Guessing the power of a transformer

jul059 · 19th October 2010, 08:30 PM

Hi all,

I have a power transformer that outputs 17-0-17 AC when plugged on 120V. Is there a way to measure, estimate or calculate the power of this transformer? I have absolutely no information other than the RMS power of the amplifier it came from : 2 x 16 watts in 8 ohms and 2 x 20 watts in 4 ohms.

Regards,
Julien

wakibaki · 19th October 2010, 08:41 PM

It's probably between 30 and 80 VA, based on the output power. You can weigh it and compare the weight with these Hammond transformers:Hammond Mfg. - Power Transformer - Dual Primary / Dual Secondary (266 Series)

w

bob91343 · 19th October 2010, 10:13 PM

You can weigh the transformer and compare with any transformer catalog. I have one right here if you tell me the weight and mains frequency.

If you can peel back the insulation and measure the gauge of the secondary winding you can look in a wire table to find the maximum current, based on a figure of about 600 circular mils per Ampere.

If the amplifier can supply a total of 40 Watts, figure 50% efficiency and add a few Watts for the other circuits, you will end up with about 85 Watts total. So about 5 Amperes secondary current may be close.

Elvee · 20th October 2010, 08:25 AM

There are some ways to estimate the power. See here:
Transformer VA rating??
Trafo with unknown power rating

19th October 2010, 08:30 PM	#1
jul059 diyAudio Member Join Date: Mar 2010	Guessing the power of a transformer Hi all, I have a power transformer that outputs 17-0-17 AC when plugged on 120V. Is there a way to measure, estimate or calculate the power of this transformer? I have absolutely no information other than the RMS power of the amplifier it came from : 2 x 16 watts in 8 ohms and 2 x 20 watts in 4 ohms. Regards, Julien

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19th October 2010, 08:41 PM	#2
wakibaki Banned Join Date: Jan 2008 Blog Entries: 2	It's probably between 30 and 80 VA, based on the output power. You can weigh it and compare the weight with these Hammond transformers:Hammond Mfg. - Power Transformer - Dual Primary / Dual Secondary (266 Series) w

19th October 2010, 10:13 PM	#3
bob91343 diyAudio Member Join Date: Mar 2010	You can weigh the transformer and compare with any transformer catalog. I have one right here if you tell me the weight and mains frequency. If you can peel back the insulation and measure the gauge of the secondary winding you can look in a wire table to find the maximum current, based on a figure of about 600 circular mils per Ampere. If the amplifier can supply a total of 40 Watts, figure 50% efficiency and add a few Watts for the other circuits, you will end up with about 85 Watts total. So about 5 Amperes secondary current may be close.

20th October 2010, 08:25 AM	#4
Elvee diyAudio Member Join Date: Sep 2006	There are some ways to estimate the power. See here: Transformer VA rating?? Trafo with unknown power rating

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