# Yet again..another basic electronics question



## greco (Jul 15, 2007)

I am sure that I will get/presently have a reputation for asking these questions.
However, I can't easily find he answers in books or online and I highly respect the level of knowledge we have access to with the members of this forum. Your help is always much appreciated.

The question is:

I have a transformer with 5 wires on the secondary 

2 brown wires...a centre wire green with a stripe (I assume this is the centre tap) and two lime green wires.

Can I choose any two of the wires to get the desired voltage I am looking for?
The voltages vary from 48VAC to 2.5 VAC when various combinations of the wires are measured.

One lime green and one brown gives me the 18.5 VAC I want.

Can I assume this is OK? The application is for basic electronics experiments. 
The text I am using repeatedly asks for 18VAC.

Many thanks

Cheers

Dave


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## keeperofthegood (Apr 30, 2008)

Hey oh Dave

You know, better to ask  it is how we all learn.

Yes, you can tape off unused wires and just use the wires you want.


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## greco (Jul 15, 2007)

Many thanks Keeps...I just never trust my level of electronics knowledge or what seems "instinctively" OK
And...I do learn a lot from asking basic questions here.

Cheers

Dave


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## keeperofthegood (Apr 30, 2008)

OH AND

Did you draw out your transformer? Primary coil || secondary with all taps?


HAHAHA I learn too. Even when I know "half" the answer, I go to google to flesh out the rest and even then others step up with more info to fill the gaps.

One thing to keep in mind is power. Even if you don't use the other taps, you are still limited to the v and i on just one section of coil as you would have if the whole coil was in use. (UNLESS I got that wrong, lets see if others will step in on that, this part usually confuses me, but I think say 10v at 1a at the 5v tap gives you 5v at 1a not 5v at 2a)


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## greco (Jul 15, 2007)

keeperofthegood said:


> OH AND
> 
> Did you draw out your transformer? Primary coil || secondary with all taps?
> 
> ...


Thanks Keeps...Yes, I will draw it out...that is quite a few permutations to record...LOL
I don't even want to TRY and figure out all/any of the power related stuff at this point.
Maybe someone will answer this (re: power) for both of us.

Cheers

Dave


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## keeperofthegood (Apr 30, 2008)

Oh for sure Dave!!

Here, this is how I sorted out a few of mine for experimenting with.

http://killingdog.webng.com/MY_Transformers.htm


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## jb welder (Sep 14, 2010)

keeperofthegood said:


> OH AND
> 
> Did you draw out your transformer? Primary coil || secondary with all taps?


 Yes, draw it out. Also an ohmeter check should give you readings somewhat proportional to the voltage readings (depending on your meter accuracy at low resistance). The green with stripe should be the center tap for the greens. If the browns are not a separate winding you should get low resistance from brown to green. For your purposes you don't want them to be separate windings. If they are separate the 18V may be a "ghost" reading that will not deliver under load.



keeperofthegood said:


> One thing to keep in mind is power. Even if you don't use the other taps, you are still limited to the v and i on just one section of coil as you would have if the whole coil was in use. (UNLESS I got that wrong, lets see if others will step in on that, this part usually confuses me, but I think say 10v at 1a at the 5v tap gives you 5v at 1a not 5v at 2a)


 Yes, best to think in terms of "weakest link". If you can figure the current rating, don't exceed it for any winding or partial winding. This will be the safest for the xfrmr.


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## greco (Jul 15, 2007)

Thanks for the information.
I will do the ohmeter checks also...very interesting to learn about this.

Cheers

Dave


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