Variac? How to wire an use?

[nothing to lose]

 Long ago I found a Variac I think it's called at the scrap yard. So yep I grabbed it up. I now need to check a device I think uses 12V AC input. I want to use the Variac, start low and work up slowly till the device works. It has a fried transformer with no markings and I am about certain it is 12V AC comming for the transformer, 2 yellow wires.

This variac has 5 connections for wires. There is like a schematic on the front just coil loops really.

 Number 1 is the left beginning coil end, #5 is up 2 loops, then go to the other end and #3 is 3rd loop from end, #2 is second loop from end, and #4 is the end.

Before I wire 120Vac to this, I want to be sure WHAT connections should the 2 wires go to?

This is a powerstat variable autotransformer, type 1260, spec BP124201, input 120Vac 60HZ 1 phase,

 output volts 0-140 15 amps KVA 2.1

 Says the Superior Electric co Bristol Conn. USA.

 output volts 0-140 15 amps, so does that mean any volts I set this transformer too is going to be 15 amps? 12Vx 15 amps= 180watts, or 140Vx15amps = 2100watts??

For right now I need to check out a stereo I am sure only has a fried 12V transformer (friend checked it and thinks so too). But I am also working on something that will be using batteries of odd volts. I am thinking about using this to charge them. I have not actually decided what voltage I am using yet, depends on the motor used (I have several DC motors you know). So if I use a 36volt set of batteries or even a 140V set, if I rectify the output of this variac to get DC and crank in the correct volts for the battery bank, is that going to charge at 15 amps as planned?

I am not familiar with these devices but it seems odd to me I would have the same amps at any voltage from 1-140AC.

Thanks for any help on this thing, I don't want to fry it (or anything else), I'd probably never find another one.

[terry5732]

You can't exceed 15 amps at any voltage. If you are pulling over 120 volts on the output you must be under 15 amp draw. for under 120 volt output you can draw up to 15 amp. Your  input is to each side of the 5 series of coils. The drawing looks like a series of loops but is actually one long loop with taps. Your output can be any two taps. Input is normally 1 and 5 for 0-120 volt adjustment. To get over input voltage connect input to 1 and 4 and output to 1 and 5. If rectifying to DC use a large capacitor to smooth it. Cap should be rated for about double the voltage you will use. Being it is old and used, check the brush for smooth continuity. Also check ohms on each segment to be sure you don't have a bad section.

A very handy device for coming up with odd voltages for vintage equipment!

[nothing to lose]

Thank you very much.

 I hope I got that correct, 1 and 5 for 120V input, less than 120V output.

 I use 1 and 4 input and output to 1 and 5 for over 120 voltage.

Although I can see it I can't tell how it was actaully made. If more stuff inside like coils or what really. Being shown the loops and the 1 5 taps at the same end I think is what kinda tossed me I was thinking each end not side by side.

Another question on this then, if it were connected wrong without a load, would it fry?

I was not sure of that, if not I geuss I could have connected wires and tested with a meter to see what comes out. Did not try it though since I did not want to burn anything up.

[Flux]

Terry's explanation fits the variacs we have in the UK, but it doesn't seem to tie up with your description if you have got it right.

I assume that the slider is identified separately and doesn't go to any of the numbers mentioned.

For normal use the supply is to the ends of the winding and the output is from one end to the slider for variable out. You can take fixed out between any pair of numbered terminals.

From your description the ends seem to be 1 & 4. You say that 5 is only 2 loops up from 1. If that is the case you must not supply between 1 & 5 as that seems to be a low % tap.

I would suggest that you supply between the ends and ignore the over voltage facility unless you can be sure that you have one end and a tap at about 80% at the other end.

Remember that a variac is an auto transformer and there is no isolation between input and output so keep the common connection between input and output at the neutral end of the supply ( not really sure how your supply is arranged in the US)

[nothing to lose]

Hmm, 1 5 did not seem correct.

  When I plugged it in everything on that circuit buzzed and UPS's started beeping too. Might have been more than one circuit since kitchen and computers should be seperate. Maybe whole house, I only had things on I could tell with in those two rooms though. Nothing blew or tripped though. I tried the 1 4 then, each end as shown in the loops/coils on the front. That worked. Checking the various connections I can get 0-120Vac fine now.

That buzz was kinda a growler, reminded me of a growler for checking auto starter armatures, probably what I had going perhaps

[nothing to lose]

Darn I am so dumb at times, I was wanting to post a pic of it but no camera. Duh, I have a pic on the board already in my files from when I first got it!

 On the left #1 is the bottom connection front end of loops, #5 top left is 2 loops up. Center Is #3 and shows to be 3 loops in from the far end. #2 is the top left and shows 2 second loop from end, #4 is the last end.

 The tap wire on the left side going to coil is #5

I did not get the rest of the case, dial or anything else, all that was there was as shown. Another of my cheap scrapyard buys and it works

"For normal use the supply is to the ends of the winding and the output is from one end to the slider for variable out. You can take fixed out between any pair of numbered terminals."

 We have the 120Vac here. I used 2 taps and can dial in various volts fine, but I only tested with a meter though, no load.

 Are you saying I should wire the 120AC input and 1 wire of my output together as a common on #1, second wire then being variable on an output tap?

 I don't know anything about these as you can tell, since I have one I should learn to use it though. And of course since I don't want to fry anything or myself I should learn to use it correctly.

The over volts I probably won't need, not for awhile anyway. Anything under 120V at 15 amps will be handy for battery bank charging and DC motors once rectified to DC.

By the way how is something like this for running a motor as a variable speed control?

Will it stand up to long heavy use or over heat and burn out?

[drdongle]

Based on the picture I'd connect the 120 VAC to the two bottom terminals on the right and left ( looks like 1&4 from here) the load connects from the bottom left and the center terminal ( 1&5?). I also suggest adding a 3 amp fuse on the secondary side ( terminal 5)to prevent damaging the Variac.

Turn the shaft fully CCW to start the test and slowly turn it CW reading voltage with a meter.

You need to mount this thing in a box (grounded) with a power cord and a 3 prong outlet.

This a great find as they are quite expensive new.

BTW if the power transformer is cooked then the output transistors in one or both channels will be shorted, making the stereo a dead short on the transformer.

[Flux]

I think #5 is meant as the tap to use in place of #2 to get the boost volt range.

Those variacs are designed to be mounted free standing or bench mounted. With bench mounting you push the spindle out the other end and fit the knob effectively on the bottom. To make volts increase clockwise you use the other end as common. For the boost condition #5 now becomes the 80% tap that #2 would be when mounted the other way up.

That is why it Growled, you put 120v on a 20v tap.

Just use the ends as you are now and it will be fine. They are continuously rated and should be fine for motor speed control. The brush is the weak point, don't push it beyond the 15A. Failure usually comes from burnt turns directly under the brush.

Flux

[Drives]

Hope this helps.

http://www.superiorelectric.com/PDF/POWERSTAT-c.pdf

[scottsAI]

I used one of these years ago, too costly to get one for myself then. Went to eBay, today found a couple that look interesting. Very useful device.

OK, for speed control on induction motors, it will change the speed. Reducing the voltage will allow the induction motor to slip... so it will give you some control, much like the lamp dimmer type does the job. If the motor is still heavenly loaded it may get warmer than normal. Light load not usually a problem. Lamp dimmer type are much cheaper for most people. With basically the same issues.

Variac can handle the power, it's a multi tapped transformer. With heavy load it may get warm, if over 50-60'c then maybe over loaded.

Variable speed control of Universal motor (brushed) works great, as with incandescent lamps.

Have fun,

Scott.

[dinges]

It just might be that this variac is an isolation transformer; I have one that looks very similar to his, but it is an isolated variac. I've only seen one in my lifetime, and I have it :-) Too bad the wire get damaged while transporting it home; it should still work, but I've cursed at myself very much for this. I wouldn't mind if an ordinary variac got damaged, but not this very nice isolated one :-( could kick myself for it.

So, NTL, check whether you have an isolated variac or the 'normal' variety, much more common, and not isolated.

Peter,

The Netherlands.

[nothing to lose]

Thanks,

 I think I will buy the kid a new one and if I get the stereo working again use it in my shop. I was hopping for just a bad transformer, if the output transistors are bad too I may have something around for parts but will take me forever to fix it. And I don't want it left on all the time after I been playing around in it either!

[nothing to lose]

" Lamp dimmer type are much cheaper for most people. With basically the same issues."

I didn't think much about that myself. How many amps can a light dimmer handle on a motor? I think of them being light duty, I would like around 10-15 amps for various motors work motors.

[nothing to lose]

Thanks.

 I will be using this for the next few days and see what I can do with it now

[finnsawyer]

Warning; Warning; Warning!  A Variac is not a true transformer.  The input and output are not electrically isolated.  Shock or ground loops can occur.  I always put an isolation transformer between the output of my Variac and the circuit under test including any test equipment.

[dinges]

It is a true transformer, just not one with isolated windings. Usually also called an 'autotransformer'.

Most variacs (brand name; what's generic name?) are not isolated, but some are; like I said in the other message, I have one here that is isolated. Didn't found that out until I got home when I bought it, but I was very happy. Less happy about the damage I did to it.

If you want to be on the safe side, assume all variacs are directly net-connected, unless you are absolutely positively sure of the opposite.

Peter,

The Netherlands.

[drdongle]

You can also put a GFI on the primary side

[dinges]

Yes you can.

This still wouldn't make it safe to touch. Why would you use a GFCI?

Peter,

The Netherlands.

[drdongle]

A Ground Fault Interupter would make it safer as would mounting it in a grounded metal box and a 3 wire cord.

[dinges]

Now I agree :-)

Peter,

The Netherlands.

[finnsawyer]

I have a "Variac", and it is an auto-transformer.  I consider a true transformer to be one were the windings are isolated from each other.  Symantic confusion can get one electrocuted.  In reality one should be careful around any kind of transformer, as it is possible for windings to become shorted to each other.

[Gordy]

NTL,

I used the lamp dimmers for my hot wire foam cutter. The cheap one was rated for 600 watts and lasted 25-30 hour, before burning out. For $3 more that dimmer was rated at 1,000 watts and still going.

Gordy

[dinges]

Hi,

You're right about the correct use of terms; it may prevent accidents, or at least it looks more professional when using the correct words.

A transformer transforms voltage (and current); isolation is not required for it to be a transformer;

When isolated, over here in NL they are also known as isolation transformers, which is usually abbreviated to just 'transformer'.

However, 99% of the transformers we encounter are isolated transformers.

It's just something that you don't want any confusion about. The risks are too big. Maybe by us 'argueing' a bit, we've made one or two people aware of the differences and what to look out for.

Peter,

The Netherlands.

[scottsAI]

Motor controllers are available for 1500 watts.

This type of controller chops the AC seen by the motor.

Motors at slower speeds under load will operate much warmer than normal.

If you vary the load the speed will vary without changing the setting on the controller.

Have fun,

Scott.