Enter Energy and Electrical Details
Example Data Table
| Energy | Voltage | Runtime | System | Approx Current |
|---|---|---|---|---|
| 120 Wh | 12 V | 1 hour | DC | 10 A |
| 500 Wh | 24 V | 5 hours | DC | 4.17 A |
| 1.2 kWh | 120 V | 4 hours | Single phase AC, PF 0.9 | 2.78 A |
| 6 kWh | 400 V | 3 hours | Three phase AC, PF 0.85 | 3.40 A |
Formula Used
The calculator first converts the entered energy and runtime into watt hours and hours. Then it calculates average watts and current.
DC amps = Power ÷ (Voltage × Efficiency)
Single phase amps = Power ÷ (Voltage × Power factor × Efficiency)
Three phase amps = Power ÷ (√3 × Voltage × Power factor × Efficiency)
Amp hours = Watt hours ÷ Voltage
Margin amps = Amps × (1 + Safety margin ÷ 100)
Use decimal efficiency in the formula. For example, 92% efficiency becomes 0.92.
How to Use This Calculator
- Enter the stored or consumed energy value.
- Select the correct energy unit.
- Enter system voltage in volts.
- Enter the runtime and choose its unit.
- Select DC, single phase AC, or three phase AC.
- Add power factor and efficiency when needed.
- Choose a safety margin for wiring and protection planning.
- Press Calculate and review the result above the form.
- Download the calculation as CSV or PDF for records.
Understanding Watt Hours and Amps
Watt hours measure stored or used energy. Amps measure the rate of electric current. The two values are connected by voltage and time. A battery may store many watt hours, but the amp draw depends on how quickly that energy is used. This calculator helps convert energy into current for practical planning. It supports DC circuits, single phase AC loads, and three phase AC loads.
Why Voltage and Time Matter
A watt hour value alone cannot give amps. Voltage shows the electrical pressure. Time shows how long the load runs. If the same energy is used over a shorter time, current rises. If it is used over a longer time, current falls. A 120 watt hour load at 12 volts over one hour is 10 amps. The same energy over two hours is 5 amps.
Battery and Inverter Planning
For batteries, amp hours are often easier to compare than watt hours. Amp hours equal watt hours divided by volts. Average amps equal amp hours divided by runtime. Inverters add losses, so efficiency should be included. AC systems also use power factor. Motors, compressors, and transformers may draw more current than simple resistive loads. That is why this tool includes efficiency, power factor, and safety margin fields.
DC and AC Current Differences
DC current uses a direct formula. Divide power by voltage. Single phase AC current divides power by voltage, power factor, and efficiency. Three phase AC current also uses the square root of three. This matters in workshops, pumps, machinery, and commercial panels. Using the correct phase option gives a better current estimate.
Using Results Safely
The output is an estimate. Real systems can vary because of cable length, temperature, battery chemistry, startup surge, inverter quality, and load behavior. Use the margin-adjusted amps when selecting fuses, breakers, controllers, and wiring. Always follow electrical codes and product manuals. For high power systems, ask a qualified electrician to verify the design before installation.
Common Conversion Checks
Many users mix watt hours, watts, and amps. Watt hours describe total energy. Watts describe the rate of energy use. Amps describe current at a given voltage. This calculator separates those ideas. It first converts energy into average watts by dividing by time. It then converts watts into current using the selected electrical system. This makes the answer easier to audit.
Practical Design Notes
Use realistic runtime values. A small change in runtime can change the final current a lot. Enter nominal voltage for basic estimates. Enter measured voltage when testing real equipment. For AC loads, use the nameplate power factor when available. If you do not know it, keep a conservative value. The safety margin can help cover surge, aging parts, warm cables, and measurement error. Results should support planning, not replace inspection. Document each assumption so future checks are simple, clear, and repeatable for every connected load later.
FAQs
Can watt hours be converted directly to amps?
Not by energy alone. You also need voltage and runtime. Watt hours show total energy. Amps show current flow. The calculator divides energy by time to get watts, then divides by the electrical system denominator.
What is the basic DC formula?
The basic DC formula is amps equals watt hours divided by voltage and hours. Written simply, A = Wh ÷ (V × h). Efficiency may be included when converters, inverters, or losses are involved.
Why does runtime affect amps?
Runtime changes how quickly energy is consumed. The same watt hour value used in less time creates higher current. Longer runtime spreads the energy use and lowers the average current.
How are amp hours different from amps?
Amp hours describe capacity over time. Amps describe instant or average current. A 20 Ah battery can deliver 20 amps for one hour in ideal conditions, or lower current for longer.
Should I include efficiency?
Yes, include efficiency when power passes through an inverter, converter, charger, or controller. Losses increase the current needed from the source. Use the product rating when available.
What power factor should I enter?
Use the load nameplate value if available. Resistive loads are often near 1. Motors and inductive equipment may be lower. A conservative value helps avoid undersized wiring and protection.
Does three phase use a different formula?
Yes. Three phase current uses the square root of three in the denominator. The formula is amps equals watts divided by √3, voltage, power factor, and efficiency.
Can this help size a battery?
Yes, it can estimate amp hours from watt hours and voltage. Real battery sizing should also include depth of discharge, temperature, aging, surge load, and backup time.
Why is the result average current?
Watt hour data usually describes energy over a period. That makes the calculated current an average over the selected runtime. Some loads may draw higher startup or peak current.
Can I use this for solar systems?
Yes, it can support solar battery and load estimates. Use correct system voltage and realistic runtime. Include controller and inverter efficiency when planning the full energy path.
Is the safety margin required?
It is not required, but it is useful. It helps cover losses, startup surge, warm cables, aging equipment, and imperfect estimates. Use conservative inputs when planning critical electrical equipment loads.