How many things do you know of where a voltmeter shows no voltage, but
the device works fine?

I bought an auto/air laptop power supply for a friend of mine, and it
was a good brand (Targus) and it's hard to imagine too high a voltage
coming from a car, but since it wasn't my computer, I thought I should
check the voltage before plugging it into his new laptop.

So, out in the car, I measured the voltage and got zero. Even though
the light was on on the brick.

It turns out iiuc that the device is so fancy that it waits until
everything is connected to decide what voltage to deliver to the
laptop, and before then, there is no output voltage present.

mm wrote:
How many things do you know of where a voltmeter shows no voltage, but
the device works fine?

I bought an auto/air laptop power supply for a friend of mine, and it
was a good brand (Targus) and it's hard to imagine too high a voltage
coming from a car, but since it wasn't my computer, I thought I should
check the voltage before plugging it into his new laptop.

So, out in the car, I measured the voltage and got zero. Even though
the light was on on the brick.

It turns out iiuc that the device is so fancy that it waits until
everything is connected to decide what voltage to deliver to the
laptop, and before then, there is no output voltage present.

Same as a "switching" power supply in a PC: No voltage until a load is
detected.

mm wrote:
How many things do you know of where a voltmeter shows no voltage, but
the device works fine?

I bought an auto/air laptop power supply for a friend of mine, and it
was a good brand (Targus) and it's hard to imagine too high a voltage
coming from a car, but since it wasn't my computer, I thought I should
check the voltage before plugging it into his new laptop.

So, out in the car, I measured the voltage and got zero. Even though
the light was on on the brick.

It turns out iiuc that the device is so fancy that it waits until
everything is connected to decide what voltage to deliver to the
laptop, and before then, there is no output voltage present.
Hi,
Heard about seroies voltage regulator? No load, no voltage!

mm wrote:
How many things do you know of where a voltmeter shows no voltage, but
the device works fine?

I bought an auto/air laptop power supply for a friend of mine, and it
was a good brand (Targus) and it's hard to imagine too high a voltage
coming from a car, but since it wasn't my computer, I thought I should
check the voltage before plugging it into his new laptop.

So, out in the car, I measured the voltage and got zero. Even though
the light was on on the brick.

It turns out iiuc that the device is so fancy that it waits until
everything is connected to decide what voltage to deliver to the
laptop, and before then, there is no output voltage present.
Hi,
If the adaptor has a built in series regulator, no load, no vvoltage.
Parallel regulator has current sink. Without load it'll show voltage.

On Thu, 18 Dec 2008 18:04:36 -0700, Tony Hwang
wrote:

mm wrote:
How many things do you know of where a voltmeter shows no voltage, but
the device works fine?

I bought an auto/air laptop power supply for a friend of mine, and it
was a good brand (Targus) and it's hard to imagine too high a voltage
coming from a car, but since it wasn't my computer, I thought I should
check the voltage before plugging it into his new laptop.

So, out in the car, I measured the voltage and got zero. Even though
the light was on on the brick.

It turns out iiuc that the device is so fancy that it waits until
everything is connected to decide what voltage to deliver to the
laptop, and before then, there is no output voltage present.
Hi,
If the adaptor has a built in series regulator, no load, no vvoltage.
Parallel regulator has current sink. Without load it'll show voltage.

Good to know. Thanks all.

On Dec 19, 2:25*am, mm wrote:
On Thu, 18 Dec 2008 18:04:36 -0700, Tony Hwang
wrote:





mm wrote:
How many things do you know of where a voltmeter shows no voltage, but
the device works fine?

I bought an auto/air laptop power supply for a friend of mine, and it
was a good brand (Targus) and it's hard to imagine too high a voltage
coming from a car, but since it wasn't my computer, I thought I should
check the voltage before plugging it into his new laptop.

So, out in the car, I measured the voltage and got zero. *Even though
the light was on on the brick.
does the device have a multi-pin connector i.e. more than 2 pins?

I think that device needs to see a programming resistor to tell it
what voltage to output..

No resistor, no output.

It has nothing to do with series vs parallel regulators.

Mark

wrote:
On Dec 19, 2:25 am, mm wrote:
On Thu, 18 Dec 2008 18:04:36 -0700, Tony Hwang
wrote:





mm wrote:
How many things do you know of where a voltmeter shows no voltage, but
the device works fine?
I bought an auto/air laptop power supply for a friend of mine, and it
was a good brand (Targus) and it's hard to imagine too high a voltage
coming from a car, but since it wasn't my computer, I thought I should
check the voltage before plugging it into his new laptop.
So, out in the car, I measured the voltage and got zero. Even though
the light was on on the brick.
does the device have a multi-pin connector i.e. more than 2 pins?

I think that device needs to see a programming resistor to tell it
what voltage to output..

No resistor, no output.

It has nothing to do with series vs parallel regulators.

Mark

Hi,
May I ask what programming resistor is?

On Dec 19, 10:07*am, wrote:
On Dec 19, 2:25*am, mm wrote:

On Thu, 18 Dec 2008 18:04:36 -0700, Tony Hwang
wrote:

mm wrote:
How many things do you know of where a voltmeter shows no voltage, but
the device works fine?

I bought an auto/air laptop power supply for a friend of mine, and it
was a good brand (Targus) and it's hard to imagine too high a voltage
coming from a car, but since it wasn't my computer, I thought I should
check the voltage before plugging it into his new laptop.

So, out in the car, I measured the voltage and got zero. *Even though
the light was on on the brick.

does the device have a multi-pin connector i.e. more than 2 pins?

I think that device needs to see a programming resistor to tell it
what voltage to output..

No resistor, no output.

It has nothing to do with series vs parallel regulators.

Mark

I doubt if its a series regulator or a parallel regulator. I would
have to be a switching regulator and these just shut down under no
load conditions. This is to protect the internal circuitry of the
regulator which would soon let all the smoke out if operated without a
load.


Jimmie

JIMMIE wrote:
On Dec 19, 10:07 am, wrote:
On Dec 19, 2:25 am, mm wrote:

On Thu, 18 Dec 2008 18:04:36 -0700, Tony Hwang
wrote:
mm wrote:
How many things do you know of where a voltmeter shows no voltage, but
the device works fine?
I bought an auto/air laptop power supply for a friend of mine, and it
was a good brand (Targus) and it's hard to imagine too high a voltage
coming from a car, but since it wasn't my computer, I thought I should
check the voltage before plugging it into his new laptop.
So, out in the car, I measured the voltage and got zero. Even though
the light was on on the brick.
does the device have a multi-pin connector i.e. more than 2 pins?

I think that device needs to see a programming resistor to tell it
what voltage to output..

No resistor, no output.

It has nothing to do with series vs parallel regulators.

Mark

I doubt if its a series regulator or a parallel regulator. I would
have to be a switching regulator and these just shut down under no
load conditions. This is to protect the internal circuitry of the
regulator which would soon let all the smoke out if operated without a
load.


Jimmie
Hi,
There is no switching regulator. Switching power supply is follwed by a
regulator circuit. Crow bar circuit is for protection.

On Dec 19, 10:16*am, Tony Hwang wrote:
wrote:
On Dec 19, 2:25 am, mm wrote:
On Thu, 18 Dec 2008 18:04:36 -0700, Tony Hwang
wrote:

mm wrote:
How many things do you know of where a voltmeter shows no voltage, but
the device works fine?
I bought an auto/air laptop power supply for a friend of mine, and it
was a good brand (Targus) and it's hard to imagine too high a voltage
coming from a car, but since it wasn't my computer, I thought I should
check the voltage before plugging it into his new laptop.
So, out in the car, I measured the voltage and got zero. *Even though
the light was on on the brick.
does the device have a multi-pin connector i.e. more than 2 pins?

I think that device needs to see a programming resistor to tell it
what voltage to output..

No resistor, no output.

It has nothing to do with series vs parallel regulators.

Mark

Hi,
May I ask what programming resistor is?- Hide quoted text -

- Show quoted text -

if it is like this one

http://www.targus.com/us/accessories_power.asp

it needs a special "tip" for each laptop. THe tip has the right
physical conector and also has some device (probably just a resistor
but maybe a diode) of the correct value to tell the supply what
voltage to put out. It's just a programmable power supply with the
programming element in the tip. They tell you which model tip to use
with each laptop.

If you are not skilled in electronics which appears to be the case (no
offense) then the best thing for you to do is buy the correct tip that
you need for the laptop that you want to use from Targus.

Mark

On Fri, 19 Dec 2008 07:07:11 -0800 (PST), wrote:

On Dec 19, 2:25*am, mm wrote:
On Thu, 18 Dec 2008 18:04:36 -0700, Tony Hwang
wrote:





mm wrote:
How many things do you know of where a voltmeter shows no voltage, but
the device works fine?

I bought an auto/air laptop power supply for a friend of mine, and it
was a good brand (Targus) and it's hard to imagine too high a voltage
coming from a car, but since it wasn't my computer, I thought I should
check the voltage before plugging it into his new laptop.

So, out in the car, I measured the voltage and got zero. *Even though
the light was on on the brick.
does the device have a multi-pin connector i.e. more than 2 pins?

Yes, 3 pins. It's a Targus, like the ones in the url you posted in
reply to Tony.

BTW, it turns out not all Targus tips will fit all Targus adapters.
They have indents and things to keep that from happening. I bought
this adapter for a friend and then his old Macintosh broke, and I
thought I could use the adapter for myself, with a tip I had, maybe
from an AC-only adapter. But the tip wouldn't fit in the other
adapter. I forget the details, but my friend bought a later model Mac
and the second tip fit it, so I gave it to him and everything is
fine.**

If you buy one of these things in the store, and it's opened all
ready, check for the tip you need before you leave the store. I had
bought one early on that was missing one tip.

**Then I fixed his old Macintosh. He got an image of a floppy on the
screen which meant the system was't on the harddrive or the harddrive
had failed. I took it apart according to the directions in the
manual, and I couldn't get the harddrive out to look at it, but while
trying, I disconnected it a couple times, and when I reassembled the
thing, it worked. It was all screwed together when this started. I
don't know how the connection went bad.

I think that device needs to see a programming resistor to tell it
what voltage to output..

No resistor, no output.

It has nothing to do with series vs parallel regulators.

Mark

I know about this now. Wish I knew about 8 months ago when I installed a
fancy pendant light.
There was a short but I didn't know that and tested the power supply to
find no voltage so I assumed the PS was bad until I learned a bit more.
Until then, I never heard of such a thing and had to admit I was wrong.
How embarrassing.



On Thu, 18 Dec 2008 17:54:16 -0500, mm wrote:

How many things do you know of where a voltmeter shows no voltage, but
the device works fine?

I bought an auto/air laptop power supply for a friend of mine, and it
was a good brand (Targus) and it's hard to imagine too high a voltage
coming from a car, but since it wasn't my computer, I thought I should
check the voltage before plugging it into his new laptop.

So, out in the car, I measured the voltage and got zero. Even though
the light was on on the brick.

It turns out iiuc that the device is so fancy that it waits until
everything is connected to decide what voltage to deliver to the
laptop, and before then, there is no output voltage present.