looking for a good quality bms for my large 14s system

I have some large BMW batteries
They range in 3s, 4s, and 5s packs, i have them configured so that i have 14s groups. i can make up to 6 strings, but for now i will start off with 2 and see how much more I can add in the future.
But for now I am searching for a good BMS, one with active top and bottom balancing, multi thermal sensor capabilitys ( I'd like to use the thermal sensors on the battery if i can. )
I have heard that Orion , Batrium and REC were pretty good units, but picking the one i need seems to be over my head.
I know i'll probably need one BMS for each string I have.
I need suggestions.
Thanks.

I use REC and Batrium. Neither have active balancing.

I have active balancing on another pack and i think it’s important to note that even with an active balancer fitted, the cells will not be balanced. The cell voltages all being equal outside the knees doesn’t translate to cell voltages being equal at top or bottom..

The reason i am currently using the REC is that it communicates with SMA inverters so allows me to have a combination of DC and AC charging, as well as control taper current for cell temperature or SOC.

Batrium has cell temp sensors, but they measure bleed resistor temp when bypassing so you can’t get cell temps while balancing.

I don’t use individual cell temp monitors- i taper charge current when over 3.5V/cell, and the cells don’t change temp - they are also in a climate controlled enclosure. ( i have a temp sensor in the middle of the pack )

For me - the ability of the BMS to accurately control the charge controller is the most important requirement.

Especially if you are using passive balancing, this needs to be done at low charge current.

Even though the REC has a balancing feature i normally use this at 3.55V so the cells aren’t 100% capacity balanced.

Thanks..
So how do i make sure the cells stay properly balanced ?
I want to make sure the cells last a good long time.. new they are supposed to be 32Kwh These being used are said to be about 27Kwh
supposedly they were only in use for about 3 yrs, I bought the batteries from BHU the 96S module, it came in 3 parts ( 3 different banks )
hood module, tunnel module and a trunk module. I think almost 1,500 pounds total. I tried looking for info on the net about this car, but i can't even find the cars ..lol

I am using a LK (Ji Kong) BMS with my 14S configured LG Chevy Bolts packs. Here is the unit I have.


I have not truly tested it's limits yet, but I have been pulling up to 80 amps out and charging at over 30 amps with no issues. It is a true active balancer. It pulls current from the highest voltage cell and pushes it to the lowest voltage cell. I have the 200 amps rated with 2 amps of balance current. It is fully configurable on the bluetooth app. The range is a bit short, but I only check it occasionally now that I have it configured. It does have a CAN port and RS-485 port, but I have not tried using them yet. Here is a screen shot of my pack.



The two battery temp sensors are on short 12 inch (30 cm) long wires. They are just RTD sensors, so they may be compatible with the BMW ones. Once I find hot spots in my pack, I will extend the leads and relocate them, for now I have one strapped on the positive output connector, and the other just taped to the top battery module.

This is not the seller I bought mine from. Several sellers have them, and the prices are all within about $25. They did not list 300 or 400 amp when I ordered mine, but the specs look about the same.

Thanks, i'll look into that one also..
what did you mean by.. the "range is a bit short" ?

The Bluetooth module is inside of the cast aluminum case. As it came from the factory, my phone would only link up from about 6-10 feet away. Once connected, it would work a little further, but drop the connection easily. I had to open the case anyways, the mounting screw holes were very shallow and I bottom the screws and damaged the tiny threads. So I took the case off, to drill and tap the holes deeper, with the board out of the case. And I saw they just drilled 5 tiny holes near the bluetooth module. On other reviews, they said they drilled out the holes. I drilled the outer 2 and the middle one, big enough that they did break into the other 2 holes. So now it has a bit of a slot by the module. This helped a lot. It now will connect at almost 30 feet, and stay connected out to about 40 feet, even through 2 (thin) walls. Where it is in my garage now, I have it behind a metal plate, so I have to go in my garage to connect, and it will stay working to just back into the house. I hay try drilling away a bit more and also cutting a hole through the mounting plate towards the house. It is not a big deal, I just check it once in a while now, it has been flawless for 3 weeks. As you can see, all the cells were within 0.001 volt. It has not had to push any balance current in over a week. And each day I have pushed my 360 amp hour pack to 98% full and down to 40% again. I am "Time of Use" shifting over 11 KwH's a day. Right now the battery is charging at about 1700 watts. 30 amps at over 56 volts. State of charge is back to 90% now and cell balance is still at 0.004 volts lowest to highest. I am measuring just 0.001 ohm of voltage drop through it at up to 60 amps. The area where the MOS FETs are using the case as a heat sink does get a bit warm, but not hot. I may still add a small CPU cooler just to carry away a little heat. It's only about 10 watts of heat at 100 amps through it, but it is inside my battery cabinet and it get over 100F in my garage.

Here is my battery bank out of the cabinet. The BMS is bolted to the top plate. The extra red wires are for up to 10 more cells. Here the 2 temp sensors are just laying on the top battery module.

Dacflyer said:

But for now I am searching for a good BMS, one with active top and bottom balancing, multi thermal sensor capabilities (I'd like to use the thermal sensors on the battery if i can. )

Click to expand...

Maybe I will be showing some ignorance here, but it is my understanding that its not possible to do both top and bottom balancing, and that all or nearly all commercial BMS' are top balancing.



I'm also not familiar with any active balancing BMS' (though I'm sure some of the high end ones do, and I believe I recently heard of a mid-priced BMS that is supposedly active-balancing), many people misunderstand what active (non-dissipative) cell balancing means, so be sure to double check the manufacturer spec's if you get recommendations for active balancing BMS' here.

edit: I believe the active balancing BMS I referenced is the same one @GXMnow owns.

I won't say that it does true "Bottom Balancing" but it certainly will keep trying to balance the cells down to a fairly low state of charge. You can choose how low of a voltage in the app. I think it can go all the way down to 1.5 volts, so it will even work on LTO cells, or even super caps. I have mine set to quit trying to balance below 3.1 volts. I figure, once it is that low, you need to charge soon, so we should not be pulling power and moving it around. It is not 100% efficient, so it is just going to eat some energy. And when the first cell goes below cutoff, it will shut down the load.

i like that set up.. looks really neat..
My batteries are in aluminum cases, they have little standoffs, so they will get plenty of ventilation.
And my rack for now consist of 2X8 boards and cinder blocks. i have 2 rows right now,, but will add more later on. the rest of the equipment is mounted on a plywood wall. I'll post pictures later on..

I have more pics of my setup posted in my "Show and Tell" blog here. "Adding Storage to my Enphase system"
Here is a wider pic of the battery bank.

I cleaned up all the little balance wires a bit since then. The whole assembly is going in a 3 foot tall steel server rack. It weighs a bit over 200 pounds.

I was tempted by the BMW batteries, but I passed because no one had torn into the packs yet to see what all was inside. I can't say I regret the Bolt packs at all. They are basically new and working great. But knowing what I do now abut those BMW packs, it is a great deal. Seeing the limits of the BMS I am using, you should have no issues using one to manage 2 series strings of 14S. One per string is the "right" way to do it, but at the currents I expect to run, I was not worried about it. Just be careful and fuse the BMS lines that tie between 2 parallel banks. I need to get more 7.5 amp fuses, some of mine are 10's and 15's. With a fuse on each balance lead to each bank, that is 30 fuses for the 14S bank. If it was just on one bank, you probably would not need to fuse it, but with those thin wires, you still should.

GXMnow said:

Just be careful and fuse the BMS lines that tie between 2 parallel banks. I need to get more 7.5 amp fuses, some of mine are 10's and 15's. With a fuse on each balance lead to each bank, that is 30 fuses for the 14S bank. If it was just on one bank, you probably would not need to fuse it, but with those thin wires, you still should.

Click to expand...

Keep in mind that if you use 26AWG wire it self-fuses at 10amps. I use and recommend this for balancing wires, less joins (and components) is always a good thing.

It is important for the BMS to get an accurate read that the resistance of each cell balancing wire is equal. Adding fuses gives an unnecessary opportunity to create a resistance imbalance.

It’s actually one of the most common errors i see - you aren’t alone in thinking you need to fuse those wires.

“active balancing” is keeping the voltages between the knees equal. This doesn’t necessarily translate to capacity balanced cells.

To capacity balance your cells you need to take them to 100% full (or 0%), and have equalised resting voltages at that point.

In practice, this is not possible without decommissioning your pack, so the compromise is to set an arbitrary top voltage (mine is 3.55V), and taper current and equalise voltage at that point. You may only end up with 90% capacity balance, but that is good enough when you cycle your cells from 20-80%.

Hi,

GXMnow said:

I am using a LK (Ji Kong) BMS with my 14S configured LG Chevy Bolts packs. Here is the unit I have.

7.4US $ 26% OFF|1a/2a Active Balance Battery Protection Board Smart Bms 7s ~ 24s 100a 150a 300a Can Rs485 Gps App Lifepo4 Li-ion Lto Jk 16s 20s - Battery Accessories & Charger Accessories - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

This is not the seller I bought mine from. Several sellers have them, and the prices are all within about $25. They did not list 300 or 400 amp when I ordered mine, but the specs look about the same.

Click to expand...

Happy to see someone else has bought one of these. I had done a search, but didn't find any here (doesn't mean there aren't any, just I didn't find them). I only purchased mine yesterday, from a different seller on Aliexpress.

I liked the option to use different number of cells in the bank, as I wanted to use 18 LFP in mine. At least as a test. If it doesn't work out, I can go to 17, or 16, then use the spare/s in a second, later bank.

Other factors are: the balancing current is 2A (bigger is better), and the charge current is the same as the discharge, not limited, as the Ant BMS is, to 50A.

dRdoS7

That is yet another feature f the JK BMS balancer section.

When I first set the pack specs in the app, it did a cycle where it measured all the cells, then pulled and pushed current to each cell and measure the voltage change, and all by itself, it calculated the resistance of all of the balancer leads. I don't know if it will do this from time to time, or if it was a one time thing though.

I seem to remember that the leads from the balancer are #20 or #22, with high temp silicon insulation. I left them all the same length, and just loosely bundled the extra to keep the resistances close. I then spliced to #16 gauge to the individual fuses that lead to each pack. The balancer should never pull more than 2 amps, but the wire and 2 fuses bridging between the 2 packs could pull a bunch of current if something goes wrong. A wire self fusing could burn the insulation. I know the #16 will be able to safely pop the 7.5 amp fuses. But I did run out of the 7.5's and a few are 10's and 15's now, and I made sure they were in matched pairs. My next amazon order will include more 7.5's. Most were assortment packs. I need 30 7.5's.

I agree, if your cells are not matched capacity, keeping the voltage matched is not going to bring them together. Looking at the voltage curve of my NMC cells, there is a very distinct curve that is happening 50.5 volts, and 53.5 volts, and all 14 cells are staying within 0.005 volts as they charge at 30 amps through the curve. From 53.5 all the way to 57.4 the voltage climb is dead linear at 1.3 volts per hour. The Schneider XW-Pro is not letting me pull the pack above 57.4 volts, and I am not seeing any knee in that end, but I am stopping at 4.1 per cell. This is giving me about 85% of full charge. LiFePo4 cells do act different, but if you watch them charge and the voltage knee on all the cells match, you should be pretty confident they are going to hold a good balance. I have never gotten mine all the way to 58.8 (4.2 per cell). From what I have been reading, the higher you run the voltage, the more stress it puts n the cells, so I am fine leaving them under 90%, and most of the time, they are down at about 50%. My system charges them while the sun is over producing, and then uses the power during the evening peak rate time. Then the cells rest until the sun comes up again. I have the 40% or so in case of an overnight power failure, and then I can crank them up to charge faster from the sun the next day. During a power outage, I won't run them as hard or as far down.

dRdoS7 said:

Hi,

Happy to see someone else has bought one of these. I had done a search, but didn't find any here (doesn't mean there aren't any, just I didn't find them). I only purchased mine yesterday, from a different seller on Aliexpress.

7.4US $ 26% OFF|1a/2a Active Balance Battery Protection Board Smart Bms 7s ~ 24s 100a 150a 300a Can Rs485 Gps App Lifepo4 Li-ion Lto Jk 16s 20s - Battery Accessories & Charger Accessories - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

Click to expand...

I believe there are a couple others who have ordered or maybe already received this BMS

I believe the BMS you bought and they bought may be manufactured and sold by a company named HeltecBMS (also known as Heltec Automation and Chengdu Heltec Automation Co Ltd).

Website
Alibaba
Aliexpress

There was one forum post recently started on this brand here, and some discussion of this BMS in this thread as well.

@upnorthandpersonal @Baja1 and maybe @Sojourner may have some experience or impression to share.

Phuuu... This is starting to get overwhelming...
I did a little more searching and thunking.. I have seen where you can buy just a cell balancer, seen a few that can do 5 amps, and i think one showed 8A per cell.. is this over kill ,,and if my inverter / charger and solar charge controller have programmable voltages for charging.. do i really need more than a balancer ?

GXMnow said:

I have more pics of my setup posted in my "Show and Tell" blog here. "Adding Storage to my Enphase system"
Here is a wider pic of the battery bank.
View attachment 21545
I cleaned up all the little balance wires a bit since then. The whole assembly is going in a 3 foot tall steel server rack. It weighs a bit over 200 pounds.

I was tempted by the BMW batteries, but I passed because no one had torn into the packs yet to see what all was inside. I can't say I regret the Bolt packs at all. They are basically new and working great. But knowing what I do now abut those BMW packs, it is a great deal. Seeing the limits of the BMS I am using, you should have no issues using one to manage 2 series strings of 14S. One per string is the "right" way to do it, but at the currents I expect to run, I was not worried about it. Just be careful and fuse the BMS lines that tie between 2 parallel banks. I need to get more 7.5 amp fuses, some of mine are 10's and 15's. With a fuse on each balance lead to each bank, that is 30 fuses for the 14S bank. If it was just on one bank, you probably would not need to fuse it, but with those thin wires, you still should.

Click to expand...

Awsome compaq system you got going there... I'll share a few pictures here soon, and look for some fed back.

Well i just got a reply back from REC. They didn't seem to be of much help.. I told them what i wanted to do,, and this was their reply....


Dear Dacflyer,

We are not familiar with EPEVER and the BMS cannot communicate with this inverter, but anyway you can use it for cell's monitoring.

Best regards,
Maja Pozar Andrejasic

Dacflyer said:

Phuuu... This is starting to get overwhelming...
I did a little more searching and thunking.. I have seen where you can buy just a cell balancer, seen a few that can do 5 amps, and i think one showed 8A per cell.. is this over kill ,,and if my inverter / charger and solar charge controller have programmable voltages for charging.. do i really need more than a balancer ?

Click to expand...

The BMS part is more important than the balancer. If the cells go out of balance, it is not a big deal, unless a cell starts to go too low or too high. If the charger and inverter settings as well as the balancer can keeps all of the cells in range, yes it can work, but that is too many if's. The main job of a BMS is to disconnect the battery if anything is causing a cell to exceed it limits. Having a good balancer is an additional function.

I almost went with a Daly BMS for the safety part, but then I wanted to add an active balancer for more current as the Daly only did 30 ma of balance current. Their new high power ones are up to 200 ma. But keep in mind, it can pull that 30 or 200 ma from any cells that are above the target voltage. The JK one only pulls from one cell at a time. If you have 4 high cells, it will have to keep switching between them. So it would only be able to pull about 1/8 of the time on any one cell. 1/2 the time is pulling from high cells, the other half of the time is pushing to low cells. So in reality, this could be as low as 1/8 of 2 amps or 250 ma average if it is pulling down 4 high cells. So the higher power Daly units are not that far behind. But the Daly just turns the higher voltage energy into wasted heat, the JK takes that power and pushes about 85% (maybe more) back into the lowest cell. So this can bring up low cells, where passive can only bring down high ones. I liked the idea of using the power and not making more heat.

I intentionally pulled 4 of my cells down about 30 mv, and then watched the balancer do it's job. The App shows the high and low cell by color and shows how much current it is pulling or pushing as it moves the energy around. It only took a few minutes for it to get all the cells back within 5 mv again. Since the high cells were all very close, it would switch around a pull a little from each one, and then switch and push to each of the low ones. If your cells are very well matched, you don't really need much balance current, but I figured at 360 amp hours of battery, I wanted some more current to try and move them at all. If you are using used cells, you probably need more balance power. As it turns out, my basically new cells are hardly using any balancing, but it is there if needed. As the cells age, it may need more intervention to keep them balanced.

Dacflyer said:

Phuuu... This is starting to get overwhelming...
I did a little more searching and thunking.. I have seen where you can buy just a cell balancer, seen a few that can do 5 amps, and i think one showed 8A per cell.. is this over kill ,,and if my inverter / charger and solar charge controller have programmable voltages for charging.. do i really need more than a balancer ?

Click to expand...

You need a BMS, not necessarily a 'balancer' specifically, but the cell level protection that a BMS provides is important. Especially consider that (1) you are using used cells (2) you are using non LFP cells (I think), and (3) if you don't buy a BMS you are the BMS, and if just selecting a BMS is overwhelming I suspect this would be more overwhelming.

I feel your pain though about it being an overwhelming and complicated topic, especially with some of the more high end BMS' with extensive customizability and featuresets.