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Seplos Mason DIY Kit - Ancillaries - Advice

 
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Last Post by MisterB 1 year ago
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 Transparent
(@transparent)
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Posts: 2370
27/12/2023 8:49 pm  

Posted by: @makia2023
↑

I'm told 48v as the cut off is the best options as that is approx 10% soc. Is this your view and can you provide any advised values for me to confirm what I've read (or not).

Also, I'm assuming Pylontech setting for the inverter should work with the seplos BMS?

Let's deal with the BMS settings first.

Very few people seem to question what is meant by an assertion that a BMS or inverter is somehow compatible with a product from a different manufacturer.
It might be referring to the voltage settings which are required for the connected devices...
... or it might be that data is being transferred across a CANbus or Modbus communications link.
That would enable measurements made by the BMS get reported/recorded by the App issued for the Inverter, or vice versa.

It may have nothing to do with protecting your precious batteries.
So beware!

 

There are also many views across the internet as to the 'best' parameters which you should apply to your LiFePO4 cells.

Will Prowse, who has been publishing hundreds of You Tube tutorials on inverters, solar panels and batteries over the years, currently suggests:

48V LiFePO4 Battery w/ BMS

  • Absorption: 58V
  • Float: 54.4V
  • Inverter Cut-off: 42.8V-48V
    ​

Individual 3.2V LiFePO4 Raw Cell (for individual cell capacity testing)

  • Absorption: 3.625V
  • Float: 3.4V
  • Low voltage disconnect for capacity testing: 2.5V

 

Whoever you choose to believe, the basic principle remains the same.

The Inverter/Charger parameters are those which you set to define the voltage envelope within which your batteries are charged and discharged.

The BMS parameters are set outside of those.
The BMS acts rather like a fuse. If there's a fault, or an error in configuring the inverter, then it will step in and disconnect the battery before any damage is done.

Putting it the other way around; The inverter parameters are inset from those of the BMS.

 

Here are the absolute maximum and minimum voltages you should consider using: with a LifePO4 cell.

LiFePO4volts

The inner pair of voltages are those which are set in the inverter (or charger) per cell.
A cell should not fall below 2.6v, nor be charged higher than 3.55v
which equates to a range of 41.4v to 56.8v for a 16S battery (sixteen cells in series).

The outer pair of voltages are applied to the BMS.
If the charge/discharge system fails, then the BMS prevents any cell falling below 2.35v or rising above 3.65v

You might suppose that equates to a maximum voltage of 16 x 3.65v (58.4v) for a 16S battery.
But that's not so.
Remember, the BMS has sense wires across each individual cell.
It will cut off the charge-current as soon as the first cell in that battery rises to 3.65v.

In practice I wouldn't configure my inverters and battery BMS units to these absolute minimum and maximum values.
But everyone will have their own opinion on how much they wish to inset from those extremes.

Save energy... recycle electrons!


   
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 MisterB
(@misterb)
Reputable Member Member
Joined: 2 years ago
Posts: 139
16/03/2024 9:57 am  

@robl when i assembled mine last year around June time i think it was, i used a piece of 18mm melamine (kitchen cupboard shelf) in the bottom, i used EVE 280AH cells and ignored the plastic strips but used the foam between the cells. Using 18mm melamine meant that i could then hold the cells in compression. 

 

some others have 3d printed a mesh type support that fits neatly in the bottom of the case. i have also recently heard that Seplos have now sorted the issue ....?


   
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