Crazy transformer?

Lisandro_P · 5th January 2003, 11:53 AM

I came across an old E-I 25v 3A transformer, small, which i beleive would be perfect for my preamp. The thing is it outputs 30VAC (give or take, measured with my multimeter) with no load at all, but when i connect it to a bridge rectifier it outputs 24VDC *and* about 12vAC on the output terminals. This happens both with a discrete bridge and a regular 30A one, so i beleive it's the trafo... but it's puzzling me. Any ideas what could be wrong here?

peranders · 5th January 2003, 02:52 PM

If you don't have any smoothing caps you will get DC AND AC! Varying DC voltage is in fact AC.

Nothing is wrong, just add smoothing caps!

Lisandro_P · 5th January 2003, 02:59 PM

Thanks

(feeling less dumb already)

BTW is that normal? I mean, 12vac it's almost 40% of the output. I have hooked bridges to transformers with no smoothing caps in the past and never had this kind of situations...

peranders · 5th January 2003, 04:49 PM

Fullwave rectified AC has quite a lot of AC. Don't have the theoretical number in my head.

Lisandro_P · 5th January 2003, 04:54 PM

Once again, thanks!

5th January 2003, 11:53 AM	#1
Lisandro_P diyAudio Member Join Date: Oct 2000 Location: Argentina	Crazy transformer? I came across an old E-I 25v 3A transformer, small, which i beleive would be perfect for my preamp. The thing is it outputs 30VAC (give or take, measured with my multimeter) with no load at all, but when i connect it to a bridge rectifier it outputs 24VDC and about 12vAC on the output terminals. This happens both with a discrete bridge and a regular 30A one, so i beleive it's the trafo... but it's puzzling me. Any ideas what could be wrong here?

5th January 2003, 02:52 PM	#2
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	If you don't have any smoothing caps you will get DC AND AC! Varying DC voltage is in fact AC. Nothing is wrong, just add smoothing caps! __________________ /Per-Anders (my first name) or P-A as my friends call me

5th January 2003, 04:49 PM	#4
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Fullwave rectified AC has quite a lot of AC. Don't have the theoretical number in my head. __________________ /Per-Anders (my first name) or P-A as my friends call me

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5th January 2003, 02:59 PM	#3
Lisandro_P diyAudio Member Join Date: Oct 2000 Location: Argentina	Thanks (feeling less dumb already) BTW is that normal? I mean, 12vac it's almost 40% of the output. I have hooked bridges to transformers with no smoothing caps in the past and never had this kind of situations...

5th January 2003, 04:54 PM	#5
Lisandro_P diyAudio Member Join Date: Oct 2000 Location: Argentina	Once again, thanks!

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