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Full Charge Behaviour (JK BMS)

Lawrence_craig

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Joined
Feb 27, 2023
Messages
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United Kingdom
Hi all.

I have just installed my DIY LiFePO4 12v 4S battery. I have full Victron charge kit (and SmartShunt) with a JK BMS.

I just wanted to check the behaviour when the battery is fully charged.

When it is fully charged (via a Multiplus on 230V shore power supply), the JK BMS cuts the charging off due to Cell Voltage Over Voltage Protection (14.4V, 3.6v/cell). The battery then stops charging. It's worth noting I am currently seeing a Cell Voltage Diff of 0.05v when fully charged if that's important. What I then tend to see what happens is the battery will sit full for a few mins, the voltage will then drop to below the OVPR (14/3V, 3.5v/cell) and the Multiplus will then pump power back into the battery (>30a @ 14.2V) for a minute or so. However, in that time the battery charging was cut off, 30amp was definitely not drawn, the other loads should have also been supplied by the shorepower anyway (current load is only 100W). This seems strange to me.

Is this normal behaviour or should I be looking into something? I have a feeling I have the OVP set incorrectly vs my Victron charge settings.

Parameters for info:

JK BMS
OVP: 14.2
OVPR: 14.1

Victron:
Abs: 14.2
Float: 13.5
 
Last edited:
The bms should be set to 3.65 or a little less then set the victron lower it should stop the charging not the bms the bms is a safety you may have to lower the victron some till the cells totally balance then keep increasing 14 volts is pretty close to full pushing that last little bit is just not worth the stress on the cells this will make them last longer
 
Exactly what rodrick said. On my JBD BMS I have the settings of 14.6/3.65 for over voltage battery/cell. Victron is set to 14.4 when actively in use, 14.2 when in storage.
 
I have a Victron with an 18-cell battery bank, so lots of cells.

My suggestions:
1) Top balance your battery again.
2) Run at 3.45v max. (More headroom to balance.)
3) Get a Venus, the Rpi version, and install this interface between the BMS and your system, for more control.
4) Victron Lifepo4 settings max is I think 3.5v per cell, you can use that option on the inverter, MPPT also has that setting.
 
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