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BMS comparison for a newbie ?

grobalt

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Jan 19, 2022
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Hi Guys,

first i have to thank you for this great forum and the chance to collect experience for Alibaba sellers. Most likely i will order in the next days 80x 280AH cells from Docan as the 2nd prefered option is sold out.

I am from Germany, 41 years old with a power price of 35 cent and 10 kwp photovoltaic on the roof connected to a solarmax 10 inverter.

32 of these batteries should go into 2 batteries, the remaining are for 2 friends. So i am digging into battery charger/inverter, bms and it is not that easy. I'm very good at computer, but no programmer. I can solder, so some diy pcb can be finalized etc. I dont want the best solution if the price is as usual twice of the 2nd best:) 98% is good enough. I see many are using Victron Multiplus 2 and the 5000 model would be powerful enough for me as well. What is the benefit of a BMS talking to the battery [inverter] beside an offline BMS and a BMV700 ? I tried to find a comparison of BMS but i was not succesful. There are 10+ BMS for 48V batteries from a few Euro to nearly 1000.

Is there an overview about that topic ?

Thanks a lot
Patrick
 
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What is the benefit of a BMS talking to the battery beside an offline BMS and a BMV700 ?
I'm not sure I understand what you mean about a BMS talking to the battery? Do you mean a BMS communicating with external devices (such as inverters & chargers)?

I tried to find a comparison of BMS but i was not succesful.
There are 10+ BMS for 48V batteries from a few Euro to nearly 1000.
Is there an overview about that topic ?
Its a pretty complicated and very fluid/evolving area. I am not aware of any good comprehensives comparisons/overviews. Some of the higher end manufacturers publish basic comparisons against their competitors, but of course, those are at least as much marketing as they are technical comparisons.

In the past a few of us on the forum tried to create a spreadsheet for comparing popular budget BMS's but it was a lot of work to keep up to date and accurate. I don't think its been updated in over a year (and a lot has changed since then) and I've lost the link.

I think if you are looking for a higher end more feature rich BMS, your best bets are to either (1) devote a considerable amount of time/research/learning to doing your own research, learning what features matter to you, and comparing (and hopefully documenting/sharing that research here) OR (2) find a seller/vendor/system builder/consultant that has in depth knowledge of the field and can give individualized advice.
 
You are struggling with the same issues I had a couple of years ago. I have spent some time researching.
BMS systems generally fall into 2 categories. All-In-One or BMS micro controllers that monitor only but control the current using external devices.

The parameters of importance with Li type cells: Individual cell voltage monitoring with high/low cut out limits, Charging & Discharging current with high cut out limits, cell temperature with high/low cut out limits. Some BMS brands include Passive cell balancing but due to the heat generated its very low current. In larger battery systems it may be necessary to include an Active cell balancer that can provide 2-5Amps or more. This would be a separate device in most cases. Although I believe JK BMS does have a product that combines both as well as stand-alone active balancers that could be added to almost any BMS.

All-In-One BMS systems (Daley for example) have all the components assembled into a single package or single circuit board. ALL of the current passes through the BMS and is controlled by FET's on the PCB which on larger systems can create a lot of heat. This may be desirable in cold climates but not so much in hot areas like Arizona. As such the current and State of Charge is also monitored directly from the PCB. Of course the individual cell voltage wires and temp probes plug into the BMS as well. This offers some convenience but the heat loss at the FET's is just wasted energy.

Modular BMS systems like Batrium or ZEVA separate the micro controller electronics/PCB from the current carrying devices such that an external shunt and magnetic solenoid or contactor controlled by a relay on the BMS are used to monitor and control the current. The magnetic contactor and shunt do generate some heat but not as much as the FET's and the heat does is not directly on the PCB. I chose this type of BMS and subsequently have developed a couple of solutions to the wasted energy from the Always Energized golf cart type contactor. Specifically control boards that allow the use of either a remote trip breaker or latching type contactor which would replace the golf cart contactor.

Victron offers a fairly comprehensive product line but everything has to be purchased separately and adds up fast. QUCC has a kind of hybrid BMS that has the convenience of All-In_One but integrates a contactor instead of FET's for current control. Of course the contactor uses about 250mA all the time.

Overall the products available to the DIY market is very fragmented and there are really no complete solutions. Another issue that is important but very under discussed is the various ways all these products communicate, it's a MESS. Some use Bluetooth with a phone or tablet app but have no Windows or MAC app. Some have WiFi or Ethernet and yet others rely on CAN bus or RS485.

Please feel free to respond to this post if I can be of any further help.
 
Thanks for your replies. First, yes, i ment communication as i said "talking to the inverter".
The batteries will be used at home and the temperature during the year will be 68-74 Fahrenheit (20-23°C) as we have insulated concrete cellars.
 
Thanks for your replies. First, yes, i ment communication as i said "talking to the inverter".
The batteries will be used at home and the temperature during the year will be 68-74 Fahrenheit (20-23°C) as we have insulated concrete cellars.
benefit of BMS+cells talking to inverter/charger (multiplus) is often that the inverter can be notified that the cells are nearing full voltage, thus, the charger can gradually reduce ampere charge into battery, to reduce cell imbalance, and provide longer time for any resistive/passive or active cell voltage balancing to occur at the top

basically communication between BMS and other device like inverter can allow the system to run softer during times when the battery cells are vulnerable, potentially maximizing operation lifetime
 
Hi Grobalt! I'm from Germany too and have a little experience with lifepo4, alibaba buying, BMS and different inverter tests since two years. If you have some questions maybe i can help you.
Grüße Ruben
 
Hi Guys,

first i have to thank you for this great forum and the chance to collect experience for Alibaba sellers. Most likely i will order in the next days 80x 280AH cells from Docan as the 2nd prefered option is sold out.

I am from Germany, 41 years old with a power price of 35 cent and 10 kwp photovoltaic on the roof connected to a solarmax 10 inverter.

32 of these batteries should go into 2 batteries, the remaining are for 2 friends. So i am digging into battery charger/inverter, bms and it is not that easy. I'm very good at computer, but no programmer. I can solder, so some diy pcb can be finalized etc. I dont want the best solution if the price is as usual twice of the 2nd best:) 98% is good enough. I see many are using Victron Multiplus 2 and the 5000 model would be powerful enough for me as well. What is the benefit of a BMS talking to the battery beside an offline BMS and a BMV700 ? I tried to find a comparison of BMS but i was not succesful. There are 10+ BMS for 48V batteries from a few Euro to nearly 1000.

Is there an overview about that topic ?

Thanks a lot
Patrick
welcome to forum!! ☀️?⚡
 
At this moment you have plenty of time to do your research, since it's CNY there is no reason to order now or in a few weeks.

Second: The Multiplus is a great device, but if it suits your needs depends on your usecase.

Great for offgrid storage and charge from grid, but it doesn't have eg a MPPT. The Victron RS Smartsolar range is the better option if you want a MPPT and storage and don't need (or have external) grid.

You also can look into eg Growatt or MPP Solar, but it all depends on your application. Here in NL, at this moment, it's not making sense to get local storage, but that will change in the future.

A hybrid might be an interesting option if you still have grid (which you need, especially in the winter time). The MPP Solar has the additional benefit of backfeeding any excess PV to the grid (in the summer, if the batteries are full, it still might be interesting to feed to the grid)

I would prefer a hybrid inverter, since it allows you to charge the cells using solar first. With a seperate inverter (your current one) you need to figure a way to tell the charger there is PV available to charge, otherwise it will just feed into the grid.
The MPP solar onces can have priority settings: Use PV to power load. Any excess PV to charge the batteries, and if load is feed, AND batteries are full, backfeed to the grid.
To me, that's what you would archieve.

Not sure about Germany tho. But in the future this also might change, there are some situations (Excess PV and wind) where the electricity price is actually negative since there is too much generated energy. That means you actually have to PAY for the power you're providing to the grid.


At this moment, I would go for 2 sets of 16S with each a 150-200A JK BMS with active balancer. But I don't have an application yet to convince me to build this :)
 
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I am on grid, so i need a parallel to grid solution. I get some money for selling exceeding power, but this is just 16 cent and i have to pay tax on that, so around 11 cent per kwh sold (that rate is fixed for another 11 years). But for the non sunny times i have to pay 35 cent, so i want to store power and use that over night.

I dont need MPPT as i already have a solid inverter which i will not replace.

I did not yet exactly understand the difference of Multiplus 2 vs GX model ... I thought usind a JBD BMS per Battery, victron inverter/charger + BMV700, Victron Energy Meter and then i am done ?
 
I want to share some experience with docan and qr code scanning.

I asked for 80 cells with the requirements: max 6 months old, 6000 cycles Eve LF280K, never used, with eve test protocoll and received a quotation with which i was fine. Then i asked how to order, so Daisy prepared the offerings via Alibaba but split them in 2 batches of 40 cells each just below 5000 USD. I found out this was to prevent a 500$ fee for large Alibaba deals ....
I payed with paypal batch one but then Alibaba blocked the 2nd paypal payment due to security reasons .. so i payed the 2nd batch without alibaba with paypal.
Then i received pictures and movies from packing and inner resistance measurements and i asked for my requested eve package list. Daisy said she cannot provide this and misunderstood and immediately offered cancellation. What should i think now ... it was clearly requested and written in the Alibaba product description as i wanted to have.
I then asked for QR codes, good quality pictures to scan. I received about 10 and the pictures were good enough quality to see the batteries are looking good and the QR code was .... not scanable - what the hell, it showed sometimes 7, sometimes 9 digit numbers. I told this to daisy and the anwer was mysterious.
As the 80 cells are for me and a friend, i forwarded the pictures to him and he scanned them as well. Succesful, all are read correctly. He was using his iphone and scanning from whereever, i used Android and scanned my PC display, an HP z27n IPS panel. So i decided to print the qr codes as i had the idea my phone camera or app has issues with the display panel. Wonder, all scans showed what they should show.

The only bad thing is the cells are labelled B4, B5 and B6, so i expect they are from April to June 2021 and not as ordered maximum 6 months old. Daisy said they are from october, warehouse said the old batches are sold out. So there is a big mismatch.
 

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The Matching of cells is done TWO ways by Vendors.
1) The most common & Frequent. They use a Yaorea YR1035+ Battery Tester. Alibaba Link Here.
Forum Article / Resource: https://diysolarforum.com/resources...-internal-resistance-meter-tester-manual.142/
This is NOT MATCHING CELLS ! This is only ensuring that the cells are within a few Millivolt & Millohms difference AT STORAGE VOLTAGE !

2) Matched & Batched cells. This is a long & costly process as it runs the cells through cycles, sampling cell IR at target voltage points during Charge & Discharge cycles. Matched 280AH cells typically test out at 290AH+ Gross and WILL deliver 280AH from the Working Voltage Range of 3.000-3.400 @ 25C Temp.

Matched cells are essential for building battery packs with Paralleled Cells within so that all cells behave the same and have same IR across the operational voltage range.

Also please review this posting:

Regarding Vendors.
The vast majority are just wholesale operations warehouses and they purchase cells from Battery Brokers. These can be used, new old stock, Grade A to Grade C and all sell "Bulk" which is usually B grade at best. Typically they have their sales reps and people in the warehouse packaging stuff up, these are also typically "Group Owned". Very few buy direct from Manufacturing due to the MOQ and contracting requirements/obligations.

The ONLY vendor I know of that is Owned & Operated by a Family who buys directly from Manufacturer only & Provides properly Factory Tested, Matched & Batched Cells with test reports is Amy Wan of Luyuan who has an outstanding reputation here. Their Bulk Cells are those which are rejected from the batch testing but are still High Spec and NEW.

So if you are interested in Luyuan Tech, here is the link:

Hope it helps, Good Luck.
 
Looks like Seplos OEM labled with SunStonPower. If you look for the partnumber i assume i am 99,9% correct ;)
As this is 15SP2 you will receive 2 of the shown "boxes" and you can have a look at Seplos DIY 100AH solution multiplied by 2.

I did some math on my own as Seplos will bring an "empty" diy enclosure for 280AH cells. 2 packs of them be cheaper than this, using same BMS with nearly same capacity
 
Thanks for the info, it does look like it.
They told me it will be only one box so I am not sure if it is the SEPLOS.
Since you are more experienced in batteries than me, should I be aware of anything?
Do you have any concerns?
I am just looking for something "plug and play" to a growatt SPF5000 ES.
Any feedback is appreciated!
 
One 100AH cell is about 2kg and 3.7cm thick. As they say 15S2P it has to be 30 cells. If it is one box, it is not 15S2P and most likely the case length is wrong as well as the 200ah cells are 50% thicker with 5,5cm. Some information has to be wrong.

But the price is not that bad for no diy ... interesting

i dont know the growatt inverter and what it needs to communicate to the BMS etc, sorry. I'm new, i just did 2 weeks of 5 hours each day research :D
 
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