SoftStarterDirect | Fairford Electronics - Soft Starters

Starting Current Calculations

Perhaps the most common question regarding electronic soft start is what reduction in starting current will be seen and whilst there are typical currents for particular application for example: -

• 2.5 - 3.5 x FLC for pump
• 3-5 x FLC for fan

The only accurate way to determine starting current is to calculate it. The actual current seen with a soft start depends on the load and motor characteristics and therefore Softstart Direct require some basic information. The required information is:-

• Load torque speed curve
• Load inertia / Motor Inertia
• Motor torque speed curve for D.O.L
• Motor current speed curve for D.O.L

From this an accurate picture can be shown for starting current and starting time.

Heat Loss Calculations

A very important factor when enclosing soft starts in boxes is the heat loss from the soft start and other components and how this heat can be dissipated. Additional panel cooling may be required even if the soft start is by-passed particular if the panel size is small or if the ambient is high. Softstart Direct are able to offer a heat loss calculation service that advises customers if additional fans are required and the volume of air to be moved. This is based on the following information from customers.

• Heat loss for panel components
• Ambient temp
• Panel dimensions

Protection Fuses

The fusing on any soft start application is very important. Softstart Direct generally recommend High Speed Fuses for semiconductor protection, in the event of short circuits. Whilst this protects the soft start the circuit still must be protected by HRC fuses and / or circuit breakers. Softstart Direct are able to offer a fuse size calculation service also.