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What does this circuit do? Why do we need it?
This board takes inputs from the DCDC converter and the Supplemental Battery and selects which source to output to the fuse box. DCDC is the power from the high voltage primary battery pack that gets stepped down to 12V through the DCDC converter. The supplemental battery pack is the low voltage 12V NiMH battery pack. When DCDC is on, the board will select DCDC, and when DCDC is off, the board will select the Supplemental Battery. The supplemental should only be selected during the ignition and the fault states. The board selects the source using a 10V zener diode that will break down once DCDC reaches 10V.
This board also interfaces with both the Supplemental Monitoring PCB and Ignition Switch:
- For the Supplemental Monitoring PCB, this board sends the voltage of the Supplemental Battery out from J1.
- For the Ignition Switch, this board sends Supplemental Power to the Controls Board through J6, which is then routed back to this board through J7 when the Ignition Switch is switched from the off position. This signal is routed to the gate of Q3 which turns on the NMOS and starts sending power to the fuse box.
Pertinent Regulation(s)
Link to Regs: https://www.americansolarchallenge.org/regulations/2024-american-solar-challenge-regulations/
Regulation | Description of the Regulation | How Regulation is Met |
8.2.C.1 | Supplemental, replaceable batteries carried in the solar car may be used to power: Main Power Switch, driver ventilation fans (if solely used for driver ventilation), telemetry, and the horn. All other systems present on the car must be powered off the main battery. | Under normal operations, all systems in the car are powered off by the main battery as the DCDC voltage should be high.
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8.2.C.2
| Supplemental battery power may be used to momentarily power the battery protection system (BPS) as defined by Reg. 8.3 to verify safe battery parameters before energizing the Main Power Switch. | Upon startup, the supplemental battery will be selected by the Power Board and be used to power all LV systems until BPS determines the battery is safe.
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8.2.C.3 | During a battery fault in which the BPS has automatically opened the Main Power Switch, the supplemental battery must be used to power the BPS, BPS Strobe, and BPS Fault Driver Indication. While in such a fault state, the supplemental battery may be used to power any other systems (signal lights, rear view camera, telemetry, etc) that do not provide motive power to the vehicle. | Under fault state, all systems will be powered off of the supplemental battery as the DCDC voltage will be low. |
Context
Location of the Board: The power board will be located in the electronics enclosure(HV section if the electronics enclosure is split).
List of I/O and Connections:
| # | Name | Type | Ideal Voltage | Notes |
|---|---|---|---|---|
| J1 | SUPP PWR MON | 1x02_P3.00mm_Vertical Female | +12V | 9.9 mm tall |
| J2 | SUPP PWR 1 | 1x02_P7.49mm_Vertical Female | +12V | 14.76 mm tall |
| J3 | SUPP PWR 2 | 1x02_P7.49mm_Vertical Female | +12V | 14.76 mm tall |
| J4 | DCDC PWR | 1x02_P7.49mm_Vertical Female | +12V | 14.76 mm tall |
| J5 | FUSE OUT | 1x02_P7.49mm_Vertical Female | +12V | 14.76 mm tall |
| J6 | SUPP OUT | 1x02_P3.00mm_Vertical Female | +12V | 9.9 mm tall |
| J7 | LV ENABLE | 1x02_P3.00mm_Vertical Female | +12V | 9.9 mm tall |
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Main
Schematic
List of Circuit Components
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- Heavy use of planes and large traces to sustain the high current flowing along the power lines
- Used MOSFETs for logic as opposed to Op-Amps due to fast switching time and to avoid feedback
PCB:
3D Model:
Additional Considerations
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