I have a 16cell 48V 280ah battery that is connected to a Growatt SPF 6000T DVM controller/charger/inverter. I've been working with a VNSZNR (Daly knockoff) 16S 200A "smart" BMS with balance charging. I've been tweaking that relationship for weeks trying to achieve a reliable 24/7/365 power source for a 240V 2HP well pump. After weeks of trying to fine tune the parameters on both components, I failed to achieve anything resembling reliability. The cell readings from the BMS were constantly spastic and the charge/discharge status was sketchy with wild swings every second. After a TOTAL of16 charge/discharge cycles the BMS went belly up yesterday. Dead as a doornail. Not a milliwatt of output allowed to flow to the inverter. So.... I bypassed it. Now the Growatt is directly wired to the battery and it's doing exactly what I've been trying to do for several weeks. I have an active balancer that I haven't installed yet and as fate would have it the wiring harness from the BMS is a perfect match to it. I am very tempted to replace the BMS with the balancer and call it system, WITHOUT a BMS. The Growatt is loaded with trip wires to protect the battery and itself from shorts, overvoltage, undervoltage, etc.. Nearly all of them are editable to taste. The active balancer is Bluetooth compliant, and I can monitor the individual cell status with the same Smart BMS application I've been using to tweak and monitor the recently departed BMS. Please explain WHY a BMS would be indispensable to this system. I can't see it as anything but a neurotic kill switch on the Growatt that significantly reduces the reliability of the system.
To BMS or not to BMS? That is the question.
- Thread starter gnomie
- Start date
Quattrohead
Solar Wizard
If 1 cell starts to run the Growatt will not know and keep charging until the cell "blows up"
You have 2-3 grand worth of cells, don't eff them up over another $150.
You have 2-3 grand worth of cells, don't eff them up over another $150.
BentleyJ
Solar Wizard
Your experience with the BMS is unfortunate because it has left you with the impression a BMS is more trouble than its worth. A properly functioning BMS is stable and is absolutely necessary for LFP cell chemistry.
Inverter settings for High and Low Voltage Cut Outs are based on total battery voltage and will NOT protect individual cells from irreversible damage. LFP chemistry is fairly robust within its operating range of 2.5V to 3.6V. Once outside of these limits cell voltage can "run" either up or down very rapidly, as in minutes, and be permanently damaged. I was surprised the first time I witnessed this behavior with bench top charging.
A balancer is highly recommended BUT is not a substitute for a BMS. Consider a JK BMS with active balancer built in and top balance your battery pack first so it starts out in good shape. A 1 or 2A active balancer could take hours or even a day or two to rebalance a 280Ah battery.
Inverter settings for High and Low Voltage Cut Outs are based on total battery voltage and will NOT protect individual cells from irreversible damage. LFP chemistry is fairly robust within its operating range of 2.5V to 3.6V. Once outside of these limits cell voltage can "run" either up or down very rapidly, as in minutes, and be permanently damaged. I was surprised the first time I witnessed this behavior with bench top charging.
A balancer is highly recommended BUT is not a substitute for a BMS. Consider a JK BMS with active balancer built in and top balance your battery pack first so it starts out in good shape. A 1 or 2A active balancer could take hours or even a day or two to rebalance a 280Ah battery.
HighTechLab
AKA Dexter - CTO of Current Connected, LLC
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One member on this forum uses the phrase "BMS or be a mess".
I don't consider a BMS as optional...unless you are intentionally trying to make your cells go to the rubbish pile where your VNSZNR is sitting.
I don't consider a BMS as optional...unless you are intentionally trying to make your cells go to the rubbish pile where your VNSZNR is sitting.
A BMS is not an option, it's a necessity. I have the same Growatt and after 2 years of trial and error, the best performance I've found is the Overkill Solar BMS and Solar Assistant. If you only have the one battery, get the UART adapter to replace the Bluetooth and have it report SOC to the Solar Assist. If you have more than one battery, use a Victron Smart Shunt and VE direct cable to the Solar Assist pi.
There's been a lot of people that would buy really shady solar equipment on Amazon for instance that turns out to be junk (breakers, busbars, etc). This appears to be because they think since it is listed for sale it must be safe/good/reliable. Amazon, Aliexpress, etc makes no guarantees relating to safety or reliability about any of this stuff being sold on their system. I'm not sure why people think this but trying to spend the least amount of money on parts for your system that directly impacts the safety of it is not wise. If you take that a step further and realize it is junk that you got and equating that to all BMSs is also not wise. If you got a junk circuit breaker (which many people have from Amazon) would you then think to fix the problem you shouldn't use a circuit breaker?
Since you have the same Growatt, did you ever get your Overkill BMS to interface with the Growatt through the Growatt BMS port, and, if so, where did you find the appropriate comms wire with male RJ45 plug?
42OhmsPA
What's in a title?
Running without a BMS = bomb manufacturing system.... Think of it that way.
The Overkill Solar BMS does not have a direct report to the Growatt. That's the beauty of Solar Assistant. It acts as a bridge between the two and much more.
Quattrohead
Solar Wizard
Don't worry yourself too much about communications, let the BMS do its job.
The Overkill won't handle more than 100A "constant" discharge. Our Growatts are advertised to handle 6000 watts continuous and 18000 surge. I'm not sure that 100A would handle the startup surge on the 2HP well pump. It pulls about 5000 watts for a couple of seconds as it starts then levels off at about 2500 watts. That's one reason I went with the Daly knockoff. It was rated at 200A discharge.
Lt.Dan
Solar Wizard
When it comes to Daly, its best to derate by 50%. I would say that Daly is only good for 100a.
And how did that work out for you? I'm not trying to sell you anything, simply relating what has worked for me.
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Got it. If the charger is supplying 58V to the bank it has no way of knowing if one cell is getting 4 volts while others are getting 2. So... to avoid an overcurrent meltdown, the BMS continuously tests the individual voltages and responds accordingly to any over or under voltage anomalies, typically shutting down the charger until over-voltages normalize or shutting down the discharge until under-voltages normalize. They also protect from charging in freezing conditions which can damage the cells. I get it. I just hate to get another BMS and HOPE it is stable and reliable. Unfortunately, I need the 200A discharge limit which isn't available on the Overkill and similar units. As far as I can find, the Daly is the only one that offers that much discharge capability. So... here we go again. Fingers crossed.
The Overkill dealer on E-Bay seems to be ready to take returns on any BMS for any reason with a LIFETIME warranty. Guess it wouldn't hurt to get the 100A 16S Overkill and try it. If it doesn't pull the starting amperage on the well then I send it back and revert back to the Daly.
Quattrohead
Solar Wizard
JBD BMS with the contactor will handle it good, this is what I started with in the early days
Bingo! Why leave your cheese out in the wind?
Lt.Dan
Solar Wizard
Free BMSs are nice. I went through 4x Dalys before I learned my lesson. Now it is just JK, or Seplos for me.
42OhmsPA
What's in a title?
Where do you source your seplos?
I'm happy with my JBD but would like to give the Seplos a go.
Lt.Dan
Solar Wizard
I get them Direct from Seplos on Alibaba.
