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Batrium BMS setup 8s3p

Jan Gils

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I'm building a new battery bank with 28 EVE 280Ah cells, and I'm wondering wether the following setup is valid. At 0.5C the battery pack can continuously handle about 400A, but in reality I will only use 200A (0.25C). Everything is designed on 400amps though. The system is 24V.

Schematic 8s3p Batrium.png


The Batrium Watchmon 4 will monitor and actively balance all 28 cells. The BMS will also control both Victron chargers, but as a fail safe it also can close the Gigavac contactor (rated 400A).

Is this setup valid, or am I missing something?
  • Is it safe to use a common contactor for the parallel batteries?
  • Should I add a MEGA fuse to limit the current to 400A (or just use 1C as max current = 840A)? Or add fuses on each of the 3 batteries to avoid high currents between the packs in case a cell short circuits?
  • Do I need protection for inrush currents on the contactor and how to do this?
 
Last edited:
I'm building a new battery bank with 28 EVE 280Ah cells, and I'm wondering whether the following setup is valid. At 0.5C the battery pack can continuously handle about 400A, but in reality I will only use 200A (0.25C). Everything is designed on 400amps though. The system is 24V.
Seems like a sensible approach
  • Is it safe to use a common contactor for the parallel batteries?
Not sure. Your design is pretty unique (one BMS for multiple battery packs) compared to what I am used to seeing (one BMS per pack). I'm curious to see how your system develops.
  • Should I add a MEGA fuse to limit the current to 400A (or just use 1C as max current = 840A)? Or add fuses on each of the 3 batteries to avoid high currents between the packs in case a cell short circuits?
My understanding (I'm no expert) is that each pack should be fused with a fuse of a suitable size and type. I understand suitable size to mean large enough not to trip in any normal situation but small enough to offer catastrophic protection. I understand suitable type to mean a fuse capable of interrupting the high current that a battery, specifically a lithium battery, could produce. Class T being the best choice, with MRBF and/or ANL being other viable fuse types.
  • Do I need protection for inrush currents on the contactor and how to do this?
Not sure.
 
Not sure. Your design is pretty unique (one BMS for multiple battery packs) compared to what I am used to seeing (one BMS per pack). I'm curious to see how your system develops.

The idea of having 3 separate 8s batteries is portability and weight: the whole setup will be mounted in a sailboat. The design I'm trying to build is a hybrid between drop-ins and fully integrated systems (like Victron uses).

By using a decentralised Batrium Watchmon 4 BMS, it will monitor all cells and have it's own protection by means of a contactor (drop-in style), but also communicate to the chargers (integrated system style).

I'm only not sure on possible pitfalls by using the 8s3p setup. When I use a 3p8s setup, I loose monitoring of the individual cells and I have to mount everything on board instead of up front due to the weight.

I talked to REC-BMS on how they would do this system and they advised using 4 BMS's (1 master that talks to Victron through CANBUS and 3 slave BMS's on each battery pack). It seemed a lot of money for something 1 decentralised Batrium possible could do.
 
Yes i would use a suitable fuse on each bank.
Use the Batrium to activate a precharge circuit along with the contactor (can use the REC precharge unit). If you don’t limit inrush current it’s likely the contactor will weld itself closed.
Unless i missed the announcement, the Batrium doesn’t actively balance your cells.

You seem pretty well on top of things, that should be a great system!
 
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That battery pack configuration will work well (watch your (+) & (-) wire lengths.
I would put a 200A Fuse on EACH PACK ! (I really came to love MRBF fuses from Bussman).
The Batrium system in this decentralized setup is perfect, you are getting what you paid for !

These 280AH Commodity cells WILL diverge and present increasing differentials as they cycle up & down, these will be most notable at the bottom & top of the SOC chart. Now, if you are being conservative and only using 80% total capacity (10% from bottom & from the top) the pack capacity is 224AH at 80% usage, you would most likely not see huge differentials. I will point out, however, that 1mv per AH is not unusual, so on the 280AH cells you can see 280mv differential between cells. Remember, these are NOT Matched, Batched & Binned according to their Voltage & IR values through cycles... Matching & Batching cells is a long costly process that can add up to $50 per cell cost for doing so.

Bottom & Top Balancing can level the cells and get them to a common full state prior to installation which will make maintaining their state easier for your hardware.

Active Balancing is being used on these larger cells as passive (dissipative) is quite slow and really pointless unless you start off without perfectly matched & batched cells. Active Balancers DO NOT FIX ANYTHING but come in handy when you have slightly mismatched cells that vary and this can compensate / correct for the low cells to hi cells. It is an ADD-ON Device that works in-line with the BMS but outside of the BMS controls. I am unsure how Batrium BMS will cope with an Active Balancer but it should not be a problem. With BMS' that have Passive Balancing, that has to be disabled when using an external Active Balancer otherwise things get terribly confused.

Reference info for you:

BU-803a: Cell Matching and Balancing – Battery University

Pre-Balancing Cells | Orion Li-Ion Battery Management System

Hope it helps, Good Luck
Steve
 
I would expect the cells to drift a little as you said, based on the difference of the IR and the error on the voltage measurements of the Batrium cell monitors. This is typical +/- 0.05V and max +/- 0.1V as per spec sheet. This accuracy seems poor for such an expensive system, although calibration is possible. Then again I'm not planning on running the system on the edge.

I updated the schematic with a pre-charge unit from REC:

Schematic battery bank.png

Any more comments? I will be measuring the amps going through each battery pack and check wether there is an equal split. The cable lengths used to connect the 8S batteries will be equal.
 

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  • Schematic battery bank.pdf
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This is very similar to the setup I am sketching on, so highly interesting!

I'm looking at a 3-phase setup with 3 pcs of Victron Multiplus II (MP2) 5000/70. Connected to batteries in 16s3p, so 48V.
Max charge capacity of one MP2 5000 is 70A, and discharge capable of 4000W AC continuous. I saw someone using a formula with adding 15% loss to count amp load on the batteries, don't know if that is correct? In my case then 4000*1.15*3/51.2 ~ 270A could be the continuous load going to the three battery banks. Should be well within the recommended load, <0.5C.

I'm looking at the Batrium BMS with 48 pcs of Blockmon-8. Expensive yes, but I like the added safety and of course the native canbus communication with the MP2s. I am looking at fusing the batteries with 200A terminal fuses. Was not planning on buying the Batrium expansion board, and for shunt I am leaning towards the larger 1000A model.

For the added safety of allowing the BMS to cut off the batteries from the inverters I was initially looking at the Schneider circuit breaker that Batrium recommends, but it is only 125A. Then I found the ZJ Beny circuit breakers and saw that several people use them in combination with Batrium. With my loads described above, I would be looking at the BD-400 model. It can be equipped with a remote trip option that enables the Batrium BMS to trip it.
What are the pros and cons of using a Gigavac contactor vs a circuit breaker with a remote trip?
 
Was not planning on buying the Batrium expansion board, and for shunt I am leaning towards the larger 1000A model.
I talked to Batrium and they recommend the expansion board for the SSR and normal relays. Because the installation is on a sailboat and we're planning on going round the world, I just buy the expansion board and several spare blockmons to be able to solve issues or in case I want to sound a buzzer on a critical failure. It's just more flexible to extend the system. Maybe add a raspberry pi / arduino and implement a logger to have a history of the bank, etc...

For the added safety of allowing the BMS to cut off the batteries from the inverters I was initially looking at the Schneider circuit breaker that Batrium recommends, but it is only 125A. Then I found the ZJ Beny circuit breakers and saw that several people use them in combination with Batrium. With my loads described above, I would be looking at the BD-400 model. It can be equipped with a remote trip option that enables the Batrium BMS to trip it.
What are the pros and cons of using a Gigavac contactor vs a circuit breaker with a remote trip?
Same here, I live in Belgium so Scheider or GE is what I normally would use, but the amperages are too low. These breakers are meant for 240V systems. Thanks for the info on the ZJ Beny, I'll look into this.

I'm no specialist, so I wouldn't know what's best. My considerations would be: inrush current, temperature and coil power usage.

Some people are leaving the contactors out, but I would like to have something in place just as a local emergency disconnect in case the canbus fails.
https://diysolarforum.com/threads/contactor-ssr-or-rely-on-batrium-and-victron-communication.4727/
 
I'm building a new battery bank with 28 EVE 280Ah cells, and I'm wondering wether the following setup is valid. At 0.5C the battery pack can continuously handle about 400A, but in reality I will only use 200A (0.25C). Everything is designed on 400amps though. The system is 24V.

View attachment 25977


The Batrium Watchmon 4 will monitor and actively balance all 28 cells. The BMS will also control both Victron chargers, but as a fail safe it also can close the Gigavac contactor (rated 400A).

Is this setup valid, or am I missing something?
  • Is it safe to use a common contactor for the parallel batteries?
  • Should I add a MEGA fuse to limit the current to 400A (or just use 1C as max current = 840A)? Or add fuses on each of the 3 batteries to avoid high currents between the packs in case a cell short circuits?
  • Do I need protection for inrush currents on the contactor and how to do this?
Wow, Something new to checkout: Wondering: Does the Watchman 4 have some computer or LCD integration option to see what is going on with all individual cell voltage readings? If so, I will be looking closer, and wondering about the cost :+)
 
Yes, you can connect the Batrium to a LAN and access it from everywhere, or access it directly through it's own WIFI, or even through USB. See also here.

The software allows for cell monitoring and parameter adjustment:


...
 
A couple of thoughts: (I have a Watchmon4 on order - so I have researched it a bit, but have not installed it yet).

You may want to enable the cooling and put a couple of small fans blowing over the Blockmon's and also to vent heat out of the compartment. Probably use one of the other relays.

Also, if you go critical and the Watchmon kills power to the contractor, that will kill power to the watchmon4. you will need procedures to restart - (probably usb power).

The power leads going to the Watchmon4 - I have seen a couple of diagrams that had 3A fuses on both the positive & negative lines. Don't know if this is necessary if the watchmon is not powering the contractor directly on its board.

With all the 3A fuses everywhere I will be using a "6-Way Mini Blade Fuse Block W/Negative Bus" from Amazon - keep them all in the same place.

I would add four 400A Class T fuses. One just in front of the Contractor, One each on every battery.

I would also use a Victron Lynx Power In to connect the three batteries together. that way it is easier to disconnect one. But with the Batrium connections on the batteries - it will take some shuffling around and changing in the software to disconnect one battery.

I do like your setup - so each cell has its own Blockmon on it.

Good Luck
 
Batrium is a Quality product family BUT you want to be careful making selections. There are a few options & choices to consider. If you are dealing with 1-4 battery packs in a bank or 5-10 packs (think longer term if there is a possibility you will want to expand) then you may want to look at options which support a decentralized model that can interact directly with Inverter/Solar system on behalf of the entire battery bank.

Now to chuck a Spanner into the Works... Ahh the Sabot into the machinery....

The Commodity Cells, EVE, Lyshen, CATL etc... appreciate the fact that they are NOT matched & Batched according to voltage & IR. Above 3.4V and below 3.1V they WILL diverge and they do. That can be as much as 1mv per AH capacity per cell. So 280mv for a 280AH cell. This is USUAL & EXPECTED ! You do not get matched cells for $80 a pop... Matching Batching & Binning can add %50 per cell cost. ANY BMS will monitor the cells for LVD & HVD (Lo/Hi volt cutoff) the moment the First cell reaches cutoff point (say 3.0V for Lo & 3.55V for Hi) the BMS will trip to safety mode, cutting off either charge or discharge, regardless of what the others cells voltages are within the battery pack. Most BMS' will pulse test (simplest way to put it) to see if discharge or charge is on the line and will enable if Charge power is there (for lo) or if discharge is not demanded. It's just a quick flip on/off. Chargers do NOT like that and Generators even less, they can trip into safety mode too, if Amps start jumping around. (Inverter Generators mostly).

Above 3.5V there is only 5AH of actual energy potential. Charge LFP to 3.65 and within an hour they'll settle to 3.50-3.55V anyways. This is normal for LFP, they NEVER sit at 3.65. 3.0V is the end of the long narrow power curve, once 3.0V is hit, the discharge will happen very fast, quite literally it's a cliff drop.

See links in my signature for an LFP Voltage Table & Power curves.
 
I would expect the cells to drift a little as you said, based on the difference of the IR and the error on the voltage measurements of the Batrium cell monitors. This is typical +/- 0.05V and max +/- 0.1V as per spec sheet. This accuracy seems poor for such an expensive system, although calibration is possible. Then again I'm not planning on running the system on the edge.

I updated the schematic with a pre-charge unit from REC:

View attachment 26055

Any more comments? I will be measuring the amps going through each battery pack and check wether there is an equal split. The cable lengths used to connect the 8S batteries will be equal.
Any Links to Sales and Prices would also be Interesting :+)
 
Watchmon4 + 14 blockmons + 500A shunt : 766USD

Gigavac GV200MA: 123USD

REC Pre-charge unit: 50USD

T-fuse holder: 3 x 45 USD

T-fuses 225A: 3 x 45 USD

Total: 1200USD

Prices are based on EU shops, often it's cheaper in the US.
 
The Commodity Cells, EVE, Lyshen, CATL etc... appreciate the fact that they are NOT matched & Batched according to voltage & IR. Above 3.4V and below 3.1V they WILL diverge and they do. That can be as much as 1mv per AH capacity per cell. So 280mv for a 280AH cell. This is USUAL & EXPECTED ! You do not get matched cells for $80 a pop... Matching Batching & Binning can add %50 per cell cost. ANY BMS will monitor the cells for LVD & HVD (Lo/Hi volt cutoff) the moment the First cell reaches cutoff point (say 3.0V for Lo & 3.55V for Hi) the BMS will trip to safety mode, cutting off either charge or discharge, regardless of what the others cells voltages are within the battery pack. Most BMS' will pulse test (simplest way to put it) to see if discharge or charge is on the line and will enable if Charge power is there (for lo) or if discharge is not demanded. It's just a quick flip on/off.
That is a great summary of an important issues about using these cells. It has influenced my future strategy with regard to the use of BMSs and pack construction. Currently I have a 2P16S pack with an expensive Orion BMS. I have always preferred a single pack with multiple paralleled cells and a single BMS during the past six years of messing around with these systems. In the past I was just using them for load shifting so I got by with used packs and did not need much capacity. That has changed due to the frequency of power outages at my current location. In addition, rate changes are beginning to favor self consumption.

For my next upgrade I am considering multiple 48 volt packs each with a separate BMS. I am intrigued with the decentralized model that Batrium has developed. The only other one I have seen that may be able to do this is Electromotus (EMUS). I am assuming they will work with 3 or more separate packs in parrallel. I am checking that assumption. I have to evaluate the cost of these versus the cost of 3 or 4 units like the Chargery.

I have six months or more to figure this out so it is a work in progress. The decision may also turn on whether I can find an cost effective way to communicate with my Outback Skybox. I am beginning that dialogue with Outback. If that is successful then I might keep my existing Orion BMS.
 
Well at four LFP packs in a bank and my Thrash & Bash, I've realized the limits of an individual BMS and inter-operability with inverter and the SCC. Fortunately the Midnite SCC is not hard to cope with, the Samlex EVO has the smarts to control it a few ways from relay signals to other. I'm working around it with a Raspi taking info and doing something to communicate or trigger relays, pending on device.

I'm not familiar with the Outback skybox, if it has CanBus or ModBus interface there is a likelihood of utilizing advanced BMS'. Alternately using a 3rd party outside agent like I'm doing with a Raspi & software controls.

Now, Another Sabot into the works, damn, running out of clogs, snow boots next ! no dang it, it's winter, ok, sandals & runners !
I know you probably looked at Tiny BMS and REC along with a few others in your quest...

Here is another to Ponder Upon.
Check out the HS-015 & HS-017 for starters.
LOOK CLOSELY at the details...
I've heard very nice things about these...
PCM,BMS,PCB for li-ion,li-polymer,LiFePO4-BesTech Power Co., Ltd

One vendor I know selling these...
LiFePO4, LiFePO4 direct from Dongguan LiTech Power Co., Limited in CN (alibaba.com)
 
For my next upgrade I am considering multiple 48 volt packs each with a separate BMS. I am intrigued with the decentralized model that Batrium has developed. The only other one I have seen that may be able to do this is Electromotus (EMUS). I am assuming they will work with 3 or more separate packs in parrallel. I am checking that assumption. I have to evaluate the cost of these versus the cost of 3 or 4 units like the Chargery.
My application is a sailboat. For me it's essential to be able to communicate with my Victron equipment on board. If you go the route of multiple parallel packs with each a separate BMS, communication is an issue. I talked to REC BMS on this topic, and they said you need a BMS for each pack + on top of that another BMS that will act as master.

For my application, this is way I eventually choose Batrium with the decentralised approach. This way there is just 1 BMS talking on the Canbus to my chargers.

The Commodity Cells, EVE, Lyshen, CATL etc... appreciate the fact that they are NOT matched & Batched according to voltage & IR. Above 3.4V and below 3.1V they WILL diverge and they do. That can be as much as 1mv per AH capacity per cell. So 280mv for a 280AH cell. This is USUAL & EXPECTED ! You do not get matched cells for $80 a pop... Matching Batching & Binning can add %50 per cell cost. ANY BMS will monitor the cells for LVD & HVD (Lo/Hi volt cutoff) the moment the First cell reaches cutoff point (say 3.0V for Lo & 3.55V for Hi) the BMS will trip to safety mode, cutting off either charge or discharge, regardless of what the others cells voltages are within the battery pack. Most BMS' will pulse test (simplest way to put it) to see if discharge or charge is on the line and will enable if Charge power is there (for lo) or if discharge is not demanded. It's just a quick flip on/off. Chargers do NOT like that and Generators even less, they can trip into safety mode too, if Amps start jumping around. (Inverter Generators mostly).

Steve, you're absolutely right. For my use case (again sailboat) I'm limited in space (existing battery box) and have only 2 real options:
  1. Custom build a battery (24 EVE 280Ah cells in 8s3p + Batrium monitoring). Batteries : 2000USD, BMS: 1500USD -> 3500USD for a total of 840Ah. Because the cells are not balanced, I can only use them between 20-90% or 590Ah usable energy. The total cost is 5,9 USD/Ah ( 3500USD/590Ah)
  2. Buy Battleborn batteries, but due to their dimension I can only fit 8. This gives me 400Ah (they are balanced so let's say 100% usage) for a total cost of 7200USD (900USD/piece). Cost is 18 USD/Ah (7200USD/400Ah).
The cost difference is huge and I can even be more conservative on the range in which I'll use the EVE cells. On top of that I have a battery system that communicates with my chargers (unlike the Battleborn dropins) and doesn't use mosfets to cut power (like all the popular chinese BMS systems), but a decent industrial contactor rated to 20kA. All the additional cell monitoring is just an added bonus.
 
I'm not familiar with the Outback skybox, if it has CanBus or ModBus interface there is a likelihood of utilizing advanced BMS'.
Yes the Skybox has CANBUS and it has been implemented with batteries like SimpliPhi and LG Chem. The Orion CANBUS documentation is very good. My project is to get something workable out of Outback. Even if I do, I think I may have to use some kind of intermediary device to translate.
 
Watchmon4 + 14 blockmons + 500A shunt : 766USD

Gigavac GV200MA: 123USD

REC Pre-charge unit: 50USD

T-fuse holder: 3 x 45 USD

T-fuses 225A: 3 x 45 USD

Total: 1200USD

Prices are based on EU shops, often it's cheaper in the US.
Like Knowing about options, even if I will most likely stick to lower cost options. Look like some veery nice equipment (at an initial glance). Appreciate the links and info ... Thanks :+)
 
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