Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
large variac




 
The AM Forum
May 27, 2018, 01:13:02 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: large variac  (Read 475 times)
0 Members and 1 Guest are viewing this topic.
W8ACR
Contributing
Member
*
Offline Offline

Posts: 571


Penta 254W


« on: May 14, 2018, 11:45:00 PM »

Here is a picture of a large variac that I picked up last weekend. I'm not sure how to wire this properly even though it is labelled well. Can somebody help me out?

Thanks, Ron W8ACR


* IMG_0524.JPG (2069.7 KB, 4032x3024 - viewed 110 times.)
Logged

The AM voice of Knox, North Dakota
w4bfs
W4 Beans For Supper
Contributing
Member
*
Offline Offline

Posts: 1212


more inpoot often yields more outpoot


« Reply #1 on: May 15, 2018, 02:40:27 AM »

how to wire it depends on what you want this versatile critter to do .... just think of it as a multitapped autotransformer .... applying 230/240 V Edison system (USA normal) is tricky and to my thinking would require an isolation transformer to keep the common in/out near ground .... 115 V  could go to either input with the lowest V out range being the 230 V input
Logged

Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
KJ4OLL
Contributing
Member
*
Offline Offline

Posts: 143


« Reply #2 on: May 15, 2018, 02:18:52 PM »

Mine is a 1256D model, similar.
I wired it for 240 in 240 out.
Used it for testing the plate transformer in my homebrew amp.


* powerstat1_1256D copy.jpg (898.17 KB, 1600x1200 - viewed 32 times.)

* powerstat2 copy.jpg (904.44 KB, 1600x1200 - viewed 33 times.)
Logged
W3GMS
Contributing
Member
*
Offline Offline

Posts: 2865



« Reply #3 on: May 15, 2018, 03:12:12 PM »

Here is a picture of a large variac that I picked up last weekend. I'm not sure how to wire this properly even though it is labelled well. Can somebody help me out?

Thanks, Ron W8ACR

Hi Ron,

Just, as been said, this variac is an auto xmfr.  You do not get any isolation through it and that is not a problem.  You isolation comes from the transformer that its feeding.  Never connect the safety ground to the common terminal.  There should be zero current flowing through the safety ground wire unless you have a fault condition.  If your using 120V to feed the variac, then the neutral will go to the common and hot wire will go to the 115V terminal.  One side of your output shares with the common connector(s) on the variac and the hot side is obtained off of terminal 3.  The only difference if you feed it with 240V is to connect the 24OV between the 230V tap and the common tap.   

I would verify that the common connection is not grounded to the frame of the unit.  It should not be and assuming that it is not, then connect the ground safety wire to one of the frame screw on the variac.

Hope that helps and good to hear your back building stuff again.

73,
Joe-W3GMS     
Logged

Simplicity is the Elegance of Design---W3GMS
W8ACR
Contributing
Member
*
Offline Offline

Posts: 571


Penta 254W


« Reply #4 on: May 15, 2018, 08:10:40 PM »

OK Joe,
Thanks for the input. The 120V connections make sense to me, but not the 240V. There are three wires in a 240V line: two hot - White and black, and one neutral - green. If I understand correctly, I would connect white and black to 1 and 2, and green to case for the primary. The secondary would be white and black to 1 and 3, and green to case. When using 240V, there would be no connection to terminal 4. The bare copper ground wires, if present, would not be connected to anything. Correct?

Thanks, Ron W8ACR
Logged

The AM voice of Knox, North Dakota
W3GMS
Contributing
Member
*
Offline Offline

Posts: 2865



« Reply #5 on: May 15, 2018, 09:00:40 PM »

OK Joe,
Thanks for the input. The 120V connections make sense to me, but not the 240V. There are three wires in a 240V line: two hot - White and black, and one neutral - green. If I understand correctly, I would connect white and black to 1 and 2, and green to case for the primary. The secondary would be white and black to 1 and 3, and green to case. When using 240V, there would be no connection to terminal 4. The bare copper ground wires, if present, would not be connected to anything. Correct?

Thanks, Ron W8ACR

What is your input voltage to the variac going to be Ron?  120 or 240V?

A 240V source from the panel can have 4 wires.  (2) for line to line which is your 240V source.  The third wire is a neutral.  You would only use the neutral if the 240 source was powering something that required both 240V and 120V.  Take for example a transmitter.  Some of the transformers within the cabinet may require 120V as well as 240.  If that is a requirement, a neutral is required.  So now we have discussed 3 wires and the last 4th wire is a ground wire.  Under non-fault condition, no current should flow in the ground wire.  Not sure if that makes it a bit clearer or not. 

If you have a 240V requirement and are feeding the variac with 240V you will only use the two wires that give you 240V.  I call that line to line at the panel.     

Joe
 
Logged

Simplicity is the Elegance of Design---W3GMS
KA2DZT
Member

Offline Offline

Posts: 2127


« Reply #6 on: May 15, 2018, 10:11:36 PM »

The output of the variac is 0-270vac.  The input can be either 115vac or 230vac.  This variac is only set up for a step-up in line voltage.  The winding has three connections.  First is the common terminal.  Next connection is half way around the winding, this is the 115vac terminal.  Next connection is the 230vac terminal.  This connection is around the winding but not at the end of the winding.  The 115vac connection is exactly half way between the common and the 230vac connection.  The rest of the winding is the step-up from the 230vac point to the end of the winding which is 270vac.

If you only input 115vac to the variac, it works as a auto xfmr from the 115vac point to 270vac.  If you input 230vac to the variac, it works as a auto xfmr from the 230vac point to 270vac.

The variac only inputs two wires.  For 115vac input it would be the white neutral wire is connected to the common terminal.  The black hot wire gets connected to the 115vac terminal.  Your output gets connected to the common and the wiper terminal (labeled output).  The output voltage will be from 0-270vac.

For 230vac input both wires are hot (no neutral).  One hot wire gets connected to the common terminal and the other hot wire connects to the 230vac terminal.  The output connects from the common and the wiper terminal. Output voltage will be from 0-270vac.  There is no neutral with 230vac input.  So, it can only be used to power a 230vac item.  Mostly a plate xfmr with a 230vac input winding.  It can not be used to power a 115vac item even if you adjust the voltage down to 115vac from the 230vac input.

The bare ground wire gets connected to the frame via a mounting bolt or some other screw that screws into the metal frame.

Another way this variac could be useful is in a xmtr that only the plate xfmr runs on 230vac.  It can be run from a 115vac line input (neutral and a hot lead).  The rest of the xmtr runs from 115vac.  The plate xfmr would get connected from the common terminal (neutral) and the output terminal.  The variac auto-xfmr would bring up the 115vac to the 230vac needed for the plate xfmr (or anywhere in between).  With this set-up the plate xfmr has one lead which is neutral and one hot lead which is adjustable from 0-270vac.  

Limiting the variac operation to no more than 230vac output,  would require modifying the connections on the variac winding.  The 230vac connection would have to be moved to the end of the winding.  Then the 115vac connection would have to be moved to the exact center of the winding.  The common terminal would remain as it is.

Fred
Logged
KD6VXI
Contributing
Member
*
Offline Offline

Posts: 1796


Making AM GREAT Again!


« Reply #7 on: May 16, 2018, 09:24:31 AM »

Red and black would be hot.  Neutral white.  Ground is green.
It's no longer code compliant to use the chassis as a return for one side of the 240.

And we use split phase on our side of the pond.  Nearly the rest of the world uses what we do in the commercial electric world.  Single hot and a return (we use 208 volts in commercial electric).

--Shane
KD6VXI
Logged
W8ACR
Contributing
Member
*
Offline Offline

Posts: 571


Penta 254W


« Reply #8 on: May 16, 2018, 03:43:23 PM »

OK, Thank you Fred and Shane. Yes, I would like to use this Variac on a large plate transformer with a 230V primary. Shane, if the two incoming hot leads go to terminal 1 and 2, and the output to the plate transformer primary go to terminals 1 and 3, what would you do with the neutral and ground leads? Just leave them unattached to anything?

Thanks, Ron
Logged

The AM voice of Knox, North Dakota
KA2DZT
Member

Offline Offline

Posts: 2127


« Reply #9 on: May 16, 2018, 10:28:18 PM »

OK, Thank you Fred and Shane. Yes, I would like to use this Variac on a large plate transformer with a 230V primary. Shane, if the two incoming hot leads go to terminal 1 and 2, and the output to the plate transformer primary go to terminals 1 and 3, what would you do with the neutral and ground leads? Just leave them unattached to anything?

Thanks, Ron

If you are going to use the variac on 230vac you would only connect the two hot wires to the variac.  No neutral wire.  Like I mentioned the ground wire can be connected to the metal frame.  If you are going to run a AC line from your panel just for this variac,  you would run a 2 conductor plus ground romex cable to the variac.  Two conductor cable will have a black and white wire,  both the white and black wires are hot.  If you are going to use a wall mounted 230vac outlet and then use a cord to plug the variac in, you would use a 20amp 230vac AC plug on the cord.  The cord would only have 2 conductors plus the ground.  The cord would have a black and white wire along with a green ground wire.

If you install a 20amp 230vac outlet, you must use the correct outlet and plug, ones designed for 230vac service.  230vac plugs and outlets are different than 120vac plugs and outlets.

Fred

Logged
W8ACR
Contributing
Member
*
Offline Offline

Posts: 571


Penta 254W


« Reply #10 on: May 16, 2018, 11:04:24 PM »

OK Fred,

Thanks. It's starting to make sense. I have never wired anything with 220VAC that didn't use the neutral wire, but now that I think about it, I see that there is no absolute need to use the neutral wire. And OK on the ground wire to the case. Yes, I am familiar with the various 110 and 220 plugs and jacks.

Thanks again, Ron
Logged

The AM voice of Knox, North Dakota
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Online Online

Posts: 6865



WWW
« Reply #11 on: May 16, 2018, 11:34:17 PM »

perhaps late reply but I know this exact model.

You put 230V in to the 230V input, or, you put 115V into the 115V input. The output is 0-270V.
If running from 115V and using it as a step up, the output must conform to the curve limits in the chart shown. as indicated by the arrow.

Brushes are still available too. Be sure to clean its contacts/brushes and lubricate it (shafts etc). It is amazingly easy to turn when lubricated and the brush/contacts cleaning should include something that is very slightly lubricating as well.

This link to a 57MB catalog of these older finest USA made units in which the chart appears.
http://lcweb2.loc.gov/master/mbrs/recording_preservation/manuals/Powerstat%20Catalog%20P258G.pdf



* powewrstat 1256 115V derate.png (497.74 KB, 672x815 - viewed 22 times.)
Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.042 seconds with 19 queries.