Increase voltage using capactior etc

[aosborn]

Hello.
I have a project where I'm making a digital picture frame/media center
out of an old laptop. I took the systemboard/lcd out of the case and
mounted in a shadow box. Everything went well. I made a power button
out of a push button microswitch and mounted a panel-mount audio
connector and usb connector for peripherals.

My issue is with heating. I bought 2 40mm 12v PC case fans to cool it,
one intake one exhaust. Obviously a laptop doesn't have headers for
fans or any molex connectors to plug them in so I'm taking voltage off
the systemboard where I can find it to power the fans.

I found +5V on the serial port (pin 3) so I soldered the black
(ground) wire to that of the fan header. I then found +5.5V on pin 2
of the PS2 port. Both of these ports I don't use. Using my multimeter
I touch the 2 headers and I get +10.6V. That sounds good.

I plug my fans into the headers and I get nothing. I barely touch the
fan blades and the fan starts spinning, but very slow. It barely
pushes any air. I plug these into my PC (multimeter reads +12.1V on
the headers) and the fans spin very very fast, normal.

Did I either solder the headers wrong (multimeter shows voltage....)
or can I increase the initial voltage someway to atleast get the fans
to spin up without me manually starting them. Such as a capacitor
which can fill up then release it's energy (as you can tell I'm a noob
with some of this, I'm a Network Engineer, not Electrical Engineer).

I know some PC modders will rewire their fan headers to use the 12v
rail and the 5v rail for ground, yielding 7V, and that makes the fans
work, just slower and quieter (for silent PC solutions). I'm getting
much higher than 7V so I thought my fans would at least move on their
own...

Thanks!

 

[Jamie]

aosborn wrote:

Hello.
I have a project where I'm making a digital picture frame/media center
out of an old laptop. I took the systemboard/lcd out of the case and
mounted in a shadow box. Everything went well. I made a power button
out of a push button microswitch and mounted a panel-mount audio
connector and usb connector for peripherals.

My issue is with heating. I bought 2 40mm 12v PC case fans to cool it,
one intake one exhaust. Obviously a laptop doesn't have headers for
fans or any molex connectors to plug them in so I'm taking voltage off
the systemboard where I can find it to power the fans.

I found +5V on the serial port (pin 3) so I soldered the black
(ground) wire to that of the fan header. I then found +5.5V on pin 2
of the PS2 port. Both of these ports I don't use. Using my multimeter
I touch the 2 headers and I get +10.6V. That sounds good.

I plug my fans into the headers and I get nothing. I barely touch the
fan blades and the fan starts spinning, but very slow. It barely
pushes any air. I plug these into my PC (multimeter reads +12.1V on
the headers) and the fans spin very very fast, normal.

Did I either solder the headers wrong (multimeter shows voltage....)
or can I increase the initial voltage someway to atleast get the fans
to spin up without me manually starting them. Such as a capacitor
which can fill up then release it's energy (as you can tell I'm a noob
with some of this, I'm a Network Engineer, not Electrical Engineer).

I know some PC modders will rewire their fan headers to use the 12v
rail and the 5v rail for ground, yielding 7V, and that makes the fans
work, just slower and quieter (for silent PC solutions). I'm getting
much higher than 7V so I thought my fans would at least move on their
own...

Thanks!
The current handling for those ports will not supply a fan..

You'd be luck if you didn't short the port.


since this is a laptop, you must have access to the power plug ?


http://webpages.charter.net/jamie_5"

 

[IanM]

aosborn wrote:

Hello.
I have a project where I'm making a digital picture frame/media center
out of an old laptop. I took the systemboard/lcd out of the case and
mounted in a shadow box. Everything went well. I made a power button
out of a push button microswitch and mounted a panel-mount audio
connector and usb connector for peripherals.

My issue is with heating. I bought 2 40mm 12v PC case fans to cool it,
one intake one exhaust. Obviously a laptop doesn't have headers for
fans or any molex connectors to plug them in so I'm taking voltage off
the systemboard where I can find it to power the fans.

I found +5V on the serial port (pin 3) so I soldered the black
(ground) wire to that of the fan header. I then found +5.5V on pin 2
of the PS2 port. Both of these ports I don't use. Using my multimeter
I touch the 2 headers and I get +10.6V. That sounds good.

The serial port has no 5V output, you are measuring a data line. As you
are seeing more than 5V between it and the PS2 port which *does* have a
5V line, it must be negative, not the +5V you think it is!

I plug my fans into the headers and I get nothing. I barely touch the
fan blades and the fan starts spinning, but very slow. It barely
pushes any air. I plug these into my PC (multimeter reads +12.1V on
the headers) and the fans spin very very fast, normal.
As expected, see below under 'Modders'.

Did I either solder the headers wrong (multimeter shows voltage....)
or can I increase the initial voltage someway to atleast get the fans
to spin up without me manually starting them. Such as a capacitor
which can fill up then release it's energy (as you can tell I'm a noob
with some of this, I'm a Network Engineer, not Electrical Engineer).

One can double a voltage using a switched capacitor converter but not
easily for the sort of current a fan needs. Mistaking -5V for +5V
does not lead to confidence in your skills with a multimeter and unless
you *have* basic electronics skills, building a boost converter, (even
from a kit) is not going to go too well. It would use an inductor for
energy storage and voltage conversion, not a capacitor. Caps are good
for keeping the voltage nearly the same while the current varies a lot,
more or less the opposite of what a boost converter has to do. Anyone
who's learnt network engineering can learn electronics if sufficiently
motivated but this particular part of your project is not a good place
to start.

Small kit projects where failure only smokes a few cheap and easily
replaceable parts or building circuits from components on a solderless
breadboard is a good start, not a project you've already invested a lot
of time into where you are risking a laptop main board that you cant
easily replace (unless you've got another identical laptop) and whatever
camera card or USB stick you are planning to load the photos from).

What is the power supply voltage of the laptop? (I'm assuming you have
removed the battery.) With no battery to charge, it should have
plenty of spare current for fans, you just need to (A) switch them on
when you have +5V on the PS2 port and (B) regulate the voltage so you
don't blow them and they aren't too noisy. It may even be possible to
wire your fans in series if they are identical and the PSU is in the 18
to 24V range (with a smoothing capacitor across each fan to keep them
happy). Linear regulators convert excess voltage into heat so if they
can be avoided when you are trying to reduce the heat, it would be nice.

A simple transistor switch in the ground wire to the fan or fans,
controlled by the +5V you found on the PS2 port, would switch them on
and off with the main power button. You also need a couple of resistors
to make the transistor switch operate correctly. More details if/when
you reply with the PSU voltage.

I know some PC modders will rewire their fan headers to use the 12v
rail and the 5v rail for ground, yielding 7V, and that makes the fans
work, just slower and quieter (for silent PC solutions). I'm getting
much higher than 7V so I thought my fans would at least move on their
own...

Thanks!

*DONT* COPY THE MODDERS, if there isn't enough load on the 5V rail to
handle the extra current from the 12V rail via the fans it will blow the
board. Its normally OK on a desktop PC, but I'd still not recommend it.
On a laptop its criminally stupid to do it that way, so always run
fans between a proper supply and ground. You got lucky the serial port
couldn't sink any significant current . . .

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & >32K emails --> NUL:

 

[JeffM]

aosborn wrote:

I'm making a digital picture frame/media center
out of an old laptop[...]
I bought 2 40mm 12v PC case fans to cool it[...]
Obviously a laptop doesn't have headers for fans[...]
so I'm taking voltage off the systemboard[...]

I found +5V on the serial port (pin 3) so I soldered the black
(ground) wire to that of the fan header.
I then found +5.5V on pin 2 of the PS2 port[...]
Using my multimeter I touch the 2 headers and I get +10.6V.
That sounds good.

Not really.

I plug my fans into the headers and I get nothing.

Your meter with a >1Mohm input impedance

was a poor model for what you connected to those points.
Measure it again with the actual load connected.
http://www.google.com/search?q=define:source+impedance

Ah. The old >100% efficiency ploy.

Such as a capacitor which can fill up then release it's energy

As Ian noted, you probably integrated a pulse train

as you already *had* capacitance in your hi-z measurement
which gave you the reading you did see.

An oscilloscope and some (load) resistors
would be good things to have to sort this out.
If all you have is a meter, you can see which lines **aren't** DC
lines
by putting a capacitor-coupled AC voltmeter on a point.

 

[Jasen Betts]

aosborn wrote:

Hello.
I have a project where I'm making a digital picture frame/media center
out of an old laptop. I took the systemboard/lcd out of the case and
mounted in a shadow box. Everything went well. I made a power button
out of a push button microswitch and mounted a panel-mount audio
connector and usb connector for peripherals.

My issue is with heating. I bought 2 40mm 12v PC case fans to cool it,
one intake one exhaust. Obviously a laptop doesn't have headers for
fans or any molex connectors to plug them in so I'm taking voltage off
the systemboard where I can find it to power the fans.

I found +5V on the serial port (pin 3) so I soldered the black
(ground) wire to that of the fan header. I then found +5.5V on pin 2
of the PS2 port. Both of these ports I don't use. Using my multimeter
I touch the 2 headers and I get +10.6V. That sounds good.

not really good, the serial port cant supply much power.

with just the 5V supply from the ps/2 the fans will spin slowly and
probbly start themselves. if you need more voltage look at using a
LM7812 (or just a resistor) to reduce the DC that the laptop runs off down to 12V