lithium batteries, bulk float absorb time? end or return amps?

[northerner]

I read that article a year ago. I even know him he is a member of a EV forum, and has done a 180 like me. If you bothered to read the whole 3 pages in detail with an open mind he points out the dangers of TOP BALANCE. He now understands the risk involved with top balance, because he destroyed two of his cells. I DO NOT CARE IF YOU DESTROY YOUR BATTERIES. You have been told. Now it is time you learned with your your money. You will be the one hurting, not me, and I like it that way. Failure and loosing money is a great teacher.

I am confident I will survive just fine top balancing, thank you. If you are raising such a concern with balancing around the stage the cells are at full charge, then shouldn't there be a concern with keeping considerable distance from that point when charging on a regular basis? IMO from all the research I have done, there is little risk of destroying a cell if you manually do the cell balance at between 3.6 and 3.8 volts. Of course you don't want to forget about leaving the charger on like that fellow did and wound up destroying 2 of his cells. These cells hit 4.55 volts! No wonder they didn't survive, and yet 2 other cells did survive somehow, likely suffering from degradation?

I will have little risk in damage from going too low, as I normally don't discharge that low in the first place. I will be fine thank you, and I don't need any bottom balancing advice!

[tasman]

12 volts at 700 AH huh? That is some funny stuff, I don't care who you are. I bet you use a few PWM controllers and 12 volt battery panels on that system huh?

FWIW I design, build commission, and help companies and people maintain off grid power systems professionally for the last 15 years for commercial operations. Been a professional EE for 35 years of my 60 years on earth. I have forgotten more than you know about power. Retired happily in Panama tax free and never have to worry about paying any bills, traveling anywhere I want, any time I want. Life is good and comfortable for me at 60 years of age. I started out dirt poor in a military family.

Thank you, your reply is exactly what is expected, so hilariously funny and way of the mark as usual. As I posted, you have a habit of taking what others post and then claiming it as your own. Then you use abuse and deride others to force your delusions, then try to deny the right to post their experiences and hands on knowledge, which shows where your head really is at.

So you're retired and yet design and build off grid power systems from Panama, your own words reveal your true veracity.

What is a 12 volt battery panel, never heard or seen one, or is it your own invention for the world. You may use PWM controllers, I and other sensible logical people use MPPT.

12 volts and 700ah of energy is nothing spectacular, it's the way it's used that counts. But if you've never designed, built and used a system that is controlled by a 21st century computer system and only use last century expensive junk bloatware, then naturally you would revert to primitive last century understandings of off grid systems, no matter what the voltage.

The panels on our house, are 24v top quality and were cheap. Changed them over when we got the first lifepo4, put 1000w of 12v panels on our MH and the rest on the workshop. Some of the 12v panels are more than 30 years old and still produce almost their full capacity. Also use a very simple solar tracker, which built myself and was told it wouldn't work by a supposed engineer. Been operating for more than 20 years and never failed, have improved it in the last few years as technology advanced.

When you utilise solar for most of your lifestyle, you step outside the constrained urban mindset permeating the minds of clones. We have no heating or cooling requirements as our home is set 1.5m below ground level and when you use a computer controlled system, your energy use is regulated, instead of a free for all of high amps. But that would be to 1980's for you.

Don't have any technical qualifications, just decades of personal hands on in the real world experience and visiting many countries to see what other real living in the real world people do. In outback Aus, there are some really cool systems which flaunt all the claims you make about them and work well.

[Willy T]

Of course you don't want to forget about leaving the charger on like that fellow did and wound up destroying 2 of his cells. These cells hit 4.55 volts! No wonder they didn't survive, and yet 2 other cells did survive somehow, likely suffering from degradation?

Seemed pretty interesting that the guy that overcharged 4, 3.2 V cells with a 12 V charger, was or claimed to be a EE, sounds familiar.

This cell and three others were over charged by one of the brightest guys in DIY LFP banks. He is also an EE. $hit happens and I use the $ for an S for a reason.

Quote:

"Charging 4 x 90Ah cells in parallel with a 40 amp 12v charger, thought I'd turned the charger off, didn't discover it till a few hrs later. The cell was at 4.55v from memory and so hot the terminal bolts burn into the finger tips. The strange smell of the electrolyte vapor, but no sign of any white cloud. The heat was similar to standing in front of an oil heater on full and was still quite noticeable the following morning. Only the 2 cells in the center bulged and they are the only two that failed. The cells at either end had better cooling, they bulged a bit, but they are still part of my battery bank 12 moths later."

[Sunking]

What is a 12 volt battery panel, never heard or seen one, or is it your own invention for the world.

Very interesting.

Some of the 12v panels are more than 30 years old and still produce almost their full capacity. Been operating for more than 20 years and never failed....

20 and 30 years ago the only panels on the market were 12 volt 36 cell battery panels that operate at 17 volts vmp. They are expensive low voltage antique relics antiquated by MPPT charge controllers, and inexpensive high voltage Grid Tied panels. Using a MPPT charge controller allows you you to use high voltage Grid Tied Panels wired in series so you can even charge a 12 volt battery with 120 volts. A battery panel cost twice as much as grid tied panels. I bet you wire all you panels in parallel to keep installation cost low seeing how you wire all your batteries in parallel huh?

[Sunking]

I will have little risk in damage from going too low, as I normally don't discharge that low in the first place. I will be fine thank you, and I don't need any bottom balancing advice!

Northerner I am really trying to help you. You are over looking or missing a few very important points. Just answer these questions honestly.

How are you going to monitor cell voltages?
How are you going to control the high and low cell set point voltages?
How are you going to charge the cells?
How are you going to prevent over charge and over discharge of individual cells?
How many days of vacation do you take a year, or gone from the house?
Do you ever have more than one cloudy day?

I know you think you have all those angles covered. But I promise there are some serious flaws in your analogy and logic you have not picked up on yet. I know how you want to do it, and it can be done, you just have to change your point of reference and thinking. Answer the questions and I will point out what you are missing. Then maybe it will click what I have been trying to tell you.

[northerner]

Northerner I am really trying to help you. You are over looking or missing a few very important points. Just answer these questions honestly.

How are you going to monitor cell voltages?
How are you going to control the high and low cell set point voltages?
How are you going to charge the cells?
How are you going to prevent over charge and over discharge of individual cells?
How many days of vacation do you take a year, or gone from the house?
Do you ever have more than one cloudy day?

I know you think you have all those angles covered. But I promise there are some serious flaws in your analogy and logic you have not picked up on yet. I know how you want to do it, and it can be done, you just have to change your point of reference and thinking. Answer the questions and I will point out what you are missing. Then maybe it will click what I have been trying to tell you.

I'm still contemplating about what battery chemistry to go with at this point. I have been off grid for about 2 years now, and I have rarely gone below 50% DOD, and if I had, was not by much. If I do go with LFP batteries, I would put in a back up battery for winter, as I can not be without power during winter months. My old set of FLA's would be perfect for that. In the "summer season", I go from about mid February till about mid October with practically 0 generator run time. This past season I ran the generator for 1.25 hours on Sept 27. So there won't be any worries about taking the bank too low. In winter, there is always someone around, and if away in summer, the power doesn't even need to be on.

I still believe there could be a cell degradation issue with taking the bank too high, which could ultimately affect cycle life of the battery. This is particularly the case when the charging rate is not a known constant, but is a complete unknown, using solar.

[Sunking]

Norhtern what are you afraid of? Does learning something scare you? Whether you Bottom Balance or Top Balance still requires some form of Automation at the cell level. You cannot do this at pack voltage levels to protect them. The difference between the two is a reference points. At the top, capacity is unknown. All that is know it is the only place the cell voltages equal. As you discharge the cells voltages seperate and at the bottom can vary by a magnitude of 2. You can be at 30% SOC (3 vpc) pack level on a Top Balanced pack and have a 1.5 volt destroyed cell without knowing it. 80 to 20% is a whole whopping .2 volts per cell or just 3.2 volts at the 48 volt pack level.

At the bottom (0% SOC of 2.5 vpc) you know exactly what the voltage and capacity of the pack and cell are. At 40 volt pack voltage all cells = 2.5 volts. Your inverter is set to 42 volts and takes nothing more than that to protect over discharge. If that fails, the cells do not have any energy left in them to drive any cells into reverse polarity. All reverse polarity means is the cell goes to a Dead Bolt Fault Resistance of a piece of copper wire of 0 Ohms. No amount of current in either direction will fix it. It takes less equipment and eliminates the possibility of ever over discharging and over charging, plus the added benefit of not losing one single amp hour of usable capacity and extends battery life. What is there to be scared of? You got nothing to loose. What you are missing is the details and trying to operate like a Pb battery. One thing you have not wrapped your head around is all batteries have their highest resistance when discharged, and lowest resistance when charged. You may mentally know that, but do not understand what it means in operation and the consequences of not understanding that. It means you cannot operate like any other battery chemistry. You cannot treat all cells like a single battery.

[northerner]

Whether you Bottom Balance or Top Balance still requires some form of Automation at the cell level. You cannot do this at pack voltage levels to protect them.

Well of course, and that's what the cell level BMS is there to protect from. If you have a robust BMS in place, then there should be no worries with going to low.

Whether one top balances or bottom balance is a personal choice, however.

[Living Large]

Northerner I am really trying to help you. You are over looking or missing a few very important points. Just answer these questions honestly.

How are you going to monitor cell voltages?
How are you going to control the high and low cell set point voltages?
How are you going to charge the cells?
How are you going to prevent over charge and over discharge of individual cells?
How many days of vacation do you take a year, or gone from the house?
Do you ever have more than one cloudy day?

These are the questions I was considering for my application when I stopped participating in this thread several weeks ago, and I still haven't gotten back to them. I was starting to get a little overwhelmed. What-ifs and options can do that.

I got as far as knowing my CC could suspend charging based on the first individual cell reaching its max voltage with a signal from the BMS, and knowing I could shut down my inverter/charger if I needed to with a signal from the BMS, which I believed could be a LVD in case of emergency. But those are only two of several needed functions. I do plan to get back to this, but my mind isn't in the right place right now. I still think LFP is for me - it's just ironing out the details.

[Sunking]

Well of course, and that's what the cell level BMS is there to protect from. If you have a robust BMS in place, then there should be no worries with going to low.

Wrong if you top balance with BMS requires Vampire Boards silly which bleeds the cell. That is why they are called Vampire Boards. The Vampire boards serves 3 functions. They Bleed your cells, They monitor and report cell voltage and temps. To Bleed them they use a Mosfet and a resistor to do that. Mosfet have two failure modes: One is Open Circuit which is no problem. The other is more likely is Shorted which = Dead Discharged Battery. Only to to keep it from discharging is to be there, catch it in time, and remove the Vampire Board. You don't use Vampire Boards if you Bottom Balance, you only monitor cell voltages with cheap PLC, not an expensive BMS and 16 Vampire Boards to fail. Risk is eliminated and added expense of BMS and Vampire Boards is avoided. What part of that do you not like or understand, or afraid of? Could it possible be you are afraid to admit you over looked something? Or do you to prefer to spend money and take extra risk to make life exciting? Come to think about that might be the case if you are considering AHI batteries over LFP or Pb.

You are half correct, it is a personal choice. Just one choice is much less expensive, less complicated, less risk, and if you want to be a minimalist requires no additional equipment. In other words one is a smarter choice than the other. Good luck.

[northerner]

Wrong if you top balance with BMS requires Vampire Boards silly which bleeds the cell.

No, what you stated isn't entirely correct, and I don't think you read my previous post, as I said I would top balance manually and not use the cell shunts. The term BMS is used rather loosely and can mean that it is a system used to keep the cells in balance. It can also mean that it's a system used only to monitor cell voltages, and then trigger an alarm if any conditions beyond normal are encountered.

The BMS I was referring to would simply be monitoring the cells passively, and only come into play to do the appropriate LVD or HVD.

Top balance or bottom balance, as long as one keeps there distance from the knees, will work out just fine.

[Sunking]

No, what you stated isn't entirely correct, and I don't think you read my previous post, as I said I would top balance manually and not use the cell shunts. The term BMS is used rather loosely and can mean that it is a system used to keep the cells in balance. It can also mean that it's a system used only to monitor cell voltages, and then trigger an alarm if any conditions beyond normal are encountered.

The BMS I was referring to would simply be monitoring the cells passively, and only come into play to do the appropriate LVD or HVD.

Top balance or bottom balance, as long as one keeps there distance from the knees, will work out just fine.

You do not need to do any of that if you bottom balance. You don't get it dude. It is above your head and you do not want to know. Forget about it. I listened to you every time and understand perfectly what your think you think. Problem is you are completely over looking things and are not capable of understanding, or afraid to admit you do not know and wrong.

Relax, enjoy, do it your way. Ignorance is bliss. You win...

[tasman]

Very interesting.



20 and 30 years ago the only panels on the market were 12 volt 36 cell battery panels that operate at 17 volts vmp. They are expensive low voltage antique relics antiquated by MPPT charge controllers, and inexpensive high voltage Grid Tied panels. Using a MPPT charge controller allows you you to use high voltage Grid Tied Panels wired in series so you can even charge a 12 volt battery with 120 volts. A battery panel cost twice as much as grid tied panels. I bet you wire all you panels in parallel to keep installation cost low seeing how you wire all your batteries in parallel huh?

Your really don't have a clue do you and absolutely no understanding of off grid energy systems, other than from an egocentic primay school room attitude. In 1981, bought a 5w military solar panel and a 20w panel. That gave us a primitive lighting system that used an old car battery, car fittings and globes.. Next bought 2 x 80w panels, made a charger out of an old car generator and motorbike and built a 300w modified sine wave inverter. Used that to build our house running of a running tractor battery, still sitting in the workshop getting used. Then built a 12v x 1500w pure sine wave inverter which is now backup for the cheapo Chinese 12v 3000-6000w shiny one I bought in a mad moment on ebay. That's worked well so far, but longevity will tell and then may go back to my trusty old one.

Over the years have added panels and used charge storage systems from old car batteries, 2v x 500ah LA batteries, AGM deep cycle and gel in mobile situations. Started using 12v LED lighting about 10 years ago which made up myself and now use 240v LED lighting in our house and 12/24v in the MH and motorsailer. In the last 2 years have changed everything to lifepo4, including AA and AAA batteries for camera's etc, at the same time changed our house panels to 24v ones and put the workshop on gel/AGM.

Posted a photo of my lifepo4 pack set up and explained the connections, even asked if it was the right way, but got no reply. If you took notice of others posts, you'd see don't use wire when connecting cells, because it's dumb and opens up avenues of failure, particularly in mobile applications.

Sensible people use copper bar, which gives good strong connections and allows for huge amperage draw if needed, plus it's very cheap compared to wiring. When making up starter packs, copper bar means big savings and security, as well as getting the most out of your cells when you need it.

The same panels are used for both grid connect and off grid, so again you're talking crap and ignoring what's been posted.

When I'm showing some one our systems, tell them setting it up requires a bit of know how and real life hands on understanding, not just school room theory.

Same with computing, people are amazed at what we use, but always tell them to start out with the basics of open source, so they learn as they go and then will be in control of their systems and not some over priced school educated wanker. Especially if you want to run you house energy system by computer, as we do.

Currently, I'mp[laying with a distro (OS) which runs in RAM, on a very old Compaq laptop with 256k RAM and 10gig HD, picked it up for $5 at a garage sale. It runs really well and exceptionally fast because the distro sits in RAM. Once I get it doing what I want,hen it will run our MH lifepo4 12v system. A raspberry Pi would be the way to go if I didn't have an old laptop.

But that's probably to 1980's for you, yet something anyone using lifepo4 should be doing, setting up a computerised system to run and control their lifepo4 packs and charging regimes. It's why you can't understand using a 12v powered system in a home, or proper pack charge regimes. Its called a 21st century approach and because our 12v system of many decades works excellently for our requirements. Not what urban and grid people waste every minute of the day.

Any one who asks me what sort of system they should have, the first thing I ask them, is to add up the wattage of all the things they want to use. Then they will have an understanding of what is required, most walk away when they discover they can't get what they want at the price they want. But those that don't, end up refining their usage to the system size and cost they can afford.

Down here, for a small house hold of 10-14 CM, a 12v system is half the cost of 24v and it also depends on where you site you system and panels if you just want 12v throughout the house. With Lifepo4, it can be situated in the centre of the building, making long runs a thing of the past and putting big wattage appliances as close to the power source as possible. There are many things which go towards making up a good system, not just voltage and balancing.

[Mike90250]

Well of course, and that's what the cell level BMS is there to protect from. If you have a robust BMS in place, then there should be no worries with going to low..........

Uh, but the problem is, interfacing the BMS to the solar charge controller. Most of the BMS have 1-10A shunts, to bypass the full cells, and a special AC mains charger they interface to, to stop the charge when the first 2 or 3 cells fill up.

But solar is a different creature, we charge at much higher rates (I hit +40a now, and can get +60a adding the generator to it). And the 10A shunt on the BMS is going to glow cherry red while 30A continues into the battery. Most solar charge controllers don't have a connection to the BMS, so they are not going to stop till they think they are done. So you have to build a special "one-of" system for your bank, and hope there were no engineering mistakes. Not that it can't be done, but that it's hard to do right.

Mike

[Sunking]

Uh, but the problem is, interfacing the BMS to the solar charge controller. Most of the BMS have 1-10A shunts, to bypass the full cells, and a special AC mains charger they interface to, to stop the charge when the first 2 or 3 cells fill up.

Mike maybe you have seen some Vampire Boards I have not ran across, but all the ones I know of are .2 to 1 amps. EV's charge a bit slow around 5 to 10 amps, but you spot on when the boards turn on they can only bypass a small fraction of the current leaving the rest to cook the cell.

Custom EV shops are dropping Top Balance, and most do nothing more than Bottom Balance, and no additional equipment with great success. They terminate charge when the pack reaches 153 volts (3.4 vpc average), and just use the motor controller LVD protect the low end where the voltages are equal. Real easy to implement on solar. Set the CC Bulk = Absorb = Float = 54 volts, and let the the inverter LVD take care of the bottom. For whatever reason Northern just cannot wrap his mind around that.

Me I went one little step further on the NEV. I use a PLC to monitor cell voltages on the charge side and terminate when first cell hits 3.4. That will be the weakest cell. I charge at C/2 or 50 amps on a 100 AH battery.