Old Autotransformer Part 1

Initial examination of an old transformer in a metal case. With valuable¹ antique² BILL 13A plug.
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1 - not valuable
2 - not antique

[@TheEulerID]

I think we can safely say that power lead is not original and has been replaced. I cannot imagine any manufacturer using a knot to stop the cable being pulled through. Knots on slippery PVC cable can slip. I would therefore not take the colour coding as indicative of the age of the device. The three pin plug has probably been reused as it's surely not contemporary with the power cable. That makes it post WW II of course, but the whole thing looks more like the product of the 1950s or 1960s than anything later.

[@Mark1024MAK]

Similar style (but isolating) industrial 110V/115V/120V, 240V/240V and 240V/110V/115V/120V transformers were still being made at least up until 1980, as they were used (some still in use, but most taken out of use over the last three years) at the company I work for.

[@TheEulerID]

@@Mark1024MAK autotransformers are still around. It's just that one looks rather old to me, along with that plug.

[@Mark1024MAK]

Steve Jones - Yes, of course. But I was referring to the style of that transformer, as made (presumably in the U.K.). A conventional metal frame, laminated iron plates for the core, SRBP sheet with threaded terminal studs etc. and often supplied in a sheet steel case painted with an enamel type blue paint.

[@station240]

I think the problem with the BILL plug is someone has swapped the neutral pin for a more modern version. The screw is quite different to the earth one. My 80's era UK plugs¹ have² the same screw in the neutral pins. 1 - not in the UK 2 - not actual present tense, as most have been converted to brass scrap.

[@extrastuff9463]

That safety police concerned about loose flex with a plug on it would probably not be happy about the electrical toolbox my dad used to keep (probably still does). It consists of a regular europlug (the flat one with just line and neutral), AC switch inline with the cord that has an indicator light for when its powered and crocodile clips on the other end. Decent crocodile clips on the handle end, but the grabby bits consist out of exposed metal that when used wrong could easily be touched by a human (or make contact with the other crocodile clip). They are attached to the flex in such a way that when dangling from a workbench they'd be a few cm apart and wouldn't easily accidentally make contact with each other though, so there's that at least.

[@staticfanatic6361]

We call those suicide cords in the U.S.

[@srfurley]

Quite large autotransformers exist, they were used for the main transformer in many ‘60s era 25 kV locomotives for example. Not sure if more modern designs still use them. I have a 1 kVA oneat home providing 120 V.

[@madbstard1]

Going to be a nice restore project. Can't wait to see the finish result.

[@ehamster]

Interesting, just took one of these out of my milling machine today. Similar size, but only running some 24V AC and 90V DC control electrics, total max 80W. Replacing it with a couple of small toroidals that hopefully won’t hum as much or have quite as much inrush current. This thing dimmed the lights when powered up. It was also used with a tapping at 110V and 115V to light some 5V bulbs. Didn’t strike me as ideal mixing these voltages behind a control panel.

[@gavinsmalley1513]

@pmailkeey Most heavy goods vehicles use 24V (peaks at 28v) and standard brake light lamps are 21W. If 24v21w would be close enough for you then a motor factor may have a better supply of lamps. So long as they're incandescent then they should be just as happy on AC as DC.

[@ehamster]

You can get 24V AC/DC led pilot lights/bulbs from RS and Farnell. I presume they have a bridge rectifier in them as they are happy with AC or any polarity of DC.

[@dogwalker666]

@pmailkeey impossible to get new i still have a box of these gls bulbs for our surface grinders

[@StreuB1]

I am a simple man. I see a video posting by JW or BigClive, I hit like. This will be a fun little repurposing project!! Honestly enjoy video series like these. Something that I can just kick back and watch and forget my hectic work and school life. Thanks for the video JW and can't wait to see how it turns out and what you have planned for it! Are you planning a little diagram session and explaining how an autoTx works?

[@stevecoatesdotnet]

You should do a teardown and review of the Sky box :)

[@samuelfellows6923]

nickhill92 😆

[@Berkeloid0]

Looks like there was a bit of an unintentional tear down of it in this episode due to the weight of the transformer!

[@add2k]

Rather than have this as a basic 240/110 transformer, will you be making all of the transformer tappings available on the front panel? This will be a useful bit of test bench type kit for voltage manipulation.

[@sbusweb]

+John Ward When using an autotransformer for a fixed facility, e.g. running 115v equipment constantly, worth talking about the risk of a neutral-break/transformer break -- you can be left with the situation where your load is just connected in series with inductor across full 230v, I think. Somebody told me they thought these won't therefore pass a PAT in some people's view because of this risk... any thoughts?.

[@jwflame]

That would be an undesirable situation, but a broken neutral always is - with a direct connection you would be left with a non-working appliance but all of it directly connected to 230v.

[@OC35]

When I worked at an advertising agency they had problems with a variac that was used to dim the house lights in their viewing theatre. A variac is an adjustable auto transformer. It was burning out the carbon brushes. It turns out it was wired in series with the lights! No neutral was connected! When I queried this I was told it was connected as per the diagram. I looked at the diagram and it was a block diagram just showing the variac feeding the lights.

[@samuelfellows6923]

Ashley Booth 😆

[@markrowland5393]

Thanks for the video, John. I think I understand how an isolating transformer works but I'm not sure how this one works. Could you please give a brief explanation, perhaps with a little diagram, for the mentally challenged like me. Thanks!

[@DanHaiduc]

This one is an autotransformer: en.wikipedia.org/wiki/Autotransformer

[@calmeilles]

One would guess that the gaping hole in the front would have been some sort of outlet; perhaps multiple terminals or more likely one set and a selector.

[@sbusweb]

+John Ward I have a couple of rather smaller autotransformers, taken out of very-old fluorescent-fittings when setting them up for Electronic-Ballast flicker-free-operation. These are marked ZUMTOBEL TRANSFORMATOR with 0,115v,240v and a 120VA rating written on them... not a lot bigger than typical choke for 58w 5ft lamp!. I'm thinking I can probably use one of these successfully to power a high-quality 115v CRT monitor i'd like to get going.... Though I wonder if the non-linear SMPSU load may bring demand over 120VA.... Will have to check ratings!

[@Mark1024MAK]

I’ve seen autotransformers that are a similar size to a conventional fluorescent inductive choke, but they were used inside the fitting to convert a CTE 110V supply to 240V AC so a standard off the shelf fluorescent lamp fitting could be used.

[@sbusweb]

@@Mark1024MAK OoooOooOOoooooh that makes much sense! Indeed I also wonder if really-old fluro-lights [not sure if 50s or 70s fittings!] might have been equally shipped to USA, possibly, though that would seem heavy/bulky/silly .... I wonder *when* building sites started USING 110v CTE or 63v-to-earth 3-phase with 110v phase-phase arrangements.......

[@grantrennie]

Thanks for the great video John 👍

[@kylebishop6233]

Good luck with the project John. May I suggest; you add a rotary cam switch to select the voltage output. Along with an RCBO built in, with an ESTOP, along with a volt meter and ammeter. RS sell, “RS PRO46x46mm meters” that fit very nicely. Direct connected for amps and volts. My big 10kW variac supply uses them. Looking forward to seeing the outcome. PS: Hammerite Hammered black is what I paint all of my equipment in I love that stuff! Kyle bishop :)

[@jwflame]

Not sure what I will fit into it yet - there isn't much room in the case. Only about 50mm depth behind the front panel (with the massive hole in it), the transformer fills up the rest of the space.

[@kylebishop6233]

John, depending on how you value the project it may be worth getting a new case. I’d say that’s the best idea personally. I have a very nice Claude Lyons Variac restoration to do soon. I think you’d agree there is nothing more satisfying than taking an old bit of it and making it look like new, and some. Kyle Bishop.

[@crazygeorgelincoln]

I'm thinking are you going to do a photonicinduction with it blowing up a vaccume cleaner or something. Looking forward to your colour choice for this device.

[@jms019]

The 36” telescope dome here runs off 200V (as did Cambridge ) and has an autotransformer by the door

[@DIMTips]

Nice tear down.

[@gloomyblackfur399]

Between you and Big Clive, I've been hearing the word "hoick" a lot lately. :-)

[@ehamster]

In the absence of any markings, is there any way to estimate the current / VA rating of an auto transformer? I have a couple of large auto transformers with no markings, each a similar size to the one shown here.

[@tonycosgrove6433]

I don't think I have ever seen a transformer that big.

[@peteb2]

John, may i ask if there is a good practice or procedure to reduce/remove the rusting of the top side (where dirt/moisture accumulates) of the iron lamination set? Should we scrub off the rust with a wire brush etc and repaint (?) I have had good transformers that work but the rusting must have penetrated deeply enough into & between the laminations so that i assume the level of eddy current flow meant the transformer would warm considerably even though no load was connected. The windings measured fine for DAR & PI tests. regards Pete

[@nophead]

The point of lamination is to reduce eddy currents by having insulation between the plates. Rust is an insulator, so shouldn't increase eddy currents. A lot of modern transformer have welded laminations, which kind of defeats their purpose. They do get quite warm and take significant power when not loaded.

[@yolot8219]

Fabulous 🎉😅

[@PaulSteMarie]

The resistance readings seemed a bit dicey. With the measurement of 2Ω on the 0-105V pair, I would have expected the 0-260V to have ~5Ω resistance

[@benbaselet2026]

I bet it's just poor contact for the probe.

[@jwflame]

Terminals were very dirty. The check was really just to confirm each one was still connected, actual resistance isn't important.

[@peckelhaze6934]

Nice one.

[@ikorbln]

What was the use of this one?

[@johncoops6897]

They are used to connect factory equipment. Multiple purposes - there is the ability to tap the normal voltage up/down 10% is handy, but this one probably did duty by converting 240V into 110V for some US equipment.Almost certainly

[@williamsquires3070]

This would make a HUGE smoke bomb if it were overloaded. 😬

[@benedictnothing]

Just realised you sound very much like George Martin! Tell me about producing Abbey Road.

[@samuelfellows6923]

Benedict Nothing 😆

[@niallgilmore2411]

Is that a 2nd sky endorsement I see 🤣🤣🤣🤣

[@NOWThatsRichy]

Maybe John is sponsored by Sky & Adidas! 😉

[@thepvporg]

Someone tried to repair it with a pin from another plug.

[@andreim841]

Ohhhh please God... Not pink🙄

[@jwflame]

Not pink. But it is metallic.

[@rambo1152]

"Hoik out all of this wiring", Now who else on KZbin might say that? Answers on a postcard please.

[@andygozzo72]

a certain scotsman, with a long beard, perhaps ? 😉

[@gtb81.]

my only gripe is you throwing so much in the bin, i don't like tossing things that are still useful

[@samuelfellows6923]

The Doctor - the neon lamp - I always save these, why did he have to throw it away if it still works ☹️

[@gtb81.]

Samuel Fellows as do I, if It is still flexible and has good insulation, I keep it, I've always been able to use it at some point

[@gtb81.]

@@samuelfellows6923 well that's probably because the lense was not replacable

[@gtb81.]

@Rick Delair yes, that was my intent when i commented, i just expressed that the lense was probably irreplaceable

[@jaycee1980]

bet that makes a lovely sound when powered on.... HMMMMMMmmmmmmmmmmm :D

[@simontay4851]

I bet it has that old electronics smell as well.