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BMS integration to Victron + system design
#21
(08-15-2019, 03:07 PM)dewki Wrote: The Winston 260-400Ah Cells are specified to a operating voltage 3.8V - 2.8V (80% DOD). Recommended charging at 3.65V per cell.
For the curious: https://www.ev-power.eu/Winston-40Ah-200Ah/

Be warned LiFePo4 cells are likely to get damaged >3.5V/cell IMHO.
You need to characterize your own cells & look for the point where the voltage starts to climb quickly on charge & drop quickly on discharge.
These points are where damage & swelling will start & there are many tails of woe re swelling cells.
The manufacturers seem to give these higher voltages (3.65 or more) to maximize the apparent capacity but max reported capacity does not equal long life....
For my LiFePo4's this is ~2.85V & 3.50V so I've set my system for ~2.9V min & ~3.41 max to "stay on the plateau" of the typical charge curve.
"Fully charged" SoC is still reached with a lower charge voltage when the tail current drops away.
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#22
Sean im One of them. At most i Ran 4 on same cell. Not doing it now but wanted to see if it was possible. I have also added multiple Ones when adding new or uneven packs.

There have been others but i can never remember names. Can be found in projecta section.
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#23
(08-16-2019, 09:54 AM)daromer Wrote: Sean im One of them. At most i Ran 4 on same cell. Not doing it now but wanted to see if it was possible. I have also added multiple Ones when adding new or uneven packs.

There have been others but i can never remember names. Can be found in projecta section.

The only way adding multiple mons (to increase the total per cell bypass current), when each mon has a slightly different bypass voltage, is ever going to work is if you charge at a rate high enough such that the cell voltage is still increasing (to encompass the parallel mons bypass voltage window), even when that cell is in bypass - which is both pointless and wasteful - you will also have to actively cool each mon, or lower its bypass current low enough so that it is safety thermally balanced (or risk thermal bypass).

The only documented mention of anyone attempting what you recommended was Paul Holmes last year on the FB group, he quickly realised the futility, which prompted Jarons comment about possibly enabling user calibration of mons.

There are no projects in the project section where users are successfully using multiple mons to increase the bypass current on a single cell - let me know if you remember who these folks are please.

(08-15-2019, 05:31 AM)daromer Wrote: From batrium you can balance 10A from a single cell if you want. Just add 10 longmons as example.

All I'm asking for is examples of anyone who is successfully doing that which you have suggested is a trivial matter in the above comment.
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#24
Yes if cells get out of balance the voltage will raise. Especially if you dont have the BMS to control the charger.
Same goes with auto-level. If you set the auto level correctly, enough mons will engage and start balance.

Unless you have tested this your self Sean i dont know why you comment stating it wont work when I for instance have done it and it works fine. I have done 4 of them on same cell equal 4A continues balancing in my setup. I do not see the issue adding 6 more doing the same... No they wont start at same time but eventually they all run when needed!

We done agree and if you want to discuss this further please create a thread about it. This have become way OT in this one.
The Ultimate DIY Solar and build place
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Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#25
(08-16-2019, 10:34 AM)daromer Wrote: Unless you have tested this your self Sean i dont know why you comment stating it wont work when I for instance have done it and it works fine.

We have tested multiple mons on single cells, at great length - it doesnt work, for the reasons I've previously mentioned.
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#26
(08-15-2019, 11:00 AM)Sean Wrote:
(08-15-2019, 05:31 AM)daromer Wrote: From batrium you can balance 10A from a single cell if you want. Just add 10 longmons as example.

How do you ensure that all mons turn on at exactly the same voltage ?

Its not ideal to run multiple cell monitors. Except temporarily whilst a cell block is in recovery when you are adding a cell block with a different SoC% to the rest of the battery string. Each cell monitor consumes 1.4mA so a single unit is significant better than multiple to keep the system in balance.

Multiple monitors only make sense typically for LiFePO4 on large capacity cells and the charger lacks the ability to charge slowly. Hence when the charger over charges any individual cell the extra monitors have the ability to accelerate the discharge back to balancing threshold.

Not sure why people do it, I dont ! Except temporarily for the scenario above until they are all back in balance with all cells held at their threshold for a period of time and then I immediately reconfigure to 1 cell monitor per cell in series.

Lithium-Ion chemistry (i.e. LMC, etc..) are a completely different characteristic and should be handled differently with extra bypass AutoLevel. For LiFePO4 chemistry beyond 3.50v this quickly goes up and when you stop charging the voltage immediately drops, there are other methods to handle this which is a different discussion and some have adopted additional monitors.
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