DIMMER DOT TECHNICAL SPECIFICATIONS :
Ratings quoted are for use in ambient temperature from -20'C to +50'C. Current derating figures for temperatures above 50'C are as follows :
Generally, when the operation is required in ambient temperatures higher than 50'C output current must be reduced according to the curve shown below:
The current that may be drawn from a "Dimmer Dot" transformer through the brush is not constant as in fixed auto wound transformers, but varies according to brush position. At 50% and 110% of the line voltage, winding heat is the current limiting factor. Near zero and line voltage, winding heat is low and brush heat becomes the current limiting factor. Both factors operate at intermediate brush positions. This is common to all continuously variable "Dimmer Dot" Transformers. The "Dimmer Dot" ratings, in terms of "Rated Currents" "Maximum Currents" etc. should be fully understood for optimum results.
It is general practice to specify the current rating of Variable Transformer by two values, the rated current and the maximum current. Dimmer Dot have two current ratings because in any adjustable auto transformer, heating of the winding varies with the brush setting. To limit these useful devices to the current that can be drawn at any setting (RATED CURRENT) places an undue restriction on the capabilities. Most load (possible exceptions are some kind of motors and incandescent lamp loads) which draw MAXIMUM CURRENT at line voltage may be safely regulated from zero to line voltage without danger of overload. This MAXIMUM CURRENT is generally 20 to 30 percent above the RATED CURRENT and this concept may be safely used to full up the gap in the capacities of the RATED CURRENT of the various model available.
RATED CURRENT :
The rated current can be drawn at any brush setting. When the over-voltage connection is used, the load should not be drawn more than rated current.
May only be drawn near zero or near maximum output voltage when t h e Dimmer Dot transformer is line connected, i.e. when connected for an output voltage range of zero to line voltage. See Current Rating Curves.
The Maximum Current can only be drawn in line-voltage connection with the listed (or lower) input voltage across the whole "Dimmer Dot" winding (e.g. 240 volts on a 240/270 volt unit), and can only be drawn near zero or at or near full output voltage. A load having linear voltage/current load, line (constant impedance load drawing maximum current at the line voltage can be controlled from zero to line voltage. The knowledge of the maximum current and the rated current for the particular end application can be useful for filling in the capacity gap for the "Dimmer Dots" in the range and thus intermediate current requirements can at time be met from the particular rating valued "Dimmer Dots".
Equals nominal input voltage multiplied by maximum current output. KVA rating for over voltage connection, equals output voltage multiplied by rated current.
OVER VOLTAGE CONNECTIONS:
A "Dimmer Dot" transformer connected for over voltage provides an output of 12 % above the supply voltage on load. Most models have terminations for line voltage or over voltage connection, at the option of the user. Rated' current only may be drawn when over voltage connected.
Although 'Dimmer Dot" are designed for arduous industrial use, damage will occur if they are subjected to short circuit or continuous severe overload.
It is therefore recommended that protective devices be fitted such as a circuit breaker in the input circuit & and H.R.C. fuse in the load circuit. It is normal practice to provide a protective device in the input circuit.
Improved core materials, permitting higher flux densities than was possible in the past, allow high inrush transient surges of up to 10 times the rated current to occur at switch on. This is not harmful except H.R.C. fuses or protective devices of instantaneous operation. It is therefore recommended that input protection "Dimmer Dot" is obtained by employing slow blow fuses or circuit breakers with slight operating delay. Input protective devices should be capable of handling 1000% overload for one cycle of the supply frequency.
It is not always appreciated that a variable transformer with an input voltage of 250 V and delivering say 10 amps to a load at 50 V (0.5 KVA), will draw a current of only 2 amps from the supply mains. It this instance, a 10 amp. fuse laced in the input circuit would not rupture until the load current reached 50 amps . It is obvious, therefore, that input protective device afford little protection to the transformer against overloads at low output voltage. The solution is, of course, to fuse the load circuit with an H.R.C. fuse link.
W A R R A N T Y
Green Dot Electric Limited (the "Company"), New Delhi, warrants to the first end user purchaser (the "Purchaser",) of equipment manufactured by the Company that such equipment, if new unused and in original unopened cartons at the time of purchase will be free from defects in material and workmanship under normal use and service for a period of one year from date of delivery for the Company or for a period of one year form the date of delivery from the business establishment of an authorised dealer of the Company in the event that the equipment is purchased from an authorised dealer.
THE COMPANY'S OBLIGATION UNDER THIS WARRANTY SHALL BE STRICTLY AND EXCLUSIVELY LIMITED TO REPAIRING OF REPLACING AT THE FACTORY OR A SERVICE CENTRE OF THE COMPANY, ANY SUCH EQUIPMENT OR PARTS THEREOF WHICH AN AUTHORISED REPRESENTATIVE OF THE COMPANY FINDS TO THE DEFECTIVE IN MATERIAL OR WORKMANSHIP UNDER NORMAL USE AND SERVICE WITHIN SUCH PERIOD OF ONE YEAR. THE COMPANY RESERVES THE RIGHT TO SATISFY SUCH OBLIGATION IN PULL BY REFUNDING THE FULL PURCHASE OF ANY SUCH DEFECTIVE EQUIPMENT.
This warranty does not apply to any equipment which has been tampered with or altered in any way, which has been improperly installed or which has been subject to misuse, neglect or accident.
THE FOREGOING WARRANTY IS IN LIEU OF ANY OTHER WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATIONS, ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, and of any other obligations or liabilities on the part of the Company: and no person is authorised to assume for the company any other liability with respect to equipment manufactured by the Company. The Company shall have no liability with respect to equipment not of its manufacture. THE COMPANY SHALL HAVE NO LIABILITY WHATSOEVER IN ANY EVENT OF ANY INCIDENTAL OR CONSEQUENTIAL DAMAGES, INCLUDING, WITHOUT LIMITATIONS, DAMAGES FOR INJURY TO ANY PERSON OR PROPERTY.
Written authorisation to return any equipment or part thereof must be obtained from the company. The Company shall not be responsible for any transportation charges.
IF FOR ANY REASON ANY OF THE FOREGOING PROVISIONS SHALL BE INEFFECTIVE, THE COMPANY'S LIABILITY IS BASED ON WARRANTY, CONTRACT, NEGLIGENCE, STRICT LIABILITY IN TORT OR OTHERWISE, SHALL BOT IN ANY EVENT EXCEED THE FULL PURCHASE PRICE OF SUCH EQUIPMENT.
Any action against the Company based upon any liability or obligation arising hereunder or under any law applicable to the sale of equipment, or the user thereof, must be commenced within one year after the cause of such action arises.