Checking unkown transformer VA by weight

nightanole · 18th January 2010, 06:25 PM

Is there a way to figure out a toroid based on weight or some other non huge load measurement? I have a 4.5 pounder with 22vac out. now antekinc puts it at 150va based on there weight. However the avel from parts express puts it at over 200va based on their weight.

I have gainclone power supply ready to go if i just have to hook up 1 light bulb across it or something else thats simple.

How to measure transformer VA?

AMV8 · 18th January 2010, 09:45 PM

The simple short answer is no, there is no real way to figure out va of a transformer without information from the manufacturer.
However "in general" audio transformers normally turn out about 100va per kilo.
To obtain an accurate answer needs more info from the manufacturer such as the designed operating temperature.
However in some respects the use you make of the transformer will have a substantial effect on the va requirement.
Please read the paper on power supplies by Nelson Pass in passdiy.
For a class AB amp - probably what you are planning - you need to make sure the va rating is at least 3 times the combined output of both channels in watts. That is 50 watt per channel needs 300va.
If you are looking at class A amplifiers I would increase the example below to 450va.
Don

18th January 2010, 06:25 PM	#1
nightanole diyAudio Member Join Date: Feb 2009	Checking unkown transformer VA by weight Is there a way to figure out a toroid based on weight or some other non huge load measurement? I have a 4.5 pounder with 22vac out. now antekinc puts it at 150va based on there weight. However the avel from parts express puts it at over 200va based on their weight. I have gainclone power supply ready to go if i just have to hook up 1 light bulb across it or something else thats simple. How to measure transformer VA?

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18th January 2010, 09:45 PM	#2
AMV8 diyAudio Member Join Date: Jan 2005 Location: near london	The simple short answer is no, there is no real way to figure out va of a transformer without information from the manufacturer. However "in general" audio transformers normally turn out about 100va per kilo. To obtain an accurate answer needs more info from the manufacturer such as the designed operating temperature. However in some respects the use you make of the transformer will have a substantial effect on the va requirement. Please read the paper on power supplies by Nelson Pass in passdiy. For a class AB amp - probably what you are planning - you need to make sure the va rating is at least 3 times the combined output of both channels in watts. That is 50 watt per channel needs 300va. If you are looking at class A amplifiers I would increase the example below to 450va. Don

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