Hi there, I'm wondering if anyone can help me verify I'm doing the right method and using the appropriate resistor to test my 18650s liion internal resistance.
I have been following a method shown by 'Tom Donnelly' on YouTube, where you first measure the cell voltage, then put the cell across the resistor and re measure voltage. Then divide that voltage by the ohm rating of the resistor to get the current. Then subtract the resisted voltage from the open voltage to get the voltage drop. And finally divide the voltage drop by the current to get the resistance. (sorry that's long winded..)
What I'm unsure about is if I'm using the appropriate resistor, it's a 1.5 ohm and 5 watt resistor. Does watts change anything in this scenario? Also the resistor states it's 1.5 ohm, but my multimeter reads 2 ohms. So I put the positive and negative of the multimeter together and it reads .5 ohm. Does that mean I should be using 2ohm in the equation instead of 1.5?
The reason I'm asking is the results I got for 10 cells I tested were all relatively high, about 130 to 220 milliohms. So im hoping I've done something wrong and don't have 160 useless cells..
The other parameters of the cells all seem pretty good, most are around 3000mah capacity, and have been sitting for a few months according to the person I bought them from, and they all read around 4.07 to 4.1 volts before any other testing was done, so don't seem to self discharge. Can a cell have good capacity, and hold its charge well but still have high internal resistance?
Internal resistance should be below 65mOhm ish right? Would anything above that render them useless for an 1500w ebike, even if the capacity and voltage seem good?
One final point is the resistor I used got warm to the touch within 5 seconds or so, is this also normal?
Do you think I am using the appropriate resistor, might I need a new multimeter, or am I doing the equation incorrectly?
Sorry for the ignorance and appreciate any answers!
Cheers
I have been following a method shown by 'Tom Donnelly' on YouTube, where you first measure the cell voltage, then put the cell across the resistor and re measure voltage. Then divide that voltage by the ohm rating of the resistor to get the current. Then subtract the resisted voltage from the open voltage to get the voltage drop. And finally divide the voltage drop by the current to get the resistance. (sorry that's long winded..)
What I'm unsure about is if I'm using the appropriate resistor, it's a 1.5 ohm and 5 watt resistor. Does watts change anything in this scenario? Also the resistor states it's 1.5 ohm, but my multimeter reads 2 ohms. So I put the positive and negative of the multimeter together and it reads .5 ohm. Does that mean I should be using 2ohm in the equation instead of 1.5?
The reason I'm asking is the results I got for 10 cells I tested were all relatively high, about 130 to 220 milliohms. So im hoping I've done something wrong and don't have 160 useless cells..
The other parameters of the cells all seem pretty good, most are around 3000mah capacity, and have been sitting for a few months according to the person I bought them from, and they all read around 4.07 to 4.1 volts before any other testing was done, so don't seem to self discharge. Can a cell have good capacity, and hold its charge well but still have high internal resistance?
Internal resistance should be below 65mOhm ish right? Would anything above that render them useless for an 1500w ebike, even if the capacity and voltage seem good?
One final point is the resistor I used got warm to the touch within 5 seconds or so, is this also normal?
Do you think I am using the appropriate resistor, might I need a new multimeter, or am I doing the equation incorrectly?
Sorry for the ignorance and appreciate any answers!
Cheers