Wolf
Moderator
- Joined
- Sep 25, 2018
- Messages
- 2,009
Discussion about the benefits of DC IR testing versus AC 1kH IR ( Impedance) testing.
2 wire vs 4 wire kelvin etc.
Primer of discussion copied from another thread.
gauss163 Wrote:
2 wire vs 4 wire kelvin etc.
Primer of discussion copied from another thread.
gauss163 Wrote:
But iirc theOpus is doing alonger timeDC IR test (vs. 1ms AC). So it is also measuring somenon-ohmic parts of the IR, i.e. additional components of the cell'sIR that don't behave linearly as in Ohm's Law and take time longer than 1mstoramp up to steady-state values(e.g. charge transfer and diffusion processes). This is why at the end of (dis)charge wesee both an instantaneous voltage change (from the ohmic part of the IR- whichbehaves like a resistor), followed bya much slower exponentially decaying voltage changethat asymptotically approaches the steady-state resting voltage (from the non-ohmic IR, which takes a long time (hours) to ramp down as various elecrochemical processes converge to equilibrium).
In many cases it is thenon-ohmic part of the IR (vs. capacity degradation)that ends uplimiting the lifetime of the cell because it can degrade at 10 times the rate of the ohmic part, and this greatly drags down the voltage under load (esp. for high-current loads). Whether or nor this is a limiting factordepends on what type of loads you puton the battery. If your device only usesshort pulses (e.g. a jump starter or vape) then the non-ohmic IRplays little role since the discharges aren't long enough for it to kick in.OTOH if you are doing longer time discharges without big spikes then the non-ohmic IR plays a big role. Some loads are a mixture of both and require more complex analysis (e.g. to see if a constant load plus occasional spikedrags the voltage low enough for long enough time to trigger undervoltage protection).