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Top balancing is killing me

Bluefreak

New Member
Joined
Nov 11, 2020
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Startet top balancing. Setup:
4x176ah Lifepo4 cells
Lab power supply UNIROI UC1030 10A 30V
Wires: 2x2,5mm per pole
The power supply charges with 10A decreasing, voltage in the display is 3,5V and all regulators are fully opened.
At the cells I measure 3,33V.
Cell voltage went from 3,32V to 3,33V within the last 20 hours.

Is that normal? Why can't I increase the voltage of the power supply? How shall I ever get to 3,6V? What am I doing wrong?
I read here a lot that first in series to 14,2V, then topping up to 3,6V parallel could be a way. Is that the solution? I'm feeling like my electrical education is completely worthless ?
 
4 * 176 = 704 Ah
704Ah/10A = 70 hours.

Presumably, they were received at around 50% charge, so you're looking at at least 35 hours of full 10A charging.

The losses in the wiring and unit (internal resistance) are causing the voltage drop between the display and the cells. You will be fighting this to the bitter end.

Recommend you disconnect power supply, set voltage to 3.65, reconnect and resume.

Remember that one of the biggest benefits of LFP chemistry is its flat voltage curve. You see it both ways... on the way up and on the way down.

Current best practices is to assemble your cells in series with the BMS and series charge at 10A as that pushes 4X the power into the cells vs. parallel. Once the BMS cuts off, you do a top balance parallel charge as you're currently doing.

On the Resources page, there is a detailed guide.
 
Impatiences causes bloated cells.

From 50% to 85% state of charge, cell voltage only rises about 40 mV. It rises quickly above 90% state of charge (>3.38v)

Don't recommend raising supply voltage limit to make up for cabling voltage drop as it can get away from you during last 10% charging when cell voltage shoots up in short period of time. Use larger gauge wire to avoid too much lead voltage drop. Keep unloaded supply voltage limit at 3.65v.
 
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