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Off grid 12kWh 48V Leaf Cell setup advice please.

JD Solar and EV

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Sep 6, 2020
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Hi All,

Posting from Queensland, Australia regarding general or specific advice for setting up a 48V off grid system using Nissan Leaf cells.

Background: I have access to 42 cells, believe they are 7.6V cells with a guessed capacity of 40Ah per cell. (Capacity test to be done in due course) I have recently purchased a large property with no services and my usage is likely to be 1-3kWh per day once the system in up and running. Like to be a bit higher as time goes on.

Could you help with the following questions?

Should I run 6 packs of 7 or 7 packs of 6 for a 48V system? i.e. Should I run a 45.6V or 53.2V setup? Thinking the 53.2V setup is the way to go.

What sort of distance can the solar array be from the battery bank?

What sort of distance can the battery bank be from the location it is been used?

What advice do you have regarding panel configuration and size?

What temperature do the cells need to be kept at? My climate is minimum 5C to maximum 37C (41F to 99F)

Believe the Watchmon 4 products are suited to this type of application. Any advice on inverter or other hardware required?

Feel free to provide any other general advice.

Cheers

JD
 
Hi All,

Posting from Queensland, Australia regarding general or specific advice for setting up a 48V off grid system using Nissan Leaf cells.

Background: I have access to 42 cells, believe they are 7.6V cells with a guessed capacity of 40Ah per cell. (Capacity test to be done in due course) I have recently purchased a large property with no services and my usage is likely to be 1-3kWh per day once the system in up and running. Like to be a bit higher as time goes on.

Could you help with the following questions?

(1) Should I run 6 packs of 7 or 7 packs of 6 for a 48V system? i.e. Should I run a 45.6V or 53.2V setup? Thinking the 53.2V setup is the way to go.

(2) What sort of distance can the solar array be from the battery bank?

(3) What sort of distance can the battery bank be from the location it is been used?

(4) What advice do you have regarding panel configuration and size?

(5) What temperature do the cells need to be kept at? My climate is minimum 5C to maximum 37C (41F to 99F)

(6) Believe the Watchmon 4 products are suited to this type of application. Any advice on inverter or other hardware required?

Feel free to provide any other general advice.

Cheers

JD

(1) Lithium NMC (Leaf chemistry) performs most like a 48V system with 14 cells in series. You have 2 cell modules, so you'd want to put 6 in parallel those groups of 6 in series. You got that right with 53.2V.

(2) Depends on the gauge of wire you use:


Anything less than a 5% drop meets NEC.

(3) The battery should be as close as possible to the inverter as that's where you'll have your high current connections - between battery and inverter.

(4) Link #5 in my signature - specify your location, panel direction and til to determine your available solar hours. Pick the worst case month's hours and divide you daily kWh usage by that number, divide again by 0.85 for inefficiencies, and you'll have your minimum kW of panels, e.g., 2kWh with 4 hours requires 2000/4/.85 = 588W of panels.

(5) No issues with your temps.

(6) No recommendations.

Ensure you completely understand the dangers associated with the use of this type of chemistry. Make sure you get a quality BMS and understand how it all works. You need to be your own expert.
 
(1) Lithium NMC (Leaf chemistry) performs most like a 48V system with 14 cells in series. You have 2 cell modules, so you'd want to put 6 in parallel those groups of 6 in series. You got that right with 53.2V.

(2) Depends on the gauge of wire you use:


Anything less than a 5% drop meets NEC.

(3) The battery should be as close as possible to the inverter as that's where you'll have your high current connections - between battery and inverter.

(4) Link #5 in my signature - specify your location, panel direction and til to determine your available solar hours. Pick the worst case month's hours and divide you daily kWh usage by that number, divide again by 0.85 for inefficiencies, and you'll have your minimum kW of panels, e.g., 2kWh with 4 hours requires 2000/4/.85 = 588W of panels.

(5) No issues with your temps.

(6) No recommendations.

Ensure you completely understand the dangers associated with the use of this type of chemistry. Make sure you get a quality BMS and understand how it all works. You need to be your own expert.

Thanks for your reply, for #4 i understand sizing of panels but I should have been more specific about the sizing in relation to charging the batteries and the recommended C rating to maximise the life span of the cells/packs.
 
Those Leaf modules won't even notice what you're doing to them at those currents. They're designed to work with very large currents from the EV, and you're going to put them in parallel to share a much lower current.

They're not like lead-acid. You can hammer them hard or soft. Just keep them between 3.5 and 4.05V/cell (49-56.7V), and they'll last for thousands of cycles assuming they're healthy to start with.
 
New Leaf cells are rated at 55 amp hour. You should get better than 40.
Agreed, 7 modules in series for a 14S setup. 6 in parallel is then a rated 330 amp hour, pretty close to my 360 AH of Chevy Bolt cells which are also NCM based. At rated capacity, that would be 17 KWH's. If they have degraded to 40 AH per cell, it is still over 12 KWH. If they are used cells from different cars, you should try to even out the parallel groups. If you pair a weaker cell and a stranger cell, it can balance out. So sort out the cells so each stack of 6 modules has the same total capacity.

Charge rate under 1C will last a long time. I am only charging my Bolt cells at 0.2C. And discharge at still less than 0.5C It is much easier on the cells than how they were used in the car.

Use a good BMS to make sure no cell group get's pulled under 3 volts, 3.2 is even better, and under 4.1 is fine. That would be 6.4 to 8.2 for the cell pairs, but the BMS also has to see the center tap on each cell pair. The center screw should also connect across the 6 in parallel so they stay balanced.

I looked at a Batrium Watchmon system, and they are good. I ended up with a Chinese BMS with active balancing and bluetooth setup and monitoring. I am happy with it so far, it has not blown up.
 
These are third life Leaf cells. 2012 Leaf then EV conversion and now storage, so while they are not capacity tested yet, the expected capacity should be around 12-15kWh. Im paying around $1200US so at that price I will be happy with however they come.
 
Charge rate under 1C will last a long time. I am only charging my Bolt cells at 0.2C. And discharge at still less than 0.5C It is much easier on the cells than how they were used in the car.

Use a good BMS to make sure no cell group get's pulled under 3 volts, 3.2 is even better, and under 4.1 is fine. That would be 6.4 to 8.2 for the cell pairs, but the BMS also has to see the center tap on each cell pair. The center screw should also connect across the 6 in parallel so they stay balanced.

I looked at a Batrium Watchmon system, and they are good. I ended up with a Chinese BMS with active balancing and bluetooth setup and monitoring. I am happy with it so far, it has not blown up.

So max 6kW system for a 0.5C charge sound about right?

Do you have a link to the Chinese BMS?
 
Pray to the Lithium gods those didn't see service in a hot climate. Those batteries got the living shit beat out of them in AZ.
 
Here is the BMS that I bought.


This is even the seller I used. Don't laugh too hard "Flower Dog Store" but they were very good and responded quickly to e-mails etc. They did have a delay because the 200 amp version was not in stock, but once it came in, I got it in just 3 more days.

The model is the B2A 24S-20P and it does not look like the top picture, it has the cast aluminum case and looks like the one about 1/3 down the page with the RS-485 and GPS modules plugged in. The price went down 2$, I paid $176, but I was then charged taxes etc that brought it almost $200 even.

There are several other sellers carrying the same board. They also list it as a 300 amp but the spec is the same, the 20P part of the part number is 20 FET's in parallel for the protection switch. At up to 80 amps, mine runs just warm and is measuring under 0.001 ohm of drop, including the wires, which is better than I was expecting. The spec sheet claims 0.0003 but the doubled #7 awg wire alone is at least that much. You can download the App on the iTunes store, have not tried the Android version, just search for JK BMS. JK is Ji Kong. Unfortunately, you can't do much on the App until it connects. It does not even show the settings available. I won't say it is the best, but so far it has been working perfectly and the balancing system is very good. My only real complaint is the bluetooth range is short. The setup is very flexible. You can dial it in to work with virtually any battery bank. It says 14S to 24S but it will actually work all the way down to just 4S, but it does need a 40 volt power feed on the 11th pin of plug 2.

When you first power up the board, it will seem dead. It does nothing at all. You need to supply a charging voltage that is 5 volts higher than the pack voltage to make it switch on. That was a bit of a problem for me at first as my small e-bike battery I tested it on was near full charge so my charger would not fire it up. I "cheated" and used only 12S to get it to turn on the first time. Once it is on it stays on, but if it loses power to that 40 volt input, you will likely have to give it the charge kick again. Be sure to have the cells wired in the correct order and have the pack negative connected, before you plug the balance leads in. And plug in the 15 pin P1 cable first. With 14S, all the cells are on that first P1 connector, but you still need the 11th pin of P2 to power the board. The wiring diagrams on some of the sites, including Flower Dog are confusing. Just know that pin 1 the black wire is cell 1 negative, and then the wires just go in order to each cell positive. And then the 26th wire (P2 pin 11) also goes on the top cell, so it get's 2 wires.

Let me know if you have any other questions.
 
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