BMS vs. Active Balancers

[Usangira]

Hi,

I am running a 3kw inverter which shuts off at exactly 40V while my Solar Charge Control has maximum voltage of 58.4V which means it is 3.65V per cell.

I am just thinking what is the additional benefit I may get for investing into a BMS instead of the active 16S balancer which takes care of the top and low voltage balancing

 

[sunshine_eggo]

Hi,

I am running a 3kw inverter which shuts off at exactly 40V while my Solar Charge Control has maximum voltage of 58.4V which means it is 3.65V per cell.

The problem is not with total voltage, but that the cell states of charge are not equal.

I am just thinking what is the additional benefit I may get for investing into a BMS instead of the active 16S balancer which takes care of the top and low voltage balancing

I'm really shocked that people can still have this mindset, especially from someone with > 1 year membership and 67 posts.

There is not a "benefit" of a BMS. Without a BMS, you don't have a complete battery. Sure, you could steer a car without a steering wheel with a pair of vise grips, but would you do that? Would you drive without brakes just because there's a hole in the floorboard and you can Fred Flintstone it?

Your balancer likely has a limit. It's likely notably less than the manufacturer says. if it says 5A, it's probably closer to 2A.

The MOMENT you use more current than the maximum the balancer can actually deliver, you run the risk of single cell overvolt or undervolt and cell destruction.

 

[Ampster]

I am just thinking what is the additional benefit I may get for investing into a BMS instead of the active 16S balancer which takes care of the top and low voltage balancing

I run both a BMS and a balancer. I turn off the balancing on the BMS so it does not conflict with the active balancer. My balancer only balances at the top,
The advantage of the BMS for me is the last resort failsafe in the event that my inverter fails to cutoff at the top or bottom. Additionally it gives me another Coulomb counter, and remote monitoring with graphs that I can quickly spot issues if cell groups start having issues at any point during charging or discharging.

 

[Steve_S]

I WAS using Charger BMS' with Passive Balancing AND QNBBM-8S Active Balancers on ALL of my Production packs.
Yes I am also the guy who rewrote the Chargery Manuals and had a small hand in the upgrades & development of the DCC's and more.
1, BMS8T+DCC = $240 USD + S&H&Duties.
1, QNBBM-8S = $145 USD + S&H&Duties.
I have these on ALL of my 6 production packs. I also have Utility Packs with JBD & JK-BMS and two different Active Balancers (Test rigs too).

Now I am replacing the Entire Shlameel with
JK-BMS [24S 2A 150A BT] with BlueTooth Part Number: B2A24S15P $143.29 USD
Product Link: https://www.aliexpress.com/item/1005003104573871.html
-plus add: CANbus Module + RS485 Module $7.73 USD each
Product Link: https://www.aliexpress.com/item/1005003451100409.html

These come with 2- 7AWG Silicone wires for the 150A model pre-attached.
2x 7AWG = 4AWG. So I am extebnding the short lines using a Tinned Butt-Splice and running 4AWG Silicone to cell & to terminal.
* This is ultrafine strand Silicone wire designed for such purposes, it is not just crap-assed copper in PVC.
On Cell side a Tinned Lug with 5/16 hole, on Batt Lug side get's a 3/8 Lug (I have passthrough terminals on all packs).

LESSONS LEARNED DEPT.
The QNBBM and other Active Balancers were NOT settable / adjustable, not great when dealing with different grade cells. They are preset andf that's what you get, not always good and not great when cells are LOW.

The JK with built-in active balancing and also fully programmable & tweakable is the best all-around solution.

Relative Tidbits. My Production Bank is: My utility packs are EVE 105AH Cell Based, not in bank.
2x, EVE 24V/280AH packs with BULK Cells.
1x, EVE 24V/280AH packs with Matched & Batched Cells
2x, Aoyoupower 24V/175AH Used EV Grade cells recovered from the ShunBin disaster.

Hope it helps, Good Luck.

 

[Usangira]

I run both a BMS and a balancer. I turn off the balancing on the BMS so it does not conflict with the active balancer. My balancer only balances at the top,
The advantage of the BMS for me is the last resort failsafe in the event that my inverter fails to cutoff at the top or bottom. Additionally it gives me another Coulomb counter, and remote monitoring with graphs that I can quickly spot issues if cell groups start having issues at any point during charging or discharging.

How often do cells misbehave ?

 

[sunshine_eggo]

How often do cells misbehave ?

When they are failing, poorly matched, and/or at different SoC.

 

[Ampster]

How often do cells misbehave ?

Not often if you are watching them. Murphy's Law suggests they will misbehave when you least expect it. LOL In One case, I was 10,000 miles away and the inverter misbehaved which triggered misbehavior in my pack.