AC DC transformer with 3 wire output

[matijalazic]

Hello guys.
So this isnt really a computer problem. I took apart 230v pc 2.1 sound system. I intend to run it on 12v instead of 230v. So it had a 230v to 12Vx2 transformer in it. There are 3 wires that come out of it. 2 yellow and 1 black. I supposed those are 2x 12v and 1 ground. I suppose you know how ac dc conversion with 4 diodes work. Well from those 2 yellow wires you are supposed to get out 12v DC and GND. Well i connected my 12v supply to the +12V dc on speaker system and gnd of my supply to gnd dc and gnd ac from my speaker system. This thing doesnt work. Any ideas? I dont think that even ac gnd and dc gnd should be connected together but they both have stuff connected to them. I connected them together ao they wouldnt be floating in air.
Thanks for the help

 

[Ironsounds]

Hello... 3-wire transformer are typically centertap... for example two 6vac outputs for use and/or 12vac also, dual voltages for consumer use, 12 or 6 volt filament Tubes.... technically no ground* that is added with your circuit design... Use just the yellow wires, and ground one of them to the Negitive side of your rectifier circuit... tape off the black wire.

Your transformer could also be 24/12 Vac if it was in a Semiconductor PS... and your wiring would differ.

As a basic concept of transformer use... high current low voltage = High voltage low current.... meaning you need a primary input at 12 vac 20 amps to make 230 volts at 1 amp... see the math and physical problems here?

 

[matijalazic]

Well i cant tape it off. There are different components connected to AC GND and different components connected to DC GND that comes out of ac dc converter

 

[Ironsounds]

Hello... Well... you can ground/neutral the CT of the transformer... that will create two lower/half voltage circuits... parallel/seperate voltage circuits. here is a picture http://engineering.electrical-equipment.org/electrical-distribution/centre-tapped-transformer.html
That is a typical Power pole to your house use... in the US 240/120. if you don't need the lower voltage you just tape off the CT.

Are you a tinkerer/hacker or have experience/education with electronics?

Now days they have very fast switching transitors and don't use transformers, just turn on-off very fast, as needed to charge the caps... this is major cost, material, and weight reduction.
You can plug powerful portable power supplies into any Voltage or Phases and it doesn't care.

 

[matijalazic]

I do have some electronics knowlege since im a student on electrical engeneering school (but i'm computer tehnician ). However I dont think you understand me correctly (or i dont understand you). I want to throw transformer out and run this system on 12v DC only. I have worked with other stuff like this and transformers usually had 2 wire outputs. Now this here is strange circuit to me. On the same black wire coming from transformer there are connected Speaker GND and led + voltage. On the same wire. No kidding. I have no idea what to make out of this

 

[Ironsounds]

Hello... OH.... Your talking about a transformer connection to a speaker, Output impedance matching transformer?
http://www.allaboutcircuits.com/textbook/alternating-current/chpt-9/special-transformers-applications/

At this point I ask a simple questions... what is your final goal here?... and what do you want to do it with?

 

[matijalazic]

Transformer is connecter to the preamp circuit. Then it divides aux input to 2.1 sound system

 

[matijalazic]

Hello... OH.... Your talking about a transformer connection to a speaker, Output impedance matching transformer?
http://www.allaboutcircuits.com/textbook/alternating-current/chpt-9/special-transformers-applications/

At this point I ask a simple questions... what is your final goal here?... and what do you want to do it with?

I want to run this sound system solely on 12V. I want to put it in my car. Well im not that much familiar with capacitors. I'm aware of thiers basic working. However this circuit is giving me some headaches. Very strange voltages. I drew you a picture of my measurements. Those resistors and capacitors are just for demonstration.

 

[Ironsounds]

Hello... Your voltage readings are correct for a 24/12 tranformer in first picture... you are using a full wave bridge and your DC positive and Common are not connected/grounded directly to the AC transformer.

1) You need to wire the transformer for just 12vac to the bridge circuit.. use the one yellow wire on the positive and black on common... tape other yellow wire.

Your R values to the capacitors are to limited in-rush charging to the caps... fuse blowing to the transformer.

2) all - side caps need to be tied to the common Black DC, from the full wave bridge.
3) all + caps need to be tied to the Red positive, from the full wave bridge.

You now have unregulated >12Vdc on the caps... capacitors are just high voltage/current batteries in your circuit.

 

[matijalazic]

Hello... Your voltage readings are correct for a 24/12 tranformer in first picture... you are using a full wave bridge and your DC positive and Common are not connected directly to the AC transformer.

Im a bit confused. Please help me with this. I connect +12vdc on 1 side of diode bridge and dc gnd to other side of diode bridge. What do i connect to place where black wire from transformer was?

Those resistors and capacitors on ym pic are without a value. I drew them just so you would understand there are stuff conected. I didnt bother with corectness.

Here is an actual pic

 

[Ironsounds]

Hello... read above... you only need two wires from that transformer because it is a 24/12 transformer one black and one yellow, tape the other yellow one off... not needed.

 

[matijalazic]

Hello... read above... you only need two wires from the transformer.

YES usually you do only need 2. I didnt make this up. Ths is an actuall wiring. 2 yellow wires on diode bridge and black one has other stuff connected to it. Should i just make something float?

The transformer from 230v was already in it. I want to make it work on 12v dc

 

[matijalazic]

Hello... read above... you only need two wires from that transformer because it is a 24/12 transformer one black and one yellow, tape the other yellow on off... not needed.

Ok i did what u said. Its working now. Partialy. on 4 way led array only half of them are working. when i put them back on transformer all of them are working.

 

[Ironsounds]

Hello... There are Two useable 12 vac circuits and one 24 vac circuit potential... you only need one 12 vac circuit from the transformer for your project.

LED's will have voltage drop across each one of them lit... http://www.oksolar.com/led/led_color_chart.htm so you need to take into account your current Load and voltage drop/losses in your design... you might want to try 24vdc operation next.

 

[matijalazic]

Hello... There are Two useable 12 vac circuits and one 24 vac circuit potential... you only need one 12 vac from the transformer for your project.

Dude 😀 I don't need transformer for 12 vdc. I need to REPLACE transformer with my own 12vdc power supply i got from pc power supply so i can run circuit which has been runing on that transformer. I dont need transfromer. I throwing it away. I need to run that circuit on 12v vdc and it seems like it isnt working in any combination.

 

[matijalazic]

Hello... There are Two useable 12 vac circuits and one 24 vac circuit potential... you only need one 12 vac circuit from the transformer for your project.

LED's will have voltage drop across each one of them lit... http://www.oksolar.com/led/led_color_chart.htm so you need to take into account your current Load and voltage drop/losses in your design.

Since there were 2 yellow wires in diode bridge, i guess there should be 24 vdc voltage coimng out right? Am i supposed to feed it with 24vdc?

 

[Ironsounds]

hello... Yes... + or - some... there is a balance and calibration to every circuit... use just 2 yellow wires and tape the black. B )

 

[matijalazic]

hello... Yes... + or - some... there is a balance and calibration to every circuit... use just 2 yellow wires and tape the black. B )

Thanks for everyhing. Its working now 😀 I just hope I dont blow my car up 😀

 

[Ironsounds]

Hello... Get a picture for me if it does... B )

 

[matijalazic]

I would love to post a pic but i got a problem. Somehow LEDs are bright but when i try to connect cables to play some music there is a short circuit aomehow and my psu shuts down. Dayum. I tought it was ok since LEDs were working

 

[Ironsounds]

Hello... 1) what were the symptom's at fail?
Transformers are a pretty durable science/part... unless something else failed and you kept putting a bigger fuse in it... then the transformer will over current.

The first thing I look for is schematic and parts list when fixing any thing electronic... it's makes so much easier at this point...

2) Can you DL a schematic of it? If you really wanna fix it I can help you look it over... cant be too hard of a science for me B )

 

[matijalazic]

Hello... 1) what were the symptom's at fail?
Transformers are a pretty durable science/part... unless something else failed and you kept putting a bigger fuse in it... then the transformer will over current.

The first thing I look for is schematic and parts list when fixing any thing electronic... it's makes so much easier at this point...

2) Can you DL a schematic of it? If you really wanna fix it I can help you look it over... cant be too hard of a science for me B )

The problem was with power. I need to buy step up from 12v to 24v. There are 3 connections to run it wit DC. GROUND, +12v DC and + 24v DC. Blac wire (common) was as u said 12v and i need to connect 12v there and i need to connect 24v and GND to diode bride. I tested it. Its working fine. When its finnished i will update you with pics. I am just happy to come to conclusion

 

[Ironsounds]

Hello... That makes sense... There are two circuits that need power from a 24/12 CT transformer... AND thus 3-wires need connected. Good Job and Good luck. B )