Chokes & Inductors


All of these items are very closely related. In fact in many cases they are the same thing only called by another name. A coil of conductor material wrapped around a core of steel lamination material will have an inductance, it will react to current trying to be passed through it and attempts to choke the flow of current, hence it may depend which aspect of functioning of these devices you are interested in as to the name you tend to know them by.

Generally they breakdown into AC or DC current types. They can be used to shunt, load, filter or smooth.

There are some common usage types listed below but whatever your application, Admagnetics would be interested to discuss your requirements with you.

Standby Power Equipment


They are power supplies which are used to provide power, from battery storage, for emergency lighting applications in the event of a main supply power failure.

The CBU contains batteries which will deliver power for a number of hours to luminaires, which may take the form of signs or actual lighting units, so that for example, a large building such as an office block, could be safely evacuated in an emergency, where the mains supply has been interrupted.

Similar units would also be used in applications such as operating theatre lighting, where for obvious reasons, an interruption to the power feeding the theatre lamps would be very undesirable.


Ease of maintenance and accessibility would certainly figure quite highly particularly where large numbers of luminaires are involved. Where individual lighting units (luminaires) are fitted with batteries they sit in the highest ambient air temperature in any room i.e. on or close to the ceiling. High ambient temperatures shorten battery life which means that batteries fitted to individual lights often need changing every 4 years or so compared to the design lifetime of 10 years for Central Battery Systems.

For the lights to be effective they need to be placed where people are likely to be walking etc. As a result accessing such lighting units individually is more difficult and time-consuming, and presents other issues such as working at height. Hence there are benefits in having a Central Battery Unit located in a plant room at floor level and with easy access panels.


In addition to supplying Central Battery Units under our own Admalite brand, we are also pleased to supply these units in a “badged” form to suit the requirements of various customers.


As well as providing our standard range of products we are pleased to be able to offer a customising service which can provide designs and equipment for differing capacities and power requirements. In addition a host of alarm and monitors can be incorporated to provide interfaces and alarms etc. as required.

Unit Combinations


In many cases, a simple stand-alone transformer is all that is required, however, once you start to use the equipment to control power or another parameter things can become more complicated.

Wherever one is dealing with an AC voltage change from one level to another there is a transformer involved. The interesting bit starts when you want more than one voltage out of the transformer.

The commonest means of obtaining voltage variation is by providing tappings on the transformer.  Many transformers have taps in the primary winding to allow for correction of the output voltage when the supply voltage differs from the nominal value. So if the supply voltage is 5% low and you have a -5% tapping you can get the correct output voltage. These taps are not intended to alter the output and if you intend to use them in this manner you should tell your supplier so he can account for it within his design.

As an alternative, taps can be used to change the output voltage. If you allow twice the number of turns required for the maximum output voltage in the primary winding and then provide a number of tapping points between the two extremes one can vary the output voltage between 50 and 100%.
To get to a wider range of variation one may consider using a tapped auto-wound transformer to feed the step-down or step-up transformer. In such a way ranges of 0 to 100% can easily be achieved. You are now starting to put together Units or Combinations of power components.

The principle disadvantage of tapped transformers is that you are limited by the number of taps you have as to how closely to your required voltage one can get and that in general one would need to switch off the transformer to change tap.

Sometimes the load’s characteristics change. For example, if glass is directly heated by passing electricity through it. When cold the glass has higher resistance so higher voltage and low current capacity is required; when hot, the resistance is lower so then lower voltage and higher current is the requirement.

There would also be consideration as to how closely one could match the required power with the delivered power.
Tappings make this more difficult to achieve so using devices such as variacs or Voltage regulating transformers to provided a continuously variable source of voltage change not only allows for close matching of the delivered power to the required power but also on load adjustment.

Of course, it might be that you need a DC voltage for say a testing application, in which case adding a rectifier to a similar arrangement could provide a continuously variable DC output voltage from 0 to 100%.

In this manner, quite complex arrangements can be produced out of simple components, and these we know as Units or Combination Equipment.

Rectifier Units


Rectifiers are converter devices which change alternating voltage into unidirectional voltage. Alternating current (AC) into direct current (DC). This is generally achieved by using semiconductor devices which only allows the flow of current in one direction.

There are many types of power converters which do this but the type that Admagnetics design and manufacture are industrial power rectifier application types.



The term variac is the common usage name for a variable ratio, toroidal transformer.

Like all toroidal transformers, the winding is wrapped around the core section and each turn inlaid next to the last to form a continuous winding around the core until it returns to near the start point. The winding is then secured to the core. Unlike other toroidal transformers, a section of the insulation is removed from the turns to form a track. Mounting a moving set of brush gear to the assembly allows the brush to pick up the voltage from any turn to create a means of providing a variable voltage source, and to carry the load current.

Some years back, with the introduction of cheaper thyristor controllers, variac use declined, but in more recent time engineers have come to appreciate the advantages variable transformers have over phase controlled AC thyristor regulators. These advantages include maintaining a high power factor even at a very low output voltage, not distorting the output voltage waveform or suffering the consequences of pulsed AC line currents etc. and of course simplicity of control. All transformer products are considered as being EMC benign, i.e. they are passive elements with respect to emission of, and immunity to, electromagnetic disturbances.

All in all there is a lot going for the simple variac in variable source test or control process applications.

Whilst we do offer standard products in our Variac leaflet (which is available for download) we are also able to offer custom made items to meet your exact requirements.

Such variations may include different input/output ranges different supply frequency, manual or motorised control, additional end of traverse limited switches/interlocks and enclosures.

In some instances a low voltage high current or high voltage low current output may be required, in which case we will be pleased to combine a variac with one of our own transformers to meet your requirements (see combination units)

Whatever specific needs you may have Admagnetics will be pleased to discuss your requirements with you.

Voltage Regulating Transformers


Prior to the improvement in ratings of semiconductors for power applications, voltage regulating transformers were the only way of varying large ratings of power on-load.

Voltage-regulating transformers have the same brilliant characteristics as tapped transformers in that they do not introduce large apparent power, maintain high power factor even when greatly reducing the level of power being supplied and introduce effectively zero distortion into the power system.
In addition, voltage regulating transformer can do all this while still supplying the load current during a time of variation of the output voltage.

Admagnetics use and supply the Ruhstrat brand of the voltage regulating transformer. Ruhstrat is a brand name of the Eisenmann Thermal Solutions GmbH & Co. KG. Unlike many other brands, Ruhstrat transformers work on the assumption of the worst case.

All Ruhstrat voltage regulators are designed for heavy-duty operation. Ruhstrat variable column transformers conform to the conditions of VDE 0552 § 5g for heavy-duty operation. According to VDE 552, heavy duty operation is “operation under extreme electrical conditions”, for example:

  1. No movement of the current collector over extended periods (24 h)
  2. Frequent switching on and off under load
  3. Operation with a current load in which the ratio of effective value to rectified value is 1.15 (e.g. phase angle control)”.

The exact final pattern of operation of the variable transformers is generally not known at the time of order placement. Therefore, it must be expected that for technical reasons there will be no regulation – movement of the contacts over a period longer than 24 h. Ruhstrat variable column transformers are designed for these heavy-duty operating conditions.

What does this mean to the user? It means that these are as robust a device as you will find available and as such should give years of reliable service.