Variac wiring help..please

[wb1ead]

Hello all..a number of years ago I gave away my ol' trusty variac..I've been using the on/off method to fire up various unknown BA gear as I acquire it lately..it does work but sure plays havoc with switches/circuit breakers and all as I try not to duplicate the "Hiroshima" effect by plugging in directly and standing back..so enter another variac but not like the ol' one that had a fancy panel and wiring attached with a receptacle plug or two ready to use..this one is definite "bare bones"..so here's the question and the details/facts on the replacement......it's a "Powerstat" variac made by Superior Elec Co. in CT...type Q116-1048..primary is 115VAC using 60HZ..output voltage is from 0-135VAC at 7.5amps KVA 1.0..basic question is where do I make my connections?..on one end is a thick plastic plate with 7 posistions..3 on the left and 4 on the right side..the 3 on the left are marked 1 thru 3 and have screw/solder terminals..the 4 on the right are 4 thru 7 and only number 5 has the terminal..the ones marked 4-6-7 have nuttin..no wiring from below goes to these..in order to "adjust" voltage it would appear it's a screwdriver type of adjustment..so I'm not sure if a ground connection is even used..there's 4 blocks numbers 1 thru 3 and number 5 that actually can be connected or where the output voltage comes..I sure would like to know just how do you connect this thing and yes I aplologize for no pics as I now have the digital camera but no attachment cord for the putor...thanks all for ur responses         73 de DAVE

[Pete, WA2CWA]

Just go to their web site like I did:
http://superiorelectric.com/index.htm

Here's the pdf for the Q116: http://superiorelectric.com/PDF/Z15pwst.pdf

[KA2DZT]

Most variacs are five terminal units.  Yours has four plus three unused locations.  One terminal is the start of the winding, one is the adjustable arm.  One is the end of the winding and the last is a tap, usually at 20 volts from the end.  Identify each on these connections by examining the winding on the core.  The tap will be nearer to one end.

The end that is NOT near the tap will be your neutral terminal (white wire).  Now you can connect the hot leg (black wire) to either the tap or the end of the winding (end near the tap).  If you connect to the tap, you will be able to adjust the line voltage about 20 volts above the incoming line voltage.  If you connect the hot leg to the end terminal, you will only able to adjust your incoming line voltage from that level down to zero volts.  In this case there is no connection made to the tap terminal.

Five terminal variacs are the same except they have a 20 volt tap near each end of the winding.  Hence, a total of five.  But why, glad you asked.  Five terminal variacs can be connected so that you can have increasing voltage either with clockwise or counterclockwise rotation of the knob.  But why, glad you asked.  It depends on how the dial is used.  A knob with the dial connected to its back rotates with the knob which works against a stationary point would be connected one way.  A knob that rotates around a stationary dial would be connected the other way.

Your variac has positions for more than five terminals.  But why, glad you asked.  Many of those 7 amp Powerstats were used in OEM power supplies.  I've seen where they used other taps on the winding to pull some voltage to light panel lights.

I've also seen some really old variacs that had more than one tap on each end.  Sometimes at about 20 volts and 37 1/2 volts from each end.  Don't ask.

When you do your connections make sure you connect to the right terminals.

Hope this helps.

Fred

[wb1ead]

Thank you Pete and Fred..here's hopeing the power grid will not dim in ur neck of the woods..the PDF is very helpful..there's just sumptin about connecting things up if it's not familiar to me at all..I appreciate ur help..I really do             73 de DAVE

[WA1GFZ]

I have the same one, mine is blue. The extra terminals allow you to set it up as 0 to line output or a boost mode where you can get up to around 0-130 volts. Check the manual.

[k4kyv]

Usually there is a 20v tap near each end of the winding.  This allows the variac to either be surface mounted so that the transformer core is in front of the panel (or the mounting bracket is simply resting on the surface of a table or the floor), or flush mounted so that the transformer core is behind the panel, and the position of  the shaft can be moved so that it comes out at either the front or back of the unit. That way, it can be made to increase the output voltage with clockwise rotation, regardless of which way it is physically mounted.

In one of my homebrew rigs I have an ancient 2 KVA one (Powerstat or Amertran) that I observed maintain unusually good regulation under full load, but it originally had no tap.  I wanted to be able to boost the output a little above line voltage, so I found a spot on the winding where the wire was fully accessible for soldering a connection, and added a tap about 8 volts below the top end, and use that for the line input, so now I can boost the line voltage a few volts above normal.  Before adding the tap, I temporarily applied line voltage between the bottom of the coil and the movable tap (with the variac set for full voltage!), with an a.c. ammeter in series with the line, then rotated the knob backwards until the line current began to noticeably increase.  That occurred at about 10% reduction, so I made sure the tap was well above that point, in order not to degrade performance by running too many volts per turn on the coil.

I still feel like kicking myself, decades later, for giving away that tapped autotransformer with the built-in heavy duty rotary switch that came out of a medical fluoroscope from the 1930s or 1940s.  That thing had absolutely no voltage sag beyond that of the mains voltage, no matter how heavily I loaded it down. I have never seen a variac that had anywhere near that good voltage regulation.

[KA2DZT]

I have a 20amp GR built into my 813 rig.  It controls the line voltage for the whole rig.  I don't notice any voltage sag beyond the normal line sag of about a volt on transmit.  Can't remember if the 1500volt plate supply runs through the variac or direct from the line.  I'll have to check it.

Just took a look at the variac,  seems the plate supply is wired through the variac.  Can't remember how I wired my own transmitter.

Fred