Variac wiring

hi i need to install a variac as a light dimmer for my recording studio. could someone tell me how to wire this thing up? I have two wires
coming from my electrical box, I just need to know which terminals they sould connect to. here's a picture of it:
http://img208.imageshack.us/img208/3923/061121radiogrcvariacw20qo5.jpg
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@yahoo.com wrote:

You can see from the remains of the original connection wires.
The supply goes to the top two terminals, (2) and (4).
The output uses the centre terminal at the bottom (3) and the common terminal at the top (4)
This will allow you to alter the voltage to your lights from zero to normal supply voltage.
--
Sue




Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
thanks for your reply. I only have two wires coming from the light switch box, so these would go on 2 and 4? To be clearer it is just a light switch box that I am connecting to. It is not being fed by a supply and used as an outlet but rather will replace the function of a normal single pole wall dimmer.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@yahoo.com wrote:

Nope. One of your wires will be coming from the supply and needs to be connected to (2) The other will be going to the lamp and needs to be connected to (3).
Unfortunately you also need a third wire, from the other terminal of the lamp, to go to (4).
You can get a different type of dimmer that only has two wires going to it but a Variac needs three wires to give a full range of control.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I see, that makes sense. I guess I will have to find an alternative solution that will not use the ligh switch box, as regular dimmers create noise in the audio signal. Thanks very much for the clarification.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I think what you need for the third wire is simply the white neutral lead that the lighting system returns to. Are you sure it is not inside the switch box? If not you will have to splice in somwhere closer to the source.
snipped-for-privacy@yahoo.com wrote:

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Palindr?me wrote:

Do you suppose connecting the Variac as a variable inductance in series with the load would provide enough range? Not the best solution, but one that could be done with only the two wires available. Anybody ever tried this?
Roby
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Roby wrote:

That thought was why I wrote "from zero to normal supply voltage".
There are three options:
1) Connect to (3) and (4), leaving (2) unconnected. The control will vary from full to dim very quickly, with only a very small part of the winding in circuit. At that point there will be 100v over this part of the winding and several hundred volts over the complete winding, as the VARIAC will operate as an off-load step-up transformer. Not exactly recommended.
Better:
2) Connect to (2) and (4) and place a dummy load between (3) and (4). If the lamp load is the same wattage as the dummy load, the Variac will give half to full power adjustment.
3) Connect to (3) and (4) and place a dummy load between (2) and (4). If the lamp load is the same wattage as the dummy load, the Variac will give from zero to half power adjustment.
By combining (2) and (3) above, using a change over switch, full power range can be achieved.
--
Sue




Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

------------------------
I can see the dummy load if the variac is used in series but what is the point of using a series connection in the first place? The dummy load destroys the whole reason reason for a variac rather than a rheostat- efficiency. It is so much simpler to simply hook it up as intended (which is what you originally said Input on 2 and 4 , output on 3 and 4. Full control is possible with a simpler setup. It is assumed that it is being used within its rating.
--

Don Kelly snipped-for-privacy@shawcross.ca
remove the X to answer
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Don Kelly wrote:

I agree entirely - which was why I didn't suggest this to the OP. But the question was specifically asked by another poster and someone might have tried it. They may not have thought of the autotransformer implications - tt is far more dangerous than using a rheostat, unless the dummy load is there and always connected.
--
Sue





Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Agree.
The OP started off by thinking they could use this variac auto transformer in the same way as a typical wall switch mounted 'dimmer'.
Two wire connection at the wall switch!
Not so.
Then it got complicated by suggesting using it as variable inductance in series with the lighting circuit.
The OP had enough sense to ask an intelligent question; but some of the suggestions are beyond a reasonable purview of someone not wanting to rewire part of their installation/building.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

--------- Too true. Thanks for the response.
--

Don Kelly snipped-for-privacy@shawcross.ca
remove the X to answer
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Just an aside:
The "standard" variacs permit producing up to 140 volts to the load and also permitted "up" to be either clockwise or anti-clockwise.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.