110volt plugs when mains is 230

[avocollector]

Here in NZ mains is 230v ac but since a lot of US gear also comes in you can often acquire 110v ac equipment. I've just had the good luck to acquire a 230 to 110 step down 1kw transformer so I'm thinking of setting it up on my service bench as a 110 v supply.

This begs the question of what sort of plugs should I put on the 110v stuff to prevent any attempts to plug into 230v - not only for me but any future users. The easieist solution I can see would be to import some US ones - is there any problem people can see with that? or do people use other solutions??

[G6Tanuki]

I normally use the standard US-types shown as "Type A" and "Type B" here: https://www.worldstandards.eu/electr...s-and-sockets/

noting that the 2-pin type-A will fit the 3-pin type-B outlet, which is handy.

I've got some kettle-leads and figure-of-8 cassette-recorder leads with these US plugs on - these days you seem to get one included (in addition to the Schuko, Europlug and BS1363 plug) with any electronic gear you buy.

[TonyDuell]

The only downside to using US 110V plugs is that some manufacturers used them for 230V. Tektronix fitted a chassis mounting plug on their 500 series 'scopes, it's the same US 110V type even if the 'scope is wired for 230V. So of course I have a cable with a UK 13A plug on one end and a US 110V socket on the other to power the 'scope. And of course a lot of UK audio equipment from the 1960s and 1970s had the 2 pin US 110V socket as a mains outlet (I can think of the Leak Stereo 20 and Quad 33 preamp). DEC were very good about using the similar 230V US socket on their machines when confgured for 230V.

But I generally use the US 110V sockets for that and just remember there are a few sockets round here that are 'misused).

The other option is the IEC60309 series of connectors. They come in 110, 220 and 400V (or so) versions, and are colour coded and keyed so you can't connect a 110V plug into a 220V socket. They are rather large for general use though.

[knobtwiddler]

There are loads of items in my workshop that need 120v. I have to confess that I managed to kill a rather nice Hakko machine in forgetting it needed 120v (no fuse...). So, my advice is to ensure that you have utmost visual / ergonomic distinction between 120 and 240 gear. I will always keep a US plug in place.

[joebog1]

A simple reminder is to buy 110 volt plugs in red. No excuse then. These fitted to all your 110 volt stuff of course.

Joe

[Skywave]

Originally Posted by avocollector

Here in NZ mains is 230v ac but since a lot of US gear also comes in, you can often acquire 110v ac equipment.

A lot of US-sourced equipment with mains transformers have dual-primary windings: each being 120-v. For a 120-v. supply, they are connected in parallel; for 230-v., connected in series (in both cases, taking account of phase). Therefore, it's worth examining such items to see if they can be re-configured.
Having said that, in the past when I have acquired a particularly valuable item with a singe 120-v. primary, I've simply replaced the mains xfmr.

Al.

[winston_1]

First of all let's get this out of the way. The US uses 120V not 110V.

In Australia, and I imagine NZ, as the regs are similar there is a special plug used for 110v centre tapped supplies on work sites. It differs from the standard Aus/NZ plug in that the supply pins are round rather than flat. Why not use this?

[Argus25]

One thing to watch out for is that most transformers step down or isolating are designed to give their rated output voltage at full load and it can be 10 to 15% higher on no load or a light load. So for a very high power transformer like 1kW it could be higher than you would like with small loads. And although the mains voltage in NZ & AU is supposed to be 230v, due to solar inputs to the grid it can be as high as 250 to 255V.

So you can end up with 135v out of your transformer and much American vintage gear with transformers is very intolerant to this because of the 50 vs 60 Hz and the transformers can run very hot.

To solve all this I run my 230:110V step down transformers from a Variac, like the one sold by Jaycar.

[Argus25]

I could add to the above remarks I was going to write an article called Vintage American transformers running hot in the Antipodes.

It's actually a big problem for those interested in vintage radios & TV's made in the USA.

One of the main issues is the frequency difference. The reason is that the peak flux density (Teslas or Webers/square meter) that the core experiences is inversely proportional to the frequency and proportional to the applied voltage. So if the frequency drops by 50/60, then say if you were powering the transformer primary by 115V (originally in the USA) on 60Hz, you would have to drop the primary voltage by 50/60 or about 0.83 X 115 to get back to where you were. That is about 96V for 50Hz operation.

That voltage may or may not be high enough depending on the secondary voltage requirements. And as noted it's not uncommon for a step down transformer to have 115v to 125V or more on its output run here. (Hence the need for the Variac)

It's quite amazing the differences in the primary magnetisation currents of old 60Hz transformers vs new ones run on 50Hz.

For example Hammond make "Univiversal" voltage transformers now that replace a lot of the original types in radios, TV's and Guitar amps etc.

Comparing two transformers of the same power, one manufactured in the USA in 1939 and a new universal Hammond type, the off load primary current in the old transformer was 1.5A on 50Hz, and in the new version about 50mA. I have had to replace a number of the power transformers in my vintage USA TV sets to avoid the high radiated magnetic fields.

It seems in a lot of the early American transformers they pushed the B-H curve to near saturation (maybe trying to save on iron) and just got away with it on 60Hz and say 115V, but out here if the transformers are run at that line voltage on 50Hz they run very very hot, bad for the old insulation and they have very high radiated magnetic fields. I have also wondered if the cores may have deteriorated on the older ones, but I have no proof of that.

[TrevorG3VLF]

The iron could be different. I think 4% silicon grain orientated is now preferred. Torroid transformers seem to be run closer to the limit as the continuous core is ideally orientated with doubtless more consistent composition.

I use a 240V isolating transformer with a secondary centre tap for 120V. I have fitted a 240V and a US 120V socket. It is a goodly lump but only has about 2% extra output voltage.

[knobtwiddler]

In support of Argus's point: I have a sideline which involves restoring US-made audio, typically made between 75 and 85. I can state for a fact that a very high proportion of the mains TFs really do not like 50Hz operation - even if run from a variac with accurate V across primary. Not only will they emit a considerable variety of highly audible buzzes, whines and whirrs, but - as Argus asserts - radiate EMI strongly, which can affect neighbouring circuitry. Radiated EMI and mechanically audible noise go together.

[Argus25]

Originally Posted by TrevorG3VLF

I use a 240V isolating transformer with a secondary centre tap for 120V. I have fitted a 240V and a US 120V socket. It is a goodly lump but only has about 2% extra output voltage.

Many isolating trannies are designed 1:1 on full load and on mild loads give a step up. So one trick I do is use them in reverse, it also helps with the higher line voltages lately because of solar inverter input to the grid which have significantly degraded the voltage regulation.

One thing to watch out for too is that many of the 230/115 style step down trannies are auto transformers and don't isolate. They are more compact for the power ratings though. The 230/115V step down types sold by Jaycar are isolating but it pays to note they bring the earth connection across to the earth pin in the 115v output.

[Argus25]

Originally Posted by knobtwiddler

In support of Argus's point: I have a sideline which involves restoring US-made audio, typically made between 75 and 85. I can state for a fact that a very high proportion of the mains TFs really do not like 50Hz operation - even if run from a variac with accurate V across primary. Not only will they emit a considerable variety of highly audible buzzes, whines and whirrs, but - as Argus asserts - radiate EMI strongly, which can affect neighbouring circuitry. Radiated EMI and mechanically audible noise go together.

This issue also becomes super obvious in a TV set because the CRT's beam acts like a sensor for radiated magnetic fields and in two of my American TV sets the beam was grossly deflected by the radiated fields, in fact one so much that it produced (traced out) a pattern that looked a little like a hysteresis curve !

In audio work I guess it would result in induced hum currents in the nearby signal circuits and be a real pain.

One trick that sometimes helps is either an external copper flux band or lifting the transformer a little off the chassis with washers, especially if it's a steel chassis.

But I'm certain you would be impressed at the difference if you replaced a lot of these transformers with the new multi-voltage Hammond ones. Can be expensive so mainly for your own amps.

[arjoll]

Originally Posted by avocollector

This begs the question of what sort of plugs should I put on the 110v stuff to prevent any attempts to plug into 230v - not only for me but any future users. The easieist solution I can see would be to import some US ones - is there any problem people can see with that? or do people use other solutions??

element14 do a basic US socket (3 pin) for $0.90 plus GST.

https://nz.element14.com/qualtek-ele...692171?st=nema

590 in their Sydney warehouse, so overnight to Auckland, two days to anywhere else in the country.

I'm putting an order in in the next for some caps for my Spectrum and Raspberry Pis for a client, so if you are interested but don't need enough other stuff to make up an order I can grab however many you need and throw them in the courier for you

[arjoll]

Originally Posted by winston_1

In Australia, and I imagine NZ, as the regs are similar there is a special plug used for 110v centre tapped supplies on work sites. It differs from the standard Aus/NZ plug in that the supply pins are round rather than flat. Why not use this?

Yes, we use the same standards - AS/NZS3112.

The plugs you're thinking of are the likes of the PDL 439/110 (although it looks more like an Australian Clipsal design than NZ PDL; both are part of Schneider) and socket 412/110. I suspect they'll be quite a bit more expensive than just using US plugs and sockets.

[eddie_ce]

For the few 110 Volt radios I have I use BS546 2A 3 round pin plugs. This prevents "overvoltage accidents" and they are adequately rated for small radios. I use a separate transformer for each outlet.

Plugs and sockets are available online.

[emeritus]

In the 1970's I recall reading that some better-quality US domestic appliances incorporated crowbar circuits using SCRs that put a dead short across the mains to blow the appliance's internal fuse if the mains voltage got too high. This was not intended to protect against inadvertant connection to a 240V mains supply, although of course it would have done it. Rather it was to cope with a not-uncommon failure mode of a common type of US domestic electrical installation in which a dwelling is supplied via a local transformer with a centre-tapped 240V secondary. This provides two 120V circuits, which can become connected in series if the common connection goes open circuit. If one leg has high current loads and the other leg a low current load, Ohm's law shows that most of the 240V will appear across the low current load, hence the need for crowbar protection. This arose in a thread a couple of years ago, where several posters said it had happened to them in the USA.

[TonyDuell]

The HP Integral (a portable, mains powered 68000 computer that runs HPUX) has a triac circuit in the PSU that is only switched in-circut if the voltage selector switch is set to 115V. Its purpose is to blow the fuse if the unit is then plugged into a 230V mains supply.

I believe the reason for including it is that it was a portable computer and was intended to be carried around the world, to countries with either mains voltage. HP wanted to ensure that there was no real damage done to the machine if you mis-set the voltage selector switch (for the record I have not had the courage to try this on either of my Integrals!).

A friend who worked for an electricity company (where 110V-ish mains was common in power stations, etc) said that one of the first things done to a new test instrument was that it was set for 115V (or equivalent) and plugged into the 230V mains. If there was any damage other than a blown fuse, the instrument was returned as not suitable

This prevents "overvoltage accidents"

Not in our lounge where we have a few scattered around switched from the three switch door switch (too many switches, I couldn't think of a better way to describe it). Anything non standard on a standard connector will eventually end up in tears.

[turretslug]

Being in Germany at least adds additional safety moat, though. I do take the point over the difficulty with choosing an absolutely foolproof solution!