# 9 + 9 =18?

Discussion in 'Electrical Engineering' started by Virginia Belle, Nov 19, 2003.

1. ### Virginia BelleGuest

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?

Thank You
Brenda

2. ### EEngGuest

I won't go into the right or wrong of it, but to answer your
question...

Strip the insulation from each of the four wires. Twist together the
negative of one adapter to the positive of the other adapter. This
leaves you two open wires, one positive, one negative, and you now
have 18V.

3. ### John GilmerGuest

I have yet to see any wall wart with a ground connection.

If your "wall warts" are designed to replace 9 volt bateries, you can cut
the part that go to the appliance in half and connect ONLY the male of one
to the female of the other. The unused male and female will have your 18
volts.

4. ### Zorin the LynxGuest

It is also a good idea to use identical wallwarts. If you use different
ones, imbalances can occur, especially if they are poorly regulated
(like most are...)

-Z

5. ### Guest

It's not a dumb question at all. 9 volt wall warts
deliver 9 volts *at their rated current*. If you
run them at a different current, the voltage could
be considerably higher or lower.

If the two wall warts have identical current specs,
you'll get 18 volts at the load for which the transformers
are rated. The problem is that MOST wall warts are not
regulated. That means that a wall wart rated 9 volts,
100 mA may put out say 12 volts if it is connected to

The bottom line is this: when you connect the
two wall warts in series and then connect the
two remaining wires to the load, you may not get
18 volts. You could get well above or well below
18.

7. ### John GGuest

Dave
She posted seperately to several newsgroups that I look at and as well as
the usual many similar answers to the same question she got them in all
sorts of variations in EACH newsgroup.
What a waste of band width.

8. ### John GilmerGuest

[/QUOTE]

You are starting to sound like someone who looks under his bed before going
to sleep.

Actually most don't even have polarized plugs.

9. ### John GilmerGuest

Sure. Putting two wall warts in series will come back to "bite you on your
ass."

Get real!

10. ### Spehro PefhanyGuest

I don't think I've seen a US/Canadian one that's a true "wall wart",
though the "brick" type, both linear and switching types, often do
have the output grounded. If the AC plug has only two pins, there's

Best regards,
Spehro Pefhany

11. ### Spehro PefhanyGuest

As I pointed out in another newsgroup, what happens to the filter
capacitor when one of the two accidentally gets unplugged and you have
not added diodes across the outputs?

Best regards,
Spehro Pefhany