Re: Dumb Question From A Lady

John Woodgate <[EMAIL PROTECTED]> wrote in message news:<[EMAIL PROTECTED]>...
> I read in sci.engr.electrical.compliance that Virginia Belle
> <[EMAIL PROTECTED]> wrote (in <[EMAIL PROTECTED]
> 2237.public.lawson.webtv.net>) about 'Dumb Question From A Lady', on
> Wed, 19 Nov 2003:
> >I Know that this is a dumb question but, I am curious anyway. 
> >
> >Lets just say that I need an 18 volt DC power source and that the source 
> >has to come from one of those transformers? that plug into the wall and 
> >change AC to DC.
> >
> >What if I only have two of those transformer devices that are 9 Volts DC 
> >each.
> >
> >Now, If I cut the insulation off of the ends of both of those 
> >transformers, take the two wire ends from each and twist the 4 ends 
> >together to make two again, plug them in, will THAT make me the 18 volts 
> >that I need? 
> >
> >9 + 9 makes 18 doesn't it?
> >
> >PLEASE tell me that I have made SOME sense here? 
> 
> Some , but not a lot. Yes.. 9 + 9 = 18, but to get 18 you have to
> connect the wires 'in series'. I'll try to make a diagram. You need to
> use Courier (or Courier New) font to see it correctly.
> 
>         .....
> trans- |     |----------  inner/colour 2
> former |     |
>        |.....|----------. outer/colour 1
>                         |
>         .....           |
> trans- |     |----------. inner/colour 2
> former |     |
>        |.....|----------  outer/colour 1
>        
> You ALSO have to get the correct two wires joined together. If the two
> transformers are identical, and they have the normal concentric plugs on
> the ends of the output cables, then the words on the diagram tell you
> how to connect them. If they have different colours, you can go by them,
> e.g. black, white joined to black, white. If not, it's not possible to
> tell you unless you understand the terms 'positive' and 'negative' AND
> you can identify which wire is which polarity.


Virginia Belle:

John Woodgate is correct.  

If somehow you reverse the connections to the second output, you will
have 9 volts minus 9 volts and no apparent output, even though eachg
unit is working correctly.   If you have access to someone with a
voltmeter, they can tell if you have made the correct connections. 
Or, if you connect the output to whatever you want to power, and it
doec not work, you will have to reverse the connection between the two
units to the other wire.  But your basic idea ia sound.  The only
problem that I can see is if the "wall-warts" havge enough amperes to
power whatever you might connect.  Most wall-warts say 9V at 300 ma
(for milliamperes) or something like that.  When you put two identical
units in series like you are proposing to do, you get double the
voltage, but still only 300 milliamperes.  So, you need to see how
much currtent your proposed equipment needs and make sure the supplies
can provide that much current.

Good luck.

H. R.(Bob) Hofmann