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Seplos Mason DIY Kit - Ancillaries - Advice

 
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Energy Storage
Last Post by MisterB 2 years ago
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 Makia2023
(@makia2023)
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Topic starter 08/12/2023 10:56 pm  

@transparent yes I'm being a tight arse/lazy. I'm trying to out science science. It doesn't appear to be working. 

 

Ok, so I have 3x units of 16 cells at 280ah (although I'm told they are 310ah by the seller).  Should I top balance in groups of 16 or should I put all 48 in series so all three packs are matched?

 



   
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 Makia2023
(@makia2023)
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Topic starter 08/12/2023 11:05 pm  

Also, I've read that you can top charge in series and then switch to parallel to do a final top balance, thus hugely reducing balancing time. Can you confirm that the 800w PSU will suffice for 18 amps at 3.65v?



   
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Transparent
 Transparent
(@transparent)
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08/12/2023 11:10 pm  

Personally I would balance in groups of 16.
Otherwise you could be waiting a month before you start assembling anything!

It must be getting late.
Are asking me to multiply 18 x 3.65 and tell you if the answer is less than 800? 😉 

I actually think 3.65v is too high anyway.
Balance to 3.6v and save a bit of time.

 


Save energy... recycle electrons!


   
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 Makia2023
(@makia2023)
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Topic starter 08/12/2023 11:19 pm  

@transparent yes I just went away and realised that 60 ish watts isn't much 👍 Top charge in groups of 4 @12v and then top balance to finish?



   
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 Makia2023
(@makia2023)
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Topic starter 09/12/2023 12:27 am  

Gone for this as it is an all in one system. 

 

https://www.amazon.co.uk/dp/B0CCL5X7N8?psc=1&smid=A37W9T108CT2UE&ref_=chk_typ_quicklook_titleToDp/

 

 



   
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 Makia2023
(@makia2023)
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Topic starter 09/12/2023 12:29 am  
Screenshot 2023 12 08 23 32 28 39 40deb401b9ffe8e1df2f1cc5ba480b12


   
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Transparent
 Transparent
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09/12/2023 8:36 am  

OK. So you'll need to be very careful not to accidentally move the knobs during the weeks of balancing!
There's no monitoring on that power supply to keep it aiming for the voltage you originally set.

Nor do we know if it will drift over time, possibly due to temperature.

 

Posted by: @makia2023
↑

Top charge in groups of 4 @12v and then top balance to finish?

The underlying chemistry of an LiFePO4 cell is such that it will almost certainly read 3.2v when it arrives.
Setting it to 12v will cause a group of 4 cells in series to discharge into the power supply.


Save energy... recycle electrons!


   
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 Makia2023
(@makia2023)
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Topic starter 09/12/2023 9:10 am  

@transparent bugger. 

Ok so current plan. 16 cells at a time in my workshop. 3.6v. 

 

Plug in, wait. With this model of bench power will I know when it is done balancing?



   
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 ChickenBig
(@chickenbig)
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09/12/2023 10:40 am  

Posted by: @makia2023
↑

With this model of bench power will I know when it is done balancing?

When the current admitted to the cells falls sufficiently low you're done. Having said that, don't over-charge (or float) the cells at high voltages for days at a time as you might get lithium plating occurring (lithium batteries are not floated). What is a sufficiently low current? If you're dealing with 16 x 280Ah cells then the overall battery is 4480Ah. 0.001C is 5A, so I would think that a few A is sufficiently low.

I would hope that the 16p phase of balancing would not take too long to perform; the bulk of the charging should take place when it is a 16s battery protected by BMS (and fuse if you are feeling cautious). This is also when you get the highest power out of the bench power supply.

 


   
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Transparent
 Transparent
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09/12/2023 11:11 am  

I'm trying not to state too many detailed technical points at a time,
but you're moving faster than I can describe the bits that matter!

The usual way you'll know that the cells are reaching the point of balance is that the current drops off.
In effect, you're setting the final voltage and then allowing the bench power supply to send as much current as it can.
The actual current which flows depends on:

  • the internal resistance of the cells
  • the resistance of the bus-bar connections you use to link them
  • the capacity of the wires (and the 4mm banana plugs) from the power supply to deliver that current
  • the internal design of the power supply to keep that current flowing as the voltage which it measures gradually reaches the set point

 

Your power supply doesn't have 'sense wires'; it's going to pump current down the same pair of wires which it's using to 'measure' the voltage.
So the display at the front won't be reading the voltage at the cells.
It will be showing what the power supply is detecting where it connects to those red/black sockets at the front.

Poorer quality power supplies will allow the current to tail-off far too early.
So although it's rated 30A, you might find that within a few hours of connecting it to the cells it's only delivering 25A for example.

To alleviate that potential problem you want to employ a really good pair of wires between the power supply and the cells.

Unfortunately that power supply doesn't have screw-down terminals which can accept a nice hefty ring- or fork-connector.

image

So you'll need to start by buying a couple of 4mm banana plugs with a current rating of at least 30A,
and as thick a flexible copper wire as can be accepted by those plugs.

That will probably be 2.5sq.mm, although 4sq.mm would have a lower voltage drop if it could be attached to a push-in banana plug.

CPC offer some ready-made patch leads rated 36A

image

You can also buy just the 4mm banana plug-end with a M4 screw-thread which you can use to clamp on a 4sq.mm wire:

image

How does that sound?


Save energy... recycle electrons!


   
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 Makia2023
(@makia2023)
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Joined: 3 years ago
Posts: 72
Topic starter 09/12/2023 11:39 am  
Screenshot 2023 12 09 10 37 37 01 40deb401b9ffe8e1df2f1cc5ba480b12

 Will these do the job ok? I see a few using croc clips to a bus bar to top balance on YouTube.

 



   
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 Makia2023
(@makia2023)
Trusted Member Member
Joined: 3 years ago
Posts: 72
Topic starter 09/12/2023 11:44 am  

Ignore my last message. I have reread the post. I will make up some leads for the high power rear connections on the supply.

Can I book up my own multimeter to measure actual voltage across the cells as it goes?



   
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