Precharge Rev 5.0 Validation Results

After troubleshooting the board for many days and finally fixing all of the backwards components, the latching works for precharge!! This page will document the results and captures in terms of timing and state of capacitors for the board during precharge and discharge.

The simulation capacitors used are 4x220uF in parallel (880uF total).

Note: the one modification made to the board for this testing was the removal of C25. The reason is that due to the nature of C25 and it’s time before charge, the state of the and out at t=0 when a9 is set to high is that there is a small period where the latch out is high and technically the contactors would be asked to close for a small amount of time. This is unideal as we never want to close the contactors until precharge is over, and until we figure out the exact purpose of C25, I am leaving it off. The other modification for this testing when using 37.7V as the input to the board, was changing R13 to be 100k instead of 29.4K(?) so that Q2 closes with the input voltage. There are no other modifications to the board except for fixing all of the assembly issues.

Firs thing to note;

• Precharge takes about 6 seconds with this capacitor and with an input of 37.7V. It stops charging when the capacitor is at 36.5V. It takes about 6 seconds to discharge to 2V. The captures seen later on will cover this

Scope Captures:

State	Scope Shot(s)	Probes	notes

State	Scope Shot(s)	Probes	notes
Precharge	Open Open	Purple = capacitor voltage level Yellow = iso_latch_out Blue = and_out	You can see that the and_out goes high temporarily to latch the iso_latch_out and keep it latched.
Discharge		Purple = capacitor voltage Yellow = latch out Blue = gate of Q3
Latch logic		Purple = Pin 2 of U8 Yellow = comp_out Blue = and_out