Using American Microwave Oven in UK

[Ron Lowe]

Yes, that's been my experience too.

This means that it can be very expensive and difficult to get a 3-phase supply, compared to here, since there is not usually 3 phases in the HV supply on the street. Of course, you can get 3 phases. But you need to pony up for it.

Incidentally, they've just put in a new 500KVA sub-station at my work ( UK ) as part of an expansion. It was quite interesting to see all that was involved in running the new section of the 11KV ring, installing the fancy switch and xfmr, isolating the portion of the 11KV ring, 'spiking' the cable and cutting it.

I was out in the rain peering at what they were doing and bugging them with questions. They seemed surprised anyone was interested, but were very happy to show me what they were doing.

[Andy Wade]

Or "volts that jolts, but mils* that kills."

• i.e. milliamps

[Fergus McMenemie]

When I moved back from the USA the wify made me bring the fancy microwave we had had there. I was not too sure what I was getting into (I have a Bsc ing Electrical Engineering) so I rented a 240v -

110v transformer as used by UK tradesman used everywhere. From memory (this was years ago) the transformer was easily rated for the ovens full power. However when plugged in and sorted to cook some bacon, the noise from the microwave was very, very loud. It was a transformer hum but very loud.

The microwave was unpluged, the transformer returned and eventually gifted to somebody else who was on their way to the US. We had to buy another transformer!

The only thing I could figure was that the microwaves internal transformer or some other internal oscilator was tuned to 60Hz operation and did not get on with 50Hz.

My transformer was most definetly 110V not 240v.

Howver this is going over old ground. (Usenet is circular). Have a look at

may matter! Look at the plate.

Regards

[Bill Davy]

I looked at that thread

- please consider using TinyURL for long URLs). Some interesting thoughts, and some pure tosh ("microwave trannies even in normal use overheat in 15 minutes" - I regularly cook beetroot for 30 minutes).

Anyway, I will post the facts, just the facts, ASAP.

Bill

PS

is irrelevant.

PPS And let's not be distracted by what exactly a "microwave tranny" is, please.

[Edgar]

read/f6edc17d8b604420/3d906598dd3cc881?lnk=st&q=%22microwave+oven%22+mai> n+frequency#3d906598dd3cc881

Your studies didn't include transformer theory? What kind of Electrical Engineering was it then. It doesn't seem to have included electrical or engineering.

Of course frequency matters.

Edgar

[Fergus McMenemie]

Yep you are right. But I/we are so used to ignoring is as a concern when messing with transformers and supplies. We look at the rating plate to see what voltage a device requires. But how often do we consciously look for and check the frequency range?

The indicated thread reminded me of all kind of things I had got used to ignoring!

[Dave]

How does reducing the voltage change the difference in frequency? I can't see how this will work. Or does a transofrmer do things different to a transformer? :-)

Dave

[Andrew Gabriel]

At 50Hz, the compressor motor is being underrun by about 17%. When you underrun an induction motor in this way, you must also reduce the voltage by about the same amount or the current increases due to reduced reactance at reduced frequency and causes the motor to overheat, although that should be 100V rather than 90V.

The danger with doing this is that there may be insufficient starting torque to get the thing started. Fridge/freezer compressors do expect this in normal operation though (happens if they try to start before pressure difference has dissipated), so they have an overcurrent cutout with timed auto-reset.

I suspect that the heat pump capacity will be reduced whereas the power consumption won't be, so it may well be less efficient than a unit fitted with a compressor designed for the correct mains frequency.

[Steve Firth]

Definitely American then.

[Dave]

Ah! I get to live and learn again. Many thanks for that logical answer.

Dave

[Appin]

The message from [e-mail] (Andrew Gabriel) contains these words:

I'm not really arguing the point, merely pointing out what's done by one of the major importers. Part of the the question relates to what the design voltage of the equipment actually is.

In the US, the nominal supply voltage has crept up since it was originally standardised at 100 volts.

The supply nowadays is variously described as 110 volts and 120 volts and usually the latter is now accepted as the normal specification. Electricity suppliers aim to keep most customers supplied between 114 and 126 V most of the time. However a distinction should be made between the voltage at the point of supply (nominal system voltage) and the voltage rating of the equipment (utilization voltage). Typically the utilization voltage is 3 to 5 % lower than the nominal system voltage. Equipment will often carry slightly lower nameplate voltages to allow for voltage drop. At 110 volts supply voltage 17% underrun would give you 91.3 volts, so maybe the guys in question had reached a reasonable enough conclusion, though they'd probably reached it empirically rather than by calculation.

Thanks for the detailed reasoning in your calculation, though. Nice to have the theory behind the practice.

[Bill Davy]

Right. The facts.

I bought a nice little toroidal auto-transformer

and ran it on that. The oven makes a nasty smell after boiling water for about twenty minutes, with or without the cover. The main mains transformer is very hot. Annoyingly, with the cover on, the air coming out from the cooling fan (which is pumping a lot of air) is cold which suggests they have not really sorted out the cooling system, but that is no help for me.

The auto-transformer stays cool.

The clock runs slow.

Hey ho, now I know.

Bill

PS

is irrelevant

[Appin]

The message from "Bill Davy" contains these words:

Not 90v or 100v? :-)

John

[Andrew Gabriel]

Without the cover, that's probably your flesh burning.

It probably wasn't designed for the transformer giving off the amount of heat it will be doing on 50Hz. It probably wasn't designed for running at full power for 20 minutes -- I suspect many other domestic microwaves might have problems with that too.