Custom power transformer requirements

[Joshua_G]

I got a quotation for 2 power transformers of 420VA from a manufacturer in India. Their quotation is way cheaper from all others I received, including shipping cost.

I don't know what to ask the manufacturer, other than voltages and currents. Should I ask finishing by dipping in lacquer, or what?

 

[sawreyrw]

You should ask about regulation, power loss and temperature rise. If it gets too hot, it will have a shorter life. A 40 to 50 degree C rise is ok; less would be better. Also, check on the voltage isolation rating from input to output and ground.

 

[Joshua_G]

Thanks.
What exactly should I ask about regulation? As I understand, certain percentage change in the primary voltage should be reflected as the same percentage change in the secondary voltage.

 

[sawreyrw]

In a transformer there are two main components to power loss. These are magnetic losses and I^2 R losses. For low frequency transfromer the dominate loss will be I^2 R losses. Thus regulation and losses are closely related, and, in effect, are determined by the wire resistance.

I'm not an expert on this, but for this size transformer losses should be less than 10% (efficiency greater than 90%). Google to find out what the efficiency is for a typical 400 VA transformer.