BMS & Leaf modules for dummies

Batteries, Chargers, and Battery Management Systems.
Post Reply
Kimmo57   1 µW

1 µW
Posts: 2
Joined: Nov 05 2019 10:04am

BMS & Leaf modules for dummies

Post by Kimmo57 » Feb 13 2020 9:46am

I'm starting an electric motorcycle project. I'm no electrician and am figuring things out as I go along, so this might be a stupid question.
One thing I'm having trouble understanding is how a BMS works with Leaf modules. I have 6 out of a 30kWh Leaf. There's a + and a - with one more connector in between. How does the BMS control 4 cells in the module with just these connections? :?:

Image

User avatar
eee291   100 kW

100 kW
Posts: 1034
Joined: Nov 05 2015 4:35pm
Location: Austria, Burgenland

Re: BMS & Leaf modules for dummies

Post by eee291 » Feb 13 2020 3:37pm

I believe they are configured 2S2P so just 2 cells that need to be monitored essentially.

billvon   1 GW

1 GW
Posts: 3051
Joined: Sep 16 2007 9:53pm
Location: san diego

Re: BMS & Leaf modules for dummies

Post by billvon » Feb 13 2020 4:09pm

Kimmo57 wrote:
Feb 13 2020 9:46am
How does the BMS control 4 cells in the module with just these connections?
With 4 cells you need 5 connection points:
Negative
Top of cell 1
Top of cell 2
Top of cell 3
Positive

Note in the picture there that you have 6 connection points.
--bill von

Hillhater   100 GW

100 GW
Posts: 10527
Joined: Aug 03 2010 10:33pm
Location: Sydney ..(Hilly part !) .. Australia/ Down under !

Re: BMS & Leaf modules for dummies

Post by Hillhater » Feb 13 2020 6:19pm

The photo confuses things a little..
The secret is in clarifying the terminology of “cell”, “group”, “sets”, “module”,
The lower module (from the 30 kWh pack) , actually has 8 cells inside it...in 2 “sets” of 4 .
Each “set” of 4 cells are configured with pairs of cells in “groups” for a 2p, 2s, arrangement with main power (larger) terminals at 7.4volts for each set of 4 and a mid connection (the smaller central terminal) to sense the 3.7volts on each pair of parallel cells.
So, the BMS connects to each of the 3 terminals on each set of 4 cells. And is effectively monitoring pairs of parallel cells....not individual cells.
And, for the full 8 cell, 14.8v, module, the BMS will need 5 connections, because one will be a common connection.
This forum owes its existence to Justin of ebikes.ca

Kimmo57   1 µW

1 µW
Posts: 2
Joined: Nov 05 2019 10:04am

Re: BMS & Leaf modules for dummies

Post by Kimmo57 » Feb 14 2020 10:15am

Great, thank you very much for clarifying. :bigthumb:

Post Reply