LiFeP04 Batteries for Solar & BMS

[Willy T]

You just lost all credibility here. SOLAR PANELS ARE CURRENT SOURCES, not Voltage Sources like a battery or utility. Look it up. Hint: Isc and Imp

Don't get all excited and wet your pants, he said they weren't Constant current sources.

[Sunking]

This is not true of all the programmable charge controllers I have come across. Charge controllers will stop charging an LFP battery after the battery reaches the Bulk Termination voltage, has gone through the Absorb phase at the Absorb voltage for a fixed or programmable time period or on some controllers until the charge current has dropped to a programmable level and then drops down to the Float voltage and the Float voltage is set low enough.

Simon you have proven again you do not understand Charge Controller or Lithium batteries. Charge controller never stop supplying power with sun light striking the panels. Absorb. Float, and EQ are all Constant Voltage Modes. Bulk is Constant Current. Look it up. You do not understand what they mean or do.

To charge a LFP battery as fast as possible with a off the shelf Charge Controller you set Bulk = Absorb = Float = Target SOC%. This forces the controller to operate in CC/CV mode. The CC will pump as much current into the batteries as the panels can generate. This is the Constant Current phase to charge as fast as possible. When the voltage reaches Set Point the CC then switches to Constant Voltage and the current will Taper Off to Zero Amps when battery voltage = charger controller voltage Lithium is the only battery that will stop charging when its battery voltage = supply voltage. All others have self discharge and thus never stop charging.

Once equalized as long as there is no load applied current will stop flowing, but the charge controller is still active siting in a FLOAT or Constant Voltage mode. If a load demands current, the panels will supply that power via Charge Controller assuming the load demand does not exceed what the panels can deliver. Works like any Float Service. The charge controller never shuts off until the sunset period end of story. The only question is did your batteries get fully charged up before sunsets

Sorry but you just clearly demonstrated you do not know what you are talking about. You do not know the basic principles of voltage sources, current sources, or even basic fundamentals electrical principles. You are not fooling anyone except yourself.

[Sunking]

What you don't seem to understand SK is that solar panels are not a constant current source

You just lost all credibility here. Even a first year electrical student knows SOLAR PANELS ARE CURRENT SOURCES, not Voltage Sources like a battery or utility. Look it up. Hint: Isc/Imp and Bulk mode charge phase.

[Sunking]

I don't know of any that use loose electrolyte. Some spiral roll the cells up and they look like a coke can. The cells are vented to the atmosphere that I know of ,GBS, CALB, Winston, Hipower , but the pouches I don't know . I sure someone will find some kind of battery that is different.

They are all the same basic battery design from the failed Thundersky Chi-Com manufacture. Same chit different colored box to identify the manufacture. Winston is on the brink of bankruptcy since Fiskers EV went belly up.

Polyymer lithium batteries are not real useful because they have very high internal resistance limiting charge and discharge rates to less than 1C. They last forever, but poor performance. Chi-Com Thundersky design is a 2 to 4C rate battery burst up to 10C. Only a Gel, Paste, or liquid electrolyte can do that. Polymer plastic sheets just don't cut it and can get the surface contact area close enough to have low resistance. Polymer ar great for low power applications, but not capable of high power.

[karrak]

There is only 1 algorithm used to charge Lithium called CC/CV which is nothing more than fixed bench DC power supply with current limit.

Do you actually charge your LFP battery from a solar panel via a charge controller?

In a Solar System you are fighting one HUGE BATTLE every day. Time, you don't have enough of it to mess around with any SATURATION. You DO NOT NEED and Saturation as it destroy CYCLE LIFE. Why would any fool want to do that? Lithium batteries are extremely easy to charge. To get to 90% SOC all they require is a Constant Current applied until the cell voltage reaches reaches 3.45 volts. So back to TIME and SOLAR. You do not have TIME on your side. The fastest way to 90% SOC is CONSTANT CURRENT, as much power as your panels can generate.

What is so damn hard you cannot understand Willy. Even a child can understand that. EV manufactures understand that. Most of the DIY EV understands that. Why can't you?. Yes you are stuck in a Pb World because you still use the 4-stage Pb mentality. Lithium Charge is clearly defined, has been for 10 years and you still do not know it. I will tell you what it is, CC/CV. It is that simple. If you only want to go to 90% to maximize battery life, Constant Current to 3.4 to 3.5 volts per cell and you are DONE. Saturate them like you are doing and you cut cycle life 30 to 50%. I am not going to allow you to tell people to destroy their batteries because of your ignorance and incompetence.

What you don't seem to understand SK is that solar panels are not a constant current source, the current varies with passing clouds and with increases and decreases in temperature. Sure you can charge to a constant SOC by going to a set voltage and terminating the charge if you have a constant current source. You cannot do it with solar panels.

Winston is LFP aka LiFeP04. When you use a Solar Panel with a conventional off the shelf charge controller, the charge controller never terminates the charge until darkness. Even if you set BULK, ABSORB, and FLOAT to 14.3 volts as you claim you are saturating the batteries to 3.575 volts which is above 100% SOC.

This is not true of all the programmable charge controllers I have come across. Charge controllers will stop charging an LFP battery after the battery reaches the Bulk Termination voltage, has gone through the Absorb phase at the Absorb voltage for a fixed or programmable time period or on some controllers until the charge current has dropped to a programmable level and then drops down to the Float voltage and the Float voltage is set low enough.

There are two ways to charge a Lithium Ion Battery:

1. Is a 2-stage Constant Current / Constant Voltage method which is basically what you are forced to do with Solar Charge Controllers on the Market.

You are saying there is only one way to charge an LFP battery with Solar Controllers on the market. I can think of three

1. As you have said Set the Bulk, Absorb and Float voltages to be the same (I think a lot of controllers on the market will not let you do this). The charge controller will charge the battery at whatever variable current the panels will supply until the controller voltage equals the set voltage at which point the current will start tapering off till it reaches zero.

2. Set the Bulk voltage to the charge voltage you want, set the Absorb time to zero if possible and set the Float voltage to less that the rest voltage of the battery at the SOC that you have charged it to. If the output from the solar panels is constant you will get the fast charge method you outlined in your method 2.

3. Set the Bulk voltage to the charge voltage you want, set the Absorb time to 30 minutes or so and the Absorb end current to whatever current you want to terminate the charge at, say C/20

Simon

[Willy T]

No plastic film electrolyte in Large Prismatic cells, they are not Polymer batteries. It is a gel inside those pouches. Here is what happens when you shoot one with a nail gun. At about 2:15 into the video you will see the electrolyte pouring out. But you can see it still frame below. The gel is translucent purple in the factory when added. Come out scorched blue.

You'd have to ask the poster, of course the story will change now that the actual inside of one has been shown.

[Willy T]

I am always interested in the "internals" of things and batteries is one category I am still in the early learning stages.

Is that the only way to make a prismatic battery or do some companies enclose the individual "cells" is a high density solution to minimize movement and possible internal damage?

I don't know of any that use loose electrolyte. Some spiral roll the cells up and they look like a coke can. The cells are vented to the atmosphere that I know of ,GBS, CALB, Winston, Hipower , but the pouches I don't know . I sure someone will find some kind of battery that is different.

[Sunking]

No Plastic film or Gooey gel to be seen.

No plastic film electrolyte in Large Prismatic cells, they are not Polymer batteries. It is a gel inside those pouches. Here is what happens when you shoot one with a nail gun. At about 2:15 into the video you will see the electrolyte pouring out. But you can see it still frame below. The gel is translucent purple in the factory when added. Come out scorched blue.

[Sunking]

Yes, just like you never want to take them to 0% SOC to do a bottom balance.

There is the part you do not understand. You are not taking them to 2.0 volts (The Cliff), you are taking them to 0% SOC at 2.5 to 2.7 volts. At that point the cell capacities are perfectly balanced to a KNOWN REFERENCE POINT of 0 Amp Hours . At Top you have no clue what the capacity is. All you know is 100% SOC, capacity unknown. In a Bottom Balance system you never touch 0 or 100% SOC and know what the capacity is at any given moment. You do not have a clue what is going on in a Top Balanced system. Once you start discharging from the top you have no clue where you are at.

Taking a LFP to even 2 volts is not a problem. What is a problem and the KILLER is when in Top Balanced systems the weaker cells get to 2 volts while the stronger cells still have sufficient capacity to drive the weaker cells into REVERSE POLARITY. When that happens game over, Cell is destroyed. With Bottom Balanced that is impossible because all cells have the same capacity and all cells reach 2.5 volts the same time. Your Low Voltage Disconnects long before you get there leaving you a lot of breathing room. 2.5 volt Lithium cells cannot deliver any meaningful current. It is Passive Protection and requires no operator or automated controls which are prone to failure.

FWIW a 1 ohm resistor can only bypass 3.6 amps, which may or may not work. If the controller is pumping more than 3.6 amps, you are still over charging the battery. With Lithium batteries the discharge curve is so flat, voltage tolerance needs to be within .001 volts which you cannot achieve either manually or automated. Only Bottom Balance can you achieve that kind accuracy both manually and automated.

[SunEagle]

Example : .... Anyone that has seen the inside of a prismatic battery knows that it is made up of many sleeved / envelope cells all paralleled to the battery posts, their size and amp hr capacity dictate the over all amp hr capacity of the battery. No Plastic film or Gooey gel to be seen.


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I am always interested in the "internals" of things and batteries is one category I am still in the early learning stages.

Is that the only way to make a prismatic battery or do some companies enclose the individual "cells" is a high density solution to minimize movement and possible internal damage?

[Willy T]

OK - Playing adult games with a kids knowledge and training?

Do you mean people that make posts like this ??

The construction method of large prismatic cells is no tan exact machining process. If you open one up it basically looks like a large sheet of metallic plastic film with a gooey gel.

Example : The above poster has never seen the inside of a large prismatic battery, this plain bs. Anyone that has seen the inside of a prismatic battery knows that it is made up of many sleeved / envelope cells all paralleled to the battery posts, their size and amp hr capacity dictate the over all amp hr capacity of the battery. No Plastic film or Gooey gel to be seen.


WinstonThundersky90ampSectionCut07.jpg


There are people that post things on here that are just plain BS. If you even thought about correcting them, it's a stick in their eye and they will bring the powers to be swoop down on you.

[karrak]

Please share how....

How to manually top Balance an LFP battery using solar power
1. Choose a nice sunny day when you will get reasonably constant power from your solar panels.
2. Set your Solar Charge Controller to Charge to whatever voltage you want to balance to. In the past I have used 3.6 volts, would probably use around 3.5-3.55 volts these days.
3. For me, I look at the realtime output from my battery monitor (if you don't have a battery monitor you can use a multimeter) and as the battery voltage gets close to the cutoff voltage, if any cell is higher that the others connect a 1 ohm resistor across its terminals until its voltage drops down to the others, then disconnect the resistor. Keep doing this until all the cells are as close to each other as you want to take them. If any cell goes above whatever safety cutoff voltage you would chose say 3.75 volts, terminate the charging but continue to bleed the highest cell until its voltage goes down to the other cells.
4. Remember to set your charge controller back to the charge voltage you would usually use.

It has everything to do with Pb batteries. TOP BALANCE systems are designed to go to 100% SOC. Last thing you want to do is take your batteries to 100%

Two GOLDEN RULES for Lithium Batteries.

1. Never Go ABOVE 90% SOC
2. Never Go Below 10% SOC

If you use a Commercial Manufactured Top Balance System you go to 100% SOC.

Yes, just like you never want to take them to 0% SOC to do a bottom balance.

As far as I can make out it is higher cell voltage and higher temperature that will age LFP batteries. I can't see any mechanism that would make SOC per se age an LFP cell. Maybe I am missing something here, maybe you can enlighten me.

I can't see that taking an LFP cell to a voltage of say 3.6 volts for a limited period of time on an infrequent basis would make much difference to battery life. Maybe I am missing something again.

Simon

[russ]

OK - Playing adult games with a kids knowledge and training?

[karrak]

I love the kid thing, at 68 I don't get that complement often. Thank you. I have yet to succumb to Cerebral atrophy and am still willing to learn. I guess you could call my learning system a toy, a $4,000 coffee making system is a better description, since thats all I have on it. Maybe a golf cart would be a better test of a PV solar system, but how many panels could I install ??

I also loved being called a kid, being 56 and retired. The memory isn't as good as it used to be, but hopefully I am a bit wiser that I used to be.

My off-grid toys are the system I described it the previous post which runs reliably as our home power system with no backup and another system I have designed and built for a friend which has been working reliably since July 2013, only problem with this system being the failure of the commercially built inverter which was replaced under warranty. Have other toys like electric push bikes but they are not so relevant to this discussion.

To date no dead or bulging LFP cells and maximum cell voltage ever attained was around 3.7 volts during a manual balance and minimum 2.75 volts due to cell imbalance when LFP battery was installed. Normal cell operating range 3.45-3.0 volts. As far as I can tell battery storage and operational characteristics are probably not much different from when I installed the LFP battery.

Simon

[karrak]

What is your background?

I am intrigued to know why you are asking and what you want to know.

I would rather try to work out how credible a person is by what they post and not what they say their background is.

Experience with the topic you are commenting on is important. Here is my experience with off-grid power systems and LFP batteries.

First off-grid system around ten years ago, simple 64W solar panel connected to NiCd batteries, ex railway locomotives obtained for free from the company I sold my business to.

Around four years ago added 4kW commercially made inverter and designed and built my own MPPT controller, increased number of panels to 800W.

In April 2013 purchased and installed first batch of LFP batteries, total storage 360ah @ nominal 24 volts. Built BMS using modified Cellog8s and JLD404 meter. No battery balancing boards, decided to do balancing manually. Increased number of panels to 1140W

Last November designed, built and programmed Beaglebone Black based battery monitoring and logging system. I have made this an open-source project here https://github.com/simat/BatteryMonitor.

Simon