Using multiple voltage transformer to get higher voltage - Page 2 - diyAudio
 Using multiple voltage transformer to get higher voltage
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diyAudio Member

Join Date: Sep 2006
Quote:
 Originally Posted by AndrewT to be able to stack (add) the voltages you will need to get inside, as Gmp described There is an alternative. Use the 15.9+15.9 as one winding. = >32Vac when open circuit. Use the 12+12+7as the other winding. =>32Vac when open circuit. But your output current is limited to 750mAac by the 7Vac winding rating. A third alternative is to add a 2A rated winding of ~7Vac to make a 31.8Vac + 31.8Vac @ 2A output. That is a total VA of 63. A lot of work for 63VA !
In addition, the lack of accurate resistance/voltage balance will generate significant amounts of 50/60Hz ripple
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diyAudio Member

Join Date: Aug 2012
Location: Florida's Gulf Coast
Quote:
 Originally Posted by AndrewT to be able to stack (add) the voltages you will need to get inside, as Gmp described There is an alternative. Use the 15.9+15.9 as one winding. = >32Vac when open circuit. Use the 12+12+7as the other winding. =>32Vac when open circuit. But your output current is limited to 750mAac by the 7Vac winding rating. A third alternative is to add a 2A rated winding of ~7Vac to make a 31.8Vac + 31.8Vac @ 2A output. That is a total VA of 63. A lot of work for 63VA !
I was trying to recycle this transformer for use in a LM4780 amplifier. It's my first build and I'm on a limited budget. I guess this is not gonna work for me. I'll need a higher VA than this will provide. From what I've read they like to see about 300, right?

 5th December 2012, 03:41 PM #13 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders I have suggested many times my preference for a minimum of 160VA for a power amplifier transformer. The general guidance spread around this Forum and elsewhere is to use a VA rating between one times and two times the total maximum power of the amplifier/s. eg. 2 channels of 50W amplifier is 50+50 = 100W of total maximum output power. Use a transformer with a rating from 100VA to 200VA. There is a third recommendation to buy and fit the biggest that you can afford. __________________ regards Andrew T. Sent from my desktop computer using a keyboard
 29th January 2013, 04:11 PM #14 diyAudio Member   Join Date: Aug 2012 Location: Florida's Gulf Coast Rather than start a new thread about this transformer, I'll update this one. I finally got a transformer for my project that fits my specs. http://www.antekinc.com/details.php?p=80 This transformer has dual 32v secondaries http://www.antekinc.com/pdf/AN-4232.pdf The PCB that I used for my amp has only 3 connection points for the inputs to the rectifiers I have measured the voltage across the blue and green wires and found that either blue to either green gives me around 32V. Should I cap one of the green wires and use the 2 blue and the remaining green for this connection, or should the 2 green be used together? Or probably there's a better way that I haven't thought of. I plan on using the connections on ESP for wiring the mains(120) minus his bridge rectifier and caps of course. Power Supply Wiring Guidelines Here is the schematic for the board Thanks for your help.
diyAudio Member

Join Date: Jan 2003
With dual secondaries you should hook them up as in the bottom of the jpg.

The red box shows where the three connections are on the pcb.

The two windings should be connected to give twice each winding when measured.

Example:

A-B 32VAC
B-C 32VAC
A-C 64VAC

Something I noticed:

Looking at the data sheet for the LM4780 suggests a maximum operating supply of 84V or +/- 42V.

A 2 x 32VAC used in this configuration will provide more than 88V or +/- 44V.

( the 94V or +/- 47V maximum rating is for no signal conditions)

None of the graphs in the data sheet go above +/- 40V

(The circuit board is labeled for 28VAC)

Perhaps someone more experienced with these Overture series amps can tell you if this is OK to do.

Hope that helps.
Attached Images
 FULL-WAVE-C.JPG (35.6 KB, 53 views)
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Last edited by DUG; 30th January 2013 at 03:50 AM.

diyAudio Member

Join Date: Jul 2004
Location: Scottish Borders
Quote:
 Originally Posted by DUG None of the graphs in the data sheet go above +/- 40V (The circuit board is labeled for 28VAC)
The Circuit board is marked 28V, but that should read 28Vdc.
IT IS NOT for 28Vac.

Check the traces and determine which is -28Vdc and which is +28Vdc.
The capacitors have the -ve marked with the white bar.
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Sent from my desktop computer using a keyboard

Last edited by AndrewT; 30th January 2013 at 09:02 AM.

diyAudio Member

Join Date: Jan 2003
Quote:
 Originally Posted by AndrewT The Circuit board is marked 28V, but that should read 28Vdc. IT IS NOT for 28Vac. Check the traces and determine which is -28Vdc and which is +28Vdc. The capacitors have the -ve marked with the white bar.
You are correct, my error.

It is marked 28V.

But it could be 28VAC and still operate within spec limits.

It does have a bridge rectifier on board.

If you applied +/- 28VDC it would not matter which of the (non-ground) terminals the + and - were connected to...the diodes would direct the supplies to the required polarity.

I just think 32VAC is a bit too much.

Or is that just me?

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 30th January 2013, 08:17 PM #18 diyAudio Member   Join Date: Aug 2012 Location: Florida's Gulf Coast Can I use this transformer if I run it through 2 FWB rectifiers and voltage regulators? Maybe something similar to this? LD1585CV - STMICROELECTRONICS - IC, REG LDO, 1.25 TO 28V, 5A, | Farnell United Kingdom I originally thought that since there were diodes and filter caps on the board that this was the rectifier portion of the circuit. Is that not the case? Thanks again
diyAudio Member

Join Date: Jan 2003
Quote:
 Originally Posted by hondatech739 Can I use this transformer if I run it through 2 FWB rectifiers and voltage regulators? Maybe something similar to this? LD1585CV - STMICROELECTRONICS - IC, REG LDO, 1.25 TO 28V, 5A, | Farnell United Kingdom I originally thought that since there were diodes and filter caps on the board that this was the rectifier portion of the circuit. Is that not the case? Thanks again
The rectifiers and filter caps are on the board in post #14.

You could build two separate (isolated) regulated supplies as in the jpg.
(don't use LM78xx regulators as the current rating is not high enough.)
I would recommend at least a 10A cct

or

You could rectify and filter before the board and drop the voltage with a couple of power MOSFET's...That way you could still use the transformer you have.

Select high current N-ch with standard gate threshold.

Or wind some extra turns on the transformer and reduce the secondary voltage.

This was covered in another thread.

Or use another transformer.

Attached Images
 FULL-WAVE-D.JPG (28.5 KB, 24 views) PS-DUAL--SPLIT-b-reg.JPG (27.9 KB, 24 views)
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"You can't stop the signal, Mal. Everything goes somewhere..."

 31st January 2013, 03:12 AM #20 diyAudio Member   Join Date: Aug 2012 Location: Florida's Gulf Coast So, I could run the transformer through a couple of rectifier/filters and regulators, and still run it through the rectifier/filter set that is already on the board? Isn't that kind of redundant? I mean, I haven't done this before, so I don't know. Would I lose anything running the rails through 2 rectifiers? My board is completely assembled already, I just used that pic for reference since it was easier to see everything. I had actually toyed with the idea of just using external rectifiers/regulators and connecting to the points that the filter caps connect to. As I say you guys know way more than I. Thanks for keeping in touch.

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