Choosing the Right Filament or Boat for Your 1 kVA or 2 kVA Evaporation Source
Before selecting a filament or boat, you must understand the voltage and current limits of your evaporation power supply. Low-voltage (LV) systems are current-driven, and filament selection must be matched carefully to stay within the system’s safe operating range.
Common LV Power Supply Examples:
| Power Rating | Voltage (Max) | Current (Max) | Total Power |
| 1 kVA | 12 V | 80 A | 1000 W |
| 2 kVA | 5 V | 400 A | 2000 W |
Your filament or boat must not exceed these limits during any part of the deposition process. Overshooting can cause:
- Power supply overload or shutdown
- Source instability
- Damage to the filament or clamps
Matching Source Resistance
Use Ohm’s Law to verify compatibility:
- Power (W) = Voltage (V) × Current (A)
- Resistance (Ω) = Voltage ÷ Current
| Power Supply | Recommended Filament Resistance |
| 1 kVA (12 V / 80 A) | ~0.15 Ω |
| 2 kVA (5 V / 400 A) | ~0.0125 Ω |
Important: The filament’s cold resistance will be lower than its hot resistance, so measure cold resistance with a multimeter and confirm it’s within safe limits.
Practical Guidelines:
- Tungsten wire filaments (basket or coil types) typically operate efficiently on a 1 kVA system.
- Boats, due to their lower resistance and higher thermal mass, often require higher current and are better suited for 2 kVA systems.
- 2 kVA sources are ideal for low-voltage, high-current applications (e.g., wide molybdenum boats or large melt loads).
- Always ramp power slowly to prevent inrush current that could exceed limits or cause filament failure.
Example: Evaluating a Boat for Compatibility – S37 Moly Boat Source
This example shows how to determine if the S37 molybdenum boat is suitable for your LV power supply.
Manufacturer Specs:
- Voltage: 1.84 V
- Current: 201 A
- Power: 370 W
- Operating Temperature: ~1400°C
- Capacity: 1.4 cc
Step 1: Calculate Resistance
R = V ÷ I = 1.84 V ÷ 201 A ≈ 0.00915 Ω
Like the S8C, this boat has very low resistance, requiring a high-current, low-voltage power source.
Step 2: Check Power Supply Compatibility
| Power Supply | Max Voltage | Max Current | Resistance Target | Compatible? |
| 1 kVA | 12 V | 80 A | ~0.15 Ω | No — Over current limit |
| 2 kVA | 5 V | 400 A | ~0.0125 Ω | Yes — Within range |
Conclusion: The S37 boat is well-suited for a 2 kVA LV supply, which can support the required 201 A.
It cannot be used with a 1 kVA source, which lacks the current capacity.
Key Takeaways:
- Even though the S37 draws only 370 W, its low operating resistance (0.009 Ω) demands high current.
- High-capacity boats like the S37 (1.4 cc) are ideal for 2 kVA low-voltage, high-current systems.
- Always verify resistance and current draw, not just total wattage.
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