Testing Internal Resistance 280Ah cells

[DWrvsolar]

I'm about to order a Yaorea YR1035+ internal resistance meter. Anyone have experience with this meter or recommend something similar?
I want to test and match my soon to arrive EVE cells into the the best configuration before top balance.

 

[Supervstech]

It is unwise to top balance cells in series.
Either parallel top balance them, or let an active bms perform the balancing.

 

[RCinFLA]

A new 280AH LFP should be in the 0.25 to 0.35 milliohm range. This is pushing it for YR1035+. Pay more attention to relative impedance matching between the cells.

Lowest scale is 20 milliohm range. Don't take 0.01 milliohm resolution spec as accuracy. It only means the display has 0.01 milliohm digit display.

If you have a battery monitor shunt you can use it to test meter accuracy. If 100A/100mV shunt then its 1.0 milliohm. 500A/50mv shunt is 0.1 milliohm. Some shunts have different resistances like 500A/75mV which is 0.15 milliohm. A 300A/75mV shunt should be right at 0.25 milliohm

 

[DWrvsolar]

It is unwise to top balance cells in series.
Either parallel top balance them, or let an active bms perform the balancing.

Not planing to balance anything in series. I want to charge and test internal resistance of each cell, then sort cells by test results. I will parallel and top balance the closest cells into two 8 cell packs.

 

[DWrvsolar]

..

 

[DWrvsolar]

A new 280AH LFP should be in the 0.25 to 0.35 milliohm range. This is pushing it for YR1035+. Pay more attention to relative impedance matching between the cells.

Lowest scale is 20 milliohm range. Don't take 0.01 milliohm resolution spec as accuracy. It only means the display has 0.01 milliohm digit display.

If you have a battery monitor shunt you can use it to test meter accuracy. If 100A/100mV shunt then its 1.0 milliohm. 500A/50mv shunt is 0.1 milliohm. Some shunts have different resistances like 500A/75mV which is 0.15 milliohm. A 300A/75mV shunt should be right at 0.25 milliohm

I've got a Victron BMV712 so I could use it's 500 amp shunt. I'm not worried as much about testing for factory spec. as I am looking for something accurate enough to compare and match the cells. Do you think the YR1035+ or one of the knocoffs would be repeatable or can you suggest a meter that would be more appropriate?

 

[cwstnsko]

Is static impedance what you need to measure to match cells, or is it a more complex concept in the context of a battery? My hobby charger reports internal resistance, but not until it has been charging for a while, and in a series pack, the values move around a bit as the pack cycles. Generally when charging an individual cell, it just reports 0.1 milliohms, which I don't find to have enough precision to be useful.

 

[DWrvsolar]

Is static impedance what you need to measure to match cells, or is it a more complex concept in the context of a battery? My hobby charger reports internal resistance, but not until it has been charging for a while, and in a series pack, the values move around a bit as the pack cycles. Generally when charging an individual cell, it just reports 0.1 milliohms, which I don't find to have enough precision to be useful.

I've got some time so my hope is to charge an individual cell, then measure it's internal resistance with enough accuracy to get a baseline, then let it sit for long enough (days or weeks) to see a difference in self discharge between cells and test again. Maybe this requires more resolution than I can get from a sub $100 meter.

 

[jony101]

Yr1035 should be good, its what I use and the readings are repeatable. If I test the cell 5 times I get about the same reading. If I have a group of cells, I test them if the reading is close to each other, its good enough for me.
Example If 5 of the cells are in the mid 30's, and 1 measures in the 80's, then you know which one is bad. It might still be good but I don't use any cells that is too far off from the rest of the cells.