Why the Voltage Must be Lowered.

Did you know ?

In the year 1995 the voltage of the AC mains in the UK was modified from 240 volts to 230 volts as part of an attempt to fit in with the "European norm". In practice, household electricity delivery remained at a level of approximately 240 volts, which is (believe it or not) within the acceptable tolerance defined for the 230-volt standard !

So the danger is you buy a stepdown in good faith, off the peg stepdown transformers have a 230 volt primary winding which when put on the UK's 240 volt will give a lot more voltage than it advertises. Typical example (cheaper for a reason, usually not an isolating type) is one with a 230 volt primary and a 115volt secondary and some even have 120 volt secondary, put that on our higher voltage mains and measure what you get !

I have been preaching this message for more years than I want to remember and now with jukebox owners having owned their machines for many many years it is usual these days to have to change the stepdown transformer for a correct type to get rid of the dangerous over voltage. Lately we have been having to change Turntable Motors that have run so hot , drying their bearings out first before they get electrical faults in their windings. Lighting ballasts too hot to touch, Amplifiers that need HT supplies rebuilding and a new set of valves is normal as they have been over run for many years.

When running 60Hz wound components (like transformers, AC motors, lighting ballasts) designed for US voltage on the UK's 50Hz grid, you must lower the input voltage by roughly 17% to 20% below the standard US nominal voltage of 120V. Instead of stepping down to 120V, you should step down to approximately 100V AC.

If you put a full 120V at 50Hz ( and beleive me some of these transformers that have been used push out up to 130v !) into a 60Hz transformer or wound component, the lower frequency causes the core to draw more current. This pushes the iron core into magnetic saturation, this generates more heat, which can cause mechanical humming, and can lead eventually to burning out windings. Typically a 60Hz AC mains motor will run slower on 50Hz mains irrespective of voltage, probably 17% slower, it will generate more heat too. Aiming for 100V is the safe zone for these components.

..... I guess one day there may well be a fire, but we certainly hope not !

Don't have nightmares.