DIY storage battery from BEV cells

[diyfan]

@diyfan
Is your existing PV system a fit one ? If so, I recommend that you leave it well alone, and add this battery system completely independent to it - otherwise it gets very complex.
You’ll have to make a G99 application I think, most probably to be successful this must be with a G100 compliant inverter - that 8.8kW sunsynk is, i think - check the exact model on the ena database. G100 means it can monitor the overall home power, and ensure you don’t export over a given power, to be agreed with the dno. The limit is set by your installer I think, in a way that you can’t override. It’s likely they would accept 8kW max overall export - as you already have that!

Hi robl,
I had my PV installed after the FIT scheme ended, so no. In any case it sounds like conversation with DNO is unavoidable. In which case I might as well go all the way and request increase in capacity. There are very few roofs with PV panels in my estate, so I think my chances of success are good. I better go and study DNO web site as they have all sorts of forms and guides on how to prepare the application. Thank you for your thoughts!

[Stinsy]

Hi @Stinsy,
I don't think I follow you at all. Do you mean I should build a single 14S20P 51V/1200Ah battery and use it with just a balancer in place of BMS? I must be misunderstanding you because it would be very unsafe to operate such battery Would you be able to elaborate on your thoughts?

Why do you imagine that to be “unsafe”?

Hi @Stinsy,

You surely must be testing my knowledge ! I am competent, I promise but okay.

Nothing lasts forever and every set up fails sooner or later (probably sooner for me as I plan to use second hand cells). And when that happens for my setup I want it to fail safely (or even have an advance warning so I know to look and prevent failure). As the BMS monitors overall battery temperature, voltages and currents, as well as each cell (or P block) individually, should it measure any abnormalities it will immediately isolate the battery from the circuit, thereby adding a layer of safety. The same level of monitoring cannot be achieved through the voltage limits on the inverter alone. Without BMS, such capacity battery has a potential to fail dramatically, without a warning.
Let's examine several modes of failure and potential for damage
1. Inverter fails to stop charging the battery past cut off voltage = severe overcharging of all cells, potentially resulting in a big crater where my house used to be.
2. One of the cells degrades much quicker than the rest = severe overcharing of a single P-block of cells (20 cells!), as above but hopefully less dramatic.
3. Inverter fails to stop discharging the battery past cut off voltage = all cells over discharged, entire battery pack ruined
4. One of the cells develops internal short = the charge from all parallel cells would discharge instantly, fire hazard due to amount of energy released, likelihood of physical damage to neighbour cells and risk of thermal runaway.

Having BMS would prevent first 3. And having fewer parallel cells in a pack would lower the potential bang for the 4). And with no parallel cells there is almost no risk if one of the cell shorts out. BMS could also have alerting capability, such as a buzzer or perhaps even cloud connection to warn of abnormal condition remotely.
I cannot think how balancer could prevent, mitigate or alert about any of the above situations. Once the battery is balanced, the job is done and there is hardly any benefit to keep the balancer plugged in. I may be missing something. Please let me know your thoughts.

The reality is that your inverter will do the over/under Voltage cutoffs perfectly reliably, a proper active balancer will keep the cells equal (and will be way better what is typically fitted in a BEV), and all the temperature management stuff is completely unnecessary in a low-C stationary application. Don’t forget these batteries are designed to be charged/discharged at 100kW, a typical domestic arrangement is 3.6 or 5kW…

[Tinbum]

The reality is that your inverter will do the over/under Voltage cutoffs perfectly reliably, a proper active balancer will keep the cells equal (and will be way better what is typically fitted in a BEV), and all the temperature management stuff is completely unnecessary in a low-C stationary application. Don’t forget these batteries are designed to be charged/discharged at 100kW, a typical domestic arrangement is 3.6 or 5kW…

I'd never ever run batteries without a bms and never without their being communication to the inverter.

The inverter doesn't know if their is a faulty cell.
Temperature measurement is required- for one it's a way to see if a cell is going faulty.

An active balancer is ok if the cells are ok but once one goes faulty it's useless. They are also only useful if they actually are switched on (at high voltages) and off (at low / middle voltages), which most are not.

Running without a BMS is a big no no- it's highly dangerous.

[Colin Deng]

Welcome to the forum
Some factory also using this kind of cells to build the battery pack
But not suggest that , cuase it can not replace easily when some cells go south
Also , the cycle life is less than the prismatic cells

For your information

Hi Colin,

Thank you. Is there a web site I could go check out pricing for new cells at a budget price? I am after about 30kwh in total. I have seen your post about moving on from your old job. Congrats, and hope you settled in well!

Thank you so much for the feedback
The new jobs is going on well, also close to my house, which is nice
And working SOHO with friends also , currently not have website for the batteries
Payment via Alibaba
And for 30kwh batteries, the EVE 280K cells will work, now the 280k cells capacity already reach to 310ah
32pcs will be more than 30kwh
And the price of the 280k cells will be 81-86$ range
For your information , thank you

[Stinsy]

The reality is that your inverter will do the over/under Voltage cutoffs perfectly reliably, a proper active balancer will keep the cells equal (and will be way better what is typically fitted in a BEV), and all the temperature management stuff is completely unnecessary in a low-C stationary application. Don’t forget these batteries are designed to be charged/discharged at 100kW, a typical domestic arrangement is 3.6 or 5kW…

I'd never ever run batteries without a bms and never without their being communication to the inverter.

The inverter doesn't know if their is a faulty cell.
Temperature measurement is required- for one it's a way to see if a cell is going faulty.

An active balancer is ok if the cells are ok but once one goes faulty it's useless. They are also only useful if they actually are switched on (at high voltages) and off (at low / middle voltages), which most are not.

Running without a BMS is a big no no- it's highly dangerous.

“Highly dangerous”?

I think you should put down the pearls and apply a bit more common sense! In the real world it all, comes down to how hard you’re running the batteries. 2C? You definitely should consider temperature measurement (and active heating/cooling). 0.2C? Just not required!

[Tinbum]

“Highly dangerous”?

I think you should put down the pearls and apply a bit more common sense! In the real world it all, comes down to how hard you’re running the batteries. 2C? You definitely should consider temperature measurement (and active heating/cooling). 0.2C? Just not required!

Yes highly dangerous.

I know common sense is highly frowned upon now but I have loads of it and use it all the time.

It's nothing to do with how hard you are running them.

[Stinsy]

“Highly dangerous”?

I think you should put down the pearls and apply a bit more common sense! In the real world it all, comes down to how hard you’re running the batteries. 2C? You definitely should consider temperature measurement (and active heating/cooling). 0.2C? Just not required!

Yes highly dangerous.

I know common sense is highly frowned upon now but I have loads of it and use it all the time.

It's nothing to do with how hard you are running them.

You're welcome to carry on thinking that. However it isn't true. Clutching pearls and spreading baseless fear isn't allowed on this forum. I'm not the policeman around here. But I should warn you that others have been booted for similar...

[Tinbum]

You're welcome to carry on thinking that. However it isn't true. Clutching pearls and spreading baseless fear isn't allowed on this forum. I'm not the policeman around here. But I should warn you that others have been booted for similar...

I could say the same to you for advocating dangerous practices, but I'm not that petty.

Do you honestly think manufactures of batteries would put a BMS in their batteries if it wasn't required.

I stand by what I say as I know it's correct.

[nowty]

I’m staying out of this one, you pays for money and you takes your chances.

[Joeboy]

I’m staying out of this one, you pays for money and you takes your chances.

Everyone has their own risk/reward profile. No such thing as 'right' in this. He who accepts too much risk has to reboot from start. (Reborn)