LifePO4 GBS Amp Hour Testing 2.5v to 3.6v per cell

[karrak]

Lithium batteries use organic electrolyte which breaks down with heating and cooling.

The electrolyte reacts with the lithium ions. These reactions occur at a greater rate as the temperature and voltage rise. Lithium plating (which is bad) occurs at the anode if the charge rates are too high at low temperature because the lithium ions can't diffuse (move) into the carbon anode fast enough.

All I am saying is in your application, heat is not an issue. Put them in an an EV in TX summer when it it 100 degree outside and go racing. Then you will have a heat problem to worry about. DIY EV buildrs that live where they have temps below 40, use electric blankets to warm their batteries while charing and just before the take off. They want their batteries at 80 to 100 degrees.

This is probably why people that do this get such poor lifespans from their LFP batteries. They should be using batteries that are better suited for the application.

Simon

[karrak]

You idiot, you just confirmed what I have been saying all this time. No BMS is required, cells do not become unbalanced, do not fully charge or discharge the batteries. Only difference is you Top Balance and willing to risk over discharging your batteries and relying on a monitor to save your dumb arse. You are such a moron you do not even know you agreed with me.

I think some sort of BMS is needed even if it is just an SOC meter and voltage monitor to make sure that any cells do not go out of their proper operating range and to flag any faults or stuffups that may happen that could damage the battery. My BMS has saved my dumb arse. As for automatic balancing, no you don't need it if you are prepared to do it manually. I have found that LFP batteries do go out of balance. It happens quicker when the battery is new as one would expect. It is quite possible that as the technology becomes more mature that this will be less of a problem.

In the past three years my battery has never gone below 10%SOC, and averages around 75%SOC so I am in no danger of over discharging it. My BMS would warn me if I were to ever to take any cell below 2.8V. A bigger worry for me is overcharging it as I try to charge it to >99% whenever there is enough sunshine to give me as much reserve capacity as possible for cloudy weather. That is why I have my battery top balanced and again my battery monitor will warn me if any cell gets higher than 3.6V.

Simon

[karrak]

I actually intend to discharge at up to 2C or 200 amps. I have a Xantrex SW 2000 inverter, a 250 amp class-t fuse, and a Victron BP-220 for the LVD. I'll be using 4/0 MTW for the cable. This is just a toy system; an experiment, so I don't know how often I'll draw 2C, but it's definitely on the radar. Use cases include running power tools like table saws, planers, drills, and even small window air conditioners.

So yeah, I'm thinking about heat.

If you are only discharging at this rate for 1% of the time and it caused say a 10 times increase is cell aging it would only cause an overall drop in the life of 10% (10*1%) which you have to way up against the increased use you will get from the battery. Because of the high capital cost of LFP batteries you have to cycle as much power through them in the least possible time to get the best return on investment.

Considering installing the battery in a temperature controlled environment is probably only worthwhile if your battery costs more than $10,000, where the cost of the power and the equipment to maintain the temperature is less than the costs of the battery aging faster.

Simon

[karrak]

No clue how accurate this theory/claim is. However, it seems the LifePO4 lifecycle claims tend to not pan out in practice for people due, perhaps, in part, to temperature. He also talks about float voltage, which we've covered pretty thoroughly elsewhere.

Thanks for the link, very interesting article.
This graph shows the effect of temperature on lifespan.
CapacityFadeTemp.jpg
It comes from this research paper researchgate.net/publication/251588109_Cycle-life_model_for_graphite-LiFePO_4_cells. This paper has lots of good information on factors that age LFP batteries. You might not understand all the detail in this paper, you can skip the maths and concentrate on the graphs and the text.

From all the research I have done as far as I can see the main factors that degrade LFP batteries are, Temperature, Battery voltage and charge and discharge rates. It looks like the article writer might have started out charging his battery at voltages that would have aged it, he has dropped his charge voltage to 3.55V/cell and floats at 3.38V/cell.

I have set my friend's system to charge to 3.45V/cell and float at 3.35V/cell. It has been running like this for most of the three years it has been operating. I recently thought that one of the cells in the battery had become defective and lost about 30% of its capacity. I replaced it and have been running some tests on the "defective cell". My first capacity test yielded a capacity of around 91Ah from a 90Ah cell, so obviously the cell is not defective and the cell has lost little if any capacity since it was installed. Unfortunately I didn't do a capacity check when the battery was first installed so can't say what the change in capacity has been.

I have always been worried about his battery because it was installed in a black tin shed where the temperature would be getting to greater than 50C (120F) in summer. Fortunately the battery has recently been moved into his house that he has been building over the past three years.

Simon

[createthis]

It was 98 degrees today.

[Sunking]

Jesse all Battery Cycle Life claims are garbage.

To the point yes heat does destroy all batteries. Lithium is no exception. Manufactures claim lithium ion batteries are not a chemical reaction which is false. If it were a pure Ion Exchange they would last forever. There is no documented Lithium battery of any kind that has made it past 1000 cycles. Lithium batteries use organic electrolyte which breaks down with heating and cooling. You will notice it in time when your Ri starts rising up.

But the kind of heat required will be such you cannot touch the batteries and hold your hand on them. Your batteries are in open air at room temps. It would be very difficult for you to even to be able to tell the batteries are warm to touch which is around 96 to 98 degrees before it feels warm to you.

Will Lithium last longer when cold. Heck yeah every battery does that. But lithium batteries perform poorly when cold. In fact most you cannot even charge when freezing or lower, They remain sluggish below 60 F. Put those batteries in the fridge overnight, pull them out and do a Ri test. Then put a load on them and voltage will sag from the Ri. Warm them back up and they are fine.

All I am saying is in your application, heat is not an issue. Put them in an an EV in TX summer when it it 100 degree outside and go racing. Then you will have a heat problem to worry about. DIY EV buildrs that live where they have temps below 40, use electric blankets to warm their batteries while charing and just before the take off. They want their batteries at 80 to 100 degrees.

[createthis]

Why?

You are not even close to pushing thermal limits. Only time to ever be concerned is if the batteries are so hot, you cannot touch them and keep your hand on them. They perform best when at 85 to 100 degrees. You will never see them get that warm in room temps @ 2C operation. Heat does not become an issue until the batteries are in an enclosed box with no ventilation, in 100 degree plus weather, in an EV pulling 10 C accelerating and cruising at extended periods of 1C.

In short your batteries were made to be in an EV. Your mode of operation is not putting any stress on the batteries.

Interesting. This is why I think about heat: http://www.technomadia.com/2015/02/l...attery-update/

When our 500AH batteries were a year old (August 2012), I was able to drain 442Ah from them before having the EMS trigger a low-battery alarm cutoff.
When they were nearing 2.5 years old (November 2013) I was able to drain 409Ah before the system shut down.
Last month (December 2014), during my most recent drain test, I was only able to drain 378Ah before cutting out.
In other words – our batteries seem to be aging way faster than they should – now giving us just 75% of their original rated capacity.

And this a bit down the page:

But while brainstorming potential causes for our diminished capacity recently, Elite let me know that in their experience heat has a huge impact – even within that operating range.
They have observed that a 10C (18F) temperature increase over a baseline room temperature of ~23C (74F) results in the number of lifetime cycles being cut in half.
This means at 33C (91F) usable battery life will be cut in half, and presumably to a quarter at 43C (109F). This is VERY substantial.

No clue how accurate this theory/claim is. However, it seems the LifePO4 lifecycle claims tend to not pan out in practice for people due, perhaps, in part, to temperature. He also talks about float voltage, which we've covered pretty thoroughly elsewhere.

[Sunking]

So yeah, I'm thinking about heat.

Why?

You are not even close to pushing thermal limits. Only time to ever be concerned is if the batteries are so hot, you cannot touch them and keep your hand on them. They perform best when at 85 to 100 degrees. You will never see them get that warm in room temps @ 2C operation. Heat does not become an issue until the batteries are in an enclosed box with no ventilation, in 100 degree plus weather, in an EV pulling 10 C accelerating and cruising at extended periods of 1C.

In short your batteries were made to be in an EV. Your mode of operation is not putting any stress on the batteries. So relax.

[SunEagle]

Sigh. Ease up with the personal attacks.

It has gotten as bad as the mud slinging political commercials seen on prime time TV. I haven't figured out to turn off the TV and walk away or just stuff cotton in my ears. The same goes for this forum and some of the threads.

[Sunking]

Sigh. Ease up with the personal attacks.

I did not start it or come here to attack anyone. Simon is here for only one reason, to attack me.

Look the moderators and owners know why Simon is here and they approve of the attacks. It is not my problem.

[createthis]

I actually agree with Sunking that at the sort of charge and discharge rates that your battery is likely to see you will not have any problems with heat. For long life you should limit the charge and discharge rates to C/2 and keep the charge voltage below 3.5V and float voltage below 3.4V . If you do this I can't see any reason your battery will not last 10+ years.

Simon

I actually intend to discharge at up to 2C or 200 amps. I have a Xantrex SW 2000 inverter, a 250 amp class-t fuse, and a Victron BP-220 for the LVD. I'll be using 4/0 MTW for the cable. This is just a toy system; an experiment, so I don't know how often I'll draw 2C, but it's definitely on the radar. Use cases include running power tools like table saws, planers, drills, and even small window air conditioners.

So yeah, I'm thinking about heat.

[createthis]

You idiot, you just confirmed what I have been saying all this time. No BMS is required, cells do not become unbalanced, do not fully charge or discharge the batteries. Only difference is you Top Balance and willing to risk over discharging your batteries and relying on a monitor to save your dumb arse. You are such a moron you do not even know you agreed with me.

Sigh. Ease up with the personal attacks.

[Sunking]

If you charge to 3.45V/cell at an end current of around C/20-C/50 you are going charge to >99%SOC. Under these conditions you do not need any balancing boards if you are prepared to do the balancing manually.I don't have any balance boards. The last time I did a manual balance was in February. Yesterday at the end of charge my highest cell voltage was 3.48V and lowest cell voltage was 3.43. This is on a battery in use 24 hours a day, 365 days of the year.

You idiot, you just confirmed what I have been saying all this time. No BMS is required, cells do not become unbalanced, do not fully charge or discharge the batteries. Only difference is you Top Balance and willing to risk over discharging your batteries and relying on a monitor to save your dumb arse. You are such a moron you do not even know you agreed with me.

[Sunking]

More rubbish, lithium ions do not change polarity, they are always positive. If they gained an electron they would be converted to lithium metal. During discharge, electrons leave the anode and flow via the external load to the cathode, positive lithium ions travel through the electrolyte from the anode to the cathode to balance the charge of the electrons. During charge the external power supply pushes electrons from the cathode to the anode, positive lithium ions travel through the electrolyte from the cathode to the anode to balance the charge. The link nova.org.au/technology-future/lithium-ion-batteries that I gave in my previous post gives a really good explanation of this with an animation of the current and ion flow.

Simon

I am not even going to bother any more with your Blather and nonsense. You are way undereducated to understand what you are copying and pasting.

[karrak]

I can take blame for not going into technical depth, and would if the audience could comprehend what was being said.

How condescending. Due to the number of things you have got wrong in the past, I don't think so. You are just using this to cover your own ignorance.

In Laymen terms, when you discharge the lead sulfate moves from the electrolyte and coats the plates in the form of soft crystals. During charge the crystals in Laymen terms are dissolved back into the electrolyte. Simon I know you are not aware of it but electrolyte is is acid, not water. Electrolyte (sulfuric acid) is diluted with water.

No Sunking, in Layman's terms when you discharge you take sulphate ions from the electrolyte and combine them with lead and lead oxide from the plates to form lead sulphate. During charge you convert the lead sulphate back to lead and lead oxide and the sulphate ions go back into solution.

The process is the same with both Pb and Li. Both are metals, and both work by moving atomic particles called ions from cathode to anode and back again. Pb is chemical, and Li is electrical.

Not correct. In all lithium ion batteries there should be no lithium metal, there are only positively charged lithium ions which go backward and forward between the anode and cathode. With lead acid batteries we have lead and lead oxide that are converted to lead sulphate in situ. The only thing that moves are sulphate ions, hydrogen ions and water which move from the plates to the electrolyte. Very different processes.

Learn how to read, you change the ion charge polarity.Again you do not know what you are talking about and cannot comprehend what is being said. I never said the positive terminal changes polarity. Only an idiot like yourself would believe that. Again the lithium ions change polarity by gaining or loosing an electron. When Li ion give up an electron, it becomes charge positively charge and moves to the negative cathode electrode. When it gains an electron negatively charged and moves to the positive anode electrode. Opposites attract, basic chemistry and physics.

More rubbish, lithium ions do not change polarity, they are always positive. If they gained an electron they would be converted to lithium metal. During discharge, electrons leave the anode and flow via the external load to the cathode, positive lithium ions travel through the electrolyte from the anode to the cathode to balance the charge of the electrons. During charge the external power supply pushes electrons from the cathode to the anode, positive lithium ions travel through the electrolyte from the cathode to the anode to balance the charge. The link nova.org.au/technology-future/lithium-ion-batteries that I gave in my previous post gives a really good explanation of this with an animation of the current and ion flow.

Simon