LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[hellosailor]

Or perhaps, that video shows an MPPT controller, using a PWM output, that is simply running as best it can. If that system is unable to produce the required voltage at all (i.e. late afternoon?) then it would produce what it could, and a common PWM design would charge a capacitor until maximum voltage (or set voltage) was reached--and then discharge it in a single pulse. Resulting in the "burst" of radio noise regularly, with a small voltage burst, just as he's seeing.

I have a small PWM controller for a small panel that acts exactly that way. Early and later in the day, the output LED on it blinks with each pulse it puts out. Midday, as it gets enough power for "constant" pulses, the LED appears to go solid, as there's enough energy to make rapid pulses.

Sometimes it is hard to tell what a system is really doing. Especially with a full battery (his statement) and a couple of other unknowns (like what was max output from the panels, even without that controller, in that light.)

[tsmwebb]

Originally Posted by hellosailor

Or perhaps, that video shows an MPPT controller, using a PWM output, that is simply running as best it can.

In a previous videos he establishes that the controller is not MPPT and takes it to pieces so you can see what's going on inside. He shows all his work. Probably worth a look if you're interested.

It is sort of PWM and it is a charge controller. It's just bad at both of those things. It doesn't hold a very steady voltage and its attempt at MPPT makes it less efficient than a proper PWM only controller could be during the bulk phase. So, comparing it to a good PWM controller it would be less efficient. Just saying that's not a problem with MPPT, it's a problem with fake MPPT plus bad PWM.

Sorry for the thread drift.

Tom.

[goboatingnow]

Dan

It's really not worry trying to educate people as to the intricacies of mppt etc. most people don't even understand how a LA battery is charged, or how CC or cV charging works, never mind that a PV panel is a current source not a voltage source etc

Best just call them all " hoovers"




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[matureee]

[QUOTE=goboatingnow;1762572]Dan

It's really not worry trying to educate people as to the intricacies of mppt etc. most people don't even understand how a LA battery is charged, or how CC or cV charging works, never mind that a PV panel is a current source not a voltage source etc

Best just call them all " hoovers"


If a man knows not and knows not that he knows not he is a fool, shun him.
If a man knows not and knows that he knows not he is a pupil, teach him.

I agree that there are many in the former category but there are also some in the later.

[Highland Fling]

SHEESH Folks I am sorry that I posted that MPPT v PWM 'question'

Can we please get back to the title of the thread.

Saying that I made another boo boo my Lab P/s is 'only' 10A and I am getting tired of watching paint dry.

Can I get my cells to the same voltage say 3.25 and then connect them up in a serial way to make a 12V battery and watch them carefully when charge them with my 200A battery charger. The charge side of my big Heart inverter charger.....OR 'MUST" I get each cell upto 3.65V before using them in a 12V battery? Obviously IF I charge them using the inverter charger I will monitor the cell voltage carefully and stop the charge when the first cell gets to 3.6V then split the cells and charge each one up individually to 3.65V

thanks in anticipation

David

[matureee]

David,
Just connecting the cells up will give you a 12V battery. The problem is that the cells will be out of balance or at different states of charge (SOC). All this messing around with cells individually or in parallel at the higher voltages is intended to get them to the same SOC or balanced. There are reams written in this forum about how to do this, a good first step would be to search for balance on this forum and read what it says.
It would also be a very good idea to read up on why automatic high and low voltage protection is necessary. It may help protect your investment in cells against tiredness drunkenness or sheer inattention one day.
Roy

[SV THIRD DAY]

Originally Posted by Flying Scot

OOOOPS I see I opened a can of worms and yes it was T1's post on MPPT / PWM charging that I read elsewhere.

BUT can someone tell me

ONE What is the 'best' voltage to top balance my WTS 200AH cells to?

TWO I have a Lab P/s with up to 30A available - what current value should I use?.

THREE Should I balance one cell at a time or parallel up 2/3/4 cells when i am going to top balance them?

thanks

kindest regards

David

Hey David
The entire point of "balancing" is to do all 4 of your batteries together, nothing would be gained by balancing them separately...well that wouldn't be "balancing" it would just be individual cell charging.

What current to use...that's not the right question...WHAT VOLTAGE to use...that's what balancing is all about really. So a 30A charger would be fine and I assume you can adjust the voltage on the charger?

Originally Posted by matureee

It would also be a very good idea to read up on why automatic high and low voltage protection is necessary. It may help protect your investment in cells against tiredness drunkenness or sheer inattention one day.
Roy

I don't have or feel I "need" automatic high and low protection, because by setting a maximum charge voltage of all my charging between a comfort range of 13.4v to 13.8v (there is debate on which is best) there is no way I can over charge my bank. Then being a full time live aboard there really isn't a way for me to take them below 10% SOC either....so I have individual cell monitoring and done.

BUT BUT BUT...David, from some of the questions you are asking (and I say this with all respect and friendship) study up on things before you start connecting things up and running with the system. I'm not knocking you at ALL....so please don't take it that way, the only way you learn is to ask....but don't go into your system not understanding the details....or....well.....we don't want a LiFePO4 horror story!

[goboatingnow]

Originally Posted by SV THIRD DAY

Hey David
The entire point of "balancing" is to do all 4 of your batteries together, nothing would be gained by balancing them separately...well that wouldn't be "balancing" it would just be individual cell charging.

What current to use...that's not the right question...WHAT VOLTAGE to use...that's what balancing is all about really. So a 30A charger would be fine and I assume you can adjust the voltage on the charger?



I don't have or feel I "need" automatic high and low protection, because by setting a maximum charge voltage of all my charging between a comfort range of 13.4v to 13.8v (there is debate on which is best) there is no way I can over charge my bank. Then being a full time live aboard there really isn't a way for me to take them below 10% SOC either....so I have individual cell monitoring and done.

BUT BUT BUT...David, from some of the questions you are asking (and I say this with all respect and friendship) study up on things before you start connecting things up and running with the system. I'm not knocking you at ALL....so please don't take it that way, the only way you learn is to ask....but don't go into your system not understanding the details....or....well.....we don't want a LiFePO4 horror story!

Not sure what you mean by doing them together. Balancing is an attempt to synchronise SOC with terminal charging conditions. You can do each battery individually once you have a decided upon balancing condition

Furthermore I think people overthink balancing. In reality where absolute SOC capacity os required, like small appliances , EV use etc , balancing has " some advantages , in our case where we typically have a surplus of storage capacity it's matters little that there a small difference in end point voltage

The impression is sometimes given that if you have out of balance conditions , something is wrong, that's not the case.

Dave


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[matureee]

Another excellent source of information is the link in MaineSails posts follow this through "compass marine how to articles" to "lifepo4 batteries thoughts and musings". There is a great article about mppt v. pwm in here as well.

[Highland Fling]

Originally Posted by SV THIRD DAY

Hey David
The entire point of "balancing" is to do all 4 of your batteries together, nothing would be gained by balancing them separately...well that wouldn't be "balancing" it would just be individual cell charging.

What current to use...that's not the right question...WHAT VOLTAGE to use...that's what balancing is all about really. So a 30A charger would be fine and I assume you can adjust the voltage on the charger?



I don't have or feel I "need" automatic high and low protection, because by setting a maximum charge voltage of all my charging between a comfort range of 13.4v to 13.8v (there is debate on which is best) there is no way I can over charge my bank. Then being a full time live aboard there really isn't a way for me to take them below 10% SOC either....so I have individual cell monitoring and done.

BUT BUT BUT...David, from some of the questions you are asking (and I say this with all respect and friendship) study up on things before you start connecting things up and running with the system. I'm not knocking you at ALL....so please don't take it that way, the only way you learn is to ask....but don't go into your system not understanding the details....or....well.....we don't want a LiFePO4 horror story!

I totally fail to understand why I cant charge and balance these cells one by one as all I am doing is getting them individually to the same SOC. so they will be in balance.......so I can discharge to the same level as the others in the 4 cell 12V battery and charge up to the same voltage SOC

I did say in a previous post that I had made a mistake my Lab Power Supply is NOT 30A and it is ONLY 10A. As I have got or will have 800AH 16x200AH cells it is going to take some time to get them all to 3.65V

BUT ATM I am only doing four cells one 12V 200AH battery (walking slowly before starting to run)

MY QUESTION was.

IS there an issue of me getting them all to the same voltage (SOC) (even though since I will be in the middle of a very flat voltage curve at say 3.4V it is 'impossible' to accurately establish what the true SOC is......So if I get each cell to 3.4V resting, then connect them in serial fashion and use my 200A charger side of my Heart Inverter Charger to bring them all up to 3.6 V OR the first one to 3.6 then go back to using my Lab P/S on each cell for the final top up OR even parallel the cells to get them all to 3.65 as a first top balance charge.

Though my understanding is that LIFEPO4 cells WONT equalise their voltage if they are connected in parallel unlike a LA cell so I can see no real practical benefit of paralleling them up to balance them.

I have posted previously what BMS and monitoring bits and pieces I will be using. I am not a newbie re using Lithium cells and LIFEPO4 cells are just another mix. I hope I understand most if not all of the issues BUT this is the first install using LIFEPO4 on a Yacht and on My Yacht.

I find the EV car forums very helpful and the Solar forums too, and yes I have read this almost 300 pages thread many times as I have it downloaded on my PC.

kindest regards

David

[Jd1]

There is nothing wrong with individually charging the batteries, with charging them in parallel or charging them in series. Do whatever turns your crank but be sure to monitor your cell voltages! You can not monitor your cell voltage with the charger if your cells are in series. You can set your charger to 3.5V and hook up all the cells in parallel but of course you will run into an issue where you will have very little current flow to each individual cell as that cell gets close to the charger voltage.
Because of the flat voltage vs SOC of lithium, the only way to know when SOC is equalized is when you get to the high voltage knee where the voltage starts to rapidly rise. Further, lithium does not like to sit at a high SOC for a long time (as in weeks or months). As a result, if you set the charger voltage and just let the batteries slowly creep up in charge you are doing them a dis-service.
It is better if you set your charge voltage higher but you MUST monitor the charging process because once you hit the knee things happen rapidly. You can't monitor this manually !!!
The closest equalization is only required in order to maximize capacity. If you are not worried about capacity you can cut down playing at the knee voltage.
The one thing you can not compromise on is monitoring cell voltage !!!
I hope this helps ....

[Highland Fling]

Originally Posted by Jd1

There is nothing wrong with individually charging the batteries, with charging them in parallel or charging them in series. Do whatever turns your crank but be sure to monitor your cell voltages! You can not monitor your cell voltage with the charger if your cells are in series. You can set your charger to 3.5V and hook up all the cells in parallel but of course you will run into an issue where you will have very little current flow to each individual cell as that cell gets close to the charger voltage.
Because of the flat voltage vs SOC of lithium, the only way to know when SOC is equalized is when you get to the high voltage knee where the voltage starts to rapidly rise. Further, lithium does not like to sit at a high SOC for a long time (as in weeks or months). As a result, if you set the charger voltage and just let the batteries slowly creep up in charge you are doing them a dis-service.
It is better if you set your charge voltage higher but you MUST monitor the charging process because once you hit the knee things happen rapidly. You can't monitor this manually !!!
The closest equalization is only required in order to maximize capacity. If you are not worried about capacity you can cut down playing at the knee voltage.
The one thing you can not compromise on is monitoring cell voltage !!!
I hope this helps ....

Thanks that fits in with my thinking.

I have the (charger) Lab P/S set to 6V with no battery in circuit and I am watching the batteries carefully (constantly when charging). With 10A charging and a 200AH cell never mind two or four in parallel the voltage is creeping up very very slowly, makes watching paint dry seem like a hyper sport

Also since we will have more than twice as many AH available and with a flat voltage discharge curve I think we will have no problems changing over to almost 100% electric cooking and reduce massively the need for propane. Plus the additional heat we add into the saloon wont be missed. We are in the Caribbean St Martin ATM so don't need extra heat in the cabin.

I think for our use I am over-thinking this balance issue and for sure I wont go anywhere near the high end knee on this initial charge as I will only charge to 3.65 V. The BMS will look after the low end knee once we are using the batteries. As well as that, I will be using some R/C cell monitoring tools to monitor each cell as well as give me 'alarms' at voltages below the upper limits and above the lower limits that will be set as the BMS trigger voltages.

I cant see how I will ever get a HVC so initially I am only looking at battery disconnect with a LVC. Something I cant see happening.

I will have at least three probably four separate 12V 200AH batteries with individual BMS's so IF one drops offline with a LVC or even one faulty cell tripping a HVC on one battery, I will still have plenty of power, so no real emergency should that unlikely event happen.

kindest regards

David

[Jd1]

Originally Posted by Flying Scot

Thanks that fits in with my thinking.

I have the (charger) Lab P/S set to 6V with no battery in circuit and I am watching the batteries carefully (constantly when charging). With 10A charging and a 200AH cell never mind two or four in parallel the voltage is creeping up very very slowly, makes watching paint dry seem like a hyper sport

David

You are likely in for a big surprise if you are manually monitoring things. Yes, things move very very slowly when you are on the flat portion of the curve but they happen VERY fast when you approach the knee.
Trust me when I tell you to not charge like that - use automated monitoring and cutoff!

[Maine Sail]

Originally Posted by Flying Scot

Thanks that fits in with my thinking.

I have the (charger) Lab P/S set to 6V with no battery in circuit and I am watching the batteries carefully (constantly when charging). With 10A charging and a 200AH cell never mind two or four in parallel the voltage is creeping up very very slowly, makes watching paint dry seem like a hyper sport

It his is a lab type power supply why not set it for 3.5V or even 3.6V? What happens when the cells get full and you're not there to shut off the 6 volts......?

[SV THIRD DAY]

Everyone has their own special way, heck I had a friend who used a potato clock to top balance.

Why tie them together in a 4 cell bank rather than separately...well I think you just hinted at it with your description of doing things manually and the potential fiasco that could cause you!

Connect them together, set your Max charge voltage and walk away. Charger hits max voltage set-point and no more amps go in....let them sit for a day all connected together without the charger on and then disconnect and verify individual cell voltage. Done...over....easy.

How easy is that compared to the kapookie dance you seem to be wanting to take watching paint dry?

Sometimes you just have to take the easy way out because it also turns out to be better.....

If there is ONE big thing that this thread has taught me is that people are always looking for their special way to do things. Rube Goldberg would be proud but why? Why make things simple more complicated and then debate and argue about how many electrons will fit on the head of a pin?