10VAC wall adaptor confusion

[uriahsky]

I need to provide a cable tester with a 10VAC power supply. The input to this tester is a three pin plug with the center pin being neutral. The other pins are supposed to be 10VAC. My question is: is this 10VAC measured 10VAC from pins 1 & 3, or 5VAC measured from center to pin 1 and center to pin 3? The neutral has to come from the center tap on the transformer right? It can't come from anywhere else can it? The actual picture of this wall wart says 10VAC, but that is all. It has to be a center tap 0-5 on each side right? Or is there some other way this could be wired?
Thanks
Russ

 

[crutschow]

The neutral is likely just a safety ground which goes to the power line ground pin. It doesn't have to go the the transformer center tap.

 

[MikeMl]

I need to provide a cable tester with a 10VAC power supply. The input to this tester is a three pin plug with the center pin being neutral. The other pins are supposed to be 10VAC. My question is: is this 10VAC measured 10VAC from pins 1 & 3, or 5VAC measured from center to pin 1 and center to pin 3? The neutral has to come from the center tap on the transformer right? It can't come from anywhere else can it? The actual picture of this wall wart says 10VAC, but that is all. It has to be a center tap 0-5 on each side right? Or is there some other way this could be wired?
Thanks
Russ

About 30 sec with an Ohmmeter should answer this.

 

[uriahsky]

I don't have the actual transformer. Is there a way to tell with an ohm meter from the device end?

 

[Sceadwian]

Definitely sound like a ground connection and the two AC lines. The output from a transformer is isolated from ground, so the ground connection is supplied if the device needs a ground reference.
It could however be a center tap to the transformer and the ground. Without testing it with a meter there's really no way to tell unless you have a datasheet for the transformer.

 

[uriahsky]

Examining the pcb on the tester shows that the center tap goes to some diodes and one side of the pins goes to power the display and the other looks to be part of 5vdc for the IC chips. To get 5VDC you need to start with a little more then 5VAC right? If that is the case then it has to be center tap with 10VAC on each side. I hope.....

 

[Sceadwian]

If it's regulated 5V DC that is uses, it's likley 10VAC rectified and fed into a regulator. Typical regulators needs around 2 volts over their regulated voltage to maintain regulation. It's really hard to say more because we don't know anything about the circuit you're using. You've only given us a vague idea of what might be going on. Pictures might help.

 

[uriahsky]

Well my guess was wrong I went with the 5VAC to each side with a center tap. I turned it on and got nothing so I turned it up to 10VAC and I got some smoke, but the display kind of kicked on. I pulled it apart and checked the rectifying diodes and found one that I must have shorted one. Replaced them all and re-flowed some solder on the LCD Screen. Then I went with the 10VAC to pin one and three leaving the center unconnected and it worked So it was not what I thought it was. I thought the whole time it was a center tap thing. I hope I learned something here. So many times I have fried things for one reason or another so it felt good seeing this one work out. Thank you Carl, Sceadwian and everyone else.
Russ

 

[Sceadwian]

Congratulations, that's great; You let smoke out AND ended up with a working device too => Now that's a good day!