did some testing of the active pre-charge. for my project i need one to protect the main contactor from damage. i can't use a simple resistor because the dc/dc converter is using some current.
first i build up the "Automatic Precharge 3" with a switch an it worked great.
nice liniare voltage rise and constant current.
next i removed the switch and got this result.
i think the high peak current is caused by the capacitor voltage divider made up by the cap in the controller and the 1uf(c1) in the circuit and the gate of the mosfet. the caps are charged through the resistor R2. the gate has the smallest capacitance and will be charged the quickest.
by adding a 10uf cap across the the zenerdiode, the voltage divider changed and gave this result.
the constant current is back, but it takes several seconds before it turns on.
to fix it i added a mosfet to the circuit.
when the battery is connected the Q2 is switched on before the main mosfet Q1. and shorting out the gate of the main mosfet just long enough for the capacitor c1 to charge up. (c2 is not used) and it works nicely.
added bonus, when the battery is disconnected and then reconnected before the circuit is discharged Q2 will reset the system.
for this test i used a 8800uf 50v capacitor