12 VAC power supply for audio amp
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 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
AndrewT
R.I.P.

Join Date: Jul 2004
Location: Scottish Borders
post5
Quote:
 you need either a centre tapped transformer 230:12-0-12vac of about 5VA or higher. Or you can use a dual secondary 230:0-12, 0-12Vac again >=5VA - And convert this to centre tapped.
__________________
regards Andrew T.

 12th January 2017, 06:44 AM #22 DIM44   diyAudio Member   Join Date: Nov 2016 Location: urban I got this one: Do I connect the two 12VAC outputs to the outer connections on the board and combine the 0 centre outputs to the connection incorrectly marked GRND on the board? Specifications: Primary Voltage Rating 230V ac Secondary Voltage Rating12V ac Power Rating 6VA Number of Outputs 2 Minimum Operating Frequency50Hz Maximum Operating Frequency60Hz The two outputs are 3VA respectively. Is that sufficient? Sorry for all the newbie questions. Nico Last edited by DIM44; 12th January 2017 at 06:47 AM.
 12th January 2017, 08:36 AM #23 AndrewT   R.I.P.   Join Date: Jul 2004 Location: Scottish Borders First ! use a continuity meter to identify the separate windings of the transformer. Does it have a single 230Vac primary? or dual 115Vac primaries? Does it have 4 different colours or four taps for the two secondary windings? Find which colour/taps connect to which other. Power rating. I gave the method to calculate the maximum DC current rating after passing through a capacitor input filter, but I'll go through it again. max continuous Iac = VA / Vac = 3VA / 12Vac = 250mAac De-rate to find the maximum continuous DC current after the filter by dividing by ~2 this gives the max current as 250/2 = 125mAdc The manufacturer should have details for that De-rating Factor, usually about 1.8, but it varies (2 is easy to remember). Now reduce your loading to give cooler operation, aim for <50%. (this step removes the need for precision in applying the De-rating Factor). i.e. your cool running continuous DC current is ~63mAdc Notice that the cool running DC current ends up at one quarter of the rated AC current ! Again an easy number to remember. __________________ regards Andrew T. Last edited by AndrewT; 12th January 2017 at 08:42 AM.
 12th January 2017, 08:56 AM #24 DIM44   diyAudio Member   Join Date: Nov 2016 Location: urban Thanks Andrew. I hope to receive the transformer by Wednesday. Then I will take a picture or at least have the visible descriptions of the outputs. For starters it has a single 230VAC primary and two 12VAC (four taps) secondaries each with 3VA power rating. Each secondary has two terminals, 0 and 12VAC. Nico Last edited by DIM44; 12th January 2017 at 09:00 AM.
AndrewT
R.I.P.

Join Date: Jul 2004
Location: Scottish Borders
Quote:
 Originally Posted by DIM44 Thanks Andrew. I hope to receive the transformer by Wednesday. Then I will take a picture or at least have the visible descriptions of the outputs. For starters it has a single 230VAC primary and two 12VAC (four taps) secondaries each with 3VA power rating. Each secondary has two terminals, 0 and 12VAC. Nico
Find which taps are connected together.

Then power ON via the Mains Bulb tester.
Measure the voltage across each secondary winding.
Power OFF.
short one tap on sec1 to one tap on sec2.
Power ON.
Measure the voltages across each winding and measure the voltage across the two open taps.
You should get about 16Vac for each winding and for the last measurement you will either get near zero volts AC, or ~ 32Vac

report back after safely insulating all the primary connections.
__________________
regards Andrew T.

 18th January 2017, 12:20 PM #26 DIM44   diyAudio Member   Join Date: Nov 2016 Location: urban I received the transformer today but the system complains about the picture that is too large to post. It has two input and four output terminals. 0-12 and 0-12VAC I will try your suggestion and take the measurements on the output terminals. If you see a huge spark you will know I made a boo-boo....
 18th January 2017, 01:03 PM #27 DF96   diyAudio Member   Join Date: May 2007 No. A huge spark means you didn't make and use a lamp limiter.
 19th January 2017, 05:39 AM #28 DIM44   diyAudio Member   Join Date: Nov 2016 Location: urban I was just kidding about the spark. I have the mains bulb tester which I made on your recommendation and propose to use it always. When I get to shorting one tap on one side of the secondary to another on the other side ("... short one tap on sec1 to one tap on sec2") (post #25) I presume it should be the same, i.e. 0 to 0 in order to establish the output VAC? You can probably tell I am a complete newbie - thanks for being patient. Nico
AndrewT
R.I.P.

Join Date: Jul 2004
Location: Scottish Borders
Quote:
 Originally Posted by DIM44 I was just kidding about the spark. I have the mains bulb tester which I made on your recommendation and propose to use it always. When I get to shorting one tap on one side of the secondary to another on the other side ("... short one tap on sec1 to one tap on sec2") (post #25) I presume it should be the same, i.e. 0 to 0 in order to establish the output VAC? You can probably tell I am a complete newbie - thanks for being patient. Nico
with 4 output taps, (label them a, b, c, d) there are two different ways to connect them in series (or two ways to connect them in parallel).
and two more ways to short a single turn.
winding 1 is a & b.
winding 2 is c & d.
Connect a to b and the bulb will light up.
Connect c to d and the bulb will light up.
Connect b to c and the bulb will not light up (yet). measure the voltage a to b and c to d and a to d. This last can be either near zero Vac or roughly double the a to b.
Connect b to d and the bulb will not light up (yet). Measure the voltage a to b and c to d and a to c. This last can be either near zero Vac, or roughly double the a to b.

You want the bulb to not light up AND for the measurement across the two windings to be DOUBLE the single winding voltage.

BTW,
a similar complication applies to wiring up a dual primary. It either shorts the mains and blows the fuse/MCB or you do it more safely using a Mains Bulb Tester. The BIG danger is that experimenting on the Primary side is VERY dangerous even through the MBT. Do not get electrocuted while trying to identify the correct wiring on the Primary side.
__________________
regards Andrew T.

Last edited by AndrewT; 19th January 2017 at 08:14 AM.

 19th January 2017, 09:18 AM #30 DIM44   diyAudio Member   Join Date: Nov 2016 Location: urban Got it thanks. I propose to permanently connect the mains input (two terminals, neutral and live) and insulate them properly with heat shrink or similar, and add the ground (earth) to the metal shroud of the transformer in case of a leak. In taht way I will kind of minimize the risk on the primary side. However, I do have some experience with electrical mains connections and already know where the "sharp" end of the danger lies. Having said that it is easy to make mistakes - like the professional electrician who connected the power to my newly built workshop some years ago. He reversed the proper connections of the neutral and ground terminals producing an exciting flash and bang when he tried to snip the wires with the mains switch off...

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Holton Precision Audio         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post totaltech Power Supplies 3 21st November 2017 10:31 PM tabarddn Class D 7 20th June 2016 08:33 PM andreyambalov Power Supplies 22 17th November 2014 06:25 PM ZLyzen Power Supplies 43 22nd December 2011 11:00 PM chuck55 Solid State 8 7th February 2006 01:22 PM

 New To Site? Need Help?

All times are GMT. The time now is 11:54 AM.