Can I parallel 14s Li-Ion and 16s LFP in the same powerwall/system?

[OffGridInTheCity]

View: https://www.youtube.com/watch?v=JcV6IIFqKt0
off grid garage conducts a very interesting test

Yes, but they're the same chemistry and this thread is about paralleling 2 different chemistries with different voltage ranges.

 

[paulie]

Yes, but they're the same chemistry and this thread is about paralleling 2 different chemistries with different voltage ranges.

point taken but still a very interesting video

 

[paulie]

Any more updates on mixing the chemistries?

 

[Wolf]

@ddalfons
Great stuff I'm glad someone else is interested in this research,
Would be interesting to see if you come to the same conclusions.
The interesting thing will be with Li-ion with LiFePO4 as the discharge curves are so much different,
Looking forward to this test,

I did a bunch of 18650 cell research in August 2019

Behaviour of cells in parallel.

I'm starting this thread to start a discussion on how cells behave in parallel in a pack. Before any of you poo poo this and say that all this has been studied and there are many papers out there on this I will concede and agree. But of all the studies that I have read they all seem to use only...

secondlifestorage.com

and March 2020

Behaviour of cells in parallel take 2

Another experiment has taken place at the Wolf's PowIRwall location. Previous posts on this subject are at https://secondlifestorage.com/showthread.php?tid=7846 I dragged out my 4p testing rig and decided to test 4 ICR18650-28A cells that had a reasonable IR at ≈ 50mΩ but their mAh testing was...

secondlifestorage.com

Some excerpts from that time.
My tester and a Charge trace

Full chart of D/C cycle

And a trace of a discharge of the cells below



I also did a pretty comprehensive study on DC IR VS AC IR,

DC IR VS AC 1kH IR measurements

Discussion about the benefits of DC IR testing versus AC 1kH IR ( Impedance) testing. 2 wire vs 4 wire kelvin etc. Primer of discussion copied from another thread. gauss163 Wrote: But iirc theOpus is doing alonger timeDC IR test (vs. 1ms AC). So it is also measuring somenon-ohmic parts of...

secondlifestorage.com

Wolf

 

[italianuser]

Any more updates on mixing the chemistries?

... I wouldn't mix them because IMO it makes no sense unless it's an emergency or you're a researcher. Batteries are all about balancing, you balance them in parallel, balance voltages, balance packs in a battery, the BMS balances, your cables are all the same section per segment so to balance.
So in this thread always IMO we're talking about making and unbalanced system. It's perfect as a discussion theme, but in real life it makes sense to me to sell one of the two chemistries and buy the same one you have (choosing the best option in terms of outcome and of money).
Maybe my parameters, in general, are too strict!

If somebody has a valid reason to mix chemistries, a part from emergency or research, I'd be glad to learn something new!

 

[paulie]

I will end up with 7s80 18650 and 8s 304ahc presently with their own bms. At the moment I plan to have one or the other bank working. The other bank on standby for power cuts etc. (unless there is a valid reason to have them both working at the same time)

 

[Wolf]

If somebody has a valid reason to mix chemistries, a part from emergency or research, I'd be glad to learn something new!

Agreed as my main Battery consists now of all 18650 cells which are all 2600mAh LG and Samsung 3x14s80p LG and 1x14s80p Samsung.
I do have a 4s3p 48V flooded deep cycle battery for emergencies which is in maintenance mode utilizing a NOCO Genius GX4820 48-Volt 20 Amp
charger. Also in an emergency I can can charge the flooded cell batteries below 0°C. However I would never mix the chemistries even though they are close in voltage.
Wolf

 

[harrisonpatm]

Any more updates on mixing the chemistries?

Been running for a few months with 14s Li-Ion and 16s LFP in parallel now, it's working quite well for me with no issues. They act like their own battery powering their own load, that just happens to be working next to another battery. Uneven load distribution as discussed earlier, each bank takes different portions of the load depending on a variety of factors. So i guess I don't have specific updates, just general observations, I don't do any data logging or anything like that.

Batteries are all about balancing, you balance them in parallel, balance voltages, balance packs in a battery, the BMS balances

All my cells are still balanced within their separate banks, within 5-20mv, both the LFP and Li-Ion.

If somebody has a valid reason to mix chemistries, a part from emergency or research, I'd be glad to learn something new!

"Valid" is relative, my reason is that I got a great deal on 2.5kwh of LFP cells locally that I couldn't pass up, and I can always break off this pack for a different use later. Maybe that's not a good enough reason for others, I would understand. I will likely be pulling off the LFP pack for the winter anyway: my main 14s Li-Ion powerwall is the one into which i've built heating and insulation to survive outdoor storage during the winter, and the LFP pack does not have that, so in all likelihood I'll just be storing during the cold snap.

If anything I see the LFP as a little helper to my main powerwall. It forces me to practice even more reduced DoD than I had originally planned ( 54.8v max charge, as opposed to the 56.6v I was planning before), which will increase cycle life in the long run. It also takes a good chunk of the load off my main powerwall; if I need to pull 60 amps, the LFP pack will take 10-30 amps of it, meaning my 14s pack sees much less stress and will last longer that way as well.

Here's a question, which I don't mean as an attack at all, but rather advice regarding what I should be looking out for. For those who don't think putting the two chemistries in parallel is a good idea, what negative effects do you expect to see? If this is a bad idea, what behaviors do I need to be looking out for that show indications of negative effects? Cell unbalance doesn't occur, as I mentioned in this post, and I am not using any active balancing. Excessive/unnecessary current flow between the 14s and 16s doesn't happen either, as observed and discussed previously. Is there something else I need to keep an eye out for?

 

[italianuser]

... which will increase cycle life in the long run.

Uhm, I didn't do any calculations but I think the life of the batteries will be reduced. If unbalanced batteries lasted longer then producers would start making them unbalanced.

On a balanced battery I can count the full cycles it does, and estimate the number of cycles I'll be able to do, the producer already tells me because he did the tests.

By setting parameters for a reduced "high-low voltage usage range" the battery is consumed, literally, less and more cycles can be expected at the price of less capacity usage.

The unbalanced battery pack, where for unbalanced in this case I mainly refer to very different charge/discharge curves, will naturally move current from the higher voltage pack towards the lower voltage pack to balance different voltages; I'm not saying when this happens only that it does happen. This process is the same as applying a load to the higher voltage battery (so discharging it); on the other side, the battery with the lower voltage is receiving current which is equivalent to a charge.

And this counts as a partial charge or discharge cycle, so you can subtract this "partial cycle" from the total cycles expected for the battery, thus increasing the battery usage "time" and reducing the number of cycles it can do.

Here's a question, which I don't mean as an attack at all,

Ops, I'm very sorry if my post didn't seem polite I'm usually very diplomatic, you should know! It wasn't meant to be a negative critique, only a "prove me there's an advantage" sort of message. Sorry if I was a bit too direct, but again, I'd say by logic that this setup possibly reduces battery's life.

 

[harrisonpatm]

The unbalanced battery pack, where for unbalanced in this case I mainly refer to very different charge/discharge curves, will naturally move current from the higher voltage pack towards the lower voltage pack to balance different voltages; I'm not saying when this happens only that it does happen. This process is the same as applying a load to the higher voltage battery (so discharging it); on the other side, the battery with the lower voltage is receiving current which is equivalent to a charge.

But, my two packs are never at different voltages. So this doesn't happen, no current transfer from the higher voltage pack to the lower voltage pack, no extra charge/discharge cycles because of it.

If unbalanced batteries lasted longer then producers would start making them unbalanced.

The batteries aren't unbalanced

 

[italianuser]

But, my two packs are never at different voltages. So this doesn't happen, no current transfer from the higher voltage pack to the lower voltage pack, no extra charge/discharge cycles because of it.

The batteries aren't unbalanced

I'll read all the thread again

 

[OffGridInTheCity]

From my perspective, I could not mix these chemistries with a single Batrium BMS due to the different indiviudal pack/cell voltages.
For example, when NMC = 3.5v/pack * 14 = 49v the LifePo4 = 49v/16 = 3.06v/cell. Having a set of 14 longmons showing 3.5v and the other 16 showing 3.06v would not work with Batrium features such as balance.

I would have to commit to 2 x BMSs - e.g. 2 x Batrium(s) for me which can be done and not hard but it would complicate my established monitoring. So I admit to a bias toward continuing with all NMC. Plus, I really do hope to get 5000, 6000, ... cycles out of my NMCs.
*I'll reach 2,000 cycles mid 2024

 

[italianuser]

...
The batteries aren't unbalanced

Uhm, they are unbalanced. When they are unbalanced you will see current movements between the two of them, because they are balancing each other. If they were balanced you wouldn't see any current movement. I read the whole thread again. You describe the effects of the "balancing the unbalanced process" multiple times, quoting:

"Here's a unique observation: I turned off the bike charger, as well as my house loads. When I checked the voltage, I was surprised to see that there was once again about 3-4 amps moving from 14s to 16s. Like when I first connected the two batteries, this lasted for only about 10ish minutes, until the transfer dropped to zero."

"when either the load or the charge current is removed, both batteries will attempt to return to resting voltage. Because the discharge curves are different between the two chemistries, the amount of movement to return to their resting voltage is different. And that's when you see unnecessary current movement between the packs. It's proportional to the amount of current that was being charged or discharge just previously"

"This means for an application with lots of significant charging or loads that start and stop suddenly, you will indeed see a lot of unnecessary current movement that stresses the cells unnecessarily"

In any case, I think this is a very good experiment and I appreciate the effort in analysing what happens and sharing the results plus the measurements.

 

[harrisonpatm]

From my perspective, I could not mix these chemistries with a single Batrium BMS

Or any BMS, really, each chemistry would need it's own BMS. Let's call that downside #1.

Downside #2, it limits the top charge voltage of Li-Ion. You mentioned that earlier:

I think that they will maintain the same voltage when in parallel and so you can't use the entire capacity range of Li-Ion when yoked to LifePo4.

As a result, I have the max voltage at 54.8v. @J_Mack58 charges to 55v. 3.92v per Li-ion cell. Mostly it's a downside, because that's a decent amount of capacity above 3.92v that isn't getting used. You could look at it as an upside, if you'd like, if your battery is big enough, because reduced DoD = more cycles. Depends on your system preferences.

Downside #3 is that you do see a little bit of "unnecessary" current transfer between LFP and Li-Ion when a large load is immediately removed. The amount of current transfer is proportional to the load. So this wouldn't be good for an EV.

Those are the 3 downsides I've observed.

 

[harrisonpatm]

Uhm, they are unbalanced. When they are unbalanced you will see current movements between the two of them, because they are balancing each other. If they were balanced you wouldn't see any current movement. I read the whole thread again. You describe the effects of the "balancing the unbalanced process" multiple times, quoting:

"Here's a unique observation: I turned off the bike charger, as well as my house loads. When I checked the voltage, I was surprised to see that there was once again about 3-4 amps moving from 14s to 16s. Like when I first connected the two batteries, this lasted for only about 10ish minutes, until the transfer dropped to zero."

"when either the load or the charge current is removed, both batteries will attempt to return to resting voltage. Because the discharge curves are different between the two chemistries, the amount of movement to return to their resting voltage is different. And that's when you see unnecessary current movement between the packs. It's proportional to the amount of current that was being charged or discharge just previously"

"This means for an application with lots of significant charging or loads that start and stop suddenly, you will indeed see a lot of unnecessary current movement that stresses the cells unnecessarily"

In any case, I think this is a very good experiment and I appreciate the effort in analysing what happens and sharing the results plus the measurements.

True. And if the load isn't large, there is no current movement. During average house loads, or when small loads are removed, there is no current movement. In my case, this rarely happens. And if it does happen, it levels off to zero after a short time. It's not a constant behavior that's always present.

Anyway, as I mentioned earlier, having the small LFP in parallel with my big powerwall means the powerwall sees less stress. So in my case, it works. This won't work for everybody. I just don't think it's an inherently bad idea off the get go. As long as proper safety precautions are being taken. Same is true with using second-life batteries in the first place. Be safe out there.

 

[Wolf]

Is there something else I need to keep an eye out for?

Don't know for sure yet, however I am waiting on @ddalfons research on this as he was working on doing a test on that combo.
I also have a bunch of (96 or so) 40Ah CALB 3.2V cells. Once back from Vacation/Holiday, I will put this on my list to build a test project.
I have been dying to use my stock of CD74HC4067 16 to 1 MUX with ESP32 for something useful. 2 of them and 30 sensor boards.
I'm tossed between going with just current measurements, MAX471, or ACS712 with the MUX or voltage and current with the INA260, INA219 or INA226.
Since I already have had an accuracy issue with the INA219, I will nix that and it appears that the INA260 module is scarce right now, I'm going to have to go with the INA226 (36V, 16-bit, ultra-precise i2c output current/voltage/power monitor w/alert)

INA226 data sheet, product information and support | TI.com

TI’s INA226 is a 36V, 16-bit, ultra-precise i2c output current/voltage/power monitor w/alert. Find parameters, ordering and quality information

www.ti.com

which just by chance has 16 programmable addresses on the I2C-compatible interface so I can NIX the MUX.
Poo I was so looking forward to programing with the MUX. So in essence that means 2 ESP32's and 30 INA226's.
I will order some of the Max471's and ACS712 also since from AliNoExpress they are reasonable enough, just to have and hold maybe for future experiments and so I can use the MUX.
So my project will be a current and voltage sensor on each cell/pack. I will test the CALB cell for Ah and build a 16s Battery. For the 18650 packs I will build a 14s xxp that mimics the Ah of the CALB ie 40Ah =~16 2600mAh cells which I have plenty of.
Also an INA228 with a Shunt (85-V, 20-bit, ultra-precise, I2C output current/voltage/power/energy/charge monitor with alert)
https://www.ti.com/product/INA228?k...ch-everything&usecase=GPN-ALT#product-details
which I have plenty of evaluation modules measuring Amperage flow(if any during normal operation) and Voltage between the Li and LFP batteries
With voltage and current sensors on each cell/pack/battery this will be a fun experiment, and a great coding experience. I'm kinda looking forward to this.

Wolf

 

[harrisonpatm]

Don't know for sure yet, however I am waiting on @ddalfons research on this as he was working on doing a test on that combo.
I also have a bunch of (96 or so) 40Ah CALB 3.2V cells. Once back from Vacation/Holiday, I will put this on my list to build a test project.
I have been dying to use my stock of CD74HC4067 16 to 1 MUX with ESP32 for something useful. 2 of them and 30 sensor boards.
I'm tossed between going with just current measurements, MAX471, or ACS712 with the MUX or voltage and current with the INA260, INA219 or INA226.
Since I already have had an accuracy issue with the INA219, I will nix that and it appears that the INA260 module is scarce right now, I'm going to have to go with the INA226 (36V, 16-bit, ultra-precise i2c output current/voltage/power monitor w/alert)

INA226 data sheet, product information and support | TI.com

TI’s INA226 is a 36V, 16-bit, ultra-precise i2c output current/voltage/power monitor w/alert. Find parameters, ordering and quality information

www.ti.com

which just by chance has 16 programmable addresses on the I2C-compatible interface so I can NIX the MUX.
Poo I was so looking forward to programing with the MUX. So in essence that means 2 ESP32's and 30 INA226's.
I will order some of the Max471's and ACS712 also since from AliNoExpress they are reasonable enough, just to have and hold maybe for future experiments and so I can use the MUX.
So my project will be a current and voltage sensor on each cell/pack. I will test the CALB cell for Ah and build a 16s Battery. For the 18650 packs I will build a 14s xxp that mimics the Ah of the CALB ie 40Ah =~16 2600mAh cells which I have plenty of.
Also an INA228 with a Shunt (85-V, 20-bit, ultra-precise, I2C output current/voltage/power/energy/charge monitor with alert)
https://www.ti.com/product/INA228?k...ch-everything&usecase=GPN-ALT#product-details
which I have plenty of evaluation modules measuring Amperage flow(if any during normal operation) and Voltage between the Li and LFP batteries
With voltage and current sensors on each cell/pack/battery this will be a fun experiment, and a great coding experience.

1/4 of that went over my head. lol

Except of course:

I'm kinda looking forward to this.

Me too.

 

[italianuser]

So my project will be a current and voltage sensor on each cell/pack

oh yes, same here, but for temperature and voltage. For temperature the lovely DS18B20 (you suggested me that some threads ago, and I'll thank you forever for that!) only uses one wire for data, can connect 14 of them with little effort. For the voltage measurements I have some MUX/DEMUX chips (74138 and 74148) and also was very curious of trying the MUX chip. My biggest doubt right now is how to read voltage from 14 packs: use 13 voltage dividers and calibrate them, or is it possible to MUX both negative and positive? Dunno really, must do some testing... and maybe open a new thread!

AliNoExpress

LOL

 

[Wolf]

it possible to MUX both negative and positive?

No not really It has a common ground which interfaces with the Arduino or ESP32. The Arduino can handle a 5V input max and the CD74HC4067
max 7V so for cell/packs 2 to 14/16 V dividers is the only way to go. So what you want for 56.7V for R1 is a 2MΩ and R2 a 140kΩ resistor giving your V divider an output of 3.709V. Then keeping the 2MΩ for R1 and adjusting R2 as you go down the line. You want a high R value so you don't kill the battery with current draw. 2.140MΩ at 56.7V is 26.49μA not even a trickle. Of course you know all that anyway. With the esp32 though you only get a 3.3V max input and all this changes.
Anyway we are way off topic, however we are discussing the OP's (@harrisonpatm) post "Can I parallel 14s Li-Ion and 16s LFP in the same powerwall/system?" by discussing how to build a testing environment to see if there are any benefits or possible pitfalls in doing this.

Wolf

 

[paulie]

Thanks for all the good information guys.