When selecting a used diesel generator for your business or project, one of the most critical factors to understand is how much electrical current (measured in amps) the unit can handle. Whether you're looking to power industrial equipment, construction sites, or backup systems, knowing how to calculate amps ensures you're choosing the right generator for your needs.
In this guide, Generators For Export walks you through the process of calculating amps in a simple, step-by-step manner, helping you make informed decisions when purchasing a used generator.
Understanding the Basics: Volts, Amps, and Watts
Before diving into calculations, it's essential to grasp the relationship between three key electrical terms:
- Volts (V) – The force of electricity, like water pressure in a pipe.
- Amps (A) – The flow of electricity, similar to the volume of water moving.
- Watts (W) – The total power, which is a product of voltage and amperage.
The fundamental electrical formula is:
From this equation, we can rearrange it to find amps:
Now, let's apply this formula in real-world generator scenarios.
Step 1: Identify the Generator’s Output Power
Most generators are rated in kilowatts (kW). If you have a generator rated at 50 kW, convert it to watts:
If your generator is rated in kVA (kilovolt-amperes), you need to convert it into kW. The conversion factor is typically 0.8 (assuming a power factor of 0.8):
For example, a 100 kVA generator:
Step 2: Determine the Voltage Level
Generators operate at different voltage levels, depending on whether they are single-phase or three-phase:
- Single-phase: Typically 230V in the UK.
- Three-phase: Common voltages include 400V (UK standard) and 415V.
The voltage level affects how you calculate amperage.
Step 3: Use the Correct Formula for Amperage
The formula to calculate amps depends on whether the generator is single-phase or three-phase:
Single-Phase Generator Calculation
Use:
Example: A 50 kW generator at 230V:
Three-Phase Generator Calculation
For three-phase generators, the formula includes a power factor (PF) (usually 0.8) and the square root of 3 (√3 ≈ 1.732):
Example: An 80 kW generator at 400V:
Step 4: Consider Load Requirements
Calculating amps is only part of the equation. You must also consider:
- Startup vs running power – Motors and machinery often require higher startup current.
- Total load capacity – Ensure the generator can handle peak demands.
- Power factor variations – If your load has a different power factor (e.g., 0.9 instead of 0.8), adjust calculations accordingly.
Step 5: Check Generator Specifications
When purchasing a used generator, check:
- Nameplate data – Provides voltage, power rating, and amperage capacity.
- Phase type – Determines which formula to use.
- Load compatibility – Match your equipment needs with the generator’s output.
Step 6: Verify with a Qualified Electrician
Although these calculations give you a solid estimate, always consult a qualified electrician before finalising a generator purchase. They can help ensure compatibility with your electrical system and compliance with safety regulations.
Why Accurate Amp Calculation Matters
Choosing the wrong generator size can lead to:
- Overloading risks – Excessive current draw can damage equipment.
- Inefficiency – A generator running below capacity wastes fuel.
- Unstable power supply – Fluctuations can cause outages or damage to sensitive devices.
By correctly calculating amperage, you avoid these issues and ensure optimal performance.
Get Expert Advice on Used Generators
At Generators For Export, we specialise in high-quality used diesel generators for various applications. Whether you need a standby power solution or a primary power source, our team can help you find the right generator to match your power requirements.
If you have any questions about generator sizing or amperage calculations, get in touch with us today!
Call: +44(0)1386 553344 | Email: sales@gfe.uk.com