Custom power transformer requirements

Joshua_G · 8th July 2010, 01:52 PM

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 · 8th July 2010, 02:50 PM

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 · 8th July 2010, 03:03 PM

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 · 8th July 2010, 03:17 PM

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.

8th July 2010, 01:52 PM	#1
Joshua_G diyAudio Member Join Date: Nov 2008 Location: Israel	Custom power transformer requirements 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?

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8th July 2010, 02:50 PM	#2
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	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.

8th July 2010, 03:03 PM	#3
Joshua_G diyAudio Member Join Date: Nov 2008 Location: Israel	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.

8th July 2010, 03:17 PM	#4
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	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.

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