LiFeP04 Batteries for Solar & BMS

[karrak]

What I read is defects usually exhibit themselves early, and Chi-Com cells have their share of defects.

I did a quick survey on another forum of people who charge their LFP batteries from solar power.

The oldest batteries were installed around three years ago, with the majority being installed around two years ago.

I got replies from 4 people who have installed around 150 cells with an energy storage of over 100kWh in around 7 systems. Of those 150 Chinese made cells there has been 1 replaced under warranty and no other failures.

Simon

[russ]

I did a quick survey on another forum of people who charge their LFP batteries from solar power.

The oldest batteries were installed around three years ago, with the majority being installed around two years ago.

I got replies from 4 people who have installed around 150 cells with an energy storage of over 100kWh in around 7 systems. Of those 150 Chinese made cells there has been 1 replaced under warranty and no other failures.

Simon

Simon - That is meaningless - you got replies from battery manufacturers for all you know.

[karrak]

Simon - That is meaningless - you got replies from battery manufacturers for all you know.

I have read enough posts from the three others in this sample to know that they are not battery manufacturers but real people who have installed real power systems where the LFP batteries are charged from solar panels. Not a big sample, maybe we have all been lucky and this sample doesn't match the quality of LFP cells manufactured in China going to the rest of the world.

Simon

[tom rickard]

Maybe the rumors of failed cells you have heard of have also come from rival manufacturers?

I have a few comments on this thread having been one of the people that has been using LFP cells in a house bank as a stand alone power supply for over 3 years.

Bottom balancing: Great for EV's where you want to take the cells close to zero charge.

It would also be fine for off-grid solar application except that the batteries do not stay balanced for prolonged periods of time. To say that you bottom balance your cells once, then run your system for the next 10 years with no difference in performance from the cells is pretty far fetched.

Also, to charge until one cell hits 3.45 (or whatever) volts, then stop the charge source is impractical in an off-grid application. You need to have the charge controller match the load as best as possible once your cells hit your chosen top voltage. (ie. zero net current from charge controller and loads)

The charge controller I use has an algorithm that reduces the charge current in a no-load situation when the first cell hits a pre-set voltage, then "balances" or shunts current at a charge current of less than 5A, tapering to zero amps. In practice, it is rare to have a no-load situation in an off-grid situation, there is always a fridge etc. chugging away.

In reality, the cells aren't being balanced when the shunts are in action, as the voltage setpoint is below the 100% SOC voltage of the cells. What is actually happening is that the charge current is being limited in a feedback situation from the shunts when there is no load on the cells. This happens at a voltage setpoint that is programmable.

To balance the cells if you feel the need, they need to be taken to a voltage of 3.6V (approx.)

So... Until you can explain how you manage to make your cells behave in an identical fashion over their lifespan, and also explain how to manage the charge controller so that it matches the load current in a fully charged situation, then I don't think bottom balancing is for me..

[Willy T]

Also, to charge until one cell hits 3.45 (or whatever) volts, then stop the charge source is impractical in an off-grid application. You need to have the charge controller match the load as best as possible once your cells hit your chosen top voltage. (ie. zero net current from charge controller and loads)

This not what the EV / Grid Charging Bottom Balancer's want to hear. They drive their EV, take it home and plug it in and charge it, unplug and it's left until they drive it again. They have no parasitic loads and no floating, they have no standby soc to worry about.

Another issue is that some here do not know or understand the features of the equipment used for Solar Charging and how it functions.

As far as it goes for Top or Bottom balancing they argue and fight about it in every thread on the DIY EV forums same as they do here.

[karrak]

This not what the EV / Grid Charging Bottom Balancer's want to hear. They drive their EV, take it home and plug it in and charge it, unplug and it's left until they drive it again. They have no parasitic loads and no floating, they have no standby soc to worry about.

Another issue is that some here do not know or understand the features of the equipment used for Solar Charging and how it functions.

I'll second that.

Good on you for putting up with the abuse

Simon

[Sunking]

I have read enough posts from the three others in this sample to know that they are not battery manufacturers but real people who have installed real power systems where the LFP batteries are charged from solar panels.

Sure about that? Anything you want to disclose. Only an equipment manufacture would standby and claim to you should use a BMS. Otherwise you are out of biz.

[Sunking]

Maybe the rumors of failed cells you have heard of have also come from rival manufacturers?

No that would be DIY EV owners.

Bottom balancing: Great for EV's where you want to take the cells close to zero charge.

It would also be fine for off-grid solar application except that the batteries do not stay balanced for prolonged periods of time. To say that you bottom balance your cells once, then run your system for the next 10 years with no difference in performance from the cells is pretty far fetched.

Well to start the thinking you do not operate a Lithium battery in a Solar system in the lower SOC range is delusional in of itself. With a Lithium system you do not normally size the batteries for 5 day autonomy like you would for Lead Acid. That line of thinking is just plain ole nucking futs. You size Lithium for 2 to 3 day autonomy, and unless you live in Utopia Green Land where the sun shines bright everyday all day, the rest of us in the real world have long cloudy spells and cloudy days. That means you spend a lot of time near the bottom before running the generator. That is just a fact of life. Deal with it.

For EV's it is great. All large format LFP technology and equipment comes from EV's. That includes the BMS and Top Balance being pushed by BMS manufactures. Cells do not stay Balanced if you Top Balance because you have parasitic loads. The Vampire Boards, Temperature and Battery monitors are attached to each cell and powered from each cell. No two draw the exact same amount of power, thus unequal load throwing them out of Balance. In Bottom Balanced system you have no Parasitic Loads. The exact same current flows through each cell every time in Series circuits.

Yes batteries loose capacity as they age. However A Bottom Balanced System is referenced at 0% capacity and SOC which never changes. Zero will always be Zero. What does change is capacity. Full capacity is what you loose, thus the Top changes, but not ZERO. Only thing you might change is the reference cell, not the reference point you are Balanced too. Zero is Zero. Expecting any battery to last 10 years is far fetched.

Also, to charge until one cell hits 3.45 (or whatever) volts, then stop the charge source is impractical in an off-grid application. You need to have the charge controller match the load as best as possible once your cells hit your chosen top voltage. (ie. zero net current from charge controller and loads)

You are taking things out of context and cherry picking. My guess is you have not read all replies and threads on the subject matter. I charge at C/2 constant Current with Commercial power. I or NO ONE EVER SAID you turn off the controller. First thing to know is there are NO SOLAR CHARGE CONTROLLERS made for Lithium batteries on the market with the exception of a Marine and toys with very limited power of 130 or so watts. A Solar Charge Controller made for Lithium would require to interface with a BMS. How do you do that since there are none available? Simple you don't. You have to deal with it and work around it and only if you know exactly what you are doing.

Well what you do, and I have said repeatable many times, is there are a couple of Charge Controllers on the market that allow you to set Bulk = Absorb = Float voltage set points to whatever the user desires. That forces the controller to quit operating as 3-Stage which is useless in any Solar Application, and make it operate CC/CV mode used for Lithium Batteries. In either a Bottom or Top Balanced system you set the voltage according to the requirements. In a Top Balanced System you would set the voltage to 3.55 to 3.6 vpc or whatever your Vampire Board Trigger voltage is set to. The problem with that analogy is the Vampire boards can only shunt .5 to 1 amps, and there is no way to tell the Controller to limit current to Vampire Board limit. When the first Vampire Board turns on, it can only shunt a small amount of current. The remaining still flows through the fully charged cell resulting in a over charged cells. Only thing you can do is turn on enough load to absorb the unknown current value at any given moment in time.

In a Bottom Balanced system you set the voltage well below 100% SOC in the range of 3.3 to 3.4 volts. The final voltage is a a bit of trial and error for the first few days. You settle when the weakest cell reaches 3.4 volts. All other cells will be just slightly lower in voltage. So in a 48 volt pack a Bottom Balanced set point voltage is something slightly less than 54.4 volts. A Top Balanced system would be 57.6 volts.

At that point the Controller is Constant Voltage keeping the batteries charged up and supplying power to the load assuming the panels are able to meet the demand.

So... Until you can explain how you manage to make your cells behave in an identical fashion over their lifespan, and also explain how to manage the charge controller so that it matches the load current in a fully charged situation, then I don't think bottom balancing is for me..

I pretty much covered that above.

[Sunking]

This not what the EV / Grid Charging Bottom Balancer's want to hear. They drive their EV, take it home and plug it in and charge it, unplug and it's left until they drive it again. They have no parasitic loads and no floating, they have no standby soc to worry about.

You have a lot of trouble with reading comprehension there Willy. I never said you stop charging with a Solar System. Only Karrak is ignorant enough to say that. As for me I use commercial power to charge at constant C/2 current. I do not FLOAT, but I could just as easily because I do have the luxury of time. . But FLOAT TAKES TOO DAMN LONG.

Another issue is that some here do not know or understand the features of the equipment used for Solar Charging and how it functions.

I agree with that 100%. People like you and Karrak do not have the knowledge or experience to Bottom Balance Lithium batteries. In that case you should use a expensive Top Balance BMS. All you have to do is wait until the Solar Manufactures start making the equipment for it.

As far as it goes for Top or Bottom balancing they argue and fight about it in every thread on the DIY EV forums same as they do here.

That is true. Me, Myself, and I were once ignorant and strongly argued for Top Balance. Go back a few years on this forum here and you will see the transformation. I evolved. That was the Engineer in me pushing Technology as a solution. Top Balance Systems require expensive equipment. something companies are in biz to do. The whole objective to any biz is TO SELL YOU SOMETHING. Bottom Balance takes no special expensive equipment. Just knowledge and common sense.

But if you look back in those DIY EV forums going back to 2007 when the Large Format LFP cells became available to the DIY crowd all of us were Pro Top Balance. It made sense to us coming form the Lead Acid World stuck in that box. Once you hang around there a few years you get to know the members. Some are users, some are in the DIY EV business. As I said all of us started out Pro BMS. It was the only game in town. Then the problems started, very expensive problems of destroyed cells from over discharge. It was discovered the Top Balance boards and Controller LVD were the root cause. A new way of thinking came about. Bottom Balance. Now if you look the crowd is evenly split. Users and some R&D engineers have switched to Bottom Manufactures selling BMS, and engineers designing BMS naturally have no choice but to stand by BMS. It is not hard to understand.

How did it start? Well for one DIY took a look at what commercial EV manufactures were doing. Yes they use a form of BMS, active BMS where they can transfer power from a strong cell to weaker cell. But what we finally realized they had a couple of tricks. Some DIY can duplicate and some we cannot. EV manufactures buy lithium batteries by the 100's of thousands at a time from top quality manufactures made to their specifications. Tolerances are very tight. What the EV manufactures do is test every cell and sort them out to be precision matched to 1% or less. They then BOTTOM BALANCE the cells before assembly. Then assemble them and do not every fully charge or discharge the cells. Chevy Volt for example only charge to 80% and discharge to 20%. That is what is called Middle Balance and what every EV manufacture uses. They are not stupid enough to Top Balance. Bingo!

A DIY cannot fully duplicate what a commercial EV manufacture can do. But we can mimic what they do and steal their ideas at no charge or royalties. We can Bottom Balance and we can limit charge and discharge. That is what you do not understand or even want to understand. So please please stick with your Top Balance. You do not have the knowledge or skills to do Bottom Balance.

[reed cundiff]

Six day autonomy with RV based LFP battery suite

Curiously enough, our RV system with LFP was designed and fabricated just about two years ago. It has a BMS (designed for EV but works great). It endured one winter that went down to -20 C while we were on holiday in Guatemala and Honduras,and has suffered very little loss in capacity (none that we have been able to measure). We have boondocked in the Olympic Rain Forest for six days, the same amount of time in heavy timber in SE Arizona, four days with 8" of snow on panels. We never went below 40% SOC. We did turn off the inverter at night and did not run the fridge on AC during the day. We still ran the micro-wave to make hot water and watched Mystery Theater DVDs at night.

The 16 Cells are CALB, fabricated by Manzanita for EV world and matched to their EV designed BMS. It is expensive but it does work. I was a senior optical physicist for US Army Research Labs at WSMR and US Army Science Advisor in Iraq. I do know physics and science.

Reed and Elaine

[Willy T]

Curiously enough, our RV system with LFP was designed and fabricated just about two years ago. It has a BMS (designed for EV but works great). It endured one winter that went down to -20 C while we were on holiday in Guatemala and Honduras,and has suffered very little loss in capacity (none that we have been able to measure). We have boondocked in the Olympic Rain Forest for six days, the same amount of time in heavy timber in SE Arizona, four days with 8" of snow on panels. We never went below 40% SOC. We did turn off the inverter at night and did not run the fridge on AC during the day. We still ran the micro-wave to make hot water and watched Mystery Theater DVDs at night.

The 16 Cells are CALB, fabricated by Manzanita for EV world and matched to their EV designed BMS. It is expensive but it does work. I was a senior optical physicist for US Army Research Labs at WSMR and US Army Science Advisor in Iraq. I do know physics and science.

Reed and Elaine

Reed, nice to hear that your batteries are performing for you. Your accomplishments are Impressive, it's good to have you here and thank you for your service to the troops.

[Sunking]

Curiously enough, our RV system with LFP was designed and fabricated just about two years ago. It has a BMS (designed for EV but works great). It endured one winter that went down to -20 C while we were on holiday in Guatemala and Honduras,and has suffered very little loss in capacity (none that we have been able to measure). We have boondocked in the Olympic Rain Forest for six days, the same amount of time in heavy timber in SE Arizona, four days with 8" of snow on panels. We never went below 40% SOC. We did turn off the inverter at night and did not run the fridge on AC during the day. We still ran the micro-wave to make hot water and watched Mystery Theater DVDs at night.

The 16 Cells are CALB, fabricated by Manzanita for EV world and matched to their EV designed BMS. It is expensive but it does work. I was a senior optical physicist for US Army Research Labs at WSMR and US Army Science Advisor in Iraq. I do know physics and science.

Reed and Elaine

Reed that only means your batteries are way over sized. Nothing wrong with that as long as you can afford it. Most cannot.

[Living Large]

I have a few comments on this thread having been one of the people that has been using LFP cells in a house bank as a stand alone power supply for over 3 years.

Bottom balancing: Great for EV's where you want to take the cells close to zero charge.

It would also be fine for off-grid solar application except that the batteries do not stay balanced for prolonged periods of time. To say that you bottom balance your cells once, then run your system for the next 10 years with no difference in performance from the cells is pretty far fetched.

So... Until you can explain how you manage to make your cells behave in an identical fashion over their lifespan, and also explain how to manage the charge controller so that it matches the load current in a fully charged situation, then I don't think bottom balancing is for me..

There was never any suggestion on this board that one could bottom balance once and be done. If you researched the threads (I think this one) you will see that this topic has been discussed in detail. What has been discussed it that they TEND to stay in balance over months. Not years. The plan was that LFP is NOT FOR EVERYONE, but someone who doesn't mind monitoring their cells regularly would see an imbalance develop slowly, by either using a DVM with sufficient accuracy or a monitoring system. This has all been covered.

The plan as far as I was concerned was to suspend charging at the top, which some charge controllers support, using a BMS monitor at the cell level.

[Sunking]

The question you should be asking yourselves is this:

If commercial EV Manufactures DO NOT USE TOP BALANCE, then why do you insist Top Balance is the way to go?

The only correct answer be is you do not know any other way, and what the risk are. All you know is what you have been told by BMS manufactures to spend money and take risk. That is all you ever learned and did not ask critical thinking questions. Even the custom EV shops are now offering Bottom Balanced systems and equipment.

EV West is the premiere custom EV builder, and they make Bottom Balanced EV's. Everything known about LFP used in solar comes from EV's.

Look you can use Top Balance. It is expensive, comes with risk, and offers no protection for over discharges the main killer of lithium batteries. It sets the conditions for over discharge. That is why commercial EV manufactures do not use Top Balance. The last two places you ever want your batteries to see is the Top or Bottom while in operation.

If you are a novice, inexperienced, lacking knowledge, or lazy you have no choice but Top Balance. That is the market it is designed for.

[reed cundiff]

Willy - thanks. Son and grandson did the design and fabrication. I was the gopher though I have been told numerous times that my showing up on a job is like having the two best workers quit.

There was an inch of rain last night in the mountains of northern NM. I guess this washed off the dirt and sand that built up while we were "holidaying" in South America. The TriStar monitor showed 1360 W and the Manzanita monitor for the BMS showed 21 amps at 54 V charge rate on the battery suite. Demonstrating once again that keeping panels clean is a good idea.

Since our RV is our only home (AK to Keys, Newfoundland, Baja, Guatemala) and we only boondock or dry camp (kids' backyards) there is no such thing as excess battery or solar.

Reed and Elaine