DIY 101 - 14 cell Nissan Leaf lithium pack

[Pat911]

I agree with Volt_Ampare, I suspect the cell has lost its internal connection.

Now that I’ve got a complete picture as to how it’s configured, what is happening makes perfect sense. Cell 14 is only half the capacity of cells 1-13 since it isn’t paralleled with a second module. That will mean that it charges faster and as a result it’s voltage will rise faster than the others. Of course it will discharge faster as well.

As others have said, let us know how it end up.

[bmuh]

Aww. That’s no fun!

Is there any way I can use the one 3.7v side of that module on my pack?

[Volt_Ampere]

Only if you parallel it with another one. I assume you are doing 14 modules - 14S, 2P. Since you don't know that internal damage you might have, the best bet is to replace it with another module - hopefully of similar capacity. The risk with Leaf modules is that many or most of them out there are at significantly reduced capacity. Leaf cars are very hard on the battery pack.

[bmuh]

I’ve ordered another module already. I guess I’ll save the one I’m replacing and maybe find a use for it with something else down the road.

While I’m waiting for this module to come in, could you guys help me locate the relays, BMS and charger for a 72v build? I found the solenoid but can’t figure out the rest… will the 120v relay be something I can swap over?

Sorry. I know I keep changing my mind on this but I may as well get the parts ordered so I’ll have them here and wired when I’m ready… shrug

[Pat911]

Plenty of choices on AliExpress....

BMS (smart with bluetooth):

This one can do 1A balance current which is better than most
https://www.aliexpress.com/item/1005...10134315%22%7D

This one is cheaper
https://www.aliexpress.com/item/1005...69398364%22%7D

Relays
https://www.aliexpress.com/item/3283...01331421%22%7D

Charger
https://www.aliexpress.com/item/1005...96588779%22%7D

The 120v relay can definitely be reused.

Cheers
Pat.

[bmuh]

Pat, Thanks for the help locating the needed parts!

Here’s an early update.

I decided to reconfigure the pack into a 10 module 72v configuration and the cart is scary fast! Hindsight it wasn’t smart because now I’m not going to be able to go back. I’ll be ordering the parts listed above today to keep things the way they currently are. Currently I’m undecided if I’ll be ordering the additional packs for the range. I guess that will be decided once I have some time on these and know if the range will be enough for my trips through the neighborhood.

Ben

Edit-

I’ve read enough on the 48v pack to know 50v is when to return to charge, but when would you guys suggest I park it with this setup?

[Volt_Ampere]

It is not pack voltage but individual cell voltage that determines when you must stop! That is why you absolutely need a BMS to monitor all of the cell voltages. IF the pack is balanced well, then the pack voltage can be used to estimate SOC. We usually "Top Balance" a pack which gets voltages equal at a high SOC. A pack that looks balanced at full charge can be much more out of balance when nearing the critical voltage cutoff point. The cells with the least capacity will have a lower voltage then.

[Pat911]

To add to that, if you go with a 20 module configuration, you would have purchased your modules in 3 deliveries and there’s a very high chance that they’ve come from different cars, and hence will most likely be different capacities.

To try and even things out as much as possible, have one of the 13 of your original purchase in each module pair. Parallel them with the 3 from the original purchase, the one you’ve just ordered and the 6 you will have to still purchase.

Top balance to at least 4.15v. Low cell cutoff should be around 3v but there’s not much left in the cell below 3.5v, about 10%.

To compare with your 50v example above, all things being equal, the 72v low point will be 50v/14x20 = 71.4v, that’s 3.57v per cell.

[bmuh]

Thanks Volt_Ampere, That makes sense. I’m still going to build the HV LV circuit for the 72v configuration, i just don’t have the parts yet. I was wondering when I should start being cautious about a possible undervoltage situation.

Pat, Will pairing the Modules the way you suggest help them be more balanced/equal?

I’ve seen some “active balancers” on amazon that claim 2a for balance current. My understanding is that it is always balancing the cells that it’s connected to. Would it be possible to add that in addition to the BMS to help balance the pack all the time? If so, it would work great since I’m not driving for miles at a time. At most it’s just a half mile at most and then hang out for a while and then drive again. So if the cell capacity varies by a bit, it could just balance it out between drives…??

[Volt_Ampere]

You do NOT want to balance the pack all the time. Only when cells are near full charge do you want to balance. It's hard to be cautious about undervoltage without a BMS monitoring all of the cells. If you start balanced and stay above 50% SOC, you are probably safe.