Another Zenith Variac question

[Warmsteel]

Greetings all

I have acquired a Zenith Type 80 variac which appears to be unusual in that it is not a toroidal type.

Attached are some photos and I am hoping that someone will be able to tell me more about this type of variac and how to connect it up to mains supply.

The photo labeled "top" shows what appears to be the connections and next to each bolt/nut is a number from "1" on the top left, to "4" on the bottom right. I am assuming these are the input and output connection but since I am having difficulty in tracing the circuit I am not sure if this is correct.
There is another block of connections on the side which connects to the top connections and I would assume this is just to provide an easier means of connection.

It also appears that the wiper doesn't connect to anything other then each winding doing the job of a physical bridge or something like that?

So, if anyone knows more about this variac or has more information such as sales literature, connection diagrams or any thing really, I would be pleased to hear from you.

Thank you and all the very best

John

[Boater Sam]

Variacs are not isolation transformers, the in and out usually share a common connection.
If there are 4 terminals, it MAY have an overwind to produce a 15% or so higher voltage than the mains?
The wiper and the common connection will be the out, the common and 1 other the in. A check with an ohm meter should reveal which is which.

[Warmsteel]

An update to what I measure following the latest advice.

The resistance between connections are

1-2 6.2 ohms
1-3 0.1 ohms
1-4 46.9 ohms

2-3 6.1 ohms
2-4 41.2 ohms

3-4 47 ohms

I think I have all the connections measured?

Also a better photo of the data plate may help.

Thank you and all the best

John

[Boater Sam]

Which reading changes with the position of the slider? Its unusual, 200/240 in but 220 out.

[Warmsteel]

Thank you boater Sam for your help.

The last readings were taking with the slider fully up, that means with the variac sat on its base, the slider was at the top of the coils.

now, with the slider at the bottom of the coils the readings are

1-2 6.1 ohms (6.2 ohms)
1-3 0.1 ohms (0.1 ohms)
1-4 90.5 ohms (46.9 ohms)

2-3 6.1 ohms (6.1 ohms)
2-4 85.2 ohms (41.2 ohms)

3-4 90.5 ohms (47 ohms)


() indecate previouse readings.

Thank you again

John

[Boater Sam]

Sorry, I can make no sense of this. There should be a pair that remain constant at a reasonable resistance as the primary, in.
But you seem to have no winding that doesn't change. And windings between 4 and 3 that change, suggesting they are the out but they never get to zero at either end of the slide.
Confused,
Sam.

[Refugee]

Perhaps it needs to be connected to a low voltage like 24V AC or something across one of the windings that read 10s of ohms.
It looks like there are two brushes on two windings.

[chriswood1900]

Rather than a normal variac it looks like you have a voltage stabiliser, on the plate it says it is a variable AC input and consistent 220v out, some I have seen are automatic and vary the circuit to maintain the output.
Chris

[karesz*]

Hi Chris,
I belive you are right; the data plate (bad to read) suggest that too:
"Input=200--240V and output=220V"...
Regards, Karl

[Mr Moose]

Hello,
I think that it may be a 0-20V 7.5A low voltage, double wound, isolating variac similar to this 10A one on ebay here (http://www.ebay.co.uk/itm/VARIAC-TRA...-/162451317132) but connected so you can buck or boost the mains supply by its output of 0-20V thus converting 200-240V to 220V by adjustment of the knob.
Yours, Richard

[karesz*]

Hello John,
I`m missing two positions on the "front" picture;
A second "wiper" (broken?)on the leftside and an connection betwen both_am I right?
@ Richard; Becouse data plate says here Type is 80-C-13, and input voltage is (possible) 200-240V, I think it has still some another internal connection as your super finding, but the resultat is same, a compensated mains voltage to 220V what adjustable is...
Regards - Karl

[Refugee]

The unit that is on sale looks like it is wired as an automatic voltage regulator. It has a solenoid to adjust the voltage.
The one we have got here looks like an attempt has been made to to convert it to a regular type. The solenoid has been replaced with a knob.

[ms660]

According to this (Fig. 13) it uses a Zenith 80c variac and shows mains in as 3-4 and voltage out as 1-2:

https://books.google.co.uk/books?id=...variac&f=false

Lawrence.

[Warmsteel]

Greetings Chaps

I appreciate the good comments and thoughts on this puzzle. I would have liked to have thought that this would have been simple such like a rotary variac but alas, not.

I have asked the seller if he would happen to know the connections as his description suggests that he does but as of yet I haven't heard back.

Karl, I think you are referring to the strap that pulls the wiper up and pushes it down, this is also seen on the ebay picture as a sort of looped strap. I don't think it is actually a connection but rather it seems to be the mechanism that moves the wiper.
Where you possibly think there maybe a broken connection appears to be not. Looking at it closely it seems that the shape is intended but also a resistance check between the wiper and the strap bolt reveals 27mohms so if the strap was part of the circuit, it doesn't make sense.

Struggling to trace the circuit I notice on the back that each of the coils has a wire coming out of the bottom which then runs up the length of the coil to the top and around to the front, 1 wire if fixed to connection 4 and the other wire appears to enter the opposite coil from the top.

There appears to be a total of 3 wires that enter the top of each coil so I may have to take it apart a little to find out exactly where each wire goes.

Lawrence, I am unable to see that Fig. for some unknown reason but I shall keep those connections safe, I wont connect it up until I am sure these are correct.

Either way this is very intriguing and thank to you all so far.

All the best

John

[WME_bill]

Zenith Variac. 80-AS-31 output 40v5A.
I have a similar one. Pictures attached. It takes normal mains input, on terminals 1 & 2. Resistance is about 5 or 6 ohms, so comparable with yours.
The secondaries are isolated, a very useful feature. Each arm is an open ended winding. One end of each coil goes to terminals 3 and 4, giving 20v The other end is just left secure but open circuit.
The slider acts as a shorting bar, to join the two secondary windings together.
Your measurements show a higher resistance with movement of the sliding bar, which seems right.
The contacts will be fairly poor in radio terms, so measurement with a multimeter will be almost useless.
Try passing half an amp (DC of course) through the windings from 3 to 4, and measure the voltage across them. That will give you a sensible idea of the resistance! Or else measure from 3 say to the track of its winding, and then 4 to the other, winding. But you will have to press hard and make sure contact point is thoroughly clean and shining.
I am concerned about the low resistance from 1 to 3. Either there is an external wire connecting the primary and secondary windings, or else the insulation has gone. Have you closely inspected the wires going into and out of the windings. They are fairly clear in mine.
I don't think you have any broken connections. But the idea of three wires into 2 coils does seem odd at first, until you realise the slider is the fourth.
I have planned to rewind the secondary coils to 240v, as very useful with the isolation, but haven't got around to it yet. Securing the outer end of the secondaries might be a problem.
wme_bill

[Mr Moose]

Hello,
Normally only the top end of the secondaries has connections but as your variac seems to have connections to both ends of the secondaries it might be connected as in the diagram below which I think would give you, by adjusting the knob, 220V out from 200V to 240V input.
The two 20V secondary windings would be opposite phase so one adds to (boosts) and the other subtracts from (bucks) the incoming mains.
The buck and boost windings might be the interchanged but it would still work but with opposite rotation of the knob.
It would also explain the 0.1 ohm connection between the terminals 1 and 3
Yours, Richard

[Warmsteel]

Greetings All

Thank you for your input and it seems that we are getting somewhere.

WME_bill you are absolutely correct, realizing the wiper is the other connection makes total sense now and it is easier to understand.
I have double checked the wires and I can’t detect any obvious insulation breakages but I can't really say if there is a break down inside the coils.

Mr Moose's suggestion makes sense too but would that then mean that the secondary is NOT isolated?

I have drawn out the physical connections and the picture is attached.
The red circles are the same as those of the photos of the actual coils, in other words the circles indicate the wires that exit the bottom of the coils at the back of the whole unit.

The arrows are representing the 3 wires entering each coil and I am unable to say which is actually connected to which, the primary or secondary coil, and I have assigned a letter to each arrow for ease of discussion.

I suppose I could always connect to the mains and see what happens but I would rather not for obvious reasons.

So, hopefully some more excellent input will follow.

Thank you chaps, you have all been very helpful so far.


John

[Mr Moose]

Hello,
I have a similar looking Claude Lyons variac with a 0-20v, 10A output which is an output rating of 0.2KVA (Bills variac is also 0.2KVA) and using the 2016 RSGB Yearbook as a size guide, mine is about the same size as yours.
Hovever yours has a output rating (from the rating plate) of 1.65KVA (220V at 7.5A) or more than eight times mine or Bill's.
If yours was a double wound isolating variac it would have to be at least eight times the volumetric size which equates to double the linear size of mine or Bill's.
The only way I can see of getting the 1.65KVA rating from the same size variac is if it is bucking or boosting the mains input with a non isolated output.
It could probably be rewired to make an 0-40V isolating variac.
Yours, Richard

[Warmsteel]

Hello Richard

Now I follow your explanation and it makes even more sense especially having seen the post http://www.vintage-radio.net/forum/s...d.php?p=863960 with your comments.

I have since tried the connections as you suggested and I get an output voltage from 200 volts to 244 volts? Would this be correct?

I don't suppose anyone would have an idea in what device this variac would be used?

If anyone else has more information, suggestions and or ideas, I welcome your input

Thanks to all for their comments and help so for.

John