[JK BMS] cutting down on balancing wires?

fRzzy · Mar 23, 2023

Hello, I'm trying to build my first pack with 8 LFP cells using JK 8-17S BMS...

In order to remove unnecessary balancing wires, I want to solder the black wire directly to the B- terminal and the last red wire to the B8+ wire. There will be only 8 wires coming out of the BMS to the cells.

I don't see any (potential) problems doing this, but I want to make sure, is there any problem if I do this?

Thank you!

fRzzy · Mar 23, 2023

Another question, from the manual it says that the BMS power requirement is 20-100V, does that mean the last red wire doesn't really need to connect to the last cell positive pole? I figure if I want to rebuild the pack to 16S I can just add 8 more wires to the balancing port to connect to the added cells, and leave the last red wire connect to the B8+ pin.

Texas-Mark · Mar 24, 2023

fRzzy said:
In order to remove unnecessary balancing wires, I want to solder the black wire directly to the B- terminal and the last red wire to the B8+ wire. There will be only 8 wires coming out of the BMS to the cells.

What am, I missing? How does that remove "unnecessary" wires? And how are they unnecessary?

RV10flyer · Mar 24, 2023

You need 10 wires. Yes you could splice that black wire into neg bat lead and the most pos into 8+, but you still have 10 wires being used out of the connector. I usually cut all other unused wires at 1.5” and cover with heat shrink for possible future use. I sometimes cut them off flush on my 16S, because I know I’ll never need 17-24.

fRzzy · Mar 24, 2023

Texas-Mark said:
What am, I missing? How does that remove "unnecessary" wires? And how are they unnecessary?

uhmm the BMS support 17S and I only have 8S, there are 9 wires that aren't connected to anywhere, aren't they unnecessary? or should I say "unused"?

RV10flyer said:
You need 10 wires. Yes you could splice that black wire into neg bat lead and the most pos into 8+, but you still have 10 wires being used out of the connector. I usually cut all other unused wires at 1.5” and cover with heat shrink for possible future use. I sometimes cut them off flush on my 16S, because I know I’ll never need 17-24.

I have already taken out unused wires by removing the terminal out of the connector, that way they are still intact and I can reuse them later as needed.

About the negative wire and the last positive wire (for the BMS power supply) I'm thinking about solder directly to the connector pin on the PCB, no wire needed.

I think no bad thing going to happen, I'll do it tomorrow and update the result with pic if you want.

JJJJ · Mar 24, 2023

You might find this helpful

JK active BMS lead removal

Ok. I am totally dense on this. I did ask someone how to remove the extra wire leads. They quickly responded but I am hitting a mental brick wall. It was suggested to use a small sharp object to move the small finger which held the wire. Alas, I confess I have not had any success and want to...

diysolarforum.com

JJJJ · Mar 24, 2023

Per another user.

RV10flyer · Mar 24, 2023

fRzzy said:
uhmm the BMS support 17S and I only have 8S, there are 9 wires that aren't connected to anywhere, aren't they unnecessary? or should I say "unused"?

I have already taken out unused wires by removing the terminal out of the connector, that way they are still intact and I can reuse them later as needed.

About the negative wire and the last positive wire (for the BMS power supply) I'm thinking about solder directly to the connector pin on the PCB, no wire needed.

I think no bad thing going to happen, I'll do it tomorrow and update the result with pic if you want.

Yeah, let us know. Thank you.

Texas-Mark · Mar 24, 2023

fRzzy said:
uhmm the BMS support 17S and I only have 8S, there are 9 wires that aren't connected to anywhere, aren't they unnecessary? or should I say "unused"?

Your post sounded like you were trying to eliminate some of the ones you needed. So just remove the extras like you said you did - problem solved.

RV10flyer · Mar 24, 2023

If I want to disconnect power to the BMS, I pull the connector. No tools needed. If you want to, you’ll need to either disconnect BMS red wire at positive terminal on Cell 8 or B- cable from Cell 1. That is the only difference I can think of.

timselectric · Mar 24, 2023

The only issue I see is that the cell 8 + won't see the same resistance as the others. Which could throw off the balancing. But if you are only talking about the power wire. I guess it shouldn't matter.

LakeHouse · Mar 24, 2023

You might get some Voltage readings that are a little off on cell #1 under load because there’s some resistance between the B- terminal and the negative terminal of battery 1.
I doubt it would make a big difference except under large currents, but that difference is presumably the reason why there’s a separate lead rather than the BMS just measuring cell 1 voltage off the B- connection.

Skypower · Mar 24, 2023

Like others have said. You may see a bit of balance issues with pairing into one lead. The last wire (power, positive) has the load of running the bms like the black. However, the black probably is compensated for since it does triple duty of power, sense and balance. The positive can’t be compensated because they have no idea how many cells you will run so hence, the extra lead. Probably the only place I’d share the last of string and the power is in the terminal as pictured. You can cut the leads you don’t need and Shoe Goop the ends. You can also remove a few by pushing the retaining barb down and pull the wire out. Don’t remove more than a few and only in the middle of the plug because they are needed to keep it in the bms. I like to pull a few for spares and in case I cut one too short, I’ve got a do over. You can cut the length of the leads as short as you need, that won’t make a difference.

fRzzy · Mar 28, 2023

Hello, I did what I planned to do and no magic smoke yet (yay)

I haven’t fully assembled the pack yet, still waiting on the enclosure.

First cell wire resistance seems to lower than the others, not sure if it’s because of the shorter ground wire?

JJJJ · Mar 28, 2023

Shorter wire can be a factor. If you still have some unused spares you can switch it out to verify.

Skypower · Mar 28, 2023

Here’s an old screenshot, the bottom is cut off so it doesn’t show all cells and I’m not at home to get another. There’s a big resistance difference from yours. Battery chemistry involved? I highly recommend this brand of ring terminals. They are much harder than normal and don’t mush away. They are plated brass. You strip twice as normal, fold insert and crimp with an MC4 crimper. Flip the jaw so the crimp selected is closest to the hinge. After crimping put dab of solder over the end to keep moisture out the use adhesive heat shrink to seal the deal.

[JK BMS] cutting down on balancing wires?

fRzzy

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fRzzy

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Texas-Mark

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RV10flyer

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fRzzy

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JJJJ

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JK active BMS lead removal

JJJJ

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RV10flyer

Solar Wizard

Texas-Mark

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RV10flyer

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timselectric

If I can do it, you can do it.

LakeHouse

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Skypower

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fRzzy

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JJJJ

Aspiring apprentice

Skypower

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