diy solar

diy solar

BMS + Balancer Lead Placement on Busbar

Mark1988

New Member
Joined
Sep 6, 2021
Messages
23
Hi There,

I'm planning on making my own busbars for an S16 48V battery and a 12kW off-grid inverter. I can see that many battery manufacturers seem to have stopped placing BMS and Balancer leads directly on the cell terminals and instead, they seem to be now placing them in the middle of the busbar or at least away from the terminal?

Q1: Is that the right approach and where exactly should I be connecting my BMS & balancer leads (e.g. terminal / center of busbar / x number of cm away from the terminal etc.)
Q2: I intend to place the cells in 2 columns of 8 cells each meaning, one of the busbars will be shorter than the rest (by approx. 1-2cm) - is that OK or will that impact any of the readings for either the BMS or the balancer?
Q3: Are ring terminals the way to go or should I solder the BMS and the balancer directly to the busbar?
Q4: Are there any issues with simultaneously using a 250A Daly BMS and an active 2A balancer?

Thanks for you input!

Cheers,
Mark
 
Sense Terminals usually goto the (+) Terminal on the cell set or in the middle of the busbar between the cells. The majority of such installations are with small tapped M4 screws into the busbar with a ring terminal. IE: https://www.digikey.ca/en/products/detail/molex/0190740012/3185976

Q2 ? not sure what you mean. There is Block Format or Straight 16S See Image Below (click to open up thumbnail)

1641902065751.png
Q3 Soldering can be done but is not usual. You would need a pretty hefty soldering iron and a good clean Copper surface on the busbar.. can be problematic. ! WARNING ! many vendors have been providing Plated BRASS busbars which have High Resistance and you can't solder much to that as it's more "white" than red so lower copper content (recycled a LOT whitens the Brass). Ensure you have COPPER Busbars and NOT Brass.

Q4 You could run an Active Balancer like a QNBBM or a Capacitive Model like those from HelTec. Idealy (really I am serious) you would be FAR BETTER OFF with a JK BMS with a 2A Active Balancer built in along with BlueTooth and optional RS485/CanBus interfaces.
 
Hi and thanks for your (very!) swift replay.

Re Q2: Yes, the block format where you have the vertical bar on the left hand side will be slightly shorter than the remaining horizontal bars - I'm not sure if that's a problem for the BMS / Balancer or not.

Re Q4: I initially wanted to use this exact same BMS but decided against it as its leads appear severely undersized for my 200A setup and there is on easy way to replace them. What exactly seems to be the issue with running a BMS and a balancer separately? Those standalone balancers appear to be very popular...?

Thanks again for your help.

Cheers,
Mark

edit: typos
 
Last edited:
Q2 actually the CXROSS Bar tends to be longer, with the 280's & 304's anyways.
20mm X 100mm Longer busbar Copper has 0.12mohm resistance, while teh 20mm X 90mm (std size) has an 0.11mohn resistance.

I presently run 6 packs with QNBBM-8s (with Chargery BMS's & Solid State Contactors) , 2 Packs with Heltec Capacitive Active Balancers (One JBD 4S & 1 JK 8S)..

The JK's with 2A Active Balancing can be better controlled & managed and when you work the numbers it is cheaper... My QNBBM's were $145 USD + S&H ea The Chargery's with the DCC's $400 USD. I am replacing it ALL everywhere Utility & Production to one common setup.

BTW: Will does not like Balancersm never has, many don't. It was my deep diving in BMS developments with Chargery & Others and using of Passive & Active Balancing brought it forward here so many talk about it now... I am what you may call a Forum Geezer here... been at this stuff a while.

Download this guide I prepared, it will answer some things fr you too.
Luyuan Tech Basic Lifepo4 Assembly Guide
 
Thanks for the PDF - it looks very interesting.

Could you clarify some of the other points for me though, I've unpacked them below like this:

1) Will's argument is that top balancing beats active balancing which I don't disagree with when you have grade A cells which I don't - mine are dented as they've been damaged in transport unfortunately - apologies, should have mentioned that before. Cell grade aside, you still rerecommended getting a BMS with an active balancer anyway so I'm not sure how to interpret this?

2) If one does go down the route of active balancing, I my mind the properly sized cabling on the Daly is more important than the convenience of having 1 app for the BMS and the balancer, mainly for safety reasons but also energy losses and excess heat etc. The undersized cabling on the JK BMS is why I've decided against it and already purchased both a Daly BMS and a separate active balancer. Am I missing something here?

3) Should the balancer also be connected to the middle of the busbar as well?

Thanks again for all your input!

Cheers,
M
 
Last edited:
OK. the JK's I just got in, come with 7-AWG Hi Temp Silicone wire, this is super fine strand hi volt stuff.... NOT crap assed cheap copper blend.
The balance sense leads at 2A is nothing much and the sense leads are also premium grade wire...

Top Balancing should be done regardless of cell grade. I always do 3 cycles before going production. but that's just me the Type-A Picky Virgo detail freak that I am.

Active Balancing transfers voltage from Hi to Lo Cells where Passive just burns off Hi Volts from cells. Several EV's actually Active Balance their cell clusters. StoreDot has combined that with healing tech in hi output cells (totally deep EV R&D stuff not general public info yet, quite limited).

The JK, heltec (same thing) can be programmed via bluetooth when to active balance & not and set thresholds etc.... the QNBBM & Capacitive Balancers do NOT allow for such.
 
That's the thing though, 7AWG x2 is not enough to carry the 200A JK rate their BMS for, which is apparently a well known issue with many Chinese manufacturers where they cut costs on the cabling. Putting those undersized cables in silicone makes them less of a fire risk (doesn't completely eliminate it though) but you still have the issue with excess heat and energy losses.
Like I said before, If you do decide to use an active balancer it seems to me you'd be better off going with a BMS with more appropriately sized cabling - unless of course I'm missing something here, which is my original question.

Cheers,
M
 
okay, maybe someone will come and give you the answer you want. do keep in mind some of us have sent obscene amounts of cash on learning these lessons and gaining these experiences.

Have Fun and Good Luck on your adventure.
 
There is no need to get defensive, I'm just trying to learn and get to the bottom of things. Having said that, if you can't explain your reasoning and instead end up appealing to spending a lot of money on expensive courses as if that was a valid argument then perhaps I should wait for someone else to come along... Thanks anyway and good luck to you too.

If there is anyone who could advise where to position the BMS and balancer leads on the busbar and explain why that would be very helpful indeed - I'm sure there are many people have the same conundrum.

Cheers,
M
 
I drilled and tapped my bars to fit a 6-32 brass screw to hold the ring or spade terminal of the BMS and active balancer connections.
Mine are approximately mid way between the main terminal connections. Doubt the spacing matters much but should be consistent.

I prefer to have no other connections on the main bus to cell connection.
 
Sorry, but One JKBMS with 2A Active Balancer, BlueTooth with Phone App is less costly than separate BMS & Active Balancer. Just trying to save you money. I was pointing out that a QNBBM is worth 140 USD + a BMS of reasonable value is at least another 150-200, when you can just buy a god BMS with Active Banalancer that you can actually manage and set params for (QNBBMS, Heltec etc do NOT have that capability) for the same or less cost. You can do what I did is build your system over 2 years, have different versions of gear attached which then complicates everything to death and then having to pull it all and replace it at great expense... Like what am I gonna do with 8 QNBB-8S Balancers and the array of BMS, Relays & Contactors etc... It is a FEW Grand worth of gear.... and did not take that long to pile up. BTW: Broad Brush Blanket statements don't go over well...

The JK's I bought (150A) they came with dual 7-AWG Silicone which BTW is equal to 4-AWG. The higher amp handling ones come with bigger wires. Everything I built previously was targetted at 300A but with a large bank of paralleled batteries, they divide the load to and rarely ever get a Hi Pull on them, as it should be. My final build includes tapping M4 Screws into the center of each busbar for consistency because every milliohm counts and connecting to cell posts can result in odd issues and constantly does.

BMS to Balancer wiring (sm)[4757].jpg
<--- QNBBM-8S Active Balancer.
Thin Wires are from BMS Harness.
Thicker Wires 14-AWG from Active Balancer to Cells.
BMS Wires are exactly the same length as are the wires from the Active Balancer to cells. Milliohms & Millivolts leave little room for furtling about.






Alternatively, you can use a MOLEX Connector as shown to accomplish similar with different types of Active Balancers such as Heltec's Capacitive ones or like this HELLA Block which use ATC type Fuses (beware of cheapo fuses).


Molex-Block.jpg Hella Splash Proof Fuse Blocks H84960111.jpg
 
Hi, thanks for both of your responses - that's very helpful. I like the idea of eliminating 1 set of cables that need to connect to the busbars by routing them via a molex connector - this is really good thinking. I've emailed Daly to see if they see any issues with that and to also check if I need to adjust the BMS voltage readings for the additional resistance introduced by the extra cable coming out of the molex connector.

I take your point re having 1 fewer devices to worry about and using a bms with an active balancer built in, as well as the cost aspect and the extra functionality etc. For me unfortunately that boat has now sailed as I've already got a Daly and a separate balancer - I'll consider that for my next battery though.

Thanks again for your help,
M
 
Anywhere on the busbar is OK for sensing or balancing wires. Identical length is not required.

Top balancing method depends on your intended application and components - the simplest way is to address any balancing issues as they arise in an already assembled pack.
 
Hi There,

I'm planning on making my own busbars for an S16 48V battery and a 12kW off-grid inverter. I can see that many battery manufacturers seem to have stopped placing BMS and Balancer leads directly on the cell terminals and instead, they seem to be now placing them in the middle of the busbar or at least away from the terminal?

Q1: Is that the right approach and where exactly should I be connecting my BMS & balancer leads (e.g. terminal / center of busbar / x number of cm away from the terminal etc.)
Q2: I intend to place the cells in 2 columns of 8 cells each meaning, one of the busbars will be shorter than the rest (by approx. 1-2cm) - is that OK or will that impact any of the readings for either the BMS or the balancer?
Q3: Are ring terminals the way to go or should I solder the BMS and the balancer directly to the busbar?
Q4: Are there any issues with simultaneously using a 250A Daly BMS and an active 2A balancer?

Thanks for you input!

Cheers,
Mark

Excellent question and thanks everyone else for the answers below. Saved me the time of starting my own thread, with less well phrased questions. :)
 
Sorry, but One JKBMS with 2A Active Balancer, BlueTooth with Phone App is less costly than separate BMS & Active Balancer. Just trying to save you money. I was pointing out that a QNBBM is worth 140 USD + a BMS of reasonable value is at least another 150-200, when you can just buy a god BMS with Active Banalancer that you can actually manage and set params for (QNBBMS, Heltec etc do NOT have that capability) for the same or less cost. You can do what I did is build your system over 2 years, have different versions of gear attached which then complicates everything to death and then having to pull it all and replace it at great expense... Like what am I gonna do with 8 QNBB-8S Balancers and the array of BMS, Relays & Contactors etc... It is a FEW Grand worth of gear.... and did not take that long to pile up. BTW: Broad Brush Blanket statements don't go over well...

The JK's I bought (150A) they came with dual 7-AWG Silicone which BTW is equal to 4-AWG. The higher amp handling ones come with bigger wires. Everything I built previously was targetted at 300A but with a large bank of paralleled batteries, they divide the load to and rarely ever get a Hi Pull on them, as it should be. My final build includes tapping M4 Screws into the center of each busbar for consistency because every milliohm counts and connecting to cell posts can result in odd issues and constantly does.

View attachment 79226
<--- QNBBM-8S Active Balancer.
Thin Wires are from BMS Harness.
Thicker Wires 14-AWG from Active Balancer to Cells.
BMS Wires are exactly the same length as are the wires from the Active Balancer to cells. Milliohms & Millivolts leave little room for furtling about.






Alternatively, you can use a MOLEX Connector as shown to accomplish similar with different types of Active Balancers such as Heltec's Capacitive ones or like this HELLA Block which use ATC type Fuses (beware of cheapo fuses).


View attachment 79230 View attachment 79231



Not much point worrying about milliohm differences, then using a fuse block or molex rail connector.

If you are experiencing problems using cell posts as sense wire locations it is because you haven’t assembled them correctly (clean and firm connection). There is no difference between cell post and centre of busbar. (and i have used both methods)
 
Not much point worrying about milliohm differences, then using a fuse block or molex rail connector.

If you are experiencing problems using cell posts as sense wire locations it is because you haven’t assembled them correctly (clean and firm connection). There is no difference between cell post and centre of busbar. (and i have used both methods)
I made a change after that and did not tap the busbars, after looking at the pile of them, Sense leads are on the (+_ post).
BTW, the cell resistance readings are all almost exactly the same across the packs.
 
Last edited:
I made a change after that and did not tap the busbars, after looking at the pile of them, Sense leads are on the (+_ post).
BTW, the cell resistance readings are all almost exactly the same across the packs.

What gear are you using to measure resistance? My non-pro multimeter (Kahweets) from Amazon measures resistance, but all I get is basically "0.1".
 
Back
Top