1s 25amp bms to capacity test cells

[NVS]

Has anyone tried a 1s 25amp bms to capacity test cells? I ordered one to try it out.

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I'm going to use this load tester as well.
MakerHawk Electronic Load Tester USB Load Tester 150W 200V 20A Resistor Adjustable Constant Current Battery Capacity Tester Module Intelligent Discharge Resistance Power Tester https://smile.amazon.com/dp/B07F3NHHST/ref=cm_sw_r_apan_i_XM4TCWVZKCXDCZNZSD9S?_encoding=UTF8&psc=1

 

[sunshine_eggo]

No.

What's the purpose of the "BMS"?

You can simply set a discharge target on that unit.

 

[John Frum]

No.

What's the purpose of the "BMS"?

You can simply set a discharge target on that unit.

The wrinkle is the current induced voltage drop on the wire means the capacity tester will disconnect before the cell voltage as measured at the terminals gets to the cutoff value.
Would be nice if somebody would make an improved version with voltage sense leads.

 

[NVS]

No.

What's the purpose of the "BMS"?

You can simply set a discharge target on that unit.

Mine really didn't come with very good instructions, so I just wanted to be sure not to mess up a cell. Also for $4.12 thought it might be cheap insurance.

 

[Substrate]

Just like the old days. If you had a 4S nominal 12v battery with 4 cells, you'd buy 4 and each cell gets one across it's own terminals.

Do the LVD and HVD specs (and their associated hysteresis delay time to account for surges) meet your application? Like the 3.75V hvd with a half-second delay time - is that ok for what you are trying to do? Ie, in a severely unbalanced bank to begin with, will your cells be ok if voltage shoots to say 4.4v for a half-second?

Note that it only has around 50ma bleeder resistance. That means it is only good for cells that are already very close in top-balance. OR, you are using them on a very small bank, where 50ma of bleeder current could actually top-balance them in a reasonable amount of time.

The usual mistake is that people would just buy 4 random cells, put one of these on each, and charge up and watch the blinky lights of bleeder discharge for a month at high voltage - because 50ma of bleeder resistance meant nothing to a large bank. Meanwhile, all that time spent near full charge on a large bank degraded the cells.

The other consideration is how nicely does it fail? Things happen. QC and manufacturing deviations are not uncommon.

So do the mosfets fail shorted or open? If they fail shorted, then you have 50ma of UNbalancing happening all the time. If it fails open, then you have NO balancing happening on that one cell all the time. Ah, the question of whether you can risk additional points of failure vs your trust in the manufacturer.

I'm just being a propeller-head a** to make sure it fits your application. Otherwise it's just slapping stuff on which is hard to learn from. So I apologize in advance.

 

[NVS]

Nope, thanks. I'm just going to use it on one cell at a time to capacity test each cell. I'll use a 4s bms with Bluetooth when I'm done and putting the pack in service. I have 8 cells total just wanted to match the cells to get the best pack.

 

[NVS]

Finally got around to testing my cells with the 1s bms. Will see how it goes soon.