Strange transformer problem

jarkaa · 9th November 2004, 06:26 AM

Hello,

Can someone help me to solve the following problem?

I have a 400VA e-core trafo salvaged from an old UPS.
There are two primaries which are center tapped and for each primary there are two secondaries.

When I feed 11,5VAC for the first primary (and leave the primary CT unconnected) I get 1,7VAC, on the two secondaries connected to it. It means that I get about 35VAC when fed with 220Vac.

The PROBLEM is that I blow a fuse every time I connect it to mains. I have used 6A slow blow, but it does not help and I have also included a 10w 8.2 ohm resistor in the primary to soften the inrush current but the result is always a blown fuse.

What is wrong?

Ouroboros · 9th November 2004, 07:05 AM

You say that there are two primaries. Are you sure that these were not connected in series for use on 230v mains?

jarkaa · 9th November 2004, 08:00 AM

Yes I am sure about the two primaries (both center tapped), since when I measure with multimeter, there is no connectoin between them.

I think that the center tap is for 110V mains. When I feed the CT and other primary with 11,5V the voltage doubles at the secondaries.

9th November 2004, 06:26 AM	#1
jarkaa diyAudio Member Join Date: Feb 2004 Location: Tampere	Strange transformer problem Hello, Can someone help me to solve the following problem? I have a 400VA e-core trafo salvaged from an old UPS. There are two primaries which are center tapped and for each primary there are two secondaries. When I feed 11,5VAC for the first primary (and leave the primary CT unconnected) I get 1,7VAC, on the two secondaries connected to it. It means that I get about 35VAC when fed with 220Vac. The PROBLEM is that I blow a fuse every time I connect it to mains. I have used 6A slow blow, but it does not help and I have also included a 10w 8.2 ohm resistor in the primary to soften the inrush current but the result is always a blown fuse. What is wrong?

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9th November 2004, 07:05 AM	#2
Ouroboros diyAudio Member Join Date: Dec 2003 Location: Nottingham UK	You say that there are two primaries. Are you sure that these were not connected in series for use on 230v mains?

9th November 2004, 08:00 AM	#3
jarkaa diyAudio Member Join Date: Feb 2004 Location: Tampere	Yes I am sure about the two primaries (both center tapped), since when I measure with multimeter, there is no connectoin between them. I think that the center tap is for 110V mains. When I feed the CT and other primary with 11,5V the voltage doubles at the secondaries.

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