Manual Control 

Corrosion Electronics has produced several transformer rectifiers incorporating manual control. Please refer to the information below for a more defined look at what manual control refers to and whether or not it will suits your needs.

DESCRIPTION:

In its simplest form, manual control can include the following:

	Tapped transformer control
	Variable autotransformer (Variac) control

In both the above types, an autotransformer is used to control the mains AC voltage into a stepdown transformer. A normal stepdown transformer has a primary and secondary winding which is isolated from each other.

An autotransformer has only 3 connections, MAINS IN and MAINS OUT with a common NEUTRAL. The magnetic transformation of power works the same as for a normal isolating transformer. The various outputs are selected either by COARSE and FINE select switches or by rotating a carbon brush mechanism across the windings on a variable transformer.

The fixed tappings are usually 4x COARSE and 4xFINE resulting in 16 equal steps between zero volts and full mains volts. The output of the fixed or variable autotransformer powers the main stepdown transformer whose secondary output is rectified to provide the DC output which is galvanically isolated from the mains input.

Both single and 3 phase manual control is available. A distinct advantage using 3 phase manual control is that with a full wave rectifier, the output ripple voltage is nominally less than 5% as opposed to 48% for single phase. The AC waveforms are sinusoidal and not chopped as with other electronic modes.

LIMITATIONS:

There are very few limitations and in fact, many advantages of Manual Control. The main limitation is that the output is essentially only "Constant Voltage" which varies significantly depending on output load. It is not possible to provide constant current or constant potential control.

In the case of a Variac, It is possible to add a motor drive and electronic controls to provide a limited feedback function. The response times of this system are very slow and will only suit some applications. We do not recommend this "pseudo electronics" means of control.

APPLICATIONS:

Manual Control is a viable option when the following operational aspects are required: 

	Only constant voltage control needed
	Generally large output rectifiers
	High immunity to lightning transients
	Remote sites / limited technical expertise

FEATURES:

	Rugged technology / low maintenance expertise
	Easy to operate
	Any size up to thousands of amps
	Single and 3 phase mains
	Inherently low ripple for 3 phase, < 5%
	High ripple for single phase, 48%
	Essentially constant voltage output
	Recovers after interruption with minimal overshoot