what do i need to use usa bought sewing machine in the uk

yangptangkipperbang

alanrowell wrote: »

Many modern appliances - even high wattage - use power supplies that can handle anything from 100 to 250V and everything inbetween. They AREN'T dual-voltage machines, they are MULTI-voltage. It's too expensive to supply different power supplies for different markets unless there isn't any choice. Even 20 years ago the primitive power supplies of the time could often be changed for different voltages by simply moving a dial or changing an internal plug

Sorry, but a "high wattage" item (such as a fan heater/kettle/cooker/etc/etc) doesn't contain such a thing as a "power supply".................. it is designed to operate on a certain voltage which is applied directly via (usually) a switch and/or a thermostat.. (See fig at end). If the item contains complex electronics such as a microwave/cooker/washing machine/ etc for timing and control purposes these will have a universal power supply to supply them with low voltage DC but the rest of the item will still be 240V or 115V hardware. The heating element will have a certain electrical resistance, when a voltage is applied a current will flow and heat is generated. If you apply a different voltage Ohms law states that a different amount of current will flow. If it is designed for 115V and you apply 240V twice as much current will flow and the item will overheat rapidly and possibly burst into flames. (I once saw the effect of this on a 115V soldering iron - quite impressive!!)

The "primitive" items of 20 years ago actually worked on ONE voltage, usually around 115V - the "dial" or "plug" you refer to just inserted an extra resistance in the circuit to drop, say, 240V to 115. This was grossly inefficient and with the emphasis of energy efficiency it is very rare to see such a device in this day and age.
It was also somewhat of a safety hazard, it was all too simple to have it set to the wrong voltage - if all you can buy in the UK is 240V equipment, it is MUCH safer.

Also, manufacturing costs come into this equation very much. When you are selling millions of an item and minimum production costs are vital - it is cheaper to have a 115V version and a 240V version. The costs of installing a voltage change-over device in every item would far out weigh the difference in costs (if any !) between a 115V item and a 240V item.

Could I suggest that you buy a 115V "high-wattage" appliance in the USA and plug it into UK 240V mains and see what happens.
Firstly make sure that your wife and children are out of the house and that you have a suitable fire extinguisher to hand..............if the fuse in the UK plug doesn't blow first !!

System

The "primitive" items of 20 years ago actually worked on ONE voltage, usually around 115V - the "dial" or "plug" you refer to just inserted an extra resistance in the circuit to drop, say, 240V to 115. This was grossly inefficient and with the emphasis of energy efficiency it is very rare to see such a device in this day and age.

It changed the taps used on a transformer to step down/up the voltage for the device. Using a resistance is highly inefficient. Having to dissipate the same amount of power as the device required (if the device is 115V and input is 240V) is a major fire risk. A resistor capable of dissipating 100W is over 2 inches long and half an inch in diameter and would probably do a good imitation of an electric fire heating element.