50hz vz 60hz and wattage

thelawnet

keystone wrote: »

OP just go buy yourself a suitable product rated for UK domestic supplies. Lot less hassle IMHO.

Apart from that how do we know whether a US product manufactured for the US market meets European standards for safety etc?

I don't see that it particularly matters, ok we have standards here, the have standards there, but the US are not getting electrocuted to death on a regular basis.

I'm just standing there sharpening a knife for a few minutes, it's not like I'm wrapping my new born baby sleep in a 120v electric blanket or something.

Product does not exist in UK btw.

Not sure if it's been damaged by the transformer though.

I chose the transformer, somewhat naively, because it was the highest wattage (150W) plug-type transformer I could find. Didn't really want a big box. Was £6.59 off ebay.

A Uk ebay seller has a slightly different 150W) plug transformer for £20, but I suppose I'm probably better off with a 250W or 300W rather than risking that........

HappyMJ

thelawnet wrote: »

I'm just standing there sharpening a knife for a few minutes, it's not like I'm wrapping my new born baby sleep in a 120v electric blanket or something.

Product does not exist in UK btw.

Knife sharpeners exist in the UK.... What exactly do you have that the UK does not have an alternative to?

Ben84

thelawnet wrote: »

I don't see that it particularly matters, ok we have standards here, the have standards there, but the US are not getting electrocuted to death on a regular basis.

They also use their US stuff on the US mains, so the conditions they're using it in are different. How confident are you that a transformer replicates a properly wired US socket which the appliance's safety features are expecting to be present?

thelawnet wrote: »

I'm just standing there sharpening a knife for a few minutes, it's not like I'm wrapping my new born baby sleep in a 120v electric blanket or something.

Someone asking for advice always has the option to take it or leave it, but people have taken time to reply to your question and you seem a little bit ungrateful for that.

thelawnet wrote: »

Product does not exist in UK btw.

Not sure if it's been damaged by the transformer though.

I chose the transformer, somewhat naively, because it was the highest wattage (150W) plug-type transformer I could find. Didn't really want a big box. Was £6.59 off ebay.

Smaller transformers are often the type which have one rather than two coils, in which case the 240V mains is attached directly to the 120V output and they're not legal to sell in the UK either. What you have I'd have to see to say for certain, but the price and buying it from eBay aren't that reassuring.

thelawnet wrote: »

A Uk ebay seller has a slightly different 150W) plug transformer for £20, but I suppose I'm probably better off with a 250W or 300W rather than risking that........

I like eBay for some things, but it has become a big seller of dubious quality travel adaptors, transformers, phone chargers and laptop chargers. Some of them use stock photos and send out something else entirely, I had a laptop lead with a plug that has no fuse in from a listing with a picture of another lead that promised it complied with all relevant UK electrical standards. Seller had loads of positive feedback too. It's hard to know what you're getting sometimes.

DVardysShadow

Ben84 wrote: »

What does not vary however is frequency (the number of times per second an alternating current changes direction). In the UK it is fixed at 50 Hz and in the US it's 60 Hz. It is essential to the function of many appliances. Synchronous clocks which plug in to the mains use the frequency to control their timing, it also controls the speed of some tape players. The mains frequency is also used at Television Centre and the Granada Studios to time the TV channel transmissions so that when they arrive at your TV, the TV uses the frequency it receives from the mains to time the speed at which the electron beam inside it scans across the back of the screen to produce the picture. Because they should be the same, regardless how far away you are or what power plant is supplying your electricity, it works. So, the mains frequency is fixed (every power plant in the country runs in synchronisation) and is very, very tightly controlled as so many appliances depend on it to function correctly. So, not everything works properly at another frequency and changing frequency is very difficult so most transformers don't do it. The result may be it doesn't work right, or it may damage the appliance through overheating.

While that information was true once, it does not apply for digital television. And I believe that even for 625 line television, the 50Hz time base was derived independently from the mains. So it only applied to 405 line television, which was abandoned in 1984 IIRC.

DVardysShadow

thelawnet wrote: »

I have a US appliance, a knife sharpener (contains a motor, powering a spinning wheel). It is labelled:

120V 60HZ 2.1A 125W

I bought a transformer, it is labelled:
220V 50Hz
to
110V 150W

It burnt out on first use.

I'm not sure if it's just a cheap and nasty Chinese transformer that doesn't deliver the rated output, or whether I do need a more powerful transformer.

As I understand it, the lower frequency, 50Hz, against the 60Hz design characteristic, means it runs slower.

But I'm not sure what the correct wattage for my transformer is???

It is a double whammy of the wrong frequency on the motor leading to overcurrent on both motor and transformer.

As frequency goes up, the magnetic flux within an iron core goes down for a given voltage. The iron core is very easy to magnetise so very little current is require to do it. But transformers and motors are designed to be magnetised at near the saturation point. Beyond this point, the iron becomes as hard to magnetise as air or empty space and a huge current is required to make the flux for the given voltage and frequency.

Basically, when running a 60 Hz motor from a 60 Hz transformer on a 50Hz supply, if you don't reduce the voltage in proportion to the frequency, you take the iron to saturation and both motor and transformer will tend towards burning themselves out to get the magnetic flux to sustain the voltage.

Ben84

DVardysShadow wrote: »

While that information was true once, it does not apply for digital television. And I believe that even for 625 line television, the 50Hz time base was derived independently from the mains. So it only applied to 405 line television, which was abandoned in 1984 IIRC.

I had believed that locking the broadcast and TV to the mains frequency was still common for analogue TV signals. Not just because it's a good signal for synchronising the two as both receive it and it should be the same, but also because AC lighting which is at a different frequency with the TV during live broadcasting would cause an annoying flickering effect.

Anyway, whatever the case, some of the things I know may be a little dated, but the general idea I want to show is that the mains frequency is used by some devices to regulate their functions. It also affects induction motors in a variety of negative ways when you change it.

Unless you can change the voltage and the frequency to whatever the device is expecting, correct function isn't assured. Also that transformers don't normally provide a 100% compatible US or whatever you're trying to emulate electrical supply.

Myser

Turntable (record player) motors used to use the mains frequency to set the correct speed.

I'm not sure if some of the high-end ones still rely on the mains frequency?

Ben84

Myser wrote: »

Turntable (record player) motors used to use the mains frequency to set the correct speed.

I'm not sure if some of the high-end ones still rely on the mains frequency?

These days I'd expect a high end turntable to control its speed with a piezoelectric quartz chip, like the ones found in casio watches, because the speed 33rpm is a defined standard that can probably be generated far more accurately within an appliance by its own circuitry.

Still, many older ones must have used the mains. My record player is from 1971, so it probably does and it works great.

thelawnet

DVardysShadow wrote: »

Basically, when running a 60 Hz motor from a 60 Hz transformer on a 50Hz supply, if you don't reduce the voltage in proportion to the frequency, you take the iron to saturation and both motor and transformer will tend towards burning themselves out to get the magnetic flux to sustain the voltage.

I don't think the transformer alters the frequency. 50Hz in, 50Hz, out.

You can, but it requires a very much more expensive device (hundreds of pounds).

Justicia

Myser wrote: »

I believe the specification changed in 1993.

Close. January 1995