Feedback - LifePO4 vs Nissan Leaf

solardad

Hi - Looking for some real world feedback on these two options for a battery bank.

I am in the process of revamping my system and looking to expand my current Leaf 48v BB from 21kWH rated to a 48v 40~50kWH system.
My BB was built from Gen1 cells so the performance is closer to 14-15kWH, roughly 70%. 

I am trying to keep my options open to other possibilities and noticed that LifePO4 cells have dropped somewhat in price since I built my BB almost 2 years ago to the point that they are close in price or theoretically cheaper than Leafs given the unknown degradation of a Leaf cell. 

I have not used LifePO4 cells but there seem to be a number of folks that have ordered them straight from China and are seeing prices between $40-50 for a 120ah 3.2v cell with shipping, whereas I could purchase a Leaf car pack (48 7.6v cells) between $40-50 at the module price point. The big Leaf unknown is degradation % whereas I am unsure what I should be on the look out for a LifePO4. 

So.... Anyone running either system? Pros or cons? 

Thanks! 

Ampster

I purchased new LFP cells from Thundersky and Winston in 2012 and 2014 with good luck. One set was in an EV conversion and another was in a hybrid inverter grid load shifting system. I sold the EV and rented out the house so I parted out the hybrid inverter and batteries several years ago. 
Subsequently I installed another  hybrid inverter with solar and powered that with a complete Nissan Leaf pack that I got for what I though was about $70 per kWh but later found out that the pack had degraded to about 70% . Even though I have 8 modules in parallel I am seeing more drift at the bottom so I am sure I have lost some more capacity.

I too am intrigued by the lower prices of LFP cells. I can probably make this pack last another year or two until my needs are better defined. I get several Public Safety Power outages in the Fall and use the hybrid inverter for ocassional load shifting as well.  The other thing I am considering is Tesla Modules. As long as I can garantee that they all came from the same car I am comfortable that they will be fairly well matched and I have more confidence in Tesla's battery management than Nissan. I would not buy more Nissan Leaf modules. The Tesla modules currently are less per kWh that new LFPs. I can use my existing BMS if I buy two but would have to spend another $500 for another BMS if I want double the capacity. In the case of LFP I could buddy pair them so I wouldn't have to buy another BMS.  I don;t use the BMS for balancing but rely on its reporting to give me insight into the quality of my pack. It also gives me more insight than the reports from my inverter. I do like the safety of LFP compared to the chemistry of Tesla and Leaf modules especially if i find I need 20 or 30 kWhs of capacity. I have a step son in China and have considered enlisting him to help me figure out the quality control process I might need to go through to reduce the risk. Interestingly his mother doesn't trust the quality of merchandise coming from China, her native country. 

solardad

@Ampster

Thanks for the info.
So what turned you off on the Leaf modules? I have a 21kw setup of them and they have been fine so far. I just wish the cost was dropping in line with LFP. 

My experience with aliexpress / alibaba has been good so far, 6 or 7 orders but I know it only takes one bad one so I only have done deals with a credit card. 

Tesla is interesting price/performance wise but I believe balancing is a must and my BMS experience has been average to poor. In fact, I no longer run the balance function on my BMS only the cutoffs as extra insurance, primary duty is with my charge controller and inverter settings. My leaf pack stays within 10-15mv naturally.

What BMS do you run?

mcgivor

Since automotive applications are typically bottom ballanced, I'm curious to know if the Leaf cells were top ballanced prior to use, this is where most BMS cell ballancing usually occurs,  perhaps the BMS is trying to correct imbalances beyond its capabilities. 

With the LiPo4 cells I use, the controller is programed to a voltage value below what  required for ballancing to occur, but still in the 95% fully charged regon, rationale being why over stress the cells unnecessarily where very little of the overall capacity is.

solardad

@mcgivor  

No , no that I know of. Bought the Leafs used from TechDirect and just did an overall parallel for 24 hrs. to even out the voltage and set them up in a 7p6s setup. I believe setting them up like this vs. 7 1p6s packs provides a buffer for the cells. Not sure what the BMS is doing balance wise, Batrium, outside of it seemed to be overcompensating and causing the cells to be more out of balance, with BMS balance 20-30mv delta, without the balance on cells went to 10-15mv +-. I guess 30mv would not be the end of the world but I would rather not rely on a suspect outside process vs. just monitoring the cells and leveraging cutoff settings in the BMS and other devices. I have noticed others with this setup reporting similar scenarios. 

For your LiPo4 cells are you happy with them, what brand/source did you use?  Would you do it again?

Thanks

mcgivor

Personally I can only speak from the experience gained from others along with extensive research into LiFePo4 , the general concensus is that all cells should be charged in parallel to the required voltage before series connection, a very slow and tedious procedure, which I would assume is the same for other chemistries.
 
The cells I purchased from http://www.aukpower.com and yes I'm happy with them,, the responsive post purchase service is outstanding. Would I purchase again from them? Absolutely if the need arrises, however in in a transitional period contemplating a move to a grid powered location, so many things to contemplate. Having a backup would be essential due to frequent outages during the rainy season, so still in the game,for now and the foreseeable future.

Ampster

solardad said:

@Ampster

Thanks for the info.
So what turned you off on the Leaf modules? I have a 21kw setup of them and they have been fine so far. I just wish the cost was dropping in line with LFP. 
..................
Tesla is interesting price/performance wise but I believe balancing is a must and my BMS experience has been average to poor. In fact, I no longer run the balance function on my BMS only the cutoffs as extra insurance, primary duty is with my charge controller and inverter settings. My leaf pack stays within 10-15mv naturally.

What BMS do you run?

I have been dissapointed with the degradation. As I near 60% capacity they drift apart as I discharge them. I run an Orion Jr BMS plus I use their Orion Connect module that lets me monitor the trends as I charge and discharge the pack. I also have turned off the balancing function since it does not have the capacity to make much difference

Ampster

mcgivor said:

Since automotive applications are typically bottom ballanced, I'm curious to know if the Leaf cells were top ballanced prior to use, this is where most BMS cell ballancing usually occurs,  perhaps the BMS is trying to correct imbalances beyond its capabilities. 
.........

Intersting, I have only heard that bottom balance philosophy in the EV conversion community where there were some strong advocates several years ago.Those advocates believed that no BMS was necessary if one bottom balanced.,  One of those has changed his tune and now sells interfaces to communicate with the BMS in Tesla modules.There is not practical way to bottom balance a Tesla module.  The only reference that I have heard from EV battery manufacturing process is binning, but maybe binning results in bottom balancing so we may be saying the same thing.