Nissan Leaf 7 Module Pack Wiring Drawing w/ Sergio Relays

[fstop]

Originally Posted by Sergio

Those two questions are somewhat related in the fact that it depends on the internal constructions and connections between cells and/or any existing BMS inside the "drop-in" box..

As long as You have access to all BMS and cell connections, You can either install your own BMS or perhaps modify the internal wiring to accommodate external handling of LV and HV shutdown.

The main reason that some BMSs use internal FETs is that they need a way to monitor current in/out in order to provide accurate SOC display.

Any so called SOC meter that only has power connections is not reliable for predicting Lithium batteries SOC, regardless of what any vendor may say otherwise.

Some more expensive BMSs like Zeva use external shunts and need to be always powered during charge/discharge in order to keep track of AH in/out.

If You were installing the Lithium pack in an EV, then I would stick with the models that accurately keep track of SOC using external shunts/hall effect sensors so you don't get stranded.

For a golf cart application I personally don't see that as critical and a "rough estimate" of SOC based on voltage reading is sufficient for most folks.

simicrintz, if the Chevy Volt pack has the BMS tap harness installed, you can tap the existing connector for installing a BMS, the photo below shows the B- and each cell tap available on that connector:

Thanks!

[ACCLR8N]

Silly question: Why do you guys like to connect the BMS leads to the other end of the busbar (next battery -) rather than directly under the screw going into the measured battery's + terminal?

[Sergio]

There are two individual batteries connected to the same bus-bar on a 7S1P pack, so a single wire can only be connected directly on top of a single terminal.

If You had a 14 module 7S2P, then you would have four terminals on four individual modules connected by the bus-bar and you still only have one balancing wire.

The assumption is that the bus-bar does not have enough resistance to affect the cell voltage being measured away from the balancing lead even when high current is passing though the bus-bar.

[Caleb_mock]

I have a different EV battery pack that is difficult to create cell level high amperage connections.

How would the wiring diagram differ if there were two individual modules wired in parallel? Would you use two BMS's to control the relay?

Specifically, I have 4 of these modules: https://batteryhookup.com/products/b...ah-2kwh-module

[Pat911]

Hi Caleb_mock,

In your case you would have to use 2 BMS's, one per pack (2 series connected modules) then connect the two B+'s and the two C-'s together to create a parallel connection. Very capable modules you have there.

Document your build so we can see how it goes.

Cheers
Pat.

[Caleb_mock]

In your case you would have to use 2 BMS's, one per pack (2 series connected modules)

Thank you so much! I was expecting to need a second BMS. Not a problem since the BMS didn't ship due to the Chinese New Year! Are these the only changes that I need to make? Will the specified relays still work?

I'm quite excited about the build, but it has a lot of challenges that I haven't anticipated. I'm planning to run this as a 15S and have a max voltage of 62V on an Alltrax XCT. I had hoped to do cell level balancing, but finding a good, clean connector is looking to be a problem.

[Pat911]

Originally Posted by Caleb_mock

I'm planning to run this as a 15S and have a max voltage of 62V on an Alltrax XCT.

No other changes should be required. Just ensure that the two batteries are at a very similar state of charge before connecting them together.

What are you going to do about the one cell left unconnected? Being NMC chemistry it is unwise to leave it disconnected and let it discharge to zero.

Which BMS are you purchasing? Many will allow you to do a good top level balance by setting the parameters accordingly. It needs to be able to balance whilst not charging for this to work.

Cheers
Pat.

[Pat911]

Actually, looking at the pictures shown, it shouldn't be too difficult to reconfigure the battery to 4P14S or 4P15S if you like. The bus bars can be cut as already shown in one of the pictures and then spot welded back together in the new configuration. You can then also remove the unused cells. Remove two for 15S or four for 14S.

[Volt_Ampere]

I would go with 14S for Alltrax. I think the max recommended voltage is 60V. My Leaf 14S fully charged would be 58.8V (I charge it to about 57.5V)

[Caleb_mock]

Hadn't thought about the extra cell being a problem. The bus bar is really easy to modify, but all the cells are glued together.

I was looking at the 100 Amp 15s smart BMS's by JBD.
https://m.aliexpress.com/item/100500...1c9cced&gclid=

Can they balance charge the way you described?

I saw on the datasheet that the Alltrax could go to 62 volts. I had planned on never charging above that.