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Old 24th Jan 2019, 6:50 pm   #1
Herald1360
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Default Variac questions

I have acquired a small variac- possible 1-2A rated. It's unidentifiable as to maker, at least by me. The only useful markings are TYPE V 6H-TS. The winding is about 4" in diameter and its inductance is about 650mH which would suggest a magnetising current of about 1.2A at 240V.

Does anyone recognise it? Is it a 240 or a 110V device? I have no variable supply to run it up on to see whether it starts saturating before it reaches 240V.
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Old 24th Jan 2019, 7:54 pm   #2
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Default Re: Variac questions

Looks like it has enough turns for 240V, why not fit a lead and 3 amp fuse and try. Three outcomes...
1, The fuse blows immediately, 110V version.
2, It gets very hot in a few minutes, 110V version.
3, Hums very quietly and only gets a little warm, 240V version.
I would have thought that a 110V Variac would be rare in a 240V region.
 
Old 24th Jan 2019, 7:55 pm   #3
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Default Re: Variac questions

The metal drive-dog on the end of the control shaft rather hints at it having been coupled to some sort of stepper-motor servo/gear drive rather than being controlled manually.

I wonder if it came from a mechanical 'constant voltage' regulator of some kind?
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Old 24th Jan 2019, 8:04 pm   #4
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Default Re: Variac questions

No idea about its provenance- as you say it looks like it's "out" of some larger system.

There's another possible scenario for the 3A fuse scene- it could just blow instantly on inrush current, even if it's a 240V unit.

I think I'll give it a go at 5A- I've actually got more of those than 3A ones. 110V should still take it out but inrush less likely. I'll connect it via the safebloc- the links on that are easier to clean up than an upset socket switch! And the fuse is easily accessible too.

Watch this space......
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Old 24th Jan 2019, 8:06 pm   #5
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Default Re: Variac questions

Quote:
Originally Posted by merlinmaxwell View Post
Looks like it has enough turns for 240V, why not fit a lead and 3 amp fuse and try.
I agree - it 'looks' like a 240V item.

Many Variacs have a tap for 110V input. But do what merlinmaxwell suggests. Stick a 100W lightbulb in series if you are nervous!
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Old 24th Jan 2019, 8:52 pm   #6
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Default Re: Variac questions

My thoughts were the same as G6Tanuki- if so, it may have been connected in concert with part of an auto-transformer winding to give a buck/boost range of 50V or so.

Still, Chris sounds like he's approaching with caution anyway, so we'll see what happens!,

Colin.
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Old 24th Jan 2019, 10:10 pm   #7
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Default Re: Variac questions

Happen to have the pictured variac on the bench at the moment. Looks quite similar. Even says 'TYPE V 6H' in the top left corner of the terminal plate. Photos are not good as I just snapped them with a tablet in poor light. Can improve the quality with a bit more time if needed.

The variac is a Zenith (Claude Lyons) circa 1960. It's 240V and rated at 3A. The overall diameter of the toroid is about 4" too.

Alan
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Old 24th Jan 2019, 10:43 pm   #8
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Default Re: Variac questions

An announcement on the Claude Lyons web-site advises that the company is closing, so I don't know if there is still anyone still in the technical department of their office who can answer your question, -they have been most helpful to me in the past,- but their web-site does have a guide with photos and outline technical specifications for many of their historic Variacs, which were marketed under the 'Regavolt' name. It may help you to narrow the field a bit.

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Old 24th Jan 2019, 11:14 pm   #9
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Default Re: Variac questions

Type V6H is shown on this web page:

https://www.claudelyons.co.uk/index....ges&Itemid=267

Pretty conclusive I think.

Alan

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Old 24th Jan 2019, 11:31 pm   #10
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Default Re: Variac questions

I've given it a go with a 5A fuse which produced no drama. Not even an audible splat as I closed the safebloc. Encouraged by that, I connected it via a plug in monitor thing which told me that the no load current was only 38mA (!) with a PF of 54%. Having apparently measured only 650mH inductance I rechecked this current with a DMM- same figure. I can only assume that the RLC meter (AVO B183) doesn't like what it's looking at for some reason. Odd, since it's supposed to be measuring at 100Hz on the Henries range.

Anyway, emboldened by all so far, I realised I had a good excuse to use one of the 200W ES bulbs I collected from Nick the D a few years back (actually the first time I've done anything at all with them) as a dummy load. Wahey- I've got a nice light dimmer . The monitor thing showed the power factor climbing to near unity almost as soon as I advanced the volts from zero and rose to about 0.9A at full chat, reasonable enough for a 200W bulb.

Alan's variac looks exceedingly like a cased version of mine- if the winding height of his is 3.5" as mine is, it looks like I've got a 3A, 240V unit, which is nice to know

Definitely calls for a https://www.vintage-radio.net/images/smilies/idea.gif and a https://www.vintage-radio.net/images/smilies/beer.gif
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Old 24th Jan 2019, 11:38 pm   #11
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Default Re: Variac questions

Mine is fitted with a 5A fast fuse although I can't be sure it's the correct rating. Hasn't been changed during my ownership (30 years!). The toroid height is indeed about 3.5".

Alan
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Old 25th Jan 2019, 11:20 am   #12
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Default Re: Variac questions

Interesting....... it would seem that cutting and pasting smileys turns them into URLs
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Old 25th Jan 2019, 1:33 pm   #13
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Default Re: Variac questions

Ah, wondered how that happened Chris. Nonetheless the sentiment was clear.

Have just had a closer look at the variac and there are a couple of design differences although it's clearly the same basic model as the uncased version you have. Your variac appears to have a supporting roller for the rotor arm which mine doesn't. You have an extra tag on the lower row of the terminal panel - not quite sure why. The full type number on the outside of the case on mine is V 6H MTF rather than V 6H TS and I guess this distinguishes one from the other.

The main reason for working on mine has been to replace the worn brush which has proved interesting! The brush protrudes from the holder by about 0.25" when new and once down to less than 2mm it's worth considering replacement. Was thinking of doing a piece in 'hints and tips' but wasn't sure how many other people would still have one of these. Now I know there's at least one!

Alan

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Old 25th Jan 2019, 2:11 pm   #14
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Default Re: Variac questions

Looking again at the pictures I think I may have mistaken part of the drive-dog for a rotor-roller.

Alan
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Old 25th Jan 2019, 6:49 pm   #15
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Default Re: Variac questions

Quote:
Originally Posted by Herald1360 View Post
Having apparently measured only 650mH inductance I rechecked this current with a DMM- same figure. I can only assume that the RLC meter (AVO B183) doesn't like what it's looking at for some reason. Odd, since it's supposed to be measuring at 100Hz on the Henries range.
Probably not the meter's fault. Iron-cored windings with no air gap are notoriously indeterminate as far as inductance is concerned. The figure you get depends on both frequency and test voltage. At low excitation the iron permeability is low, so inductance seems low. At higher excitation the permeability increases and inductance rises. At really high excitation you approach saturation, and the figure falls again.

Measuring it is like trying to measure Young's modulus of warm chewing gum. All you can say is it's super-easy-stretchy.
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Old 25th Jan 2019, 8:33 pm   #16
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Default Re: Variac questions

If it's of any comfort I tested mine, after replacing the brush, @ 2.8A continuous running for two hours using an electric fire. Well, it was cold outside at the time. Touch testing proved to my satisfaction that there was no appreciable warming of the toroid, the brush housing or the shorted turns. The only thing that got too warm was the kitchen.

Alan
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Old 26th Jan 2019, 11:39 pm   #17
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Default Re: Variac questions

Many variacs don't have the over-voltage taps at each end of the winding, to provide a 0-275V output range, so that's a nice feature. Although if you want a connection setup that passes the neutral through directly, then the variac just provides the more typical 0-260V output range for a 240V input.
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Old 15th Feb 2019, 10:04 pm   #18
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Default Re: Variac questions

Hi folks,

A while ago this thread stopped!

Anyway, to re-start it, I have uncovered a variac I'd like to use for radio restoration. No immediate identification other than some name stamps on the metal base of the wiper . They read "Enfield Middlesex" and "Made in England" - which suggest a 230 Volt device. Anyway, tested the winding resistance which was 9.4 Ohms. Connected across 230 VAC this would draw about 24 Amp which seems rather a lot.

Can anyone verify if this is about right?
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Old 15th Feb 2019, 10:20 pm   #19
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Default Re: Variac questions

My 8 amp Variac measures about 3 ohms (as measured on an analogue meter) but the key issue is that you will be using it on AC, so the impedance of windings comes in to play. Consequently, the current flow is much less than the resistance alone would allow.

Be sure to use an analogue meter when testing windings as some (most?) digital meters put out pulsed DC, which again is sensitive to the inductive impedance.

B
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