ISE Frequently Asked Questions - Variacs
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1 Are additional limit switches available for our motor driven Variac transformer? I want to use with an external circuit to signal position of transformer.

Limit switches control at the lower and upper limits of travel prevents over travel. We recommend that these switches remain adjusted as shipped. Additional limit switches may be added for customer purposes and can be used to control of auxiliary circuits…

2 Are there flux-coupling problems with variable transformers mounted closely?

Coupling should be minimal but heating could be a problem - Provisions to allow heat to escape should be provided.

3 Calibration of MP Control on a Variac System (Models with Display)

Calibration of MP Control on a Variac System (Models with Display) Single Channel Monitoring (MPAxT): 1) Connect a Voltmeter (standard) with an uncertainty of less than +/- 0.2 VAC across the monitored output (Phase A on multi-phase units). 2) Power the system.…

4 Can I vary the speed of my motor with a variable transformer?

Many motors can use a variable transformer for speed control. Motors that usually can be controlled by varying the motor voltage: Universal Motors Series Wound Motors Torque Motors Shaded Pole Motors Motors that sometimes cannot be varied by changing the…

5 Choosing a Variac for a Guitar Amp

A Variac provides an output voltage that is a ratio of the input voltage. The 3PN1010B-DVM and the 3PN1010B are the most common models used with guitar amps. They provide an output of 0-117% of the power source voltage. This equates to a nominal 0-140V output…

6 Communications Notes for the MP Series Variac Variable Transformer Motor Control

Switch Settings To communicate the following switch must be set: SW2-3 Needs to be set to ON Communications Settings As standard the communications settings are as follows. Your communication device must match these parameters: Baud: 9600 Data Bits: 8 Stop…

7 Field Calibration of Variable Transformer with the DVM Option

The voltmeter has been calibrated prior to shipment and should provide years of service. If it is found that the voltmeter needs recalibration it is recommended that the transformer be returned to ISE for calibration. If the customer has qualified personnel…

8 How can I protect my three phase variable transformer from excessive currents?

You may (and it is highly recommended) place a fuse in each phase between the variable transformer and the load. On the models listed the ouputs are terminals #3 on the three coils. One other caution: These units should be connected to a Wye (3 hot wires,…

9 How do I control a motor operated variable transformer?

Standard motor driven variable transformers have synchronous motors. They typically can have motors speeds of 60, 30, 15 and 5 second travel times from 0-100%. As the variable transformers gets larger then faster motor speeds are not available. The motor…

10 How do I select and use a Variac variable transformer as a noise free light dimmer in my recording studio?

Our VariacĀ® 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…

11 How much can I overload my Variac and for how long?

To calculate overload ratings, maximum overload time and cooldown time: Short Term Overload Calculations.

12 How to add external output modules to MP series control for Variac

Occasionally power systems with excessive surges and/or other power anomalies it is preferable to add external output modules to the system. Below are instructions for installation and wiring of external output modules: Required Hardware: Single Phase Control:…

13 I have a MP motorized Variac controller. How do I set up the to control the Variac output voltage setpoint with an analog signal?

To control the MP controllers setpoint with an analog DC signal the MP control must have the "S" option. Units that include the S option include U40 an U42 integrated circuits on the main controller board. To configure the controller to accept the analog…

14 I have a very old Variac. Which model can be used to replace this variable transformer?

The following link will cross reference most models. Variac Cross Reference Most models have the same mounting dimensions. If your model is not listed please contact ISE for assistance.

15 Is any kind of calibration required and/or beneficial for a Variac?

We do not consider our variable transformers as devices that require calibration unless they include a digital or analog meter. A variable transformer only provides an output that is a ratio to the input. This is accomplished using transformer action (turns…

16 Reforming Capacitors on Variable Frequency Drives (VFD) with Variacs

There are large capacitors in a typical VFD (Variable Frequency Drive). If the drive has been stored for a period of time the capacitors will build up an oxide coating between the plates. This can cause the VFD to be damaged. Normally this is done by raising…

17 The transformer dials shown on the site indicate from 0 to 100, yet out put is greater than 100v (140v). How does one know the output voltage when in use if not a Digital model?

The variable transformer dials are marked as 0-100% of rated output voltage. It is recommended that the dial to be used for estimating the output voltage only. If the voltage needs to be set to a particular value then a separate voltmeter should be used.…

18 Variacs and Guitar Amplifiers

Variable transformers are used for several purposes with guitar amplifiers. Tubes in amplifiers last longer if voltage is gently increased during power up. The filaments in the tubes are not stressed as much as when power is applied all at once. When the…

19 Variacs for my amp! I own an All-Tube (analog power) 100w guitar amp, and have recently been informed of a way to hook up a Variac to the amp.

Variable transformers (VariacsĀ®) are commonly used with various tube type amplifiers and other tube type devices. The primary purpose is to bring the AC voltage up slowly in order to extend the life of the tubes. Variable transformers have the unique ability…

20 What are the standard Temperature, Humidity and Altitude Ratings for Variac Transformers?

VARIAC Standard Environmental Ratings Temperature: 0-50C; Relative Humidity: 0-95% Non-Condensing; Maximum Altitude without de-rating: 10,000 Feet

21 What is the difference between constant current and constant impedance ratings on Variac variable transformers.

Constant Current Rating: This is the maximum continuous amperage rating at any output voltage. Constant Impedance Rating: This is the maximum continuous amperage resistive load at 100% voltage output that the transformer is rated. The transformer has to be…

22 What is the inrush current on a Variac variable transformer?

Inrush current is not possible to calculate since it is heavily dependent on your source impedance, source wiring and other factors beyond the transformer. With larger hardwired units a separate breaker or fused disconnect should be installed for the transformer.…

23 What is the setpoint range for a FRC-20 Variac motor control that is configured for limited range?

When the controller is set for limited range then the full range of the setpoint or potentiometer signal will be the upper 1/3 of the range. 1) If the FRC-20 is configured for 0-150V then the setpoint signal range will be approximately 100-150V. 2) If the…

24 What size VARIAC variable transformer do I need for my hot wire applicaiton?

A little more information is required to properly answer your question. A variable transformer is normally rated for a maximum continuous amperage at any voltage. Exceeding this rating for long periods of time will damage the transformer. The Following Information…

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