I need a 5 volt supply

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Packrat1947

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Someone gave me a nice older Sony 12” laptop (512meg ram & XP). The CPU heatsink fan is not running because the terminal on the mainboard is dead. The 5v. fan works when jury rigged.

I want to run the fans leads out of a hole, and have an external source of voltage. I'm thinking of a 3 cell – AAA flashlight housing. I'm thinking of “velcro-ing” it to the speaker area, or on the lid. The wires will have a jack-plug connection for removal.

How would you handle this? This will be a loaner computer for when I have to bring a customer's box back to the lab.

I have a lathe/mill so I can machine just about anything.

Packrat1947

www.pbase.com/packrat
 
I'll be honest. If someone gave me some crazy-rigged contraption for a loaner, I would be scared about how they're gonna fix my stuff.
 
My electronics knowledge is lacking, but perhaps solder a resistor to the main, full voltage circuit? and run the fan from that? Im sure someone at radioshack could figure it out.

The battery pack idea is resourceful, but it would have to be turned on and off with the pc, and I wouldn't trust anyone to actually do that. So im guessing with that setup the pc wouldnt last long, as a customer would let it overheat and destroy itself.

If the only thing on the mobo that isn't working is the fan circuit, I would try to trace it (the circuit) to the item (i dont know what it would be called, a resistor? a diode?, you get the idea) that steps down the voltage. Maybe you will find something burnt, bloated, bent or loose. Then it would just be a matter of desoldering and resoldering in a new one from radioshack.

Additionally, its possible the mobo or bios or os just isnt telling the fan to turn on. Maybe the internal temp sensor is broken. I find it odd that on an otherwise functional mobo, that the fan circuit would fail, considering its low voltage and load. At any rate, good luck!, I love challenges like this.
 
This lappy has been running a long time in this condition, so maybe a fan isn't really needed - but still desirable. Perhaps milling slots in the removable cover plate (over the 'sink) would help out a bit. I'll use one of the CPU monitoring progs. and see what's going on.

Many times I leave my HP at a site, but thought that this would be a good "kids" machine. I would hate to throw it away for something so minor.

Another fellow is giving me a 2 year old 15" Dell. That will be a loaner too.

I'll look at pulling the full battery voltage down to 5v. That should be do-able. Thanks.
Cheers,
Ron N.
 
What's wrong with an internal flying lead? If the rest of the laptop is functioning you must have a source of ?12 volts. A replacement 5V regulator is a small and easy thing, a 5V zener even smaller.
 
But then you would need (generally not always i know) a heatsink for the regulator and extra space. Going via the usb header, you will only need two wires which could be squeezed in more easily and avoid the extra heat output of the regulator.
 
Thanks for all the replies.

I'm thinking tapping into the USB wires would be the best way. I don't know why I didn't think of it. Numb brain I guess. Sometimes the answer is right in front of me, but I don't see it. Tunnel vision??

Right now I'm working on a T43 screen replacement, so the little Sony will have to wait a bit.

Cheers,
Packrat1947
 
My suggestion is to either use a resistor to cut down the standard 12v source, or as someone suggested above, run it off one of the 5v USB port leads.

As mentioned above, if someone offered me a loaner machine jury-rigged with a battery pack attached with velcro, I'd definitely be looking at them like they had a square head. *chuckles*
 
Put a blinking led on it. Tell them it's the spherical convergent focus electrostatic ion accelerating laser spectrographic analysis attachment device. LOL. nooooooo... don't do that. Seriously, you should never rig up anything. If it caught on fire and burned down their home, the engineer with the electrical tape and screwdriver will be held responsible, and probably sued.
How could this happen you ask? What if your design fails, and the cpu overheats and doesnt shut off... What if the current draw on the cpu fan motor has a huge microAmp pull when it first kicks in due to counterelectromotive force in the motor windings, and this shorts out the usb bus and puts the power supply into a short circuit which overheats and causes a fire.
Never never never pretend you are U.L. labs.

* funny story that happened to me once... *
My father asked me to repair a machine at our small rug manufacturing business. The part I needed would be rather exotic. I went to radioshack and asked the man at the counter for a 120 volt 3.5 amp single pole double throw momentary contact illuminated pushbutton switch with a 3/4 " round shank. The man looked at me and said "Sir, all our switches are over there..." LOL LOL LOL. I thought I would die of laughing. I actually did find a suitable switch in their supply, exactly like I wanted. Well needless to say, my "genius" design worked great for several months, but then I had failed to take into account the need for a small capacitor to prevent electrical arcing due to the high impedance from the counterelectromotive force in the motor circuit, so much like how old cars with a point-condensor type ignition system will burn up the points if the capacitor fails, my short sightedness eventually burnt up the motor contactors and set the entire thing on fire.
 
Resolved [5 v. power]

As a follow up. Tonight I had nothing important on the bench so I pulled the little Sony apart. I ran leads from a USB port to the fan, and all is well.

Actually, the fan is a bit too loud, so I'll try to "resist" it down a bit.

Thanks for all the leads and considered thought.

Packrat1947
 
Ah excellent - thats good to hear! Could actually turn it into a "feature" if you done it right. Put a pot through to the outside of the case and voila - user controlled cooling! :D
 
I was able to quiet the fan with a Radio Shack potentiometer (271-342). This is a small rectangular block with a screw adjustment. I set it at 20 ohms. The fan is quiet, but still starts with authority.

Cheers,
Packat1947
 
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