Opus bt-c3100 v2.2 discharge cutoff for 18650's

[pdirt]

How/when are you measuring the termination voltage? This must be done while it is discharging, not after it has finished (since the cell voltage quickly rebounds immediately after the discharge ends).

I kept an eye on the charger the last few times. When the mA dropped to 0 for li-ion, the voltage would be about 3.4-3.5. Within a few hours, it would rise up to 3.5-3.6. But this is no where near the 2.8v spec of the charger (unprotected 14500). I do not have any unprotected 18650's to try this with, but I see a similar pattern with NiMH cells as well.

 

[Gauss163]

I kept an eye on the charger the last few times. When the mA dropped to 0 for li-ion, the voltage would be about 3.4-3.5. Within a few hours, it would rise up to 3.5-3.6. But this is no where near the 2.8v spec of the charger (unprotected 14500). I do not have any unprotected 18650's to try this with, but I see a similar pattern with NiMH cells as well.

That won't work well because the charger updates the display very slowly but the voltage is dropping very quickly near the end. Instead you can connect a DMM and use it to monitor the minimum voltage (or try to eyeball that). This should give you a much more accurate reading of the actual discharge termination voltage.

 

[pdirt]

That won't work well because the charger updates the display very slowly but the voltage is dropping very quickly near the end. Instead you can connect a DMM and use it to monitor the minimum voltage (or try to eyeball that). This should give you a much more accurate reading of the actual discharge termination voltage.

Ah, that is good to know!

Forgive the rookie question, but if I understand you correctly, by "connect a DMM", you mean to connect a multimeter to the cell while it is in the charger slot while the cell is being charged/discharged?

 

[Gauss163]

[...]Forgive the rookie question, but if I understand you correctly, by "connect a DMM", you mean to connect a multimeter to the cell while it is in the charger slot while the cell is being charged/discharged?

Yes. Be sure to use a DMM that has a decent display update rate.

 

[pdirt]

Yes. Be sure to use a DMM that has a decent display update rate.

I have two DMM and one analog one. Both the DMM's seem to have a display update rate of perhaps 0.5-1.0 second, which I assume is adequate. Any idea what the display update rate is on the Opus BT C-3100?

 

[Gauss163]

^^^ They should work well since the BT-C3100 voltage display is refreshed only every 30s starting in V2.1 (60s prior to V2.1), see the changelog here.