Step-up/down transformers

Contact your supplier.

Rami very interesting q
I had noted in my youth this happens sometimes if for instance the transformer ("receiver")' is of heavier duty than required

However it might also be that you had simply forgotten that the step-up doubles the load you might have expected according to the freezer's rating

You might cite some figures

Yes. When any transformer is connected to the supply there is what is called an 'inrush' current lasting several cycles of the AC waveform. This is because the iron core of the transformer needs to get magnetised. Inrush current is also sometimes known as surge current, and is always higher than the normal operating current of the equipment. It can be between 5 to 100 times greater.



He has a 220 V refrigerator; he must therefore (assuming a domestic supply) be stepping up from 110 V; the refrigerator is rated 123 W (constant rating) which gives a secondary current of around 1.8 A and a primary current of 3.6 A (we will ignore power factor although fridges do have motors).

A fuse's marked rating in amps is the current that it will carry indefinitely without blowing; if that current is exceeded then the fuse should melt after some time. Whether it just quietly gives up the ghost after some seconds or minutes or goes out with a BANG as soon as you throw the switch depends on the the size of the overload.

Sometimes a fuse of higher rating and/or a slow-blow type may help with inrush surges drawn by transformers, and as you note, Dale, a 500 VA device is getting a bit big for a domestic setting without any special arrangements such as these.

Bottom line SPEAK TO AN ELECTRICIAN. Monkeying about with circuit protection can result in fires or damage.



E.g. the rating of the fuse that blows.

Thanks Con for that inrush exp, I had always wondered about that. It's not everyday…...

Inrush current is something that sometimes gets ignored when people are rating equipment. On an AC electrified railway you don't want too many locomotives in the same track section putting up their pantographs in a short time otherwise the combined inrush currents can trip the breakers at the supply point.

Summary: the transformer is probably blowing the fuse because it is too big for the houses' electrical installation. Fuses are there for a reason, and their ratings are chosen for a reason too. Alteration of a fuse type or capacity should only be done following consultation with a qualified electrician, and due consideration must be given to any implications affecting wiring code, fire insurance, etc.