Ideas for what to do with old transformers - Page 1
Forum section: electronics / projects

author: cigmas
author_rank: Regular Contributor
timestamp: October 15, 2019, 06:39:04 pm
content: I have a few transformers from old "Razor Only" outlets. Any ideas for making use of them or their components?Other than paper weights of course.

author: Gyro
author_rank: Super Contributor
timestamp: October 15, 2019, 06:47:47 pm
content: - They make nice low wattage safety isolation transformers (as long as you don't screw up the wiring when re-mounting them). Assuming UK, they're normally rated at around 15VA with 115V and 230V output taps.- If you're thinking of getting into low power valve equipment, you could use then for HT transformers.- Put one (with appropriate socket etc.) in front of a small switch mode wall wart to eliminate Y-cap leakage current?- ... still thinkingDon't bin them though.

author: cigmas
author_rank: Regular Contributor
timestamp: October 16, 2019, 01:11:47 am
content: Thanks for the ideas. Those aren't uses that stand out for me at this point, but I'll hang on to the transformers in case something else comes up.Annoyingly, most of them hum, which was a prime reason, along with practicality and safety, why I replaced them in the first place.

author: soldar
author_rank: Super Contributor
timestamp: October 16, 2019, 11:32:44 am
content: Don't forget they can be used as inductances for filters or other uses.Also to transmit and isolate signals rather than power.

author: cigmas
author_rank: Regular Contributor
timestamp: October 17, 2019, 05:37:22 pm
content: At worst I'll just give them away locally... immediately after which I might just find some use.

author: Macbeth
author_rank: Super Contributor
timestamp: October 17, 2019, 06:12:24 pm
content: Use it as an isolated supply to astring of stacked REF5010's, put into a project box with a suitable rotary switch or just a whole series of binding posts as a precision high voltage reference from 10V to whatever your secondary will allow in 10V steps

author: LaserSteve
author_rank: Super Contributor
timestamp: October 18, 2019, 01:38:42 pm
content: Do You Own a Boat? Sorry, could not resist...Steve

author: cigmas
author_rank: Regular Contributor
timestamp: October 18, 2019, 08:58:32 pm
content: @Macbeth To my understanding these are 1:1 transformers.@LaserSteve Sorry, I don't get the joke. But I'll take any excuse to laugh.

author: Bud
author_rank: Super Contributor
timestamp: October 18, 2019, 10:21:18 pm
content: You could use them as boat anchors

author: Macbeth
author_rank: Super Contributor
timestamp: October 19, 2019, 12:09:51 am
content: Quote from: Bud on October 18, 2019, 10:21:18 pmI still don't get the joke. "Boat Anchors" are the massive rack cabinet test equipment typical of the middle of the 20th century. Mr Carlsons Lab youtube is a good example.A shaver socket isolation transformer is not a boat anchor, ok I dunno, maybe in the USA they have all those union guys and crap to make it weigh 50 lbs? I doubt it.

author: cigmas
author_rank: Regular Contributor
timestamp: October 19, 2019, 12:32:09 am
content: Probably fine for HMS Rubber Ducky. The provenance is from bathroom outlets after all.

author: sleemanj
author_rank: Super Contributor
timestamp: October 19, 2019, 07:16:32 am
content: If nothing else old transformers and inductors are endless sources of bare copper wire, pull a length through some sandpaper a few times makes short work of the enamel.

author: Gyro
author_rank: Super Contributor
timestamp: October 19, 2019, 09:17:02 am
content: They are indeed not boat anchors, at least in the UK. They (in their wall outlet fittings) are designed for use in bathroom Zone 1 areas, requiring high levels of isolation integrity. The are nice and compact too.

author: LaserSteve
author_rank: Super Contributor
timestamp: October 19, 2019, 10:23:48 am
content: Sorry, In the US, travel transformers and shaver transformers used to be large chunks of iron. Widely regarded as just as capable of killing you or catching the bathroom on fire, as getting you a shave on the road.Mea culpa.Steve

author: Zero999
author_rank: Super Contributor
timestamp: October 19, 2019, 12:48:56 pm
content: Quote from: LaserSteve on October 19, 2019, 10:23:48 amIn the UK, shaver sockets fit to a standard wall fixture and have a small transformer inside. The one linked below is rated to just 20VA, which is small, even on 50Hz.https://www.go-banana.com/products/Lighting-Electrical/Plugs-Switches-Sockets/Indoor-Switches/Shaver-Socket-115--230V-Dual-Voltage-Polished-Chrome-364479.html?gclid=EAIaIQobChMIns7Vrqyo5QIVibbtCh1dcAwMEAQYAyABEgIARfD_BwE

author: cigmas
author_rank: Regular Contributor
timestamp: October 19, 2019, 08:01:39 pm
content: Yes, the copper wiring was on my mind, though I don't have a need for bare wire at the moment and I'm not sure what diameter it is. Part of me wants to disassemble one just out of curiosity, but I don't want to create a mess.I'm not sure what the UK ones look like, but mine look identical to this:

author: Macbeth
author_rank: Super Contributor
timestamp: October 19, 2019, 08:56:33 pm
content: Looks like a good candidate for my high(ish) voltage precision calibration source.

author: Gyro
author_rank: Super Contributor
timestamp: October 19, 2019, 09:07:24 pm
content: Wow, do lots of people have beards in your country?(Sorry)Err, no. The UK ones invariably have split bobbin construction for high isolation.Maybe you might be better salvaging the copper.EDIT:Actually, on second look, yours may be better quality than it looks, split bobbin under the outer insulating sleeve too. I was thrown by the wire nuts. lack of transformer frame earth etc.

author: james_s
author_rank: Super Contributor
timestamp: October 19, 2019, 09:37:22 pm
content: Quote from: Macbeth on October 19, 2019, 12:09:51 amThere is no USA equivalent to the UK shaver socket. Here we just put an ordinary receptacle in the bathroom, it is of course required to be protected by a GFCI (RCD) but otherwise there's nothing special about it. Here it is also perfectly acceptable (and commonplace) to have the switch(es) for the light and vent fan inside the bathroom too, the fan often being on a wind up or occasionally electronic timer switch.

author: cigmas
author_rank: Regular Contributor
timestamp: October 19, 2019, 11:41:39 pm
content: @Macbeth It's a cool idea, just not one I'm familiar with or have a particular need for. But still thanks for the suggestion.Quote from: Gyro on October 19, 2019, 09:07:24 pmThey must because nobody uses these outlets.@james_s Exactly, I replaced these things with GFCI receptacles, and now wonder if the old hardware could be reused in some way. Also, some places don't have light switches inside bathrooms??

author: james_s
author_rank: Super Contributor
timestamp: October 20, 2019, 03:09:35 am
content: IIRC the UK doesn't allow any receptacle or switches in bathrooms, at least every bathroom I saw over there had one of these isolated shaver sockets if anything at all, usually a pull string to control the vent fan and the light switch was always outside the door in the hall.I thought the transformer shaver sockets were a UK only type of thing, that's the only place I've ever seen them.

author: cigmas
author_rank: Regular Contributor
timestamp: October 20, 2019, 03:58:16 am
content: Interesting. Learned something new. I had never heard of those pull cords. Apparently the requirement is to have switches at least 60cm away from baths or showers.

author: Electro Detective
author_rank: Super Contributor
timestamp: October 20, 2019, 04:12:31 am
content: FWIW a single or dual pole switch fitted and wired to the primary would get rid of that humtill the tranny needed to be used, in which case hum is goodwith bonus isolation from the mainsIf you had a number of these, you could in theory wack them in a box and parallel them all up for more output, or series for 220/240 volts,or paralell/series combo...Paying special attention to the phase/polarity thing, in and out, otherwise no diceor

author: Gyro
author_rank: Super Contributor
timestamp: October 20, 2019, 09:27:24 am
content: Quote from: cigmas on October 20, 2019, 03:58:16 amAs you say, you learn something new every day. I always thought Zone 2 extended more than 60cm! That's well within misdirected shower head range - or my wingspan come to that!It's only recently that I replaced the wall switch in our downstairs WC with a pull cord (before replacing the carpet upstairs). That was barely 60cm from the sink. It looks like I needn't have bothered!The curious thing is that wiring regs aren't retrospective on existing installations, so it is quite possible to have a wet switch on a circuit without an RCD. I suppose that's why pull cords are common in Zone 3 here.

author: SeanB
author_rank: Super Contributor
timestamp: October 20, 2019, 10:45:57 am
content: Yes your older installations have to comply with rules as of date of installation. This means a repair has to be like for like, so you can replace a switch, socket or light fitting with an identical function one, but if you do an upgrade the upgrade has to comply with current regulations. So, you can have a switch in the bathroom, and it fails, so replace with exactly the same model (or equivalent manufacturers model) switch, but if you say want to install a light dimmer that needs to have the modern standards apply, so is going to need rather a lot of work. Same for the light fitting, you cannot replace with a LED fitting without all new standards applying, but you can replace the lamp screwed or plugged into the socket inside the fitting with CFL or LED no problem, as they are not part of the fixed installation. Shaver socket you have to replace with one, not a regular socket, unless it is not in the wrong zone, and is connected to a RCD protected feed.Also if you have an old house with 5A round sockets on the floor, you can only replace with another 5A socket on the floor, probably with an upgrade of having a switch, but still a 5A socket. If you want 13A/16A socket outlets you have to bring the installation up to current spec, which will probably involve removal of the old gutta percha wire and pulling new PVC cable in, with a separate ground wire, as the regulations now prohibit using the conduit as ground, to get the insulation resistance up to the modern standard. Then you need to have modern breakers and RCD devices for the new circuit, to comply with current regs, installed in a housing to the current regulations. Gets very expensive, as you are then basically rewiring the entire house to fix one fault, as disturbing the old gutta percha wire will cause multiple faults from brittle insulation.Just did that this weekend, to replace 2 light fixtures from a failed cable. 33m of new cable through the conduits, new fixtures, and new covers for the old junction boxes, and good luck finding BA size screws in long lengths for those 60 year old boxes. Just glad I am not the electrician who cut the cable I fixed, he now has to replace 50m of 16mm mains feed wires in another steel conduit, and the bet is that they will not pull out of that conduit they have spent the last half century in without a fight. Will probably need 70m of Airdac cable instead, to go the long way through ducts, as that cable is cheaper than direct burial armoured cable

author: Zero999
author_rank: Super Contributor
timestamp: October 20, 2019, 07:48:00 pm
content: Quote from: Electro Detective on October 20, 2019, 04:12:31 amThe UK shaver sockets do have a primary side switch. It's integrated into the socket and is automatically closed when a plug is inserted.QuoteThey already have a 120V/240V output, which is either selected using a rocker switch, two different sockets or a socket with three poles, for the two pin plug, which gives a different voltage, depending on how the plug is inserted. In the type with two sockets, an interlock prevents two plugs being inserted simultaneously.Be wary when connecting the secondary windings of transformers from different manufacturers or of different sizes in parallel. Even if they're the same voltage and you get the phasing right, the turns ratio might be slightly different, causing increased losses. Connecting them in series is fine, up to a point when the insulation will fail and cause arcing, but I think you'll be fine up to a few kV, with shaver isolation transformers.

author: Electro Detective
author_rank: Super Contributor
timestamp: October 21, 2019, 03:38:56 am
content: Quote from: Zero999 on October 20, 2019, 07:48:00 pmabsolutelyif trannies don't measure pretty much the same as singles, it's a no go doing parallel,and a mismatch series job can have dramaEven with (or without) the perfect match up, I would run them a bit lower than the theoretical twofer expectations, due to losses, interactions, heat, blah...Current/clamp readings, temperature checks and looksee of proceedings on a cro or dso doesn't hurt eitherIn the case of pairing up transformer welders for more zap, duty cycle, or compensate for long electrode and work return cables,'oops' or 'my bad..'on a wire up is not an option

author: cigmas
author_rank: Regular Contributor
timestamp: October 27, 2020, 08:20:06 am
content: After destructively opening up one of the transformers, I'm not sure there's much to be done with them if the others are similar, which they appear to be. What do you think?Even the copper wire's insulation is worn off with the copper corroded at various places. I wouldn't be confident salvaging the wire since it's not always easy to see where it's exposed. Continuity testing revealed many uninsulated areas.

author: Zero999
author_rank: Super Contributor
timestamp: October 27, 2020, 05:16:58 pm
content: That brown/orange substance appears to be a resin, not rust, which helps to insulate the windings. It's possible you damaged the insulation, when you distructively disassembled it, because it would have stuck to the resin and peelled off, as it was pulled apart.You're better off earing on the side of caution, as it's safety critical by not using it, you feel uncomfortable with it. Take them to your local scrap dealer, where they can be recycled.

author: cigmas
author_rank: Regular Contributor
timestamp: October 28, 2020, 03:57:12 am
content: It's difficult to see in the pictures, but there are sections that are darker, instead of the typically brighter copper color, which had continuity.As for the resin or orange sheets, it was already flaking off before opening it up.Maybe I'll unwind some of it to check deeper layers. Is there a clever method to test continuity to all sides of a wire at once?Or as previously suggested, I could use it as bare copper wire, though I don't have a need for that at the moment.

author: Zero999
author_rank: Super Contributor
timestamp: October 28, 2020, 08:31:51 am
content: Quote from: cigmas on October 28, 2020, 03:57:12 amHave you tried powering any of them up yet? Do they run extemely hot? The one you've dismantled has a thermal fuse (the shiny object, withthe white band in the middle, on the right).QuoteI normally hold one probe of the meter, in one end, clip the other the other probe to an uninsulated part of the wire and move the wire through my fingers. The resistance of my body is in the hundreds of kOhms to MOhms region, which is what the meter will read, if there's a break in the insulation. A more reliable method is to connect the uninsulated end of the wire to one probe and imersing the wire and the other probe, in a bowel of salt solution.

author: LondonNight
author_rank: Contributor
timestamp: October 28, 2020, 06:29:37 pm
content: They are useful as bucking transformers when restoring old tube radios. Those tube radios are sensitive to the mains voltage, if you live in europe, then the mains voltage is 240VAC nominal, but when the tube radios were made, they were made for 220VAC nominal. 20V doesn't seem much, but if you do power one with 20V more, you will see the filament voltages go up much more than they should. The different voltages inside the radio also go up, again, not a good thing. I attached a schematic on how a bucking transformer is used. Just make sure the primary winding of that transformer is capable of carrying the current. From my experience, if they are properly sized for the application, they are good and safe.

author: Gyro
author_rank: Super Contributor
timestamp: October 28, 2020, 07:36:14 pm
content: Quote from: LondonNight on October 28, 2020, 06:29:37 pmThe OP's transformers are shaver outlet isolation transformers. They have a 230V secondary with 115V tap.For voltage reduction using low voltage secondary transformers, I generally wire them in an autotransformer configuration rather than 'bucking' configuration. This improves regulation and the lower voltage on the primary winding reduces core losses, leading to reduced operating temperature and better efficiency.P.S. I agree, mains voltage reduction transformers are useful for valve/tube gear. Most modern mains transformers are wound for a nominal 230V European harmonized standard, while mains voltages, in the UK at least, can easily be 246V or more. The resulting secondary voltages aren't great for valve heaters.

author: cigmas
author_rank: Regular Contributor
timestamp: October 28, 2020, 08:25:16 pm
content: Quote from: Zero999 on October 28, 2020, 08:31:51 amThey have not been powered since they were removed. They were constantly warm and buzzed (reason why I replaced them) even with no device plugged into their socket.Btw, there is no white band. That is light reflection from an angled part of the metal.Taking accurate pictures is tricky, especially with shiny metal.Quote from: Zero999 on October 28, 2020, 08:31:51 amClever tips, thanks!Quote from: LondonNight on October 28, 2020, 06:29:37 pmThanks for the idea. I'm in 120VAC territory, and don't think I have tube transistor equipment, but still good to know.

author: TheMG
author_rank: Frequent Contributor
timestamp: October 29, 2020, 12:55:05 am
content: You could use them as a small 120V to 240V step-up transformer if you ever need to power some small 240V-only equipment. Take two of them and wire the primaries in parallel, and the secondaries in series.The shaver outlets with an isolation transformer were a way of providing an additional level of safety (by having no path for current to flow to ground) long before GFI/RCD were even a thing.Nowadays, GFI receptacles are installed in bathrooms instead of isolation transformers because people like to use power-hungry devices such as hair dryers, curling irons, etc, which would require an unreasonably large isolation transformer to handle. Also the GFI probably has lower standby power consumption that the transformer losses.While one could argue that a GFI does not provide an equivalent safety benefit due to the possibility of the circuitry failing to trip (you're supposed to test them regularly, but who does? hardly anyone.) however I guess they've been deemed a reasonable compromise as far as providing some safety benefit against shock, with the convenience of having the full 15 or 20A of current available for power-hungry bathroom gadgets.

author: Zero999
author_rank: Super Contributor
timestamp: October 29, 2020, 08:39:23 am
content: Quote from: TheMG on October 29, 2020, 12:55:05 amOr just one transformer with the the 115V secondary to the mains.QuoteIsolation transformer shaver sockets are pretty common in the UK, where no other type of socket is allowed in bathrooms. They have a different type of socket, than the standard UK three pin plug, so won't take hair dryers. I suspect the reason why it has to be an isolation transformer, rather than an RCD, is due to the possibility of the latter failing to trip.

author: richard.cs
author_rank: Super Contributor
timestamp: October 29, 2020, 03:20:53 pm
content: Quote from: Zero999 on October 29, 2020, 08:39:23 amWell, in a normal UK-sized bathroom there is no space far enough from the wet areas to be allowed under UK rules (3m, though I saw something about this changing to 2.5m), except inside cupboards and stuff (zones end at doors). You can (or could? maybe it's changed since brexit?) choose to wire a house or a section of a house to the equivalent standards of another EU member. A friend of mine wired his bathroom to German rules, so his wife could have a (schuko) socket for the hairdryer. It caused a little kerfuffle with the paperwork but was ultimately accepted.