Can I use a 240v input variac on 110vinput?

[Daley]

Hello there

I am a novice at electronics and am wondering if someone here can help me.

I have a Powerstat Variac mode l3PN216C. It is rated for a 240v input. I would like to use it on a standard 110v electrical outlet. It has a 110v cord and plug on it but the outlet is different, the two pins are in the opposite direction. Can I simply shange the outlet for a 110v one and use it or do I need to change something inside? There are 7 Terminals inside and I have ound a link to the diagram here


https://www.danaherspecialtyproducts.com/uploadedFiles/Siteroot/Superior_Electric/Products_and_Solutions/POWERSTAT%C2%AE_Variable_Transformers/INSTR_116C-217C%28213709-063C%29.pdf

Maybe I cant use it and need to get a 110v one but I hoped to get some expert advice before giving up on it.
Many thanks in advance for any input.

 

[Pommie]

It depends on what you want to run on it. If it's a 500VA variac then you can do approx 125VA on it. Hopefully one of the analogue guys will confirm of shoot me outa the water on this. I'm a digital guy.

Edit, Thinking about it, you should manage a higher rating than that.

Mike.

 

[jpanhalt]

Yes. Check this link: http://www.danaherspecialtyproducts.com/uploadedFiles/Siteroot/Superior_Electric/Products_and_Solutions/POWERSTAT®_Variable_Transformers/INSTR_116C-217C(213709-063C).pdf

It appears that you can even run it in "step up" mode .

John

 

[KeepItSimpleStupid]

Just a reminder:
The wiper of the Variac is normally fused.

The windings will only support a certain current. e.g. 120 V at 10 A. It also means 20 V @ 10 A. If you fuse the primary all bets are off. Fusing the primary MAY protect against a 240 V application to a 120 V configured Variac providing the fuse is sized properly.

As John pointed out, you look to be in luck that Variac supports 120 V. You can,in general operate a primary at a lower voltage. Watch how the dial is marked. You may find that you can turn the dial over. Some 120 V Variacs are marked 0-140 which is the approximate max voltage setting.

Variacs are not isolated. They are a variable auto-transformer.

 

[jpanhalt]

If you have a problem with a properly rated fuse or CB opening, remember that a Variac has a high "starting" current, much like a motor. Try a slow-blow fuse or CB. I don't think that will be a problem at all running a Variac designed for 240V on 12oV.

John

 

[crutschow]

It depends on what you want to run on it. If it's a 500VA variac then you can do approx 125VA on it. Hopefully one of the analogue guys will confirm of shoot me outa the water on this. I'm a digital guy.

Edit, Thinking about it, you should manage a higher rating than that.

Yes.
The output current rating remains the same but the voltage is 1/2 so the VA rating is also reduced by 1/2.

 

[Daley]

Wow thanks for all your help.

I am only looking to control a small 20w fan so I don't think I will be overloading it?

Looking at that chart though, if I am reading it correctly, which I am probably not, it looks like the model I have only has info for running on 240v?

In order to connect my 110v device where would I connect the wires for a 110v outlet? Do I simply take the wires off the outlet that is on it and put them on a 110v outlet? The outlet on the variac has the two pins horizontal instead of vertical.

 

[jpanhalt]

It is like any power transformer. So long as the voltage is no greater than its specification, and the frequency is likewise within limits, just plug it in. It is not isolated, as others have mentioned. I would still connect the high side of the coil to L1 (black/colored and not green, not white) wire and the bottom (common) to the white or grounded wire, if you are in the USA.

John

 

[KeepItSimpleStupid]

The VA rating is always determined and limited by the (max output current) and the voltage out.
AT 100 V out you have 100 V *10A or 1000 VA, but at 30 V out you have 30 V * 10A = VA or 300 VA max.

 

[spec]

Just one more bit of theory: You say that your Variac is specified as 240V input, but you didn't mention the frequency. Normally 220V to 240V mains suplies are 50Hz and 100 to 125V mains supplies are 60Hz. That is 20% higher.

The magnetising force (or in basic terms, the stress an inductor [transformer and Variac] has to support) is proportional to the voltage of the mains and inversley proportional to the frequency. So your 240V 50Hz Variac will not only be 46% understresses because the voltage is 110V rather than 240V, but a further 20% because the frequency has increase from 50Hz to 60Hz. This means that overall your Variac will only be suporting 37% of the magnatising force it was designed for. On that basis it should have a very pleasent time and be extremely reliable.

There is a catch though, as always in life. Because the frequency is higher it means that the eddy current losses in the Variac transformer core will increase, and not necessarily linerarly. In theory this could cause a problem by over heating the Variac core. In practice this is highly unlikely with modern transformer core materials, besides which, Variacs, by their very design, are pretty rugged things. The way to check that all is well is to listen for any buzzing or other noises and to ensure that after the Variac has been plugged into the 120V supply for an hour or more that the windings are not hot- make sure you unplug the Variac from the mains before you do this.

This is just a bit of theory. As the other members imply, it is very unlikely that you will have a problem.

I have just noticed that your your Variac is specified for 50Hz and 60Hz. Ah well the theory still stands- perhaps I had better go back to bed

 

[KeepItSimpleStupid]

Well, this is one of those questions that works better when the location is filled in.

There's a few countries with 60 Hz 2xx V. See: https://en.wikipedia.org/wiki/Mains_electricity_by_country

In an industrial setting in the US, 240 V Variacs MIGHT be common and it would be 60 Hz.

 

[spec]

Well, this is one of those questions that works better when the location is filled in.

There's a few countries with 60 Hz 2xx V. See: https://en.wikipedia.org/wiki/Mains_electricity_by_country

In an industrial setting in the US, 240 V Variacs MIGHT be common and it would be 60 Hz.

Quite right, as usual Keep

 

[Daley]

This forum is great, thank you so much for taking the time to give me this info. I really appreciate it.

I plugged her in and tried with a make shift 110v outlet wired into the outlet that is on it but as soon as I switched it on I got some sparking so I turned it off immediately. Taking the cover off showed a lot of black around the sweeper brush so I took that off for a look and it doesn't look in good shape, its not an even smooth surface and is quite jagged so I guess I need a new brush set before I continue with this project.

Thanks again, I am learning.

 

[Daley]

oops, sorry I will fill that in, I am in USA and I believe it is 240v 60hz.

 

[spec]

This forum is great, thank you so much for taking the time to give me this info. I really appreciate it.

I plugged her in and tried with a make shift 110v outlet wired into the outlet that is on it but as soon as I switched it on I got some sparking so I turned it off immediately. Taking the cover off showed a lot of black around the sweeper brush so I took that off for a look and it doesn't look in good shape, its not an even smooth surface and is quite jagged so I guess I need a new brush set before I continue with this project.

Thanks again, I am learning.

I am surprised that you had sparking. Something is not correct with the wiring. Is the wiper made of carbon. If so is there still some carbon on the wiper or has it all gone and the metal carrier is touching the winding's of the transformer. If there is still some carbon you can still use the variac. just clean all the mess and crank the handle back and forth to smoth the carbon wiper again. Don't plug in again until it can be established what is going on.

 

[Daley]

Yes there is still carbon there but it seemed a bit rough. I have never used this before and bought it from Ebay, The copper inside all looks fine but I don't know?? It was sold as tested and working but it is for 240v and yet has a standard 3 pin 110v plug, although the outlet is not a standard 110v, I am not sure what it is as I have never seen one but I assume it is for 240v appliances. I'm a British expat so I am not fluent with all the different electrical bits and pieces here.

 

[KeepItSimpleStupid]

IF these are what I remember, the brushes sort of "push and twist" to remove. You also have to move and adjust the back dial when you install a new brush. Allen screws on the dial.

If you happen to have a few incandescent lamps on the order of 40 to 100 W, place one in series with the input to the variac. Replace the wiper fuse to Something small. Say 3A slow blow.

A brightly glowing lamp is not a good thing in this set-up.

 

[KeepItSimpleStupid]

Take a pic and post it.

 

[Daley]

I will go grab some pics and figure out how to upload them.

 

[spec]

Yes there is still carbon there but it seemed a bit rough...

In that case it will be OK to use. Just clean the muck off the coils and wiper first.

I assume it is for 240v appliances.

Not sure what you mean here

I'm a British expat so I am not fluent with all the different electrical bits and pieces here.

Im a Brit in Britland and Keep is an American in the USA so you are in good hands- Welcome to ETO by the way.