LifePO4 batteries for use with Midnite Classic 150?

[PNjunction]

Worse is relative to EV usage.

Since we are in a "sub-C" application, the performance issues you state are lessened severely.

In other words, the GBS are just fine for housebank use, but not for racing golf-carts. If you still have the golf cart rig and want to race it, go A123 or perhaps a stack of Headways, both of which are "power cells".

The GBS cell performance could be likened to "energy cells", even Winston, or lower-rung CALB's. That is just fine for solar-housebanks. Essentially, they are also known as the "3C" cells, being that they only spec out to 3C for short bursts unless you seek the higher end models. (and pay more natch...)

Heh, we'll never do 3C in our application - not even 1C, but more like 0.2C max where GBS and others like them will live a boring life.

[Sunking]

PN I think you would agree the CALB's are the best of the Chi-Coms. Would you not agree with that?

That being said The CALB's are less expensive and twice the warranty/cycle life of GBS and Winston. Knowing that which one would you buy?

FWIW I do not have the GBS cells anymore, sold them to another fellow. Today i have Leaf cells in the cart operating at 96ish volts. Mucho Better performance. Very low voltage sag when accelerating, and very little capacity loss for their age. Me and a couple of friends down here bought a set of Leaf Batteries from a salvage yard.

However if I could buy a set of A123 if the price was the same I would. Unfortunately A123 is some 200 to 300% higher in cost. My salvaged Leaf batteries cost less than 10-cents per watt hour. That is less than new FLA.

[karrak]

It's strange that Midnite would recommend top balancing with a BMS while this forum recommends bottom balancing with no BMS. I understand the logic, I'm just not sure why Midnite is misinformed. It makes me think that not many people are running LFP. I know LFP is big in the boat scene though.

There are a few people on this forum who recommend bottom balancing with no BMS. I know of over ten off-grid/grid-connect systems with over $1,000 of LFP batteries on each system and know of only one of these being bottom balanced and this system does have a BMS. I have designed and am resposible for two systems that have been in use for nearly three years, both have a BMS and both are manually top balanced. I think you will find the vast majority of larger LFP batteries in stationary applications are top balanced and have some sort of Battery Management/Monitoring system.

It is great that Midnight can take the output from a BMS to stop battery charging. There are a number of BMS on the market that will provide the signal to shut down your solar controller. The Batrium equipment is fully programmable, provides logging and optional automatic balancing. Cleanpower also make BMS units that would be suitable. If you wanted to do it on the cheap you could also use a Cellog8 connected to your Midnight, if you are running a battery with more than six cells you should carry out a simple modification to the Cellog8, just google Cellog8 modification for more details.

Simon

[Living Large]

It's strange that Midnite would recommend top balancing with a BMS while this forum recommends bottom balancing with no BMS. I understand the logic, I'm just not sure why Midnite is misinformed. It makes me think that not many people are running LFP. I know LFP is big in the boat scene though.

Whoa, hold on. On what basis are you concluding that "Midnight is misinformed"? I don't agree with that assessment at all. You stated that "I understand the logic" of bottom balancing without a BMS. If you gained that logic from reading threads here, you should understand why Midnight recommends top balancing with a BMS.

I'll admit, the threads are lengthy here. Yet the explanation to an apparent contradiction is contained in them. The best answer is to re-read the thread on LFP and use of a BMS. The topic has been beaten to death.

For Midnight Solar to make a recommendation that covers all users, it would need to publish a white paper that is 20 pages long on balancing and the use of a BMS with LFP, and leave it to the consumer figure out what works best for their application, knowledge and desired maintenance schedule. And they would have to field calls from consumers asking technical questions and debating what solution to choose. Instead, they take the high road, give a one-sized fits all recommendation (one that may limit their liability), and leave it at that.

[createthis]

I've decided I'm going to top balance. Since this is a portable system, cycle life is less important than weight/capacity.

Point me to a BMS or system where I can get an overvoltage alarm from the BMS I can use with the Midnite Classic's AUX2 to stop charging. My problem right now is the only BMS I can find via google with an overvoltage signal is the GBS BMS: http://jumpycalm.com/file/User%20Man...S%20System.pdf and it duplicates a lot of the functionality my Victron BMV-700 already does and does better.

[Sunking]

If you Balance the cells right to begin with, all you need to do is set the voltage correctly on the controller. You do not want to fully charge the batteries or have your controller turn off mid day and start using power while there is still sun power available. Once LFP cells are balanced, they do not get unbalanced unless you use Vampire Boards or Monitor Boards. You set the controller voltage low enough the cells never reach 100% where danger is.

Here is the catch, there is no BMS that can Balance new LFP cells. Most of the Balance Boards can only use 150 to 300 ma as Balance Current. That can take years to Balance your new cells. Here is your problem and challenge. You know nothing about Lithium Cells. 99% chance you will destroy them from ignorance in a short time. New cells must be Balanced with external equipment you do not have or know how to use. So be careful what you ask for because you are asking for a disaster. New cells are NOT BALANCED, you have to initially Balance them, and no BMS is capable of doing that.

[inetdog]

OK, related to that useful advice, I have a few questions:

1. If you build a battery bank out of random off the dealer's shelf cells, all the same brand and model and hopefully same or similar manufacturing date, how likely is it that the cells will be reasonably (within the capacity of the BMS to handle) balanced as to SOC when you get them?
2. Same question but a group of cells ordered new from the factory or from a large internet dealer as a single order? Better or worse than the first situation?
3. Same question but this time you buy a preassembled battery pack with an integrated BMS?

Regarding Vampire and Monitor boards: Clearly any differences in current consumption of the boards is going to cause a growing imbalance as the cells sit idle or discharging. But if the cells are on almost constant charge at a high enough voltage that current difference is not going to matter. Where between those two extremes do the boards continue to make sense? Clearly not for typical solar PV where charge/float time is limited, and especially if you deliberately never bring the bank to 100% SOC where the cell bypass function kicks in.

[createthis]

If you Balance the cells right to begin with, all you need to do is set the voltage correctly on the controller. You do not want to fully charge the batteries or have your controller turn off mid day and start using power while there is still sun power available. Once LFP cells are balanced, they do not get unbalanced unless you use Vampire Boards or Monitor Boards. You set the controller voltage low enough the cells never reach 100% where danger is.

Here is the catch, there is no BMS that can Balance new LFP cells. Most of the Balance Boards can only use 150 to 300 ma as Balance Current. That can take years to Balance your new cells. Here is your problem and challenge. You know nothing about Lithium Cells. 99% chance you will destroy them from ignorance in a short time. New cells must be Balanced with external equipment you do not have or know how to use. So be careful what you ask for because you are asking for a disaster. New cells are NOT BALANCED, you have to initially Balance them, and no BMS is capable of doing that.

Christ, Sunking. The Midnite Classic has Absorb, Bulk MPPT, and Float voltages. That's it. What are the correct voltages in your opinion? I'm growing extremely tired of you replying to every question I ask with "you can't do that because you're too stupid" statements. The only way I'll learn anything is if you reply with actual useful answers to the question instead of negative you can't statements.

[SunEagle]

Christ, Sunking. The Midnite Classic has Absorb, Bulk MPPT, and Float voltages. That's it. What are the correct voltages in your opinion? I'm growing extremely tired of you replying to every question I ask with "you can't do that because you're too stupid" statements. The only way I'll learn anything is if you reply with actual useful answers to the question instead of negative you can't statements.

I could be wrong but I believe the problem is that the Midnite Classic does not have the logic to perform "balance charging" of each cell which is required for Li chemistry batteries.

[createthis]

PN I think you would agree the CALB's are the best of the Chi-Coms. Would you not agree with that?

You realize just about everything is made by the Chinese these days, right? Were you in Vietnam? We don't really call them Chi-Coms anymore.

[createthis]

I could be wrong but I believe the problem is that the Midnite Classic does not have the logic to perform "balance charging" of each cell which is required for Li chemistry batteries.

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.

[inetdog]

I could be wrong but I believe the problem is that the Midnite Classic does not have the logic to perform "balance charging" of each cell which is required for Li chemistry batteries.

You are in part wrong, but mainly you are not relating to the problem and the terminology.

No CC which does not have connections to each of the individual cell terminals (i.e. six cells requires seven wires) can actually balance a bank of cells.
You do not balance individual cells, you balance a set of cells. That balancing may involve charging each cell individually to a known SOC (top balancing) and then connecting them.
Once the battery bank (or string) is balanced the Classic can be set with Bulk = Absorb = Float with the voltage being the 80% or 90% SOC voltage of that particular cell type.
That setting, along with neither Vampire nor Monitor boards on individual batteries, should allow the bank to stay balanced for a long time. The one remaining component that is absolutely essential is a low voltage detector that both disconnects loads AND inhibits normal high current charging when the voltage drops below a set limit.
That function is not, AFAIK, part of the repertoire of the Classic.

Continuous balancing is NOT required for Li chemistry, but at least periodic monitoring IS. Then rebalancing can be done manually if necessary.

[Sunking]

You can set all 3 voltages to equal. thereby making it a CC/CV charger 1 stage charger. Midnite Solar is not made or intended to work with LFP batteries period. All you can try to do if you know how, is work around the incompatibility. You do that by setting the controller voltage well below 100% SOC so you do not gfry your cells. There is only one I know of made by Genasun using their integrated battery. Problem is limited to a 140 watt panel and their battery.

Chargers intended to work with LFP batteries communicate. What you do not know is how Balance Boards Work and that is what the killer is. All they do is turn ON when the cell is fully charged and bypass a small amount of current to be passed onto lower cells. Sounds great huh? It sucks. That can only work if your charger can then cut back current to the limit of the balance boards.

Now stop and think about that a moment. I bet it never occurred to you what is happening or what can happen. So you batteries are charging along at full power, say 25 amps. First Balance Board turns on when it gets fully charged and turns on and bypasses say .3 amps. That leaves 24.7 amps still flowing into a fully charged cell heating it up and causing damage. No Solar Charge Controller except Genasun has the ability to cut back current, they can only regulate VOLTAGE, not CURRENT. A real LFP chargger can do that and you set what that amount of current is to match the balance boards.

Secondly no Balance Board (BMS) can Balance an a out of balance battery bank in any meaningful time frame. Why you ask?. I already told you because they can only bypass a very small amount of current. All they can do is make for very small minor corrections.

Now if you completely understand how LFP works, what destroys them, and how to protect them you can work around all that. So your first challenge is when you receive the cells, HOW ARE YOU GOING TO BALANCE THEM? Can you even answer that? Give you a hint, you need some expensive equipment you do not have.

I am trying to prevent you from making a huge mistake. But it is yo money to loose, I really do not care, have at it. But smart money in you case is FLA batteries, much cheaper and will last longer. In you rcase much longer because you will destroy your first set of LFP batteries. Your choice.

FWIW Inetdog and PNJunction are telling you the same thing. You might want to listen to one of us.

[Sunking]

You realize just about everything is made by the Chinese these days, right? Were you in Vietnam? We don't really call them Chi-Coms anymore.

What do you call Chinese Communist? I call them what they are.

[Sunking]

Let take another pass at this. First read this thread as it may help you understand charging algorithms.

OK assume you want a 12 volt 100 AH LFP battery or 4S. About the size of a large trolling motor or truck battery. So you buy 4 100 AH Chi-Com cells like CALB, best of the Chi-Coms Those will cost you roughly 45-cents per wh. Really good LFP'slike A123 Pouch Cells cost $2/wh or 4 times as much as Chi-Coms

So your cells arrive. You have to Balance them before you can use them. Manufactures do not send them out fully charged because fully charging them is stressful, and storing them fully charged is a recipe for destruction. So take that hint from the manufacture. They will arrive to you from as low as 40%SOC to as high as 70% SOC charged. That means the lowest charged cell is 40 AH,a nd highest at 70 AH a 30 AH spread you have to BALANCE OUT. somehow.

So not knowing any better you use your BMS and it uses 300 ma Balance boards on a 50 amp charger made to work with LFP batteries with a BMS. So you start charging at 50 amps, and 45 minutes later the 70 AH cell is fully charged, and signals the charger to cut back charge current to 300 ma from 50 amps.If the charger cannot cut back keeps right on pushing 50 amps through your fully charged battery So now your low 40 AH cells has charged up to 70 AH with 30 AH more to go to 100% when the charger cuts back to 300 ma. So now you are charging at 300 ma. It will take another 30 AH / .3 A = 100 hours to charge up and Balance if you are using a AC charger running 24 hours a day. That is 5 days. If you tried that with solar on a 4 hour sun day it will take 25 days to Balance. Do you have a problem with that?

Now once Balanced clear sailing because LFP cells do not become unbalanced or drift much. Maybe a few mah each day and your BMS can handle that OK in a short period of time. Say th imbalance is 30 ma only takes 10 minutes to balance at .3 amps.

But guess what? No Solar Charge controller can cut back current to match your BMS charging current.

Here is something else to think about. No Commercial EV manufacture allows the customer to charge their batteries to 100% SOC. It is the only way they can offer a 5 year warranty. They do have a BMS, but their cells are matched at the factory and BALANCED at the factory. There BMS only has to make small corrections from time to time when the computer detects there is a imbalance. 99% of the time, the built in charger works as a 1-Stage CC/CV charger. The computer controlling the BMS allows the charger to charge at full rated current until the PACK Voltage reaches 80 to 905 then shuts off. No Balance is done. They only Balance from time to time when needed which is not often.

Can you mimic what they do? Yes. Question is do you know how,a nd what the consequences are if you get it wrong. A Midnite Solar Controller cannot do any of that. To make it work you have to force to act as a 1-stage CC/CV charge which is easy to do. You set Bulk = Absorb = Float and disable EQ. You set the voltage less than 100% so the Balance Boards never turns on. and no reason to shut down the Controller if you set the voltage to lower than 100% pack voltage. When the batteries reach the voltage SET POINT charge current stops all by itself. So if that happens at say 2 in the afternoon with good sun hitting the panels, load current comes from the panels, not the batteries unless load demand current exceeds what the panels can produce. You cannot do that with a BMS set up to charge to 100%, nor can your charge controller support a BMS.

Lastly if you use a LFP battery you have to protect them from Over Discharge. To do that you must have a Low Voltage Cut Off (aka LVC) circuit between the batteries and Load. That consist of a Heavy Contactor and a Voltage detection circuit Again your controller will be of no use to do that.

Do you see any problems with any of that? How are you going to do that?