9 + 9 = 18 ?

[Virginia Belle]

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?

Thank You
Brenda

 

[ApacheJoe]

On Wed, 19 Nov 2003 14:54:44 -0500 (EST), BRWVABell@webtv.net
(Virginia Belle) wrote:

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?

Thank You
Brenda

Brenda,

Your two transformers would be wired in parallel. You would only get
9 volts, but if you took the 9v side of one and attached it to the
ground of the other, you'd get 18v between the two leads that aren't
taped together. (That is called "series")

But Radio Shack will sell you an 18v xfmr for about $12 with any kind
of connecter you want on the output end. (i personally love that). So
if the bugglegum and baling wire fix doesnt work, try that.

You can probably find some pretty good tutorials on dc circuits on the
web. Just search using those words. And no...it's not a dumb
question. But the answer is 9 + 9 = 18 sometimes.

cheers
aj

 

[mike]

ApacheJoe wrote:

On Wed, 19 Nov 2003 14:54:44 -0500 (EST), BRWVABell@webtv.net
(Virginia Belle) wrote:


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?

Thank You
Brenda


Brenda,

Your two transformers would be wired in parallel. You would only get
9 volts, but if you took the 9v side of one and attached it to the
ground of the other, you'd get 18v between the two leads that aren't
taped together. (That is called "series")

But Radio Shack will sell you an 18v xfmr for about $12 with any kind
of connecter you want on the output end. (i personally love that). So
if the bugglegum and baling wire fix doesnt work, try that.

You can probably find some pretty good tutorials on dc circuits on the
web. Just search using those words. And no...it's not a dumb
question. But the answer is 9 + 9 = 18 sometimes.

cheers
aj

Be aware that many of the cheapie 9V unregulated wall warts have open
circuit voltages up to 12V or so. When heavily loaded, they may be 7V.

So, 9 + 9 = 24 Sometimes...and sometimes it's 14.
There's also the issue of current rating.

Most consumer grade devices are designed to be as cheap as possible.
One way to save $$ is to design the wall wart to be part of the whole
system. That is, the voltage/current parameters of the wall wart are
matched to the load in such a way that it barely works on a good day.
That's one of the reasons, in addition to greed, that they charge you
$69 for an ac adapter to power a $99 device.
You mess up that precarious balance when you substitute without knowing
exactly what the designer intended.

Cellphones, laptops etc. expect regulated supplies, which most random 9V
wall warts aren't. They also take advantage of closely controlled
current limit profiles to match the system load.

Bottome line: If the thing you're powering costs more than the wall
wart, it's probably lower overall risk to use the correct adapter.
mike

--
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laptops and parts Test Equipment
Honda CB-125S
TEK Sampling Sweep Plugin and RM564
Tek 2465 $800, ham radio, 30pS pulser
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