arshah6-notebook.md

Self-Heating System Project

Lab Notebook: Heating Subsystem Contributions

Week of 9/18

Initial Project Proposal

• Collaboratively brainstormed potential designs for the self-heating system. Focused on integrating a robust heating subsystem with proper ventilation.
• Prepared the project proposal outlining the main components: a nichrome heating element, steel pipe enclosure, thermistor-based temperature sensing, and a fan-driven ventilation system.
• Highlighted potential challenges in power management, safety mechanisms, and integration of off-the-shelf components.
• Finalized initial high-level requirements:
  • Temperature modulation within 3°F of the setpoint.
  • Noise levels below 60 dB for quiet operation.
  • Energy efficiency within 1000-1500W power consumption.

Initial System Design:

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Week of 9/25

Initial Heating Subsystem Design

• Selected nichrome wire as the heating element for its corrosion resistance, high melting point, and superior resistivity.
• Calculated power requirements using:

$$P = \frac{V^2}{R}$$

Where:

• (V = 24) volts.
• (R) (resistance) determined experimentally to optimize heat output.

Resulting in:

$$P = \frac{24^2}{3.5} \approx 165 \text{ W}$$

• Tested initial nichrome lengths and gauges, refining configurations through iterative testing.
• Decided on nichrome-80 as the material for its high-temperature resistance and mechanical flexibility.

Mathematical Analysis of Heating Subsystem

• To better understand the relationship between key parameters, the temperature rise (\Delta T) of the nichrome wire was derived as:

$$\Delta T = \theta \cdot \frac{V^2}{\rho L^2}$$

Where:

• (ρ): Resistivity (or resistance per unit length).

• (L): Length of the wire.

• (θ): Radial thermal resistance of the wire to ambient (a constant).

• This formula indicates that the temperature increase is proportional to the square of the applied voltage and inversely proportional to the square of the wire length:

$$T \propto \frac{V^2}{L^2}$$

• This relationship guided the selection of wire lengths and voltages for balancing efficiency and safety, ensuring proper heat dissipation.

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Week of 10/15

Ventilation System Implementation

• Integrated PWM-controlled fans to manage airflow through the steel pipes.
• Developed a 6-stage PWM curve for dynamic fan speed adjustment:
  • Optimized exhaust temperatures while minimizing noise levels.
  • Verified airflow with thermistors, achieving a 28°F temperature delta.
• Used oscilloscope to calibrate PWM signal parameters for the fans.

PCB Buck Converter Designs (ON-BOARD)

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Week of 11/2

Heating System Prototyping

• Wrapped nichrome wire around steel pipes to serve as heating elements.
• Performed tests to balance heating efficiency and safety:
  • Recorded instances of overheating and electrical shorts due to direct contact between nichrome and steel.
  • Applied Rust-Oleum insulating spray to mitigate shorts and maintain uniform heating distribution.

Gauge	Length (cm)	Res. (Ω)	Heat	Melted?	Amps	Power (W)
18	106	2.3	Yes	No	10.43	250.43
18	54	0.94	Yes	Yes	20	376
18	24	0.33	Yes	Yes	20	132
24	45	1.6	Yes	No	10.62	254.88
24	54	3.1	Yes	Yes*	7.74	185.81
24	106	5.83	Yes*	No	4.12	98.80

(Notes: "Yes" indicates partial melting occurred or required additional insulation adjustments.)

Shorts Observed with just Nichrome and Steel Rod Setup:

Coating with Rust-Oleum - FUN! :) :

Diagram of Heating Setup:

+---------+        +---------+        +---------+
| Nichrome|  --->  | Steel   |  --->  | Heated  |
| Wire    |        | Pipe    |        | Airflow |
+---------+        +---------+        +---------+

Final Setup:

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Week of 11/15 (Some during thanksgiving break)

PCB Design Challenges

• Designed PCB to integrate power delivery and sensor interfaces:
  • Added safety features for high-current traces and voltage regulators.
  • Verified operation of DS18B20 sensors for precise temperature measurements.
• Encountered issues with MOSFETs:
  • MOSFETs overheated due to insufficient gate-to-source voltage (V_GS) and high drain-to-source resistance (R_DS).
  • Analysis of the drain-to-source voltage (V_DS)​ vs. drain current (I_D)​ curve revealed operational limits. The MOSFET’s junction-to-ambient thermal resistance Rθ_jA​ and case-to-sink resistance Rθ_CS caused rapid temperature rise:

$$P_{\text{max}} = 2.8 \text{ W}$$

This was insufficient, leading to failure at:

$$P_{\text{actual}} = 3.5 \text{ W}$$

• Replaced MOSFETs with 24V relays for reliable switching of the nichrome wire.

Circuit Model of Nichrome and relay (modeled as switch):

ESP Flashing Setup

• Due to issues soldering and setting up serial converter and USB-C connecter we switched over to a more standard flashing setup to be able to program the ESP.
  

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Week of 11/25 (Thanksgiving Break)

System Testing and Optimization

• Conducted end-to-end testing of all subsystems:
  • Measured exhaust and ambient temperatures, ensuring safe operating limits.
  • Validated PWM fan control under varying load conditions.
• Power consumption stabilized at:

$$P \approx 253.1 \text{ W}$$

• Demonstrated compliance with noise and energy efficiency requirements.

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Week of 12/2

Final Integration and Demonstration

• Assembled the final system:
  • Unified heating, ventilation, and control subsystems.
  • Verified operation under simulated user scenarios.
• Presented final prototype, achieving:
  • Temperature modulation within ±3°F.
  • Energy consumption under 600W.
  • Noise levels measured at 55 dB during operation.
• Suggested future improvements:
  • Use of infrared heating panels to improve efficiency.
  • Replace metal enclosures with ABS plastic to reduce thermal losses.

Fried ESP32 Chip:

• We somehow during assembly fried our ESP as well two of our external Buck Converters
• Damage occurred while adjusting IO/power pins during operation. This led to us having to resolder a new PCB entirely.
• However this time we implemented safety measures to make sure we didnt fry another ESP:
  • Powered down all systems before modifications.
  • Added current-limiting resistors.

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Key Completion Points:

1. Developed and optimized the nichrome heating subsystem.
2. Designed a robust ventilation system with PWM-controlled fans.
3. Overcame PCB design challenges, ensuring safety and reliability.
4. Integrated DS18B20 sensors for precise temperature tracking.
5. Established safety protocols to prevent hardware failures.
6. Demonstrated a fully functional prototype meeting all requirements.

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Reflections:

• Successfully implemented a cost-effective, energy-efficient self-heating system.
• Learned valuable lessons in hardware troubleshooting, safety design, and subsystem integration.
• Addressed challenges through iterative prototyping and testing, meeting all project goals.