LifePO4 batteries for use with Midnite Classic 150?

[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]

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.

[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.

[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.

[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.

[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.

[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

[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.

[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]

Well I must say GBS is the worse of the Chi-Com batteries. Three points.

1.They are the most expensive of the Chi-Coms.
2. They have the shortest cycle life of the Chi-Coms
3. They have the longest Short Circuit Discharge Time of any LFP manufacture. (Highest Internal Resistance per AH)

1 + 2 = Real Expensive Deal Breaker.

They are just not worth it, I speak from my own loss and experience. FWIW to learn how to work with with LFP, you use a couple a $5 cells to destroy, and not a $2000 set.

[Sunking]

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.

You are misinformed. Any commercial application demands top balancing and using a BMS. Reason is you do not need to know anything about LFP batteries, and consumers don't know chit from shinola. Problem with Top Balance is it shortens battery life, and prone to failures which destroys the batteries.To Bottom Balance takes a lot of knowledge and know how which you do not have. Many DIY EV builders and a few Solar users use Bottom Balance to extend battery life, eliminate over discharge, and a lot less expensive to implement.

[PNjunction]

In that case, which BMS/Battery combo would you recommend? Is the GBS stuff any good? It seems to be the most visible on the internet at the moment.

GBS is fine for our purposes. I run them in a simple 4S / 12v bank. GBS are more an "energy cell" than a "power cell", as far as capabilities go, and that is actually way more capable than we need *if you treat them in a sub-c application*. Like a solar housebank for instance, that doesn't usually see more than about 0.2C charge / discharge. 3C is available in short bursts, but we don't do that!

And along with good inter-cell connectors, they come with a 2-cent purple cover for each cell! Amazingly safe - since with other brands YOU have to build your own cell covers, (dropped wrench syndrome), and in your haste to get up to speed, these little covers might save your *ss right from the start.

Everyone has their own idea of how to run LFP. Much of it is spot-on depending on your application and your skill level.

If you are willing to take on some responsibility, YOU can become the BMS, which is made far easier for a low voltage - low current application.

Here is what I do for a solar application. YMMV. Generally I'm running from a max of about 10-80% DOD. That's about worst case, since with LFP, you want to stop thinking this way since there is no need to fully charge all the time. So, don't skimp on your battery and force it into a high-current application by getting too little capacity.

1) Charge each cell to full upon receipt. You can do this with a "nominal" 3.2 (three point TWO) volt single-cell charger, or your own variable bench supply. Set it to 3.6v, at no more than .5C (.3C or so preferable) and let the current fall to .05C, which for a 100ah bank would be 5A. Stop and move on to the next cell. You can do this to each cell individually while they are strapped together even.

2) Discharge normally with your regular loads, but don't let any cell fall below 2.7v while under charge. So that means some form of monitoring and of course an LVD. My personal LVD is set for 12.7v at the pack level. BUT, I try not to go there. That is a dead-man's catch - which is actually not deep enough to hurt the cells, but will start to get my attention.

3) When recharging, don't use the single cell charger - that's only for initial charging and PM maintenance down the road. Set your solar CC or ac charger to no more than 3.45v per cell. In my case, I have boosted that a teeny bit to 3.425v. This way, you won't exceed about 90% SOC, AND you'll never actually fully charge the battery if you mistakenly forget about the charger. Note that I'm not advising that floating the battery forever is ideal - this is just a "I forgot" kind of thing for a day or week or so.

Note, when dealing with the small range of voltages for LFP, one had better TRUST their multimeter for accuracy! Flukes of course do nicely - plenty of multimeter threads around.

In essence, my charger is the HVC. I run a small Powerwerx LVD at 12.7v. I have fully charged my batteries upon receipt, and am trusting in the GBS retailer to be providing me cells that are reasonably close in both capacity and internal resistance. Actually I have measured each, but that's the gist.

But that's me. Some may want to go in a totally different direction. Bottom balance, full-blown individual cell monitoring, automatic balancing - the list goes on and on. For me, if I have to treat LFP like if I sneeze it will die, I don't want to have anything to do with it. Still, I'm safe and I think what I'm doing is sane for a "sub-c" application like ours.

I have a bevy of lithium charging setups, balance chargers and so forth that I could use on my GBS cells. And I have! One can take it to that point if they want to like they would with an RC modeling setup, or racing EV setup. BUT, in this case, I stick to a simpler KISS method, with just a tad of sanity, and find it quite easy to handle.

Probably the best way to start out is to get a bank already assembled for you - that means already linked, and the pack strapped. Some guys do it themselves, but forget the strapping - and if you put some external force on your bank from a loose object, and the terminals twist or bend - bad news. Of course, get your cells from a reputable distributor, NOT some used junk or deal too good to be true. Lot's of LFP sharks out there waiting for the next sucker to buy junk.

You might be ready for LFP too - but maybe not the guy next door! I think a simple 4S / 100ah GBS bank is entirely manageable for someone who actually takes an interest in their batteries, and doesn't just ignore them.

[inetdog]

It is outside my area of expertise to make a concrete recommendation. Try PNJunction instead.

[createthis]

RE = Renewable Energy. Daily cycling to far less than the full energy capability of the batter.
Do not believe the 50% figure for AGM. I do not think anybody here would recommend that for a long term off grid installation.
The discharge extremes that the battery can handle without immediate damage and the low and high end cutoff points that give you the most watt-hours over the lifetime of the battery are two very different things.
If you are trying to size the battery as small as possible to minimize weight or initial cost, then maybe you do want to go closer to EV design rules of thumb. Sunking?

Yeah, I know 30% is better than 50%. Less discharge equals more cycles.

So, if I want to maximize the capacity of the battery at the expense of cost and cycle life, I want to top balance with a BMS, right? I run the risk of the BMS failing and destroying the battery, but I get the most capacity per cycle, though not most capacity over the life of the battery.

In that case, which BMS/Battery combo would you recommend? Is the GBS stuff any good? It seems to be the most visible on the internet at the moment.

[inetdog]

RE = Residential?

You're saying EV designs for max power output and residential designs for max longevity? That's weird though. If you cut off the bottom 20% and the top 20%, you're cutting off 40%. That's only 10% better than AGM's 50% DOD. I thought LFP usually could handle 80% DOD. Since this is a portable system, I have to wonder if I should design it more like an EV system. Maybe the additional cost of the BMS makes sense from a weight savings/power capacity perspective.

RE = Renewable Energy. Daily cycling to far less than the full energy capability of the batter.
Do not believe the 50% figure for AGM. I do not think anybody here would recommend that for a long term off grid installation.
The discharge extremes that the battery can handle without immediate damage and the low and high end cutoff points that give you the most watt-hours over the lifetime of the battery are two very different things.
If you are trying to size the battery as small as possible to minimize weight or initial cost, then maybe you do want to go closer to EV design rules of thumb. Sunking?