Wanna power this laptop since I fried my system today.

MikeHunt79 · 07-03-2003, 06:31 PM

The laptop requires 15v, and I've got a car PSU that gives out 20v and another car PSU that gives out 5v. I got thinking, the potential difference between the two PSU's positive wires is 15v. Would this be ok to power the laptop?

I`m thinking of trying it tomorrow, but somehow I get the feeling it's gonna cause ground loops and all sorts of havoc, so it might not be worth bothering.

I'm gonna get a proper 15v PSU eventually, it's just that the E-bay auction doesn`t end for a couple of days,

and I`m stuck with silence in my car since I fried my computer this morning.

Here's how it happended:

I powered up my computer today, except it didn`t fully power up. The power LED came on, thats about it. So I tried it in the house, and measured the voltage coming outta my sproggy.... All was good until I found the 5v rail was actually giving out 8v! So, I unhooked the sproggy, and tried a mains PSU on the computer and it did the same thing.... sat there with just the stupid *** power LED on, and nothing else.

I reackon the sproggy fried the motherboard.
I tried powering up the sproggy with nothing attached, and it gave out 12v on the 5v rail.

So, just for the sake of curiousity, I tried wiring it up to a crappy old quad speed CDROM drive. It appeared to work. Even tho the 5v rail was now giving out 10v. I pressed eject, and the tray shot out faster than i've ever seen in my life. It almost took my hand off.

I gave up after this, thought "sod it", and got straight to work on the laptop. Btw, If anyone has had a similar thing happen to thier sproggy? I'wanna try and fix it for mark 4 (see sig).

Ricky327 · 07-04-2003, 01:08 PM

Wow..thats a crazy idea. LOL dont bother im sure you can live without music for another 2 days or so.

So you want to connect the 0V of the laptop to the +5V supply and then connect the +15V of the laptop to the +20V of the other supply to give you 15V in total. It can work it just that your laptop 0V is +5V above the cars ground.

Its easy to forget this and connect another circuit that can short your +5V supply.

And how about the current rating of the regulators?

Naah leave it...sound too messy.

MikeHunt79 · 07-04-2003, 01:50 PM

Ricky327: U r right, it's a lot of trouble, and it probably won't work well.

Instead.... I tried wiring the laptop straight upto my car battery today, and it worked! 12v isn`t quite the required 15v, but the laptop doesn`t seem to mind.

Needless to say, I'm much happier now, I now have tunes again. I should have some pics soon, I`m currently copying songs onto the laptop as I type this.

Ricky327 · 07-04-2003, 01:55 PM

Yeah that should work...I guess your laptop battery will never get charged properly but im sure you dont mind that...you got plenty in your car + the alternator =)

MikeHunt79 · 07-04-2003, 01:59 PM

I've actually ditched the imbuilt laptop battery, since it would never charge - it just seemed like a waste of space.

In it's place I got my small 5v PSU for the 40x4 LCD. I just hope it's ok when cranking my engine... we'll have to see. I have yet to take it for a journey.

mp3hombre · 07-07-2003, 12:10 PM

I found a circuit that could've saved a lot of trouble. It's the classic crowbar. It's only purpose is to blow the fuse in case of an overvoltage. I have never tried it myself but some say it works.

MikeHunt79 · 07-07-2003, 12:24 PM

Thanx, I think I`ll add it to my sproggy when I get it fixed.

Still got lots of other stuff to do before MK4 is ready tho...