[Coco] Step down transformer for use in UK / Use on TV in UK

[jdaggett at gate.net]

On 15 Feb 2007 at 15:30, Gene Heskett wrote:

> >If you use a step down transformer, be careful about the ac
> >frequency.
> > 50hz power supplies used at 60hz have been known to overheat.
> 
> Its the reverse of that Leon.  Using a 60 hz tranny on 50 hz, you need
> to derate it about 20% because of the lower frequencies increased heat
> due to core saturation effects.  And some real borderline, not enough
> iron in them cheapies are just asking for an unexpected visit from the
> fire dept.
> 
> Running a 50 hz rated transformer on 60 hz usually results in much
> cooler operation overall.  The core never comes anywhere near
> saturation then so its nice & efficient.
************

Hy steresis loss in a transformer is directly proportional to frequency for a given core 
material and operating voltages. Operating a core designed for 60 Hz at 50Hz will have 
less hysteresis loss. This loss is manifested as heat within the core material. 

Core saturation is dependant on flux density and is directly proportional to current through 
the windings that will induce that current. Once a core becomes saturated, any additional 
current is manifested in heat and heat losses due to IR losses in the windings. These all 
contribute to the core heat build up. 

james