Transformer Current Ratio

Ip / Is = Ns / Np

Quick answer

This calculator solves Ip / Is = Ns / Np for Primary Current. With Secondary Current 4.4 A, Primary Turns 0.5, Secondary Turns 1.1, the result is 9.68 A. It solves in 4 directions, so you can enter the values you have and get the one you need.

Calculator

Primary Current (A)
—

Formula

Ip / Is = Ns / Np

Description

In a transformer the current ratio is the inverse of the turns ratio: the winding with more turns carries less current. This follows from conservation of apparent power (Vp·Ip = Vs·Is) combined with the voltage being proportional to turns. A step-down transformer that lowers voltage therefore raises the available current proportionally.

Variables

  • Ip — Primary current (A)
  • Is — Secondary current (A)
  • Np — Primary turns
  • Ns — Secondary turns

Practical Notes

Use this to size winding wire gauge: the high-current (low-turns) winding needs thicker wire. The current ratio assumes an ideal transformer; magnetizing current adds a small extra primary current.

Symbols and units

Symbol Meaning Default unit Accepted units
Ip Primary Current A pA, nA, µA, mA, A, kA
Is Secondary Current A pA, nA, µA, mA, A, kA
Np Primary Turns — —
Ns Secondary Turns — —

Step by step

  1. 1. What you know: Secondary Current 4.4 A, Primary Turns 0.5, Secondary Turns 1.1
  2. 2. The relation: Ip / Is = Ns / Np
  3. 3. Substitute: Is = 4.4 A, Np = 0.5, Ns = 1.1
  4. 4. Result: Primary Current = 9.68 A

Worked examples

Minimum range

Given: Secondary Current 4.4 mA, Primary Turns 0.025, Secondary Turns 0.055

Result: Primary Current = 9.68 mA

Low range

Given: Secondary Current 44 mA, Primary Turns 0.25, Secondary Turns 0.55

Result: Primary Current = 96.8 mA

Typical

Given: Secondary Current 4.4 A, Primary Turns 0.5, Secondary Turns 1.1

Result: Primary Current = 9.68 A

High range

Given: Secondary Current 0.22 kA, Primary Turns 0.8, Secondary Turns 1.76

Result: Primary Current = 0.484 kA

Maximum range

Given: Secondary Current 2.2 kA, Primary Turns 8, Secondary Turns 17.6

Result: Primary Current = 4.84 kA

Solving for each variable

Solve for Primary Current

Secondary Current 4.4 mA, Primary Turns 0.025, Secondary Turns 0.055 → 9.68 mA

Solve for Secondary Current

Primary Current 2 mA, Primary Turns 0.025, Secondary Turns 0.055 → 0.9091 mA

Solve for Primary Turns

Primary Current 2 mA, Secondary Current 4.4 mA, Secondary Turns 0.055 → 0.121

Solve for Secondary Turns

Primary Current 2 mA, Secondary Current 4.4 mA, Primary Turns 0.025 → 0.01136

How Primary Current changes with Secondary Current

Secondary Current (input) Primary Current (result)
0.44 A 0.968 A
1.1 A 2.42 A
2.2 A 4.84 A
3.3 A 7.26 A
4.4 A 9.68 A
6.6 A 14.52 A
8.8 A 19.36 A
17.6 A 38.72 A
30.8 A 67.76 A
44 A 96.8 A

The same result in other units

Unit Value
µA 9680000
mA 9680
A 9.68
kA 0.00968

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Frequently asked questions

How do you calculate Transformer Current Ratio?

Use Ip / Is = Ns / Np. With Secondary Current 4.4 A, Primary Turns 0.5, Secondary Turns 1.1, Primary Current works out to 9.68 A.

What is the formula for Transformer Current Ratio?

The formula is Ip / Is = Ns / Np. In a transformer the current ratio is the inverse of the turns ratio: the winding with more turns carries less current.

How do you find Secondary Current when you know the other values?

Rearrange for Secondary Current: with Primary Current 2 mA, Primary Turns 0.025, Secondary Turns 0.055, Secondary Current is 0.9091 mA.

How do you find Primary Turns when you know the other values?

Rearrange for Primary Turns: with Primary Current 2 mA, Secondary Current 4.4 mA, Secondary Turns 0.055, Primary Turns is 0.121.

What units does Transformer Current Ratio use?

Primary Current is shown in µA, mA, A, kA. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

Related Concepts

All Magnetics & Transformers formulas →
Transformer EMF Equation Transformer VA Rating Transformer Voltage Regulation Transformer Current Ratio Transformer Copper Loss Transformer Iron (Core) Loss Transformer Turns-per-Volt Transformer Impedance Matching

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