Overkill BMS settings

ian123

New Member
Joined
Feb 20, 2021
Messages
19
My battery pack is 272amp, 4 cells, 12v. The cell spec is attached.
I've connected with an Overkill Solar BMS - config also attached.
I've top balanced the pack.

Only way I can get to 100%, 272amp charge is at 14.4v ie 3.6v per cell.

So, Im thinking (Im not confident as 100% new to this, so be nice) that my BMS config is not correct.

Help please! TIA.
 

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mikefitz

Photon Sorcerer
Joined
May 28, 2020
Messages
1,160
The value shown in the BMS app are protection limits and the voltages for state of charge are to allow the BMS to estimate state of charge.
Any voltage over 13.6 volts will eventually charge the battery to near 100%. Typically 13.8 or 14.0 volts are considered suitable for low stress charging.
The start balancing voltage of 3.45 seems somewhat high as do the capacity settings, 3.40 volts per cell (13.6 v per 12v pack), is more typical. Cell under volts and release seem very conservative, (too high).
The listed values (Battery at rest) for capacity also seem high compared to accepted values.
This chart from Resources, ( actual values for your cells would have to be determined by testing)
state of charge.jpg
There is also info on the Overkill site regarding BMS settings and in the Resources setion.
 
Last edited:

Gazoo

Dumb Dumb
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May 12, 2020
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Location
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In addition it appears as though balance only while charging is turned off?
 

time2roll

Photon Sorcerer
Joined
Mar 20, 2021
Messages
3,416
Looks like you increased all the cell voltages in the state of charge stack. Full charge comes at 3.4 IIRC. Put them back.
Balance only when charging is recommended.

The minimum battery voltage at 10 is redundant because you set minimum cell at 3 from 2.5 volts. I think you are better to set the battery voltage at 12 and set the cells a bit lower like 2.6 or 2.8 volts.
 
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