purely a matter of curiosity.
the balancing circuit boards i am using use 2mA. that means in my case it would take 11 years to discharge the lithium battery to 50% SOC. ( taking what you said that there is absolute no internal self discharge in lithium batteries.)
read this here:
http://forums.energymatters.com.au/off-topic/topic6629.html
Kurt went through the trouble to measure all the details of the balancing boards for the people that are interested about it.
(we generally believe those circuit boards do balancing at a somewhat too high of voltage)
if you could take the time to give us those measurements we would all appreciate it.
thanks in advance for your effort
urs
I'm going to agree with Cniemand on the bottom balance. Do it right and set you OVP and LVD properly, and except for an annual double check, there's nothing else to do. do you trust the LVD in a $5K inverter, or a dozen PCB's with questionable QA?
And the balance boards, in a 48V bank, you have a dozen chances or more, one will fail and take out a cell with it.
It's not like NASA where the contract is awarded to the cheapest bidder !! (but the DESIGN is fail-safe or redundant)
I think by using a reasonably conservative primary inverter LVD and backing that up with cell level board LVD as a secondary measure. You have double redundancy.
I actually have a 3rd backup that is my Auto start generator(never gets used other than emergency backup) It will kick in if the bank SOC gets to 20% SOC and will recharge it to 80% SOC.
So not likely that my cells will be drained to 0% soc.
My issue is that bottom balancing isn't a once off thing (no balancing is) and to get a accurate bottom balance you need to drain the cells down to a very low SOC. So every 3 - 6 months (or how often you are doing it) it would be very difficult to hold a bank at such a low SOC while the system was in use (actively powering your home) Then your stuck with a flat battery and a offgrid house ....(wife & kids) that wants the tv, lights and fridge to work and couldn't give a rats about your 10% SOC bank and balancing.
You only get the opportunity to see how well balanced the pack is when you drain it down so low. As most people would spend the most part with there bank in the 40% SOC - 95% SOC range. Top balancing you get some indication of balance every time you hit absorb. Sure it's not as telling as when you take the voltage up higher to do a proper balance. Though you still get some clue that something isnt way out at absorb voltage level.
A bottom balanced bank you are going to have no clue whats going on until your willing to drain the bank almost completely.
What I do agree with and I think most of us do is balancing is only done to keep the cells aligned at the extreme ends of SOC both low and high to avoid issues of capacity scope limitation .
So it's not good saying . I want a bottom balanced bank as I don't have to rely on $30 electronics that could fail to protect from low voltage" because the same can be said for a bottom balanced bank and high voltage..... whats protecting your bottom balanced bank from a run away charger as the cell balance is going to be out at the top end. If your charger....(electronics) didn't stop charging or did some stray EQ or over charge situation the cells will be toast. You need the electronics to save the day.
At some point with lithium cells we need to really on electronics. Having multiple stages of protecting is the key .
Using the 5k inverter example isn't a good one as Im sure the components within the inverter that monitor and trigger LVD/HVD are most likely only a $5 portion of that 5k. At least with the cell boards they have just one function HVD/LVD and the full $15 - $30 is dedicated to that one function.
Kurt
Wish we had a "like , Like " button or something , It's good to read others thinking .
VT
like always,
well said Kurt
No offence, folks, but this thread has gone far afield from a blacked out MNGP issue.
Should I go back and split it off to a new topic or do you want to start another thread for it.
It makes for better search results later on as folks hunt answers.
Tom
Quote from: TomW on April 03, 2016, 11:50:17 AM
No offence, folks, but this thread has gone far afield from a blacked out MNGP issue.
Should I go back and split it off to a new topic or do you want to start another thread for it.
It makes for better search results later on as folks hunt answers.
Tom
Tom.. I vote to split it off, so the topics are better searched.
@ OFFGRIDQLD : What mechanism is causing the "bottom balanced" pack to drift that creates a need for quarterly rebalancing? The idea behind it is to balance at near 0% and then charge them all up to the level of the smallest capacity cell. So a range of 0-98aH (in a 100aH pack) so that you never see the voltage deviation/spikes at the top. In this thread I have read about some people adding slight charges at the top which of course would "ruin" a bottom balanced pack. That would be the only way to disrupt the balancing as you switched it to be a "top balanced" pack.
I, Personally do not see a Top Approach as a balanced pack. The variances are inherently there. You are relying on shunt current around to keep it all going.
@ Austrolsolarier : I could measure each cell specific. I may edit back and do so, but what occures is thus. In my 16 cell 100aH setup I have 15 cells that are above capacitance than one cell in particular. I've programmed the Classic to charge the pack at 3.5vpc and as the pack fills up each cell is in very tight tolerances (within a mv or two) of each other (having been balanced at 0% SOC years ago). When it gets close to FLOAT, cell # 2 begins to deviate several mV and then starts to shoot off. (due to having a lower aH capacity than others = full = higher voltages) at which the whizbang jr aids the Classic to switch over due to it reaching a ENDAMP of 5a. The surface charge is slowly burned off from the pack and they all register the same voltages across the pack while in FLOAT mode. At night as they draw down, they remain within a couple mV of each other. Rinse. Repeat. 3 years later.
EDIT : Also, If you all are suggesting that most people do not use a majority of their LIFE cell capacities, (which is probably true. I rarely use more than 40-50% of my pack on a daily run. My Pack rarely is below 55%SOC in the morning) why are those that believe in "Top Balancing" trying to eek out every last drop of their packs and risking the problems of having voltages deviate and shoot while playing with that portions of the charge curve? You guys aren't really gaining any real useful capacity through it. Just more headaches having to deal with shunting amps around to keep it all together....
Quote from: TomW on April 03, 2016, 11:50:17 AM
No offence, folks, but this thread has gone far afield from a blacked out MNGP issue.
Should I go back and split it off to a new topic or do you want to start another thread for it.
It makes for better search results later on as folks hunt answers.
Tom
Tom I'm with John, split for an easier search. I personally get frustrated.with difficult searches and so far it has been great here!!
Walt
Quote from: offgridQLD on April 02, 2016, 08:55:32 PM
You only get the opportunity to see how well balanced the pack is when you drain it down so low. As most people would spend the most part with there bank in the 40% SOC - 95% SOC range. Top balancing you get some indication of balance every time you hit absorb. Sure it's not as telling as when you take the voltage up higher to do a proper balance. Though you still get some clue that something isnt way out at absorb voltage level.
A bottom balanced bank you are going to have no clue whats going on until your willing to drain the bank almost completely.
I would counter that in Top Balancing... you never have an indication of a balance. One is still allowing the system to use every available aH in the pack. Cells only begin to deviate once they start to fill up based on their own specific capacity irregardless of the others in the pack with them. All Lithium batteries will reach a certain voltage indicative of a certain SOC. A 85%SOC 100aH cell will have the same voltage as an 85%SOC 400aH cell.
I'm very curious as to why everyone wants to use every last drop in their cells? Over-charging cells is just as detrimental to cycle-count as over-discharging....
I think your misunderstanding how often we are top balancing. Its a bit like me saying "oh your running your bank down to 0% soc all the time as your bottom balancing every day"
I'm not using every last drop of my cells . I charge to the same conservative absorb voltages as you mentioned... 3.5v pr cell. Your making it sound like people top balance every day. Going over 3.5v pr cell once every few months is not a issue. Im not shunting current around all the time. In-fact I don't really use the shunt feature on my boards. I just give the low cells a zap with a single cell charger while doing a very slow low rate high absorb every few months.
I'm not to worried what the MV variation is in the middle of the SOC as it's meaningless and is always tight (within a MV or two) in this SOC range with lifepo4. Even if the cells are out of balance. Every body's bank holds a tight MV reading in this area no matter what balance condition its in (well within reason)
Te way I see it if you have a one cell that shoots high first then its just the same as a person who top balance's and has one cell that shoots low first. Though every time that cells shoots a little bit high its getting slightly out of balance to the other cells. Its a tiny amount but over time it grows.
there is no perfect battery. expensive OEM cells like the ones in my Electric car are very good. All 88 cells hold tight and are always within 5mv of each other at full SOC. They are absolute abused in comparison to stationary storage batterys .Though there is a cost to this kind of uniformity.
As mentioned just out of interest run the cells down to the very low SOC what ever voltage you initially used to bottom balance and report back on how well balanced they all are now 3 years on.
Edit: at 3.5v pr cell average absorb voltage setting your using. What voltage do you see on (Cell 2, the low capacity cell that shoots high first) befor end amps are triggered?
Kurt
Cniemand,
nobody here is criticizing or saying anything you do or say is wrong.
all i asked is the voltages. we top balancers are aware of those top voltages, because every so often, once a month or every three months, we look at them. and take action or at the very least worry when some voltages go apart.
so just out of curiosity i asked for YOUR voltages. i can then compare them. get information.
the charging procedures of those lifepo4 batteries is still in the experimental stage. mostly because the chinese manufacturers just manufacture and sell them and don't seem to be interested to figure out proper charging algorithms, etc. as a matter of fact i do not think they would really care if 40% of their cells fail after 5 years.
so the top balancers generally absorb the battery 3.5V/cell, the same like you. we then go up to about 3.6V every so often to give us an idea if there is a big divergence of battery capacity. we go up there not to eek out the last .01% of capacity, but to get an indication. we then either manually balance the cells or let the bms circuit boards do the balancing.
seeing how well kurt's battery bank is balanced, it would probably take ten years to create problems with inbalance. how ever there is another person we know of that seems to have a serious problem with one of his cells. to the degree where he thinks about replacing it. but it probably is still 95% of the rest of the cells.
so we check our investment, as you would check the oil levels in your car, or the water level in lead acid batteries.
greetings urs
I think I will stick with the FLA trojans for now and let time sort out the pros and cons of lithium batteries.
Hopefully in another few years the designs and construction will be better and cheaper.
Anyone know what the age of the oldest fully functioning lithium cell is?
Don't know for solar - but I have a LiFePo4 48v 10ah battery on my electric bicycle and have been using it for 5+ years . I only replaced a cell or two but that was because I my charger failed and I didn't know what I was doing so messed them up. But all in all I have about 10,000 miles on that battery pack and I would say it is still 60 to 70 % of original capacity despite having it bounce around and get wet in the back carrier of my bike. No way lead acid would ever have come close to this kind of performance.
Larry
Where was that particular cell made Larry?
They are called Headway cells - got them on a group purchase - at the time they were hard to come by .
Lots of places sell them now but who knows if they are all from same source .
I just did a search and found this supplier
http://www.headway-headquarters.com/lithium-lifepo4-cells/
Endless Sphere is great place for battery and electric vehicle info
https://endless-sphere.com/forums/viewforum.php?f=14&sid=f49fbb0f722e6a339e4388db7bdad922
Reason i ask is I was watching a doco on lithium salt mining in a semi-desert part of the states (can not recall exact area).
From memory it was being used for medication and battery manufacture.
Also there was not a lot of suitable areas in the states fro lithium production.
Surely lithium cells made in the usa would be a better more reliable item than a lot coming out of china?
I assume you mean the LiFePO4 ones in use daily by a consumer and not lab variety for life....
Anyone know what the age of the oldest fully functioning lithium cell is?
russ drinkwater
that lithium mining area is in nevada. giant factory making batteries for the tesla.
as for the lasting of lithium batteries, your friend Kurt seems to have a bicycle battery he reckons he charged a 1000 times, if i remember correctly. and is still going strong. and abused into the bargain.
Yeah, I know he has several different lithium packs he has picked up second hand and also purchased new.
Being in the right place at the right time, lol.
Just curious what life the lithium cells in the PC towers have as well.
Some are well designed and made to last and there is also the other end of the spectrum which is just crap and disguised
to appear as a good product. But has inferior performance and no longevity.