Our Variac® variable transformers are often used for light dimming where electrical noise from common electronic dimmers is a concern. Our variable transformers dim the lights using transformer action and do not introduce any electrical noise and do not cause audible noise at the lamps.
Selection of the correct variable transformer:
Maximum
Example:
300 Watts/120V = 2.5 Amps
Select a variable transformer with a higher amperage rating than your results.
Mounting:
Special boxes and plates are not available for the Variac®s. The electrician usually supplies or custom hardware is made onsite.
Variac® variable transformers are very efficient devices. Efficiency is approximately 98% when set to full rated output voltage. Even with this high efficiency they will generate heat. The electrical box and plate need to have a surface area that is large enough to dissipate this heat. Tightly packing insulation around the electrical box limits this heat dissipation.
Example:
Assuming 98% efficiency with 300W of lamps installed approximately 2% will need to be dissipated as heat at the variable transformer. This would equate to 6 Watts in this example.
|
Maximum allowable temperature rise |
Approximate surface area required in square in/ watt |
|
10°C |
18.4 |
|
20°C |
9.2 |
|
30°C |
6.1 |
|
|
|
All uninsulated surfaces of the box and mounting plate can be used to dissipate the heat according to the approximations in the above table. The variable transformer is rated to 50°C.
A slight audible noise can occur as with any transformer. Some have found the need to dampen this noise with sound deadening washers when mounting the Variac® transformer. Washers should not significantly limit thermal transference since the mounting plate helps dissipate heat.
Wiring:
1) FOLLOW LOCAL AND NATIONAL ELECTICAL CODES FOR WIRING AND CIRCUIT PROTECTION.
2) Generally the source circuit breaker should not exceed 125% of the transformer amperage rating.
3) Variable transformers do not positively shut off voltage to the lamps.. A small voltage may be present at the lamp socket when the Variac® is at its minimum setting even when there is no visible light. This small voltage can pose a shock hazard under certain situations such as when replacing lamps. A switch should be used to positively shut off the input voltage to the Variac®.
4) It is recommended that circuit protection be installed on the output of the Variac®. A Variac® is a transformer high currents at low voltage settings can be present if the lamps or wiring have a fault. A fuse or circuit breaker on the output would protect against such an occurrence.