Transformer Testing
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 6th March 2002, 02:04 PM #1 SteveS diyAudio Member   Join Date: Feb 2002 Location: Bedford, TX Transformer Testing Good day all! I have an old (cheap) receiver that passed away a few years ago and want to use the power supply, heatsink and case in a new project. The problem I have is with the power transformer. The rear panel on the receiver stated that the total power consumption is 380VA (is was a 100W/ch stereo receiver). The transformer is a multi/center tapped trans and measurements have shown +/- 40V AC and +/- 17.5V AC taps. With this information can I safely assume that the 40V taps are capable of 4.375A total (350VA/80V : I used 350VA to be a bit conservative). If so are the 17.5V AC taps capable of the same current since they are tapped off the same guage wrapping wire? If I cannot assume this, how can I test my trans to give me something to design around? Thanks, SteveS
 6th March 2002, 03:58 PM #2 paulb   diyAudio Member   Join Date: Jun 2001 Location: Calgary The sticker on the rear panel may not be a good guideline. Better to work from the power output. Is the 100W/ch an RMS specification? If so, you can calculate what DC power you'd need to get the 100W/ch. 2x40VAC should give you around +/-52VDC. Note that AC Volt-amps for a transformer aren't the same as DC watts. Generally you divide by a factor of, say, 1.5 or so. Do you plan to use the 17.5V taps to run a Class-A amp, so need the higher current rating? If you're sure they are indeed taps, and not separate windings, you should be safe pulling the same current (whatever that is) off the lower voltage taps.
 6th March 2002, 11:53 PM #4 Jocko Homo   Banned   Join Date: Feb 2002 Location: As far from the NOSsers as possible The only way to know what the transformer is good for is to know the cross-sectional area of the lamination stack, and the wire size. The wire size alone ought to get you close. Jocko

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