US -> UK appliance conversion - any ideas ?

[Phil]

Hi - I have a US 70's food blender I used to use when I lived in the US. I now live back in the UK and want to use it here.

I assume I can't plug this in here - the info on the base shows :

Volts = 115v Freq = 25-60 cycles Amps = 5.2 Watt = 575

I'm no expert but strikes me a transformer for this would be pretty big so ideally I need to get the motor replaced for a UK spec one - if that's possible.

Any ideas how / who could do this. ?

I know everyone will say buy a Uk blender but this thing is awesome.

Cheers

[Christian McArdle]

Building site transformers are often better value than "consumer" converters. You could hide the big yellow box behind a cupboard and run a cable to a suitable outlet above the worktop. You need a 600VA type or larger.

advantage of this method is that it will run lots of old US appliances (if compatible with 50Hz), should you wish to, although it is expensive and requires space to mount the transformer and time to run the cables.

Christian.

[The Natural Philosopher]

Christian has told you how to do it.

My take is that it simply is not worth doing.

[S Viemeister]

I have a US food processor which I use with one of those travel converters and a plug adapter. It's been working away quite happily, since 1998. I use the same setup with my US sewing machine.

[Andrew Gabriel]

When I was young in the 1960's, the family lived in the US. My parents came back to the UK with a number of US kitchen appliances, although they were all heating appliances, not motor ones. For years, they were used on a large variac auto-transformer, using the (fixed) centre tap to derive 120V.

Around 10 years ago, I built a circuit to chop the middle out of each half mains cycle to produce 120V RMS for the heating elements. I chopped the middle out in order to minimise the peak voltage in the heating elements, which were only designed for 120V AC. Even so, the peak is slightly higher than they were designed for, but less so than would be the case using a phase control dimmer circuit. The circuit uses a pair of power MOSFETs to switch the mains, and a fast acting fuse to limit damage if one of the MOSFETs was to short and deliver full 240V to the 120V heating elements (which has never happened).

I suspect such a design would also work with universal motors, but it would probably be necessary to include much more protection for the MOSFETs than I did for resistive loads.

[S Viemeister]

Interesting. I've copied your post, so that Himself can have a look at it.

[JohnDW]

Be careful, though, if the blender uses an electronic speed controller. These assume a sine-wave supply and, in it's simplest form, a SCR switches off the supply at every zero- voltage crossing point of the sine wave and switches it on later in the half-cycle. If you remove part of the half-cycle, then the SCR could fail to start to conduct after the delay if the voltage at that point is also zero, due to Andrew's chopper circuit's action.

If the OP is able to redesign the speed controller, (using approx. 400v peak components...) then they could make its maximum speed setting start at an approx. 90degree delay instead of 0deg. The motor should be able to cope with the higher peak voltage of the 240v waveform.

Quick thought -

As a cheap alternative, for a universal motor, why not try a simple series diode of suitable current rating. That will remove every other half cycle, thereby reducing the RMS voltage to around 107v. It could still present a problem for an electronic speed control, though.

[Andrew Gabriel]

Goot point. It would be easier to build the speed control into the chopper by chopping out progressively more. I have an internal adjustment to set where this happens anyway. (IIRC, it's chopped out from something like 42º to 138º and same on following half cycle. I do recall the maths was a real bastard to work this out, and stretched my calculus which I hadn't used for many years to my limit.)

Ouch -- both these points are wrong. Removing every other half cycle, or half of every half cycle will reduce RMS voltage to 1/sqrt(2), or 170V on a 240V supply, which is too high. You would have to remove every other half cycle _and_ half of the remaining half cycle to get 120V RMS. Also you still have 340V peak which is significantly higher than the appliance will have been designed for.

[JohnDW]

Oops - Thanks Andrew - I'm thinking of average instead of RMS values - I shouldn't work things out late at night...

The OP /should/ be OK with the greater peak voltage assuming it was just a universal motor load. There would probably be more problems with overheating due to the 50Hz versus 60Hz, if it is running for some time. Most US 110v wiring and some component parts I've seen have over-specified insulation anyway. Since they have both 220vac and 110vac in houses, they need to accommodate the higher peak voltage when designing insulation. The original speed controller, if electronic, and any noise filter capacitors would most likely need replacing anyway, so a transformer solution would be the best, if it is irreplaceable.