LifePO4 batteries for use with Midnite Classic 150?

[createthis]

Which is to imply you once did ?

I think by "we", I meant people in the USA, in general. But really, deep down, if I'm being honest about it, I excluded myself from the "we" and meant baby boomers. I've never referred to anyone as a Chi-Com. I think the Chinese deserve at least a bit of respect considering they supply the world with most of their electronics these days.

[Living Large]

There is a lot of misinformation and assumption in this thread by all, myself included. It's been incredibly difficult for me to separate signal from noise. This would go away if charge controller manufacturers like Midnite Solar would just start supporting LFP directly, so I'm not mad about it. It's just been difficult sifting through the noise for the information I need.

There are multiple answers to how to use LFP in a PV system, so the "information you need" depends on your knowledge, your philosophy and your application. Expecting a one-sized fits all solution or answer will lead to frustration on your part. That is understandable. It took me several weeks of asking questions here to figure out for myself, based on the input from multiple members, what would work best for me.

I would not consider the competing views "misinformation", but each person does have "assumptions" - and each application and owner will force certain assumptions and constraints. I found I had to overcome some of my own assumptions, in order to sift through everything and formulate a solution.

[createthis]

There are multiple answers to how to use LFP in a PV system, so the "information you need" depends on your knowledge, your philosophy and your application. Expecting a one-sized fits all solution or answer will lead to frustration on your part. That is understandable. It took me several weeks of asking questions here to figure out for myself, based on the input from multiple members, what would work best for me.

Agreed. I didn't realize when I started this thread that some people prefer to bottom balance without a BMS. I'm not going to go that route, but it's good to know it's an option.

[Sunking]

There are dozens of BMS you can use. In fact over 100. I have not bothered telling you because non of them are compatible with Solar. But knock yourself out. Here is a link with a BMS selector of every BMS made. One issue is many are already out of biz. Most are too large for your application. You need single cell or 4 channel as 12 volt LFP is really a toy not meant for anything serious, so that severely limits your choices. Here is the Home Link to Elithion. David is a leading expert in all thing Lithium. This is the Home page contains links to every lithium battery manufacture, battery module manufacture, every Lithium Battery Charger, every BMS manufacture, every IC manufacture made for BMS, tutorials, presentations, books, and his line of BMS. David has TI custom make a IC for his method of BMS. It will take you a month to go through it all. What you are going to find out is I know WTF I am talking about and you do not know enough to work with LFP. By the time you click the two links your head will be spinning and very frustrated.

What you are having trouble with is there no meaning or definition of a BMS. It is a MARKETING TERM with no meaning.

I have a 16 channel Orion Jr I would love to sell you for $400. It cost me $600. You will have to design the interface hardware and program it for your application.

I am trying to make it KISS, but you want no part of that and want to throw money away, so good luck, I cannot help you anymore. I will not be responsible.

[createthis]

Sigh. Well, I guess we'll find out if Sunking is off his meds, or I'm really as stupid as he thinks I am. If he's right, no harm in burning a little money to eliminate my ignorance. I've done worse things in life.

[karrak]

Correct. It needs a BMS for that. I'm just trying to find one to buy. I think that's pretty obvious if you read the thread.

Contrary to what some posters say, looking after an LFP battery is not rocket science and can be done with equipment that is available at the moment.

The complexity and how automatic you want the Battery Monitoring/Management system to be depends on how autonomous you want it to be, how much risk you want to take and how technically competent you are. If you only have a small battery that has not cost too much and you are fairly hands on then a simple system is probably all that is required. The system can always be upgraded at a future date.

The most important thing to do is monitor the individual cell voltages and keep them in the safe operating range. If you are going to be around when the battery is being charged or discharged this could be something as simple as a Cellog8 programmed to give an audible alarm which you would act on.

In battery based systems being charged by solar energy it is most likely that a cell could suffer from overcharging so the next level of protection is to use the overvoltage alarm output from the cell monitor to shut down the charger (in your case the Midnight 150). The Cellog8 has a programmable alarm output that could be used for this purpose.

In my case someone will always be around if the battery is going to get anywhere near fully discharged so I have decided that an audible alarm is all that is needed for undervoltage as someone will disconnect any load if this occurs. If you want to go to the trouble of automating this then use an undervoltage alarm output from the cell monitor to do this.

Battery balancing, although important is not as critical as cell voltage monitoring and disconnection of the load or charger in the event of an overvoltage or undervoltage event. Again contrary to what some posters say this is not as complex as it is made out to be.

Firstly, before you put the battery into service you have to make sure it is initially balanced. This is best done by placing all the batteries in parallel and charging them up to 3.6 volts with an end charge current of less than C/200. If you have a small battery this can be done with reasonably cheap equipment that is sold for the Radio Controlled model market. You can also see if the battery supplier will do it for you.

If the battery is initially balanced correctly it will only go out of balance very slowly, this is the reason that balancing circuitry that can only dump an amp or so of current work just fine with standard charge controllers like your Midnight 150. If you have a battery monitor that can shut down the charge controller if any cell voltage goes above the overvoltage cutoff voltage there is no way you can damage your battery when you are balancing it.

You can either do the balancing manually or automatically. I do it manually and have found that it needs to be done every 11-12 months.

I started out with a Cellog8 on my $4,000 battery and have since designed and made my own Battery Monitoring/Managements system https://github.com/simat/BatteryMonitor. Others that will work are http://minibms.mybigcommerce.com/tem...ower%20BMS.pdf and http://www.batrium.com/wp-content/up...et-Ver-1.1.pdf

Simon

[Sunking]

Sigh. Well, I guess we'll find out if Sunking is off his meds, or I'm really as stupid as he thinks I am.

I never said you were stupid or called you stupid. That is all on you. I am just trying to keep you from doing something stupid. What I have said is you do not know what you are doing and way over head about to make a very stupid expensive mistake.

I agree with Karak LFP is not rocket science, but they are tricky. They are very sensitive and do not tolerate abuse. FLA batteries are bruits and can take tons of abuse. What everyone is telling you, is YOU DO NOT BUY a $1000 BATTERY to learn with. Guaranteed you will destroy it from lack of experience and knowledge. That is Stupid, not you.

All Lithium's are sensitive to Over Charge, and especially Over Discharge. Some Lithium types like LiCo will be destroyed and/or catch fire if over charged. They must also use thermal management. LiCo batteries are the ones that give lithium a bad name with all the fires.

LFP is less sensitive to over charged and safest of all the lithium's out there. That does not imply you can over charge them. Charging them to 100% cuts cycle life in half. Leave them stored at 100% and you will damage them. However LFP and any Lithium is extremely sensitive to over discharge. All it takes is one over discharge and you have a boat anchor.

There are two ways to manage LFP batteries. Top Balance and Bottom Balance. Any commercial application sold for consumer use will use Top Balance. However commercial producers can do something YOU CANNOT. They can match there cells, YOU CANNOT do that. With matched cells (capacity) makes no fricking difference if you Top or Bottom Balance. Once full charged and Balanced they all arrive at full charge at the same time, and they all arrive at fully discharged at the same time. A Balance charged is rarely if ever needed with matched cells. BUT YOU CANNOT DO THAT, you cannot buy 1000 cells to find 4 matching cells.

There is a couple of things you can do. 1 is buy a battery module like the one you found for $1000. It is 100% higher than buying 4 cells. For that you get matched cells and a half baked BMS in the battery container box. However there is nothing you can interface with or monitor what is going on inside. All you can do is take a risk and charge it to 14.6 volts, or eliminate that risk and only charge to 13.6 volts Your choice roll the dice or take the safe route. You want to gamble and cut cycle life in half charge to 14.6 volts. Not me, I would be good going to 13.6 Volts and eliminate the risk and double cycle life. But that is just me, Perhaps you like living on the edge and gamble with no gain. If for any reason you over discharge down to 10.5 volts game over, you have a $1000 boat anchor and not chit you can do about it. No Charge controller will save you. That takes a LVC circuit to protect you.

Smart money using Chi-Com cells is Bottom Balance. Here is why and escapes Karrak. Chi-Com cells capacity tolerance is SLOPPY of -3/ +15%. That means if you buy 100 AH cells the lowest can be 97 AH and highest is 115 AH. Real SLOPPY tolerance and gives you a big problem to have to work around.


So you want to Top Balance and you r4 new cells arrive, and you have to balance them The lowest cell is 97 AH and largest is 115 AH. You hook all the cells up in Parallel. You now have to buy a single cell LFP charger like a Cell Log 8. It will require a rather large expensive DC 18 volt 50 amp power supply. You got one of those yet. The Cell Log 8 will cost you $250 plus a power supply. You charge all the cells up to 100% SOC Every cell voltage at rest is 3.6 volts. Voltage is equal but not capacity. Your weak cell is 97 AH, and your strong cell is 115 AH. So you now hook all of them up in series and you measure 14.4 volts or 100% SOC. Life is good.
A weak later you notice your inverter will not stay on. For whatever reason you let you battery voltage drop to 11.5 volts. Everything should work with 11.5 volts. What is wrong? You measure cell voltages and you notice 1 of them, the weak 97 AH cell is 2.2 volts and the rest are around 3.1 volts. What happened?
You failed to monitor cell voltages with an expensive BMS that monitors each cell voltage with a Low Voltage Cut Off relay to disconnect the battery when the weak cell reached 2.9 volts. Th eweal cell reached 0 AH capacity and the three stronger cells eat it with reverse current. Your brave weak cell sacrificed it cell so the three stronger cells could survive. So he self destructed and you now have a $150 worthless battery to replace. If only you had spent another $500 in BMS that could have prevented that o ruse your expensive Cell Log 8 to somehow get your attention and shut down. That is the risk with Top Balance. The way you prevent it with Top Balance is a very expensive BMS with built in LVC and cell monitors with logic control. Nope you used Vampire Boards that only bypass current during charge.
But there is another way to do this. You have to know your stuff. Bottom Balance. You get your new cells. Again weakest is 97 AH and Strongest is 115 AH. We connect them all in parallel just like Top Balance. Except this time we discharge them, not charge them. We can use a large high wattage resistor or if you bought the Cell Log 8 we use it. We discharge them to 2.5 volts at rest. When at 2.5 volts we now have equal capacity and equal voltage Every battery has 0 AH and 2.5 Volts.


You connect all discharged cells in series and you measure 10 volts. Connect your charge source and set it to 13.6 volts to 14.3 volts and monitor cell voltages One cell when you get near fully charged will be higher than all the others. That cell will be the weak cell of 97 AH. You stop charging when it reaches 3.4 to 3.45 volts. Do not let it go to 3.6. Stop charging and note pack voltage. Should be around 13.6 volts. reset your charger to that voltage. Your Inverter default cutff is 10.5 volts which is fime because we do not want to go below 10 volts. Even better set the Inverter LVC at 12 volts as there is not much left below 12 volts. All cells will be around 10 to 20% SOC when pack voltage is 12 volts. Now you have two passive over discharge protection schemes that cost you nothing.

1. Your Inverter will shut off long before you get to 10 volts.
2. If that fails and you go to 10 volts, all cells will be empty at 10 volts and quit supplying current and shut themselves off by the very nature of them.


The magic of Bottom Balance is the cells always have EQUAL capacity because they are referenced at 0% capacity. The capacity is limited to the weakest cell in either Top Balance or Bottom Balance. With Bottom Balance requires not BMS of any kind, just a different mindset and strategy. Only the discharge side you have two passive defenses of your Inverter LVD and just by Bottom Balance making it impossible for the stronger cells to eat the weak cell. It is not Rocket Science, it is just knowing the science and is easy. At the Top. we never allow any cell to go to 100%. Again a passive protection requiring no BMS. With Top Balance you go to the Top to Balance and risk over charge.
If you Top Balance you had darn well better have a LVC circuit because Top Balanced systems are prone to over discharge in a DIY system using cheap Chi-Com cells. Top Balance is expensive to implement correctly because you must monitor every cell, every second of the day with logic controls. Manufactures love it because it means much higher profits.


So you have a few choices:
1. Spend $1000 dollars fora modular battery that has a micro BMS built in and roll the dice.
2. Spend $500 on Chi-Com cells. Decide Top Balance or Bottom Balance. If you top balance you have to figure out the BMS, how it works, and the level of automation/controls you want. That will be expensive, but less than a modular battery maybe. I gave you the link already to find your BMS, but you have to do it. No one else is going to do it for you. You bare all responsibility.
3. Smart Money buy a good quality 12 volt 125AH FLA battery for $125 and call it good. Wil last longer and match performance for a fraction of the cost. No fuss, your charge controller is made for it.
You are on your own, figure it out.

Lastly next time you whine about SK, you had better think my friend. No one on this forum or anywhere else will go to as much trouble, detail, and time to help you as i will. No one but SK will do that for you.

[Living Large]

Hallelujah.

[karrak]

Guaranteed you will destroy it from lack of experience and knowledge. That is Stupid, not you.

If you have a an individual cell monitor that will shut off the charger or load or warn you and you are around to shut things down you will not destroy your battery.

If for any reason you over discharge down to 10.5 volts game over, you have a $1000 boat anchor and not chit you can do about it. No Charge controller will save you. That takes a LVC circuit to protect you.

You have given the solution to the problem. You do not rely on the overall battery voltage disconnect that the inverter gives you. You use your individual Cell Monitor to either shut down the load or give you an alarm and you manually shut down the load.

Smart money using Chi-Com cells is Bottom Balance. Here is why and escapes Karrak. Chi-Com cells capacity tolerance is SLOPPY of -3/ +15%. That means if you buy 100 AH cells the lowest can be 97 AH and highest is 115 AH. Real SLOPPY tolerance and gives you a big problem to have to work around.

It doesn't escape me. I have made up two systems using Chinese made Winston Batteries. The variation I have is more like a few % and hasn't caused any problems.

You now have to buy a single cell LFP charger like a Cell Log 8. It will require a rather large expensive DC 18 volt 50 amp power supply. You got one of those yet. The Cell Log 8 will cost you $250 plus a power supply.

The Cellog8 costs less than $30, for a 100Ah battery you could use something like this http://www.hobbyking.com/hobbyking/s...e_Charger.html to do the initial balance.

A weak later you notice your inverter will not stay on. For whatever reason you let you battery voltage drop to 11.5 volts. Everything should work with 11.5 volts. What is wrong? You measure cell voltages and you notice 1 of them, the weak 97 AH cell is 2.2 volts and the rest are around 3.1 volts. What happened?
You failed to monitor cell voltages with an expensive BMS that monitors each cell voltage with a Low Voltage Cut Off relay to disconnect the battery when the weak cell reached 2.9 volts. Th eweal cell reached 0 AH capacity and the three stronger cells eat it with reverse current. Your brave weak cell sacrificed it cell so the three stronger cells could survive. So he self destructed and you now have a $150 worthless battery to replace. If only you had spent another $500 in BMS that could have prevented that o ruse your expensive Cell Log 8 to somehow get your attention and shut down. That is the risk with Top Balance. The way you prevent it with Top Balance is a very expensive BMS with built in LVC and cell monitors with logic control.

I don't call $30 expensive. Anyway if you have your battery being charged by the sun on a daily basis and the battery and solar panels have the right capacity to supply your load it is rarely if ever that your battery will ever get fully discharged and then your $30 Cell monitor will warn you or disconnect the load.

But there is another way to do this. You have to know your stuff. Bottom Balance. You get your new cells. Again weakest is 97 AH and Strongest is 115 AH. We connect them all in parallel just like Top Balance. Except this time we discharge them, not charge them. We can use a large high wattage resistor or if you bought the Cell Log 8 we use it. We discharge them to 2.5 volts at rest. When at 2.5 volts we now have equal capacity and equal voltage Every battery has 0 AH and 2.5 Volts.

Big problem with this approach is that if the cells are balanced at the bottom end they will not be balanced at the top end unless their capacity is the same you are in real danger of overcharging some cells and damaging them.

Lastly next time you whine about SK, you had better think my friend. No one on this forum or anywhere else will go to as much trouble, detail, and time to help you as i will. No one but SK will do that for you.

No one but SK will go to as much trouble to get you to use Lead Acid batteries...

Simon

[createthis]

Simon, would a B6AC V2 work? It's only 50W, but capable of delivering 6A. You said C/200, which for a 100ah cell is 0.5A right?

[createthis]

I'm really not opposed to bottom balancing with the cell-log8's alarm wired to the midnite classic via AUX2. Seems like a nice clean redundant solution, and I'd have a convenient way to monitor cell voltage anytime I want via the cell-log8.

[Mike90250]

Midnight and Morningstar both make excellent controllers. Their top of the line models are fully programmable, and I use one of each, on different solar PV arrays to charge NiFe batteries which have a wide voltage range. You need to be aware of the needs of the batteries, and not use the lead acid default setpoints. You have to chose and implement your own setpoints and failsafes. And disable the temperature compensation, which will ruin your batteries from overcharging. And set up a method to prevent charging when the batteries are cold (below 33F)

[createthis]

Midnight and Morningstar both make excellent controllers. Their top of the line models are fully programmable, and I use one of each, on different solar PV arrays to charge NiFe batteries which have a wide voltage range.

NiFe. Nice. How do you like those? I read they have terrible efficiency, but man do they last and last. For a stationary installation, I'd have to think real hard between NiFe and LifePO4. NiFe would be tempting.

[karrak]

Simon, would a B6AC V2 work? It's only 50W, but capable of delivering 6A. You said C/200, which for a 100ah cell is 0.5A right?

You could use something like that. If you connect up the individual 'balance' wires from each cell to the B6AC you can do the initial balance with the cells in series using the balance program. You can easily purchase a premade wiring harness and adapt it to suit your needs. The batteries are usually shipped with a 50% charge so you would need 0.5*100*3.25*4=650Wh of power to charge the battery to full. If the B6AC will charge at 50W it will take 650/50=13 hours to charge which is not too bad.

If you are going to use a Cellog8 I would hook it up at the same time as you are doing the balance charge as a safety check. If you set the alarm point on the Cellog8 to slightly less than the voltage that the B6AC will charge to you can check to see if the alarm function has been programmed correctly and is working correctly.

Do you already own this charger?

Simon

[createthis]

Yup. I use the B6AC V2 for my RC quad copters.