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13.6v on the 12v rail

Posted: Thu Mar 05, 2009 1:00 pm UTC
by hack124x768
Now that I have your attention... ;)

I'm getting a free computer from a friend. P3 533mhz, no pci slots, onboard video sound etc...
The cool thing about it is the weird relationship the motherboard and power supply have. ONLY 12v and 5v, no atx plug, just molex.

So my question is: How long do you think it will last with 10-14v on the 12v rail (with stable regulated 5v)?

The reason I ask is that I hear newer computers are VERY dependent on the 12v rail for power to the cpu and accessories, which to me means that older computers (such as this early pentium 3) are not so dependent on 12v...

I'm putting it in my jeep for the heck of it, and don't really care if it dies. It will be running debian lenny, if anyone cares.

If the magic smoke is let out I will be sure to post pics. :D

Re: 13.6v on the 12v rail

Posted: Thu Mar 05, 2009 3:35 pm UTC
by thanksbastards
sounds interesting... keep us updated.

Re: 13.6v on the 12v rail

Posted: Thu Mar 05, 2009 3:51 pm UTC
by Amnesiasoft
Well, it has lasted this long...so I can only assume it will continue to last unless the voltage regulation gets even worse.

Re: 13.6v on the 12v rail

Posted: Thu Mar 05, 2009 7:18 pm UTC
by ATCG
What I would worry most about are voltage transients on your (nominally) +12V supply. I don't know much about the subject, but here's one article with some background. [EDIT: I had first provided this link, not realizing site registration was required.] Google seems to bring up a fair number of relevant links.

If you are willing to spend a few bucks, automotive computer power supplies can be found here and a raft of other places. Googling 'automotive "ATX power supply"' brings up 118,000 hits. From your description it sounds like you would have to jury rig an adapter from an ATX supply to the Molex connector on your motherboard, but I can't see that being a showstopper - and if you mean the standard 4-pin Molex on most peripheral devices, then the appropriate connector is undoubtedly already available out of the supply.

EDIT: Bah! I hadn't realized that the first link I gave needed a site registration. An alternative link has been provided.

Re: 13.6v on the 12v rail

Posted: Fri Mar 06, 2009 12:42 am UTC
by akashra
Most power supplies are shipped allowing a 15% error... which is huge, I know.

Re: 13.6v on the 12v rail

Posted: Sun Mar 08, 2009 8:47 am UTC
by imontheroof
hack124x768 wrote:So my question is: How long do you think it will last with 10-14v on the 12v rail (with stable regulated 5v)?

The reason I ask is that I hear newer computers are VERY dependent on the 12v rail for power to the cpu and accessories, which to me means that older computers (such as this early pentium 3) are not so dependent on 12v...


I think this guy is implying that he will wire the pc directly to the battery, and supply his own regulated 5v for the board. This is sure to smoke, you realise how much the car battery fluctuates, and the damage.

So why do it? Use a 12v dc-dc, it will be better in the long run.

Re: 13.6v on the 12v rail

Posted: Sun Mar 08, 2009 9:25 am UTC
by Carnildo
hack124x768 wrote:I'm putting it in my jeep for the heck of it,


If you're hooking it directly to the alternator, you're not going to see "10-14 volts". You're going to see 8-20 volts minimum, and you could go even higher or lower. A car's power supply is very dirty.

Re: 13.6v on the 12v rail

Posted: Sun Mar 08, 2009 9:27 am UTC
by hack124x768
imontheroof wrote:
hack124x768 wrote:So my question is: How long do you think it will last with 10-14v on the 12v rail (with stable regulated 5v)?

The reason I ask is that I hear newer computers are VERY dependent on the 12v rail for power to the cpu and accessories, which to me means that older computers (such as this early pentium 3) are not so dependent on 12v...


I think this guy is implying that he will wire the pc directly to the battery, and supply his own regulated 5v for the board. This is sure to smoke, you realise how much the car battery fluctuates, and the damage.

So why do it? Use a 12v dc-dc, it will be better in the long run.


Yeah, connecting the 12v rail to the battery (through the cigar lighter, so regulated somewhat and fused) is what I mean. I know the range at which a car battery is expected to operate within (10v cranking, 12v sitting, 14v running, in my jeep with a brand new battery). I don't know that capability of the hardware to handle +/-2v. I will be playing with the computer today most likely, so I should be able to get an update for you. Let the smoking begin!!!

Re: 13.6v on the 12v rail

Posted: Sun Mar 08, 2009 11:27 am UTC
by imontheroof
It will kill it, no doubt. Its not meant to handle that. The lighter socket is not regulated in any shape or form and is just about the most unclean power you can get.

Go run 240v though the 12v line, same result; less waste of your time.

Re: 13.6v on the 12v rail

Posted: Sun Mar 08, 2009 3:39 pm UTC
by hack124x768
imontheroof wrote:It will kill it, no doubt. Its not meant to handle that. The lighter socket is not regulated in any shape or form and is just about the most unclean power you can get.

Go run 240v though the 12v line, same result; less waste of your time.


I would think that 2 over would do less damage than 228 over, but that's just me...

Edit: Yeah, it's regulated. If it wasn't, it would pop your battery and accessories whenever it was revved. The regulator is on the back or the alternator (at least on mine).

Re: 13.6v on the 12v rail

Posted: Tue Mar 10, 2009 6:16 am UTC
by imontheroof
If there is a regulator, explain the 'closed hood' charging systems (regs. don't work both ways!)!

Oh well, no big loss. Good luck!

Re: 13.6v on the 12v rail

Posted: Tue Mar 10, 2009 9:05 am UTC
by hack124x768
I really am curious why so many people seem to think car power is unregulated, and more importantly, if those people consider themselves car people.

Quote from wikipedia:
"Modern automotive alternators have a voltage regulator built into them. The voltage regulator operates by modulating the small field current in order to produce a constant voltage at the stator output."
http://en.wikipedia.org/wiki/Alternator ... lternators

It is apparently true then that *some* cars to not have a regulator, but every car and motorcycle I have worked on has one (from dads huge 1 ton ford van down to my friends 50cc honda scooter). Maybe if the windings were REALLY precise, you wouldn't need one... maybe. More likely they are just talking about French cars. Silly French cars. :p


Took the computer apart today and checked out the power supply. 12v 5.5 amp, and 5v .8 amp. With a direct 12v line from the car, and an lm7805 for the 5v it should run fine, in theory. If I can dig up that dang regulator from my box of junk, I might have something for you tomorrow. (Yes, I know I have said that 3 times. Meh.)

Re: 13.6v on the 12v rail

Posted: Tue Mar 10, 2009 9:29 am UTC
by Carnildo
The alternator is regulated, yes, but what about the rest of the electrical system? Is there protection against the spikes and dips from the spark plugs discharging? From the surge generated by the vent fans turning off? The ripple from the wiper and turn-signal relays? How about the low-voltage conditions caused by running the rear defrost, the headlights, the wipers, and the front vents while stopped at a long-cycle light in the middle of a snowstorm?

Re: 13.6v on the 12v rail

Posted: Tue Mar 10, 2009 6:26 pm UTC
by hack124x768
Carnildo wrote:The alternator is regulated, yes, but what about the rest of the electrical system? Is there protection against the spikes and dips from the spark plugs discharging? From the surge generated by the vent fans turning off? The ripple from the wiper and turn-signal relays? How about the low-voltage conditions caused by running the rear defrost, the headlights, the wipers, and the front vents while stopped at a long-cycle light in the middle of a snowstorm?


Newp, and that's where the fun is. :D However, from careful monitoring, I know exactly where all of those conditions will peg my voltage. The only wildcard is actually my subwoofers.

Perhaps worth noting; Load related voltage dips affect all circuits. I think you over estimate the severity in a car.

Re: 13.6v on the 12v rail

Posted: Wed Mar 11, 2009 4:30 am UTC
by hack124x768
Ok, I made it work today. So, to recap, a low power pentium 3 WILL boot and run fine with 13ish volts on the 12v rail (from car cigar lighter) and LM7805 regulated 5v 1 amp on the 5v rail. Only worked when the car was running though, so I suspect the ground for my cigar lighter is bad, as it should still be upwards of 12 volts when the car is not running.

Those of you planning for computing in a post apocalyptic age should find this info useful.

Re: 13.6v on the 12v rail

Posted: Wed Mar 11, 2009 8:36 am UTC
by imontheroof
hack124x768 wrote:Ok, I made it work today. So, to recap, a low power pentium 3 WILL boot and run fine with 13ish volts on the 12v rail (from car cigar lighter) and LM7805 regulated 5v 1 amp on the 5v rail. Only worked when the car was running though, so I suspect the ground for my cigar lighter is bad, as it should still be upwards of 12 volts when the car is not running.


Or that the higher voltage makes something go dodgy.

Oh and by the way, sorry to burst you bubble. Its not regulated. Fused, but not regulated.

To prove my point I went through lets see, 5 cars today and tried it. No reg.

Re: 13.6v on the 12v rail

Posted: Wed Mar 11, 2009 10:11 am UTC
by hack124x768
imontheroof wrote:
Or that the higher voltage makes something go dodgy.

Oh and by the way, sorry to burst you bubble. Its not regulated. Fused, but not regulated.

To prove my point I went through lets see, 5 cars today and tried it. No reg.


On. The. Back. Of. My. Alt. There. Is. A. Regulator. As that's the highest voltage in the car, that's good enough regulation for me, and obviously for the computer.

I don't understand this bubble of mine you say I have. Bubble of what? Bubble of misinformation about my charging system? I have an old chevy (80s style) charging system, and it has a voltage regulator on the alt. I quoted wikipedia for cars in general; do you want a quote from my chilton guide, or a picture of it, or what? I know what it is and what it does, and I *think* I may know what you are confused about, but still not quite sure, as you just keep saying the same thing.

Re: 13.6v on the 12v rail

Posted: Thu Mar 12, 2009 6:38 am UTC
by imontheroof
Tehe; anyway. Yours does, mine doesn't. Excellent!

Now the point is it works. Whats it going to do?

Re: 13.6v on the 12v rail

Posted: Thu Mar 12, 2009 9:13 am UTC
by hack124x768
Damn, that was a fun argument. Anyway...

I was going to to simply load it up as a headless dump mp3 squirting box, but then a friend gave me the idea to use it as a data logger. I am paranoid of driving in ice, so temperature and barometric pressure along with gps is what I am currently thinking. It has a soundcard with a gameport, so I have 4 easy to get to analog inputs available, and I have a usb gps receiver in box somewhere.

The only thing it can't do is play video files (466mhz), so going in the media center direction any further than mp3s is not going to happen.

Here's what I did for the wiring to the board... (hard drive and such power comes from the motherboard,so I didn't have to do anything for them)
Image

Re: 13.6v on the 12v rail

Posted: Thu Mar 12, 2009 1:47 pm UTC
by aireoth
I am nerdifically excited to see how this works out, as both a personal computer enthusiast and a car nut.

I am currently rewiring my car from the wiring harness of the engine to the dashboard as I'm converting right to left hand drive and the wires need extending. I have been thinking about the idea of branching off some wires and creating a power source for a laptop or old rubbish computer to record information regarding lateral G's, road conditions, gps etc as I am an amature rally racer. I have most of the computer parts apart from a lat G sensor.

Re: 13.6v on the 12v rail

Posted: Thu Mar 12, 2009 2:06 pm UTC
by hack124x768
aireoth wrote:I am nerdifically excited to see how this works out, as both a personal computer enthusiast and a car nut.

I am currently rewiring my car from the wiring harness of the engine to the dashboard as I'm converting right to left hand drive and the wires need extending. I have been thinking about the idea of branching off some wires and creating a power source for a laptop or old rubbish computer to record information regarding lateral G's, road conditions, gps etc as I am an amature rally racer. I have most of the computer parts apart from a lat G sensor.


Way to go! None of that right land drive junk. :p

What kind of car is it? I can't see it being very worthwhile in a newer one.

You might want look at the mp3car forums. They have a lot of info on using standard computer hardware for car audio, but they branch out into stuff that might be more useful to you, such as gps and engine monitoring.

Re: 13.6v on the 12v rail

Posted: Thu Mar 12, 2009 2:43 pm UTC
by aireoth
Its a 2000 Subaru 2.5 Impreza, 2 door, dark blue. I love the two door look and the more subtle spoiler (to the giant washboard of the STi), so when I wrecked it I decide to keep the hulk and rebuild it. After years of collecting parts I have all the internal pieces of a 2002 Japanese STi. Basically I started replacing everything inside, and since the JDM is right hand drive, and mine is left, I had to extend the wires, in the process of doing that right now, but as a result I have an opportunity to 'mod' it, probably have at least 40hrs of wiring work to do, so I'm taking my time and making sure its done right.

I've done some work on other cars, my favorite was modding a Delorean into a Back to the Future replica for a car show. Really unique looking car, and I think its got wicked style, but its not the best drive, not by a long shot.

Re: 13.6v on the 12v rail

Posted: Thu Mar 12, 2009 6:27 pm UTC
by hack124x768
I had assumed it was a classic or something, a 2000 must have a ton of wires. You may as well splice in some aux power pugs here and there, even if you don't use them. They could be handy later, either for a computer, gps, cb, or whatever.

Hope that project works out for you. Subarus are fun cars.

Re: 13.6v on the 12v rail

Posted: Sat Mar 14, 2009 3:08 am UTC
by Emu*
aireoth wrote:I have most of the computer parts apart from a lat G sensor.


People have been using Wiimotes with PCs... The accellerometers in a wiimote should give you at least Skyline R32 levels of G-info!

Re: 13.6v on the 12v rail

Posted: Thu Mar 19, 2009 9:21 pm UTC
by scurrminator
burnt?

Re: 13.6v on the 12v rail

Posted: Fri Mar 20, 2009 11:58 pm UTC
by imontheroof
scurrminator wrote:burnt?


Probably.

Re: 13.6v on the 12v rail

Posted: Sat Mar 21, 2009 12:51 am UTC
by hack124x768
imontheroof wrote:
scurrminator wrote:burnt?


Probably.


Nope, Just can't find my usb gps, so I haven't done anything with it. No magic smoke yet, sorry to disappoint. :p

Re: 13.6v on the 12v rail

Posted: Wed Mar 25, 2009 5:59 pm UTC
by omglolbah
Someone mentioned the regulated point of the alternator being the highest voltage in the system.

This is a flawed argument as inductive loads can bumb the voltage up something fierce.

An example:
Connect 12 volts to a big solenoid, using an oscilloscope measure the voltage across the solenoid... then disconnect the power-supply.

Sometimes you can see spikes in ranges of hundreds of volts. These might not harm "slow" electro items like bulbs and leds but will fry ICs quite fast and well :(

Your earlier schematic has a regulator (7805) on the 5 volt rail. I would suggest seeing if the voltage on the 12/13 volts of your car supply is sufficient to run a 7812 regulator. That way you would get a much cleaner 12 volts.

Also.. when using a 78xx ALWAYS use capacitors on the input and output. Without them you get fairly bad regulation and a lot of rippling on the output. Just a little tip I learned from painful experience when doing work with rfid readers :)

Re: 13.6v on the 12v rail

Posted: Thu Mar 26, 2009 1:07 am UTC
by hack124x768
I had it plugged into my cigar lighter, which was only giving 12.7v while the engine was running (poor ground I think).

Do you have a schematic for the capacitors?

Re: 13.6v on the 12v rail

Posted: Thu Mar 26, 2009 1:27 am UTC
by omglolbah

Re: 13.6v on the 12v rail

Posted: Thu Mar 26, 2009 10:42 am UTC
by hack124x768
omglolbah wrote:http://www.sminntech.com/images/7805datasheet.gif

Ah, so just filter caps to ground. Makes sense.

Re: 13.6v on the 12v rail

Posted: Thu Mar 26, 2009 9:36 pm UTC
by Earlz
not exactly that I know much about cars.. but do you think it's safe to run a harddrive(one not designed to be portable) in such a bump-ride as a jeep? lol

Re: 13.6v on the 12v rail

Posted: Thu Mar 26, 2009 9:54 pm UTC
by Emu*
Earlz wrote:not exactly that I know much about cars.. but do you think it's safe to run a harddrive(one not designed to be portable) in such a bump-ride as a jeep? ¡This cheese is burning me!


take the silent pc route and suspend it using elastic rope; in normal situations this would isolate the case from the drive's vibrations but it works both ways!