trafo outputting higher than rated Vdc

timsch75 · 1st November 2004, 12:50 PM

I'm working on the PS of my gainclone and have a couple of CHIA YU LU (sp?) trafos that I'm running through MUR860 diode bridges. When I hooked it up and powered it, I read ~+-22Vdc. A few days later after putting snubber caps (.022mfd, 200V) across each diode, it now reads ~+-26Vdc. I'm no EE, so could someone please clue me in on what might have happened? Can caps raise the output voltage? If so, it's certainly news to me. BTW, I smelled and heard nothing indicating any problems and the voltages were steady across all four output voltages.

thanks
tim

richie00boy · 1st November 2004, 02:01 PM

I wouldn't worry. Probably just mains at lowest limit on one day, highest the next.

UrSv · 1st November 2004, 02:07 PM

Did you have any capacitors after the bridge or were you measuring with no caps?

A difference of almost 20 % sounds a bit high for normal mains variation (I'm used to a few percent maximum).

timsch75 · 1st November 2004, 05:59 PM

Both times I measured there were no connections after the bridge

blmn · 1st November 2004, 06:05 PM

Put out the snnubers and check de DC output again.

I think it has not to be with the snnubers, but...

K-amps · 1st November 2004, 06:23 PM

Is the amplifier loading the PSU or is this a stand alone PSU? A heavy bias can lower supply rails. However if the PSU is stand alone, I'd rip out each component and see whats wrong, a 22 to 26 volt jump is not good.

timsch75 · 1st November 2004, 07:25 PM

The amplifier chips are not hooked up to the PSU yet. I just checked the voltages coming out of the bridge with it hooked up to nothing.

The thought of pulling off those 16 caps off to test is a bit of a drag. It was a minor PITA soldering those p-t-p across the mur860's.

cunningham · 1st November 2004, 07:54 PM

Rated voltage is at rated current. If the transformer is not loaded, you will see slightly higher voltage.

timsch75 · 1st November 2004, 08:02 PM

I made the same measurement before without snubber caps and without load and got +-22Vdc. I have another set of trafos that measure +-18Vdc at the bridge without load, which is its rated voltage. So two out of three measurements saw no significant increase over rating without load. What would be different here?

Tim__x · 1st November 2004, 08:11 PM

If there is no load snubbers act as tiny little supply caps. Put a very light load on the psu, 47-100k and then measure it.

1st November 2004, 12:50 PM	#1
timsch75 diyAudio Member Join Date: Mar 2003 Location: austin, tx	trafo outputting higher than rated Vdc I'm working on the PS of my gainclone and have a couple of CHIA YU LU (sp?) trafos that I'm running through MUR860 diode bridges. When I hooked it up and powered it, I read ~+-22Vdc. A few days later after putting snubber caps (.022mfd, 200V) across each diode, it now reads ~+-26Vdc. I'm no EE, so could someone please clue me in on what might have happened? Can caps raise the output voltage? If so, it's certainly news to me. BTW, I smelled and heard nothing indicating any problems and the voltages were steady across all four output voltages. thanks tim

1st November 2004, 02:07 PM	#3
UrSv diyAudio Member Join Date: Jan 2002 Location: Sweden	Did you have any capacitors after the bridge or were you measuring with no caps? A difference of almost 20 % sounds a bit high for normal mains variation (I'm used to a few percent maximum). __________________ UrSv Those who say it can't be done should not stop those who are doing it.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Using higher rated ouput transistors??	tgferg67	Solid State	11	6th January 2007 06:14 AM
Subwoofer not outputting	bubbers214	Car Audio	4	5th March 2006 10:56 AM
Is it true that the higher the BL of a subwoofer, the higher its lowest playable...	454Casull	Subwoofers	16	19th March 2004 04:28 PM
Flying higher and higher with the Doede Dac	Lucas_G	Digital Source	139	27th February 2004 06:40 AM
Super-power amps - higher current better than higher voltage	Circlotron	Solid State	34	28th June 2002 04:01 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

1st November 2004, 02:01 PM	#2
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	I wouldn't worry. Probably just mains at lowest limit on one day, highest the next.

1st November 2004, 05:59 PM	#4
timsch75 diyAudio Member Join Date: Mar 2003 Location: austin, tx	Both times I measured there were no connections after the bridge

1st November 2004, 06:05 PM	#5
blmn diyAudio Member Join Date: Feb 2001 Location: .	Put out the snnubers and check de DC output again. I think it has not to be with the snnubers, but...

1st November 2004, 06:23 PM	#6
K-amps diyAudio Member Join Date: Nov 2003 Location: Indiana	Is the amplifier loading the PSU or is this a stand alone PSU? A heavy bias can lower supply rails. However if the PSU is stand alone, I'd rip out each component and see whats wrong, a 22 to 26 volt jump is not good.

1st November 2004, 07:25 PM	#7
timsch75 diyAudio Member Join Date: Mar 2003 Location: austin, tx	The amplifier chips are not hooked up to the PSU yet. I just checked the voltages coming out of the bridge with it hooked up to nothing. The thought of pulling off those 16 caps off to test is a bit of a drag. It was a minor PITA soldering those p-t-p across the mur860's.

1st November 2004, 07:54 PM	#8
cunningham diyAudio Member Join Date: Jun 2004 Location: Knoxville	Rated voltage is at rated current. If the transformer is not loaded, you will see slightly higher voltage.

1st November 2004, 08:02 PM	#9
timsch75 diyAudio Member Join Date: Mar 2003 Location: austin, tx	I made the same measurement before without snubber caps and without load and got +-22Vdc. I have another set of trafos that measure +-18Vdc at the bridge without load, which is its rated voltage. So two out of three measurements saw no significant increase over rating without load. What would be different here?

1st November 2004, 08:11 PM	#10
Tim__x diyAudio Member Join Date: Jun 2004 Location: Edmonton area, Alberta	If there is no load snubbers act as tiny little supply caps. Put a very light load on the psu, 47-100k and then measure it.