在 2000年4月12日星期三 UTC+8下午3:00:00，Kirk Lindstedt写道：
I believe Variac's are VARIable AC transformers. Not DC as you stated. I think
these are essentially autotransformers, ie a primary and no secondary winding.
Instead, they have a wiper on the primary that taps off different voltages based on
the position of the wiper. Similar to the old Lionel train transformers. You can
set an AC voltage and it somewhat remains constant within some varying loads.
Since there is no secondary winding, there is no isolation from the AC main power
like a true transformer. Hope this helps.

GaryH82012 wrote:

Price seemed good, so I bought an electronic device called a Variac at an
auction. It was described as a DC transformer, but I don't know. It plugs into
120 volt outlet and has the same style receptacle on the side for plugging
into. There are two meters on the front: AC volts (0-150) and AC Amps (0-10)
The needle on the AC volts moves when the big dial on the face is turned. I'm
guessing it puts out variable AC voltage and, under load, displays AC amps.
It''s about 12 inches tall by 8 inches wide by 4 inches deep. What can I use it
for ? Thanks for replys, Gary Hastings

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A variac can only accept AC power input, but with Rectifier installed it can switch output from AC to DC.

Variac mainly used as a light dimmer, speed controller , machines for motor test and repair ,experiment machines for teaching or lab test and also industrial use.

Well, some people call it variac and others say variable transformer, we can understand from the name that it basicly used to give out constant adjustable voltage. For example single phase input 220v ,the standard output is 0-250v ,three phase input 380v output 0-430v. Please note that these are just standard output ,we can make the input and output range as your needs.
For frequency all good to use 50 or 60hz.

First lets check out the manual adjust type, as we can see it has four terminals on the front panel ,to connect in and output cables. And also a panel meter that display the output voltage. Which we can also use LCD display. Now on the top of it we can see a black wheel, the output voltage will goes slowly up or down while we rotate it.

Here is a motor drive type, we can see terminals and meters are same but a motor on top instead of the wheel. By using this type you can connect the motor to a control box to adjust the output from distance, like you can use a 10 meters or 20 meters wire to control the variac in another room. We now have AC and DC motors for option.

Now lets talk about the fancy motor type. Well we can see those meters display our output voltage and current. We can control the power on and off ,up and down by push button switches here. For example if we want the volt up we just press this button and when it reach the volt we can release it. The accuracy is 1 volt. Inside is the main switch control the power and coils and terminals for cable. Moreover, we install a temperature sensor inside which will cut off the power and make alarm noise when the temp. Hit 100 degrees.

For all variacs we can do max 1000kva now and we can install a rectifier to make the output switch from AC to DC.
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