okashira wrote:Sorry, I was thinking you were using for general current sense (ie for SoC calc)
I will be using it for this, but I'm looking at adding short protection as well if I can do it without any compromises.
okashira wrote:if it's high inductance, so what, it will just make the signal even faster because the shunt terminals will see high voltage pretty quick.
okashira wrote:Now that I think more about it, it may actually be desirable to have the shunt have high inductance for short circuit detection. This way it will pick up a high voltage even before the high current occurs
Can you please explain this in a bit more detail? What I understood (or misunderstood) from the discussion
was that a high inductance shunt would smooth the current running through it and make the voltage across the shunt rise slowly.
The current flowing through the shunt will be exactly the current flowing though the rest of the circuit. Nothing you can do about that. (conservation of mass, Kirchhoff law, etc.)
If the shunt has inductance, then the voltage across the shunt terminals will be a function of not only the current, but a function of dI/dt. We can assume the shunt capacitance will be zero.
Further, we can assume the circuit that which the shunt is measuring current will have a very high inductance relative to the shunt itself. (battery lead length... etc.)
an inductor will show a high voltage if the dI/dt is high. So, a shunt with a high inductance will show a high voltage if the dI/dt is high.
Thus, a current shunt with a high inductance will display a high voltage (interpreted as a high current by the bms) during the time with the current ramps from zero to short circuit condition.
Thus, a shunt with high inductance will have no negative effect in terms of short circuit detection - in fact it may be able to detect short circuit before it actually fully occurs due to the high dI/dt that should occur during a short circuit event itself!
There may be negative end user effects due to this - for example if a poorly designed controller allows the user to ramp from 0 to 100% throttle without any damping. Or the system doesn't have any precharge spark suppression circuit, it could trigger the short circuit detection in this instance when there isn't really one.