How did I trip the Protection circuit on Ultrafire 3000mAh 18650 with a DMM?

[Pulsar]

the panasonics look far from discharged at 3.6v.
maybe i was remembering wrong lol… but i could have sworn i had them down that far before.

[ri_chevy]

Why is it safe then for the Panasonic NCR18650 cells to go down to 2.5v’s if there is no power left? I do not understand?

[PilotPTK]

Resting Voltage vs. Under-Load voltage. Additionally, There is power left - it is not ZERO percent. There is just not much power left - not enough to do anything very productive with.

PPtk

[ri_chevy]

@PilotPTK

Resting Voltage vs. Under-Load voltage. Additionally, There is power left - it is not ZERO percent. There is just not much power left - not enough to do anything very productive with.

PPtk

Thank you for the response. According to the table above, at 3.2v, the cell has nothing left. I just wonder why Panasonic would state that it is OK to take the cell down to 2.5v? Does not seem safe or good for the cell.

[HKJ]

@ri chevy

@PilotPTK

Resting Voltage vs. Under-Load voltage. Additionally, There is power left - it is not ZERO percent. There is just not much power left - not enough to do anything very productive with. PPtk

Thank you for the response. According to the table above, at 3.2v, the cell has nothing left. I just wonder why Panasonic would state that it is OK to take the cell down to 2.5v? Does not seem safe or good for the cell.

The above voltage is unloaded, when loaded you can get considerable lower, depending on discharge current.

You can see that on all my battery test curves.

[ri_chevy]

Thank you HKJ. And PilotPTK.

[501_sea]

@DimBulb

A real world cell can be thought of as an ideal voltage source of V volts in series with an internal resistor of R ohms.

Measuring the open circuit voltage with a voltmeter is safe and gives you the value of Voc.

Ideally, you could put an ammeter [whose internal shunt resistance is zero ohms] across the battery and get the value of the short circuit current Isc which gives you Rint since Rint = Voc/Isc. Now the cell is completely defined. It’s the Thevenin Equivalent Circuit.

But, most batteries don’t like being shorted. Isc for a car battery may be 12.76 V/0.01 ohms = 1300A.

Another way to characterize a battery at some load current and temperature is load down the battery with a resistor so that Voc drops maybe 10%, measure the voltage across the resistor, and calculate the internal resistance. Then you’ll have Voc, Isc and R. Let me know if you want the formula.

Thanks for the offer of the formula

It seems a bit too involved for me, unfortunately, though…I’m the type of guy that just knows that Volts x Amps = Watts. The Rint and Isc stuff is a bit above my head, thanks all the same

[DimBulb]

@501 sea

@DimBulb

A real world cell can be thought of as an ideal voltage source of V volts in series with an internal resistor of R ohms.

Measuring the open circuit voltage with a voltmeter is safe and gives you the value of Voc.

Ideally, you could put an ammeter [whose internal shunt resistance is zero ohms] across the battery and get the value of the short circuit current Isc which gives you Rint since Rint = Voc/Isc. Now the cell is completely defined. It’s the Thevenin Equivalent Circuit.

But, most batteries don’t like being shorted. Isc for a car battery may be 12.76 V/0.01 ohms = 1300A.

Another way to characterize a battery at some load current and temperature is load down the battery with a resistor so that Voc drops maybe 10%, measure the voltage across the resistor, and calculate the internal resistance. Then you’ll have Voc, Isc and R. Let me know if you want the formula.

Thanks for the offer of the formula

It seems a bit too involved for me, unfortunately, though…I’m the type of guy that just knows that Volts x Amps = Watts. The Rint and Isc stuff is a bit above my head, thanks all the same

You’re welcome.