Please Help Me Choose a BMS

[kenryan]

I am about to pull the trigger on 8 X 280 AH cells to make a 24 volt battery. I will be connecting this battery to a Magnum MS4024-PAE which has a continuous power output rating of 4000 WA. I would not expect to run the inverter at maximum very often, if ever. So I guess 150 amp BMS would be the minimum, but 200 amp might be better.

I would like suggestions on specific BMS that knowledgeable forum members would recommend for my application, along with the best place to buy it.

Thanks!

 

[Samsonite801]

You sure 150a is sufficient? It should say in the manual for the Magnum what you need to size the DC load for.

For example, I have an MS2812 (2800w @ 12v) and in my manual it shows the following:




Here's one I just pulled up on yours:

 

[kenryan]

Thanks @Samsonite801 So you think I need 250 or even 300 amp BMS? What do others think? I'm new at this battery building stuff. Seems these LiFePO batteries are usually rated 1C discharge, right? Maybe that is what I should be using to pick my BMS???

 

[Samsonite801]

Sure no prob all all...

What application is it for? (mobile or stationary)

Does physical size of bank matter, like space constraints?

Will it run at freezing temperatures in the Winter?

 

[time2roll]

I would be at 250 for the BMS and fuse if you will ever use max power.

 

[Tecnodave]

I have a MagnaSine MS4024AE, and i confirm it can push 250 amps under load, 2 X 2/0 or 1 strand 4/0 and 300 amp fuse is recommended by Magnum Energy. the AE model is the forerunner of the PAE series, same core inverter, more features.

The Magnum will not have a problem with freezing, I do not think it is wise to let LFP batteries get that cold.

 

[Samsonite801]

The Magnum will not have a problem with freezing, I do not think it is wise to let LFP batteries get that cold.

I was mainly asking about if he freezes because it may help him in whether he ought to find a BMS which disables charging at freezing (low temp cutoff), to protect the batteries...

 

[Tecnodave]

I was mainly asking about if he freezes because it may help him in whether he ought to find a BMS which disables charging at freezing (low temp cutoff), to protect the batteries...

@Samsonite801 ,

I understood that, sometimes it is not clearly understood by newcomers to technology.

 

[kenryan]

Sure no prob all all...

What application is it for? (mobile or stationary)

Does physical size of bank matter, like space constraints?

Will it run at freezing temperatures in the Winter?

Mobile. It will be mounted in a Ford Transit conversion van. It will both serve the van and serve as emergency backup power for my house.

Physical size, seems like that "is what it is."

I live in Alaska. Cold weather protection if vital.

 

[Steve_S]

Deep Northern Ontario here... 24V System with Samlex EVO-4024 Inverter/Charger.
I run a bank with 2x280+2x175 and my final 280AH is just being completed for a total of 1190AH/30.4kWh.
System is wired to handle 300A+. BMS' & DCC Solid State Contactors etc are all rated to 300A.
Fuses & Main Breaker are 250A. Note I use a Midnite Solar E-Panel alongside of my Midnite Classic-200 Solar Controller.

Its always best to look at the maximums, not because you will be pulling that constantly but because the system can get there and even over it with Surge Loads. To be perfectly straight forward about it... How would you feel at 01:00 hrs you turn on something in your grogginess and blow a use/breaker and having to futs with it when it's -30 outside.... To me, that generates a LOT of Blue-Air ;-)

As such, When I upgraded from a 3000W Inverter/Charger to 4000W / 12,000W surge handling) I upgraded to Royal Excelene 4/0 as my wire runs are also 14' from battery pack(s) to DCBus Bars to Inverter and even with that when I pull 250A or push 150A the wires warm up a bit. Let me just say this simply, you ONLY want to buy that wire ONCE - it's ridiculously expensive and only getting more costly. There are some things that you should only ever have to buy ONCE and Batt Wires are one of those.

NOTE: Royal Excelene by Southwire is very fine strand pure copper Welding Wire, it's tough, flexible and outperforms many other cables because of the super fine copper. Somethings are like a Foundation to a House, it has to be right because everything totally depends on it and going overspec on this is more often the wisest thing to do. Largely because tomorrow will bring changes and we never know what but it is usually upgrades.

Royal Excelene table: Look at the strand count then compare with others. suggest being seated when doing so.


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[kenryan]

Thanks @Steve_S

Do you have a specific BMS recommendation, and where to source it?

 

[Tecnodave]

kenran,

LFP Batteries are not tolerant of being charged at the temperatures which you have there. They can be damaged by charging frozen. Others can tell you more than i can about LFP, but i can certainly tell you about surviving in Alasks....born in Matanauska-Susitna, Territory of Alaska.......Sourdough they call it.........

 

[kenryan]

kenran,

LFP Batteries are not tolerant of being charged at the temperatures which you have there. They can be damaged by charging frozen. Others can tell you more than i can about LFP, but i can certainly tell you about surviving in Alasks....born in Matanauska-Susitna, Territory of Alaska.......Sourdough they call it.........

Right, that's why I will use a BMS that has low temperature charge protection.

 

[Steve_S]

Thanks @Steve_S

Do you have a specific BMS recommendation, and where to source it?

I stopped recommending BMS' because when someone bought one, messed up, they'd blame me for suggesting it to them. Sadly, too many folks have zilch ideas about fine electronics, static electricity and common sense. Or worse having the BMS harness connected to the BMS when they are attaching the leads to cells (75% chance of Smoking the BMS). RTFM is not in those peoples vocabulary, they are "Instant Rice Society " folks.

I myself use Chargery BMS8T-300A with Chargery SolidState 300A DCC (Contactors) which were designed and built from our user input here.
This is a Relay/Contactor controlling BMS NOT FET Based board. Being in the deep north and subject to -35C/-31F I had to have Cold Temp cutoff, which Chargery reprogrammed their BMS' to handle it for us. One of the Very Rare Few who interact with clients, listens & HEARS what is wanted & needed. (and to think some hostile morons shooed him out of here because "they" had issues, so he only pops in rarely now). not one did RTFM, or they used selecting reading and skipped things making assumptions. Will being one of them who decided to calibrate the shunt when not needed failed to follow the instruction, got frustrated and slammed the company & product in his Videos, he also used the old Chinglish Manual instead of my rewritten English one, which I will not do again).

The GOTCHA's: FET Based BMS' are only now starting to reach 200-250A and they MUST be derated by 20% because the specs are to the "edge capacity" and it is never good to push them that far. When they fail it is fugly. Relay/Contactor system with N.O. (Normally Open) Relays or Contactors if they fail, they won't stay ON (safer). That being said, the higher end FET BMS' are pretty good now, compared to a year ago when they were extremely rare.

DIY Gotcha. Because we DIY we have to use more "generic" BMS' because they have to be flexible & adjustable to various use cases. Unlike EV's or Tesla Powerwalls and such which have very specialized BMS' specific to the application, we get to deal with Compromises ! That means there is "no perfect solution" and always certain quirks, foibles will be apparent. Does not matter if it a $100 cheapo BMS of a $1000 Orion Setup, generic = compromises.

BMS' used by folks here are DALY (I do not like them AT ALL), JBD/Overkill also rebranded by many, HelTec, QUCC, TinyBMS, RECbms, OrionBMS going from cheaper to ludicrousness.

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NOTE: BMS with Balancing !
Passive Balancing is intended only for Matched, Batched & Binned cells and for Low Capacity cells 50AH or less. It only burns off High Voltage from cells.
Active Balancing transfers High Voltage to Low Voltage cells and they come from 1A to 10A transfer capabilities. Higher the amperage capability = more $$$$

Even though I have Chargery with Passive Balancing @ 1.2A it is not enough. They are finalizing their new P series with Active Balancing. In my case, I have a QNBBM-8S Active Balancer on every pack, even the newest one with Fully Matched & Batched cells.

For more info, details & docs/resources, please follow the links in my signature. "About my System" may also help with seeing how that is done and there is even more REF info in there too.

Hope it helps, Good Luck

 

[gmbeihl]

Will the Chargery P series active balancing current will be more than 1.2A then?

 

[kenryan]

Being in the deep north and subject to -35C/-31F I had to have Cold Temp cutoff, which Chargery reprogrammed their BMS' to handle it for us.

Did they add another temperature probe, or were they just able to "reprogram" it for you. I'm curious, if it is just a matter of reprogramming, why didn't they do that in the first place, and why wouldn't they be doing it now to all every BMS?

 

[Steve_S]

Believe it or not, over a year ago there were VERY FEW that had Cold Temp cutoff. There is a long dormant thread about it going back to when this forum opened. Many still do not ! The Chargery's was designed for LEVs originally hence the Relay/Contactors. NO EV uses anything else, it is Relays & Contactors where appropriate simply due to the loads handled. Chargery has dual temp probes anyways. Jason issued new firmware and it's now up to 4.05 each addressing issues we raised.

The new P Series coming is quite a step up but I cannot provide much info other than more capable, better communications interfaces CanBus, RS232/485 etc Active Balancing and more... The software is being done now, hardware testing is pretty much done and production ready. Chip shortages messed up things and pushed dates to heck.

 

[Samsonite801]

Mobile. It will be mounted in a Ford Transit conversion van. It will both serve the van and serve as emergency backup power for my house.

Physical size, seems like that "is what it is."

I live in Alaska. Cold weather protection if vital.

The reason I asked about mobile, is I would recommend clamping the cells so they aren't subject to movement while driving (putting more stress on the bus bars). Most cells come with flexible bus bars now too, which helps with movement. You want the cells to stay tight, and don't want stress around the bus bar bolt bosses.

Physical size question, had to do with the possibility of using twice as many cells to build 2 packs of smaller Ah, so you could potentially use 2x 8s BMS and run them in parallel packs. But mobile application usually doesn't have sufficient space for this anyways.

Since you live in Alaska and require cold weather protection, the freezing temp cutoff is a good safety to have for protecting your batteries, but I would also recommend following the people here who use heat pads under a plate (with thermostatic switch controller) to keep the cells warm, so you can still charge when the cells would normally get too cold.

I have heard good things about the Chargery BMSs and external relay, I had considered them, but already had a pair of 200a BMS I purchased prior, back when I didn't know what I was getting. In my case my BMSs were unmanaged, so I bought some JK-BMS active balancers to work with my setup to add bluetooth voltage monitoring (to salvage a bad buying decision).

If I were doing mine again from scratch, I would likely use Chargery, especially if they are coming out with a model soon to support active balancing. I have never had a chance to play with them though before, so I have no real idea about them (would read some other threads here about people's experiences using Chargery). Sounds like Steve_S is a good resource, but as he said, don't hold him responsible on the purchase. Do your diligence of course.

 

[Samsonite801]

HRTKD 'Jim' installed heat pads, and here is some info and pics:

LiFePO4 Battery Warmer Install

This is my install of a custom set of battery warmers from Ultra Heat. I had contacted them through email asking about a warming profile for LiFePO4 batteries. They responded with a design to my specifications, including warming pads that fit my batteries exactly. While I initiated the...

diysolarforum.com

I have some heat pads I bought for mine, but I don't have them all installed yet... Jim has been using his, so he has actual experience with making it work in his RV.

Notice also, how he has his cells clamped. People have used wood or aluminum to clamp cells with. I used aluminum on mine so it has an aluminum floor plate for the heat pad which can help transfer heat below the cells.

 

[kenryan]

Ordered a 300 amp Daly from Amazon. Fingers crossed.