Amps per Hour Calculator

Introduction

Amp-hours (Ah) measure a battery’s stored charge, but understanding how that translates to current draw over time—amps per hour—is essential for sizing battery banks, planning off-grid power, and predicting runtime of devices. This guide explains how to calculate amps per hour both manually and with our built-in calculator. You’ll learn formulas, unit conversions, and real-world U.S. examples—from vehicle batteries to power tools—so you can design systems that meet your needs.

Usage Guide

1. Enter Battery Capacity: Provide amp-hours (Ah) as rated by the manufacturer (e.g., 100 Ah).
2. Enter Time in Hours: Specify the duration over which you draw current (e.g., 5 hours).
3. Alternative Input: If you know watt-hours (Wh) and voltage (V), enter those plus time to derive amps per hour.
4. Click “Calculate Amps”: The tool computes average current draw in amps (A).
5. Review Result: Use the figure to choose wiring, fuses, and load planning.
6. Save or Share: Copy link, print, or download results for documentation.

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Secondary Keyword: amp hour calculator

A reliable amp hour calculator helps translate battery specifications into actionable current figures. By combining Ah, time, and optional Wh/V inputs, users get versatile calculations for diverse U.S. applications—RV systems, marine batteries, solar setups, and backup power.

Understanding Amp-Hours and Amps

Amp-hour (Ah) indicates how much current a battery can supply over one hour. A 100 Ah battery can theoretically deliver 100 A for one hour or 10 A for ten hours. However, voltage and efficiency affect real-world performance.

Amp (A) measures electrical current flow per second. Calculating average amps per hour informs:

• Sizing conductors and overcurrent protection.
• Estimating device runtimes.
• Planning solar charge controllers and inverters.

Manual Calculation Formula

Use either method:

1. From Ah and Time: Amps = Ah ÷ Hours.
2. From Wh, Voltage, and Time: Amps = (Wh ÷ Voltage) ÷ Hours.

Example: 1200 Wh battery at 12 V over 4 hours: (1200 ÷ 12) ÷ 4 = 25 A.

Practical U.S. Examples

Car Battery: A typical automotive battery is ~48 Ah at 12 V. If you draw for 2 hours: 48 ÷ 2 = 24 A average draw—use 30 A fuse.

Cordless Drill: A 5 Ah battery pack at 20 V powering a drill for 0.5 hours: (5 ÷ 0.5) = 10 A average.

Solar Bank: A 200 Ah marine battery bank at 12 V used over 10 hours: 200 ÷ 10 = 20 A average continuous draw.

Unit Conversions and Tips

• Convert minutes to hours: minutes ÷ 60.
• Ensure voltage matches battery nominal rating.
• Allow 20% margin for Peukert’s effect and inefficiencies.

Choosing the Right Components

Once you know amps per hour, select:

• Wire Gauge: Use NEC tables—e.g., 20 A requires 12 AWG copper.
• Fuses/Breakers: 125% of continuous draw (e.g., 24 A→30 A fuse).
• Inverter/Charger Rating: Must handle peak and continuous amps safely.

FAQs

1. What is difference between Ah and A?
Ah measures capacity over time; A is instantaneous current. Divide Ah by hours to get A.

2. How do I account for battery efficiency?
Multiply Ah by 0.8–0.9 for lead-acid, 0.9–0.95 for lithium to adjust usable capacity.

3. Can I use multiple batteries?
In parallel, capacities add; in series, voltage adds. Calculate Ah per string accordingly.

4. How often should I recalculate?
Recompute when load or usage pattern changes significantly—monthly for systems under heavy use.

5. Where find authoritative guidance?
See DOE Solar Homeowner Guide and NFPA electrical codes.

6. Is this tool offline-compatible?
Yes—runs entirely in-browser with no external dependencies.

Disclaimer

This calculator provides estimates only. Consult qualified electricians or engineers for system design and safety compliance.

Conclusion

Calculating amps per hour from battery capacity or energy storage is essential for electrical design and power planning. Use our interactive calculator and this guide to determine current draw, size wiring and protection, and optimize runtime of your devices. With accurate figures and U.S. code references, you can build safe, efficient power systems in any application.