When choosing fans as components for a device, it is essential to implement safeguards that prevent device burnout in cases where the fans become stuck or when current fluctuations occur during startup. This paper focuses on analyzing the fan’s current behavior.

Since fans are powered by motors, they inherently undergo current fluctuations—a characteristic of motor-driven systems. The current initially decreases gradually after the fan is powered on and stabilizes at a nearly constant level during normal operation. This paper outlines the fan’s current variation in three distinct phases: power-on, startup, and steady-state operation.

 

Power On

The fan drive circuit includes smoothing capacitors and other components that begin charging immediately when powered on, causing a large surge of instantaneous current known as inrush current.

The peak of the inrush current is determined by the fan’s drive circuit. This peak is the highest point of current flow but lasts only briefly.

Start-Up

When the fan starts, even at low speeds, it generates a peak current called startup current. This current spikes immediately after startup and gradually decreases as the fan’s rotational speed increases.

This reduction occurs because spinning fans generate a counter-electromotive force (CEMF), which is proportional to their speed.

The startup current typically lasts less than 10 seconds, though this varies by fan model.

Normal Operation

Once the fan reaches a stable speed, it operates at its rated current. Due to CEMF and other factors, minor ripple currents occur during operation. However, since these ripples are periodic and consistent, they have little impact on the average rated current listed in catalogs.

Locked Rotor Burnout Protection

If the fan blades are obstructed, a high current similar to the startup current can occur. To prevent damage from this peak current, fans can be equipped with a “locked rotor burnout protection function.” For example, DC fans use a “current cut-off system” that automatically cycles the current on and off to protect against burnout.

在选择风扇作为设备组件时，必须采取防护措施，以防止在风扇卡住或启动时电流波动的情况下发生设备烧毁。本文主要分析风扇的电流行为。

由于风扇由电动机驱动，电动机系统固有的特性使得风扇在启动和运行过程中会经历电流波动。电流在风扇通电后会逐渐下降，并在正常运行过程中稳定在一个近乎恒定的水平。本文将风扇的电流变化分为三个不同的阶段：上电、启动和稳定运行。

上电

风扇驱动电路包括平滑电容器等组件，通电后这些组件开始立即充电，导致瞬间大电流的涌现，称为浪涌电流。

浪涌电流的峰值由风扇的驱动电路决定。这个峰值是电流流动的最高点，但持续时间非常短暂。

启动

当风扇启动时，即使在低速下，也会产生一个称为启动电流的峰值电流。启动后，电流会迅速上升，并随着风扇转速的增加而逐渐下降。

这种下降是因为旋转的风扇会产生一个与转速成比例的反向电动势（CEMF）。

启动电流通常持续不到10秒钟，尽管不同风扇型号有所不同。

正常运行

一旦风扇达到稳定转速，它就会以额定电流运行。由于反向电动势和其他因素，运行过程中会出现轻微的脉动电流。然而，由于这些脉动是周期性的且一致的，因此对目录中列出的平均额定电流几乎没有影响。

锁转保护功能

如果风扇叶片被阻碍，可能会发生类似启动电流的高电流。为了防止这种峰值电流导致损坏，可以为风扇配备“锁转保护功能”。例如，直流风扇使用“电流切断系统”，该系统会自动切断电流并重新启动，以防止风扇烧毁。