electronic questions

I have a few questions. I got a transformer that takes 120 volts and give 12.6 at 3 amps.(http://www.thesource.ca/estore/Prod...=Online&category=Transformers&product=2731511)
it has 3 output wires. How would i get 12 volts out of it. I also have a rgb led but i can't light up the red with any other color at the same time. I can light blue and green at the same time but no green and red or red,green and blue.Thanks

You can try testing the leads with your multimeter, to see which ones will give the voltage you want

The transformer is most likely center-tapped, meaning there is a connection halfway through the secondary winding. You'd just need to take your meter and find between which two wires you get 12v from. If you get the center-tap connection you should read around 6v.

Not sure about your LED, got any information on it?

jamilm9 said:

I have a few questions. I got a transformer that takes 120 volts and give 12.6 at 3 amps.(http://www.thesource.ca/estore/Prod...=Online&category=Transformers&product=2731511)
it has 3 output wires. How would i get 12 volts out of it. I also have a rgb led but i can't light up the red with any other color at the same time. I can light blue and green at the same time but no green and red or red,green and blue.Thanks

Click to expand...

Hey Jamil...
it looks like you have a 12.6VAC center tapped Xfo.... The 2 Yellow wires will
no doubt give you 12.6 VAC and between the Black wire and any Yellow wire you should
get 6.3VAC... just confirm the voltages with a DMM.. (I know you have one... :)...

I would need to see a spec sheet on your LED... to help you...

Jerry

I think you wire the transformer like this, for rectifying:


As for the LED I think you forgott the resistors. Do you have a link to it?

FireMyLaser said:

I think you wire the transformer like this, for rectifying:

As for the LED I think you forgott the resistors. Do you have a link to it?

Click to expand...

Yeah.... that will give him Full Wave Rippled DC... he would need to filter that
output to get some clean DC...

Jerry

That'll give you ~12VAC between the two yellow secondary wires.  Single black is the center tap, which you won't use. Two black on the other side are primary or 120VAC input.  You'll need to build a power supply circuit to get DC, which essentially consists of a bridge rectifier (or just some rectifier diodes) and some smoothing caps (big electrolytics) and will actually give you around 16VDC.  To get 12VDC regulated, you'll need to use a regulator IC (good 'ol LM317 or it's voltage-specific cousin, 7812) to step down the voltage and regulate it to 12V.

This website gives some good explanations and illustrations:
http://www.kpsec.freeuk.com/powersup.htm

FireMyLaser:
That diagram you show would actually give you HALF the voltage of the transformer.  Since you're taking negative from the center tap, you're essentially only getting voltage from half of the secondary at a time, or about 6.3VAC, then rectifying it.  Using a smoothing cap would be recommended, otherwise the circuit is going not going to get true DC, rather just an oscillating voltage from 0 to full voltage at double AC frequency of 60hz120hz.... a complex circuit probably won't like that or an LED connected straight to it (with the resistor) would end up blinking 60 120 times/second.

Thanks for the fast reply's . I got the transformer problem fixed.I was measuring dc instead of ac. I'm going to use it to power a plasma speaker.
I'm using this led http://www.dealextreme.com/details.dx/sku.4530
with this power supply at 150ma http://www.dealextreme.com/details.dx/sku.1133

The problem may be that it's common anode, or the 150ma rail only share one resistor.

well i have to experiment. Now i'm looking for a 12 volt regulator that can handle 3 amps. :

From what DX says....

   *
Red: 2.5V ~ 3.0V, 350mA
   *
Green: 3.2V ~ 3.8V, 350mA
   *
Blue: 3.2V ~ 3.8V, 350mA

- Note: each color channel is able to take a maximum of 350mA of current, thus a 1050mA combined current input and the 3W rating.


It looks like your "Power Supply" is probably not supplying enough current to
the LEDs... (That is only an LED Tester... not really a Power Supply)
Are you using a current limiting resistor... :-?
What is the output voltage at the Power Supply's LED contacts... :-?

Jerry

well i put a diode on the red contact of the led and now they can all light up :question

i made the bridge rectifier without the ic and i am getting 18 volts use the cap from a camera, ouch.

jamilm9 said:

i made the bridge rectifier without the ic and i am getting 18 volts use the cap from a camera, ouch.

Click to expand...

a flash cap doesn't have enough capacitance for a power supply, you'll want something on the order of several thousand [ch956]F

ok