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Based on the requirements, it was determined that the high voltage from the battery would be reduced to 5-12V using two resistors in series, and an instrumentation amplifier would measure the difference in voltage across the pre-charge resistor. Once the differential is minimum, the main relay would then be closed with a MOSFET. The discharge portion of the circuit would simply be a normally closed relay that would open when the vehicle is in it's run state.
Requirements
| # | Title | User Story | Importance | Notes |
|---|---|---|---|---|
| 1 | Voltage Isolation | High voltages must be isolated from the 12V rail of the vehicle, so in case of a failure in the resistors, HV will not go into the 12V rail | Must Have |
Optoisolator | |||
| 2 | Reliable Operation | Must reliably initiate pre-charge and discharge when powered on and powered off | Must Have |
| Discharge is entered whenever power is cut to the board with a SPDT relay |
Questions
Below is a list of questions to be addressed as a result of this requirements document:
| Question | Outcome |
|---|---|
| Minimum differential voltage before the main relay can close | < 0.7V should be enough to prevent any arcing |
| P-ch MOSFET goes to DCDC and Pre-charge relay, with RC circuit going to Pre-charge relay for >5ms. What voltage does DCDC need? Add another N-ch MOSFET for higher current? | 12VDC for DCDC, Use Additional mosfet and RC circuit for time delay |
Proposed Parts
Changes:
- Look at Chaos MOSFETS
- Change to N channel mosfets, standardize
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