Growler (electrical device)
A device for detecting shorted coils in motor armatures.
A growler is a tool for checking motors for shorted coils. It has a wire coil wrapped around an iron core that connects to an alternating current supply. When set on a motor’s armature or stator core, the growler works like a transformer’s primary winding, with the armature coils acting as the secondary. A thin steel strip, often a hacksaw blade, serves as a feeler to detect shorts.
During motor testing, the growler’s alternating magnetic flux passes through the armature windings, creating an alternating voltage in them. If a coil is shorted, it forms a closed circuit that behaves like a transformer’s secondary, with the growler as the primary. This induces an alternating current in the shorted armature, which produces an alternating magnetic field around that coil. A flat, broad, flexible iron-containing metal piece—commonly a hacksaw blade—detects this field. The field is strong at the armature’s surface, and when the feeler lightly touches the iron core of a winding, small currents in the feeler generate a third alternating magnetic field around it. With the growler powered, the feeler is moved from slot to slot. Over a slot with a shorted coil, the alternating field alternately attracts and releases the feeler, making it vibrate in time with the current. A strong vibration and a growling noise indicate a shorted coil.
Beyond this main use, a growler can test series and interpole fields from a DC motor, determine phasing and polarity in multiwinding armatures, test rotors in rotating frequency changers and wound rotors, check for shorts between turns in taped coils before installation, serve as a low-voltage isolation transformer, act as a high-voltage autotransformer for bucking or boosting in various equipment tests, and preheat or bake armatures and rotors.
- Primary use
- Testing a motor for shorted coils
- Components
- Coil of wire wrapped around an iron core, connected to AC source
- Detector tool
- Feeler (thin strip of steel, e.g., hacksaw blade)
- Operating principle
- Acts as primary of a transformer; armature coils act as secondary
Lore & Background
The growler operates by setting up an alternating magnetic flux that passes through the windings of the armature coil, generating an alternating voltage in the coil. A short in the coil creates a closed circuit that acts like the secondary coil of a transformer, inducing an alternating current in the shorted armature. This current in turn causes an alternating magnetic field to encircle the shorted armature coil. A flat, broad, flexible piece of metal containing iron—commonly a hacksaw blade—is used as a feeler to detect this magnetic field. When the feeler is lightly touched to the iron core of an armature winding, small currents are induced in the feeler, generating a third alternating magnetic field surrounding it. With the growler energized, the feeler is moved from slot to slot. When moved over a slot containing the shorted coil, the alternating magnetic field alternately attracts and releases the feeler, causing it to vibrate in sync with the alternating current. A strong vibration accompanied by a growling noise indicates that the coil is shorted.
Reader's Guide
The growler is notable for its role in motor testing, specifically for identifying shorted coils in armatures and stators. Its significance lies in its simplicity and effectiveness: using a basic transformer principle and a common hacksaw blade as a detector, it provides a reliable method for locating faults without complex instrumentation. Beyond its standard application, the growler can be used to test series and interpoles fields from a DC motor, determine phasing and polarity in multiwinding armatures, test rotors in rotating frequency changers and wound rotors, test shorts between turns in taped coils before installation, serve as a low voltage isolation transformer, act as a high voltage autotransformer for bucking or boosting in various tests, and preheat or bake armatures and rotors. Its legacy is that of a versatile, practical tool in electrical maintenance and repair, documented in references such as Hubert's 'Operating, Testing, and Preventive Maintenance of Electrical Power Apparatus' and Heller's 'The Growler: Design and Application'.
Did You Know?
- A growler consists of a coil of wire wrapped around an iron core and connected to an alternating current source.
- A hacksaw blade is commonly used as a feeler to detect shorted coils.
- When a shorted coil is detected, the feeler vibrates in sync with the alternating current and produces a growling noise.
- The growler can also be used as a low voltage isolation transformer or a high voltage autotransformer.
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