Nissan Leaf Battery Upgrade

jerichorick · 05-03-2020, 01:53 PM

My AGM house battery bank is 10 years old and very tired. My stepson suggested that I replace the 6 batteries in the bank with a set of Nissan Leaf packs. I am gathering parts and gaining understanding as to how to accomplish this as I write. Here is what I have learned so far.

The packs are available on ebay. They are salvage packs from Nissan Leaf battery power plants. When the capacity is degraded to about 70% life the plant is replaced. Folks like TechDirectClub at eBay offer these packs. The G1 packs are from the first generation of the Leaf and are not as strong as the G2 or second generation pack.
About the packs. These are LiFePo4 chemistry configured to 7.5V and 66Ah. The 30% degrade leave these packs with about 46Ah. Because of the chemistry they don't have to be filled to working capacity which makes this storage medium great for my project. I really don't know what the actual working Ah of my bank will be but I am shooting for 315Ah or so.

I bought 14 packs that were sold as a 48V set. What I got were the packs, screws, jumper straps, side plates, threaded rod, washers and nuts. The rod holds the plates to the outside of the pack assembly for securing them. For my configuration I need to do some modifying by using longer rods on one set of packs.

Because 2 packs in series have a value of 15V I knew I would have to discharge them somehow. But to what value? This is where I learned about the BMS or Battery Management System. I did a lot of research here. There are so many flavors and configurations to choose from. Finding a valid spec from the available eBay vendors was a challenge. Finding the quantity I needed, 7 in this case, available from a single vendor was also a problem. I ran into a snag here but I think I have resolved it. I bought 5 from one vendor, all they had at the time, and 2 from another. The 2 I did not trust when I got them and will not know for certain if they are compatible until I test them. I ordered 2 more from the original vendor because they became available.
Packs and BMS functioning: Each pack has 2 cells. (Within the pack there are 4 configured to provide the engineered spec.) The working cells come charged to about 3.75 volts or half the pack voltage. The BMS is designed to meet a predetermined set of values. The main function of the BMS is to keep the cells at the same voltage as its neighbor when charging or discharging. It is designed to disconnect the battery if the voltage of a cell goes too high or too low or if the currant is too high. The BMS I require is designed to balance 4 cells. It is known as a 4S 12V BMS.

I am designing a 14.6V battery charge value. My cells should equalize at 3.5V with this BMS or a working battery voltage of 14V. My pack cells are charged to 3.75V and I need to shed that down before I build my 14V battery. How can I do this safely working on sawhorses and plywood next to the RV in sunny California? How about using a plain old batter tester! Yea. That should do it. The BMS I chose is a 50A charge and 60A discharge rating. At max I should not pull any more than 37A from any one battery when the microwave is running. My inverter is a Magnum MS2800 and I can adjust it to the charging values required for this project.

Not so fast buck-o. I found out, very quickly, that that resistor bank gets very hot very quickly. I burned the first one out. I bought a new one from Harbor Freight. This one is working fine with the help of a Milwaukee 18V leaf blower as a cooling fan.

To discharge to packs, place the load tester across the large terminals, turn on the blower directed into the tester vents and flip the tester switch on. I simply felt for heat on the case and when it started to get warm I released the switch and cooled the tester off. I put a battery strap from my kit on the + and - terminals to attach the load tester clamps to. Once each cell was down to about 3.4V I marked the pack with masking tape and wrote the final values on it. I did all the packs this way. To my surprise the packs gained .1V overnight so I needed to discharge them again to the 3.4V value. I chose this value so the BMS would be active when the battery was charged. For clarity, I am calling a battery 2 packs in series. When all the batteries are configured in parallel I am calling this the bank.

I am installing a Victron SmartShunt blue tooth monitor in the battery so that I can see the condition of the bank on my phone when I need to. I have a Victron smart battery charger on the way. I will use this to charge and balance the batteries before I put them into the bank configuration.

I hope I can post pictures as I do the build. More to come...
Rick Y

**creativepart** · 05-03-2020, 02:21 PM

Wow Rick... you're really breaking sort of new ground. I know other's have done this, but I've not heard the details about their setups.

Good luck. Were you tempted to switch to 48v to go with the bank you purchased without more modifications? A 48v to 12v converter would make that easy wouldn't it?

jerichorick · 05-04-2020, 07:28 AM

Quote:

Originally Posted by creativepart

Wow Rick... you're really breaking sort of new ground. I know other's have done this, but I've not heard the details about their setups.

Good luck. Were you tempted to switch to 48v to go with the bank you purchased without more modifications? A 48v to 12v converter would make that easy wouldn't it?

I am doing a direct swap. To reconfigure the coach for 48V was way out of my price range. The packs can do the job for a 12V system and retain good capacity because they are not being filled to capacity then discharged. Well, this is how I have come to understand these things through my research. I hope this will be my last set of batteries before I have to go off the road (big gamble here) and loosing about 330# is a huge plus.

99dart · 05-04-2020, 08:46 AM

Wow, sounds fun! I think you have a better understanding than I do for building this! I did a bunch of research when I built our ebike. I built a 4p 13s pack out of 18650 samsung batteries. The bike turned out pretty good. Good luck with the build!

BobC · 05-04-2020, 08:54 AM

I'll be checking this one every day. This will be interesting.

HappiHenri · 05-14-2020, 01:04 PM

What you are undertaking is extremely ambitious and way beyond what most RVers would ever attempt. Many, many concerns & issues. And dangers of using a higher voltage battery pack.

Best that you review the work whicht Will Prouse has one on related issues to this. His website is : https://www.mobile-solarpower.com/

He has written a book on this, as his expertise is in advanced battery systems, solar power, etc for both RVs and homes. He has done work with buying used Tesla battery packs - but typically using them for home solar systems and power walls.

Not sure he has actually done a 48v battery system for his own RV as he usually recommends replacing the RV OE house batteries with good quality drop-in replacement Lithium batteries. But check out his site, and watch some of his many Youtube videos on all this.