Variable Voltage Auto Transformers


Air Cooled | Motorised | Oil Cooled | Metered

Open Back / Panel Mount
Portable / Bench Top

Open Back / Panel Mount
Portable / Bench Top
Available as a complete unit

Rugged design
Robust cooling tubes
Portable / Bench Top
Voltmeter / Ammeter
Analogue / Digital
Voltmeter with Plug Base

Variac Technology

Dimmer Dot Technology
Dimmer Dot is a variable auto transformer (Variac) which provides continuously adjustable AC voltage. In it’s “Auto transformer” form it is an efficient, reliable method of controlling AC voltage from zero to line voltage by amplitude modulation of the AC waveform. Since the current, power, heat, light and motor speed are further functions of the voltage, the Dimmer Dot Variable Transformer finds its varied use, but is not designed to provide AC mains isolation.
Green Dot Electric
Green Dot have been at the forefront of variac / variable transformer technology since 1979. From their new premises in Sahibabad India they carry out their total in house manufacturing of their Dimmer Dot range of toroidal variable auto transformers and Servo Dot Voltage Stabilisers. They have become world leaders in their market.
EMC Compliance
Tested in Australia by a NATA accredited laboratory
ERAC approval
This regulatory compliance mark is a mandatory requirement for Australian EMC & Safety approval by ERAC for most electrical / electronic products sold that are manufactured in or imported into Australia.​
Energy Efficient
Australian Rectifiers supports green energy initiatives to lower power consumption while maintaining high & controlled outputs.

Salient Features

The Dimmer Dot Variable Transformer, consists of a single-layer winding on a toroidial silicon-steel core. As the control knob is rotated, a carbon brush traverses the winding, tapping off a portion of the total voltage across the winding. The brush is in continuous contact with the winding, and the voltage between turns is always less than 1 volt even in the largest model. In the smallest model it is only about 0.3 volt. The discrete voltage increments obtained as the knob is rotated are always less than the voltage between turns. Since the brush spans more than one turn, the change in voltage is practically continuous. The brush is so designed that excessive heating cannot occur in the turns that it spans.

Dimmer Dot has many operating advantages over any other manually operated voltage control devices for alternating current use.

Good RegulationOutput voltage is substantially independent of load.
Smooth ControlThe Dimmer Dot can be set very closely to any output voltage within its range.
High EfficiencyVery low losses under all load conditions. Greater than 96% efficient.
Long LifeWith the exclusive Dura Dot contact surfaces, the life of the Dimmer Dot Variable Auto Transformer is essentially the same as that of any standard fixed-ratio power transformer.
Linear Output VoltageOutput voltage is continuously adjustable from 0-112% of line by approximately 340°. The dial reads directly in no-load output voltage at rated line voltage or some dials are calibrated for percentage of the full range control.
Mechanical DesignRugged construction and robust parts. Two or more units can be ganged on same shaft. Shaft is also reversible for simple conversion from front to back of panel mounting.
TemperatureHigh ambient temperature tolerence. Current rating up to 45°C
Sine Wave PurityVirtually no radio interference, wave shape distortion or harmonics created, unlike SCR-Thyristor and Triac AC power controllers.
Lower Input CurrentInput power consumption is proportional to output unlike electronic Thyristor controllers which still maintain high input RMS currents.
Current Ranges1 Amp to 28 Amp – Air Cooled
40 Amp to 1,600 Amp – Oil Cooled
Special Voltage RangeDimmer Dot is available in standard Single phase 240 V and Three phase 415 V 50 Hz. Other special input voltages can be supplied. Two phase models are also available
Technical AssistanceOur engineers are well qualified to advise and assist you with the selection and applications on Dimmer Dot Variable Transformers
WarrantyTwelve months from date of purchase

Find out more

Enquire or ask a question. Your Information will remain private.

Your enquiry has been sent

Australian Rectifiers will contact you within 1 business day. For urgent enquiries, please call us.