DC Formulas: I = P / V | P = I × V | V = P / I
Example: 240 W at 12 V draws 20 A of current
Use for: Fuse sizing, wire gauge selection, battery discharge planning
About This Calculator
What this tool does: Converts DC watts and amps directly for battery, DC bus, and low-voltage system sizing.
Core idea: For DC, the ideal relation is straightforward: P = V * I.
Mini Example
A 120 W DC load at 12 V draws about 10 A.
Quick Literacy Notes
- At low voltage, current rises quickly for the same power, increasing cable losses.
- Use worst-case voltage (often minimum bus voltage) to size current paths safely.
- Connector and fuse ratings should include temperature derating and continuous duty.
Common Mistakes
- Sizing at nominal voltage instead of worst-case minimum voltage.
- Ignoring current rise and cable losses at low-voltage DC.
Key Takeaways
- For DC, the ideal relation is straightforward: P = V * I.
- At low voltage, current rises quickly for the same power, increasing cable losses.
- Avoid this mistake: Sizing at nominal voltage instead of worst-case minimum voltage.
Practical Checklist
- Size current paths at minimum bus voltage to capture worst-case amps.
- Account for cable voltage drop in low-voltage, high-current circuits.
- Apply temperature derating to connectors, terminals, and protective devices.
FAQ
Q1: Which DC voltage point should be used for worst-case current sizing?
Quick Answer: Validate this first: At low voltage, current rises quickly for the same power, increasing cable losses.
Engineer Note: If this assumption drifts from real conditions, downstream outputs can remain numerically neat but operationally wrong. Confirm with measured or site-specific inputs before locking decisions.
Q2: What mistake usually underestimates cable loss in low-voltage systems?
Quick Answer: Avoid this first: Sizing at nominal voltage instead of worst-case minimum voltage.
Engineer Note: In practice, the next failure mode usually follows: Ignoring current rise and cable losses at low-voltage DC. Address both together; correcting one while keeping the other often leaves the design bias unchanged.
Q3: When should I perform full protection-device coordination checks?
Quick Answer: Use this calculator for fast screening and scenario comparison.
Engineer Note: For procurement, warranty, compliance, or commissioning decisions, move to detailed verification with datasheets, measured conditions, and project constraints. Core rule: For DC, the ideal relation is straightforward: P = V * I.
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