Overkill BMS setting for Lishen 272amp battery pack

ian123

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I built 2 X 272amp 12v Lithium battery packs using the Lishen 4 X 3.2v cells and an Overkill BMS. All balanced, charged up and good.

When I look at the BMS, at +/-3400mva charge per cell (13.7v for the pack) the amp capacity is only showing 85%. This cant be correct. To get 100% ie 272amp hours, the battery would need to be at 14.6v charge!

Im looking for the Mva setting for full charge, 80%, 60%, 40%, 20%??

To get the pack up and running, I just went with the Overkill default settings - maybe this is throwing out the numbers.

Ive asked Lishen and they send me the charging current chart - not helpful! I know max cell charge voltage is 3.65v. Their data sheet says nominal voltage is 3.2v.

I know others have built packs using the Lishen cells, so info to help? TIA
 

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JeepDaddy

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Your fully charged voltage is set to 3500mV (not mva). To reach the 100% reading, you need the battery to be at or above that point or 14v for the entire pack.
 

snoobler

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Those numbers are as good as any, and they're only used for approximation. Lishen does not publish those values, and they're pretty much worthless. SoC can only be reliably determined by counting net current.

Since you've gone with the 3.5V full charge value, you need to get your battery to 14.0V for it to reset, and you need to allow the battery to charge at that voltage until it drops to about 10A .
 

ian123

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So, IF the 3.5v full charge value is correct?? then I would need to change the Float charge in my Victron Multiplus to 14.0v whereas its currently set at 13.7v?

Then I read you shouldn't have a Float charge happening with a Lithium battery?

So how does this correlate with Lishens specs of 3.65v max charge and 3.2v nominal?
 

snoobler

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So, IF the 3.5v full charge value is correct?? then I would need to change the Float charge in my Victron Multiplus to 14.0v whereas its currently set at 13.7v?

Then I read you shouldn't have a Float charge happening with a Lithium battery?

So how does this correlate with Lishens specs of 3.65v max charge and 3.2v nominal?

absorption should be set to at least 14.0V

Float should be set to 13.6V, 13.7V is too high.

The origin of the need for float is that lead-acid batteries need to be "floated" at a voltage to prevent their self-discharge. LFP retains its charge, so it doesn't "need" a float; however, the concept of float is important for powering loads.

In a solar power system, you need to specify a float. If you don't, the inverter happily drains the batteries while the solar charger does nothing until the battery discharges enough to trigger a new bulk charge. This results in multiple small daily cycles rather than just holding the battery near full and allowing the solar to power the loads. Setting a float defines the threshold where the solar kicks in, holds the battery near full and the powers any loads.

If you're using this in a standby system where the batteries are not cycled regularly, LFP isn't the best choice. They deteriorate when stored at high states of charge. Lower temperatures help mitigate this.
 

JeepDaddy

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So, IF the 3.5v full charge value is correct?? then I would need to change the Float charge in my Victron Multiplus to 14.0v whereas its currently set at 13.7v?

Then I read you shouldn't have a Float charge happening with a Lithium battery?

So how does this correlate with Lishens specs of 3.65v max charge and 3.2v nominal?

"Full charge" is whatever voltage you consider that to be.

I would change your BMS settings to what the battery needs. Snoobler's 13.6V is a good float charge number, so 3400mV per cell for fully charged is good.

You can change your other % charged numbers accordingly. I'm using 3350 = 80%, 3300 = 60%, 3250 = 40%, 3200 = 20%, 3000 = Empty
Those are probably conservative and based on voltage, not on true SOC. It will get you in the ballpark.

You will get different opinions from different people about what those numbers should be. YMMV.

I run a Victron Smartshunt for a more accurate SOC measurement.
 
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