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'[EE]: Why does a PC need 12V?'
2002\08\30@101730 by Pic Dude

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I need to build a power-supply to run a PC in a car, so I'm
trying to figure out why I really need +/- 12V, which may be
tough to produce with the ignition off (not enough overhead
for the regulator).  I could build a DC-to-DC coverter that
would raise the voltage, but that means $$$.

Thinking of a regular desktop PC with a MB, audio card, video
card, fan, and IDE drive only (no floppy or CD)...

- MOTHERBOARD:
   - 5V around board, which may be regulated to lower for
     processor, etc, but that should not affect me.
   - The motherboard has a 12V requirement (standard ATX
     PS), but does it really need it, or does it pass on
     the 12V to other devices?
   - AFAIK, the parallel port does not require 12V.
   - AFAIK, USB does not require 12V.
   - Does the built-in serial require a +/-12V supply?  Or
     does it generate +/-12V (like a MAX232 for example)?
     If I need to supply it, and decide not to use serial
     comms, then can I just ignore it?  Or can I just supply
     it with +/-5V (as an RS423 device) and make sure the
     other end handles that level?

- COOLING FAN:
   - I can always get or modify the fan for 5V use, or I
     could generate 10-ish volts for that.  So no prob
     here.

- AUDIO CARD:
   - I believe line-out sound levels go to 10V, so +/-12V
     is probably needed there.  Any way around this?

- VIDEO CARD:
   - No idea?  Anyone know anything about these?  Or would
     it vary by manufacturer?  (Which I doubt).

- HARD DRIVE:
   - Have an IDE laptop drive which says 5V at 500ma, so I
     should be okay here.

Anything else I'm missing?

Cheers,
-Neil.

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2002\08\30@103958 by mike

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On Fri, 30 Aug 2002 10:14:18 -0400, you wrote:

>I need to build a power-supply to run a PC in a car, so I'm
>trying to figure out why I really need +/- 12V, which may be
>tough to produce with the ignition off (not enough overhead
>for the regulator).  I could build a DC-to-DC coverter that
>would raise the voltage, but that means $$$.
>
>Thinking of a regular desktop PC with a MB, audio card, video
>card, fan, and IDE drive only (no floppy or CD)...
>
>- MOTHERBOARD:
>    - 5V around board, which may be regulated to lower for
>      processor, etc, but that should not affect me.
>    - The motherboard has a 12V requirement (standard ATX
>      PS), but does it really need it, or does it pass on
>      the 12V to other devices?
>    - AFAIK, the parallel port does not require 12V.
>    - AFAIK, USB does not require 12V.
>    - Does the built-in serial require a +/-12V supply?  Or
Usually.
>      does it generate +/-12V (like a MAX232 for example)?
>      If I need to supply it, and decide not to use serial
>      comms, then can I just ignore it? Probably - the only possible issue I can think of may be to do with
continually asserted ring interrupts.
> Or can I just supply
>      it with +/-5V (as an RS423 device) and make sure the
>      other end handles that level?
Possibly. May be easier to remove the RS232 driver and replace it with
MAX232 etc. +/-8v would probably work fine.  
>- COOLING FAN:
>    - I can always get or modify the fan for 5V use, or I
>      could generate 10-ish volts for that.  So no prob
>      here.
>
>- AUDIO CARD:
>    - I believe line-out sound levels go to 10V, so +/-12V
>      is probably needed there.  Any way around this?
You may get away with less than 12V, as this is likely to give
headroom for the analogue stuff.
>Anything else I'm missing?
There may be things that use the 12V rail to get a clean 5v supply,
but 8v or so ought to do here. Probably most likely on audio or video
cards

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2002\08\30@105116 by Nick Veys

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Serial Communication...

Many, many car-computer power supplies people have made for mp3 players
and such just didn't put a 12V supply in and had no problems.

spam_OUTnickTakeThisOuTspamveys.com | http://www.veys.com

> {Original Message removed}

2002\08\30@105907 by Pic Dude

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Mike Harrison wrote:

> >    - Does the built-in serial require a +/-12V supply?  Or
> Usually.
> >      does it generate +/-12V (like a MAX232 for example)?
> >      If I need to supply it, and decide not to use serial
> >      comms, then can I just ignore it?
> Probably - the only possible issue I can think of may be to do with
> continually asserted ring interrupts.

Not familiar with ring interrupts.  I don't use serial at all,
should I be able to get away w/o supplying 12V at all, or are you
suggesting that the ring interrupts require 12V in it's "dormant"
state?

> >Anything else I'm missing?
> There may be things that use the 12V rail to get a clean 5v supply,
> but 8v or so ought to do here. Probably most likely on audio or video
> cards

Hmmm... never thought of this.  Will have to look at the regulators
on the board (when I get one).

Thanks,
-Neil.

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2002\08\30@110300 by Pic Dude

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So this suggests that the audio card does not require 12V.
And the video card.  So I could clip the +/-12V lines on a
desktop system and use it w/o any probs (if no comms)?

Cheers,
-Neil.


> {Original Message removed}

2002\08\30@110753 by John Ferrell

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Worst case scenario is to use an off the shelf AC converter. If you can keep
the power requirements down to 100Watts they are available for about $45.

I would like to replace the Compaq Laptop I use in the Winnibago with less
costly components.
One of the major stumbling blocks is that of the display. There simply is
nothing available that competes with the laptop's display. Everything else
is way too big/expensive.

The GPS mapping program becomes indispensable once you become accustomed to
it.
Current project is invesitgating a USB Web Cam for better side/back
visibility.

Keep us posted, it is an interesting project!

John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
Dixie Competition Products
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"

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2002\08\30@111840 by Morgan Olsson

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Easiest would be to buy a all in one +5V only motherboard for embedded apps.
I´ve seen somewhere a pentium compatible to good price.
/Morgan

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2002\08\30@112155 by Pic Dude

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John Ferrell wrote:

> Worst case scenario is to use an off the shelf AC converter. If
> you can keep
> the power requirements down to 100Watts they are available for about $45.

You mean an inverter to convert 12V to 120VAC, then plug in the PC?
If so, I'm really avoiding that route since it seems inefficient, and
bulky.

If I find that I need 12V, I may still go the route of building a
custom PS with an internal voltage doubler etc to be able to properly
regulate 12V, or get a DC-to-DC converter, etc.

But I've got my fingers crossed that I will 100% not need 12V.

> I would like to replace the Compaq Laptop I use in the Winnibago with less
> costly components.
> One of the major stumbling blocks is that of the display. There simply is
> nothing available that competes with the laptop's display. Everything else
> is way too big/expensive.

You mean too big.  I can get CRT displays for $20, which is far cheaper
than any LCD I've found.  But you're right...LCD is a must just for space
requirements.  I'm even considering replacing my 17" desktop monitor in
the house with an LCD panel (just sucking up the cost and getting a 15"
LCD) since they're soooo much smaller and I move so often.

> Current project is invesitgating a USB Web Cam for better side/back
> visibility.

FYI, you can get these with very small monitors built into the mirror
nowadays, and supposedly only a couple hundred bucks.  But being a
piclist subscriber, you probably want to build one, like I would.

Where's Julian NC?  I'm currently cooling my heels in Raleigh with
my cousins for some weeks.

Cheers,
-Neil.

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2002\08\30@112208 by Dennis Noordsij

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Hi,

The power cables for hard drives and cd-rom drives have both 5 volts and 12 volts. CD-ROM for example needs 1 amp @ 12 volts peak. (Excluding special parts such as the laptop drive you mentioned).

I'd guess the 12 volts is to power motors inside the drives, etc, while the 5 volts is for the rest.

The 5 volts should be kept as stable as possible, but I don't think the 12 volts is as crucial (assuming a peak voltage of about 14.2 volts while charging, and 11.8 volts for a basically dead battery).
The serial ports might use the 12 volts directly, but you can have a look if they use some IC's similar to the MAX ones.

Of course - don't try it with your new GeForce 4 :-) Have a look around, maybe probe some voltages while running off a normal supply.
Don't take just my word for it! I would hate to hear it didn't work!

If you build the power supply yourself completely, make it big enough to power the whole system (dozens of Watts for a Athlon/P3+ system with CD, drives, etc).

Goodluck, and let us know how it turns out!
Best wishes
Dennis

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2002\08\30@112621 by Alan B. Pearce

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>Worst case scenario is to use an off the shelf AC converter.
>If you can keep the power requirements down to 100Watts
>they are available for about $45.


I am looking at this too for the oldish Dell Laptop that I have. However it
requires 18V at 3.5A (at least that is what the power pack says it can
deliver) and I have been thinking seriously of doing a converter to get to
this instead of going to 230V to drive the power pack.


>The GPS mapping program becomes indispensable once you become
>accustomed to it.

Yeah, this is where I'm coming from as well. Going to try it out this
weekend on a trip.

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2002\08\30@112631 by Pic Dude

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Morgan Olsson wrote:

> Easiest would be to buy a all in one +5V only motherboard for
> embedded apps.
> I4ve seen somewhere a pentium compatible to good price.
> /Morgan

Really?  Where?  I've searched and searched, and all I found
was PC/104-type boards at close to $1000 a piece!  And many
still using 486-level processors.

My requirements are simple -- small size, 300-400Mhz processor
(I was thinking Celeron since they were designed for cooler
operation that the PII's, etc), and perhaps 2 PCI slots.  Need
to support 2 HD's and that's all.

Would love to hear of anything you've come across that meets
these needs.

Up to this point, I'm planning on using a Micro-ATX MB (or just
smaller like a Shuttle MB) in a custom case, with no removeable
drives/floppies/CD's, etc.  Transfer of files, etc will be via
USB or ethernet.

Cheers,
-Neil.,

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2002\08\30@113803 by Mark [DAN/PICK]

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Have you considered the VIA EPIA platform along with an ITX case ?  The
motherboard was £90 and the case was £60.

Visit ...
http://www.viavpsd.com/product/epia_mini_itx_spec.jsp?motherboardId=21

Of most interest to you, there is also a link on this page for compatible
cases, one of which (Cupid 2677) used a 12V DC input !!

I have just build such a machine (EPIA, Cupid 2677, 15" TFT, 256Mb SDRAM,
40G HDD), and it runs Windows 2000 just fine.

Regards
Mark

{Original Message removed}

2002\08\30@114553 by Pic Dude

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Doesn't your PowerPack have automatic 120-240V operation like
the Dell and Thinkpad PS'es I have?  This way you won't need
to go all the way to 230, but can raise to 120V.  Still if
this up and down can be avoided...

Cheers,
-Neil.


Alan B. Pearce wrote:

> I am looking at this too for the oldish Dell Laptop that I have.
> However it
> requires 18V at 3.5A (at least that is what the power pack says it can
> deliver) and I have been thinking seriously of doing a converter to get to
> this instead of going to 230V to drive the power pack.

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2002\08\30@115811 by Pic Dude

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No I hadn't considered it since I did not know it existed.
Did not even know of an ITX format.
This is really sweet!!!  More expensive that I had planned on
but I might just bite.  I was going to use a board just
smaller than a Micro ATX (9" x 7" IIRC), that would support
a Celeron 300 and cost US$24.  But you're swaying me.

I'll have other things going in my case (like a EFI-engine
controller) so my case will be very custom.

Thanks,
-Neil.



Jackson, Mark [DAN/PICK] wrote:

{Quote hidden}

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2002\08\30@121317 by Alan B. Pearce

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>Doesn't your PowerPack have automatic 120-240V operation like
>the Dell and Thinkpad PS'es I have?  This way you won't need
>to go all the way to 230, but can raise to 120V.  Still if
>this up and down can be avoided...

Yeah it is a 100-240V input pack, but I was figuring if I could just do a
1.5 times boost, it would run fine off the car battery :)

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2002\08\30@123506 by Dennis Noordsij

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On Friday 30 August 2002 18:24, you wrote:
> >Worst case scenario is to use an off the shelf AC converter.
> >If you can keep the power requirements down to 100Watts
> >they are available for about $45.
>
> I am looking at this too for the oldish Dell Laptop that I have. However it
> requires 18V at 3.5A (at least that is what the power pack says it can
> deliver) and I have been thinking seriously of doing a converter to get to
> this instead of going to 230V to drive the power pack.

Hi,

Similar laptop here, and 18V power adapter. However the internal battery is only 10-ish or so volts. If the actual charging ciruit (which is tricky for laptop batteries) is inside the laptop, you can probably hook it up with anything 11-18 volts and be happy. I doub the external charger has the volt/current/temp/etc sensing circuits in it, it's most likely just a wallwart thing.

The official 12 volt accessory for this laptop costs 150 euro's from Dell. It's probably nothing more than over/under voltage protection and spike supression (of course very important, but not 150 euro's worth).

I have friends with old laptops hooked directly to the car battery, granted the internal batteries are dead anyway (as in, 5 minutes of charge) which is why they ended up there, but they together with the charging circuit inside the laptop keep the voltage very nicely at the intended voltage (= internal battery output).

Try to find some more info on the net about your model,
Goodluck
Dennis

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2002\08\30@124858 by Bob Barr

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On Fri, 30 Aug 2002 10:14:18 -0400, Pic Dude wrote:

>I need to build a power-supply to run a PC in a car, so I'm
>trying to figure out why I really need +/- 12V, which may be
>tough to produce with the ignition off (not enough overhead
>for the regulator).

Speaking of regulator overhead, the "ignition off" condition isn't the
lowest voltage that you're going to have to be able to deal with.
During cranking, your battery voltage can drop *significantly* below
nominal. (A weak or old battery can drop even further than a new one
will. Cold-weather starting can also worsen the situation.)


Regards, Bob

<snip>

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2002\08\30@131045 by Alan B. Pearce

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>Similar laptop here, and 18V power adapter. However the
>internal battery is only 10-ish or so volts.

The battery in mine is a 14.4V Li-Ion unit. It is a Dell Latitude XPi CD. I
suspect it needs a good 12V to drive the CD motor.

>The official 12 volt accessory for this laptop costs
>150 euro's from Dell. It's probably nothing more than
>over/under voltage protection and spike supression (of
>course very important, but not 150 euro's worth).

Ouch. Certainly not going to spend a hundred quid to do that.

....

>Try to find some more info on the net about your model,

Yeah have found the service manual from the Dell site, have not gone digging
yet to see if the input voltage is critical.

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2002\08\30@131721 by Michael Rigby-Jones

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> -----Original Message-----
> From: Pic Dude [SMTP:.....picdudeKILLspamspam@spam@PILOTTOOLS.COM]
> Sent: Friday, August 30, 2002 3:14 PM
> To:   PICLISTspamKILLspamMITVMA.MIT.EDU
> Subject:      [EE]:  Why does a PC need 12V?
>
> I need to build a power-supply to run a PC in a car, so I'm
> trying to figure out why I really need +/- 12V, which may be
> tough to produce with the ignition off (not enough overhead
> for the regulator).  I could build a DC-to-DC coverter that
> would raise the voltage, but that means $$$.
>
Some modern motherboards (notably P4 boards) use the 12v supply to derive
the high current CPU core voltages, but this is unlikely on an older system.
12v is used for serial comms, BIOS programming voltage and some sound cards
use it.

Regards

Mike

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2002\08\30@142756 by mike

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On Fri, 30 Aug 2002 11:00:01 -0400, you wrote:

>So this suggests that the audio card does not require 12V.
>And the video card.  So I could clip the +/-12V lines on a
>desktop system and use it w/o any probs (if no comms)?
>
>Cheers,
>-Neil.
Try it & see - you shouldn't smoke anything.

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2002\08\30@143520 by Pic Dude

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> Try it & see - you shouldn't smoke anything.

I shouldn't?  Okay, I'll stop then.  :-) :-) :-)

-Neil.

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2002\08\30@144245 by Peter L. Peres

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On Fri, 30 Aug 2002, Alan B. Pearce wrote:

>>Similar laptop here, and 18V power adapter. However the
>>internal battery is only 10-ish or so volts.
>
>The battery in mine is a 14.4V Li-Ion unit. It is a Dell Latitude XPi CD. I
>suspect it needs a good 12V to drive the CD motor.

No but the backlight almost certainly won't run on voltages below 12V.

Peter

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2002\08\30@144256 by Nate Duehr

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Look into mini-ITX PC motherboards and pre-built cases built for 12VDC
if you want to save some time and hassle.  A motherboard with CPU (no
RAM, no HD) and 12VDC case can be found for around $200 US delivered, if
you look around at the different vendors.

http://www.mini-itx.com is a project site dedicated to these little
boards.

There a few 12VDC cases available, all very small, like the motherboard
and chipset.  Feature-rich, relatively fast (for most "car"
applications), and pulls about 2.5A @ 12VDC once operating, including
hard disk power.

Great for little "embedded" applications...

Nate

On Fri, 2002-08-30 at 08:14, Pic Dude wrote:
{Quote hidden}

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2002\08\30@150831 by Byron A Jeff

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On Fri, Aug 30, 2002 at 10:14:18AM -0400, Pic Dude wrote:
> I need to build a power-supply to run a PC in a car,

Join the club.

> so I'm
> trying to figure out why I really need +/- 12V, which may be
> tough to produce with the ignition off (not enough overhead
> for the regulator).

You'll need a Low DropOut regulator.

>  I could build a DC-to-DC coverter that
> would raise the voltage, but that means $$$.

And extra hardware.

>
> Thinking of a regular desktop PC with a MB, audio card, video
> card, fan, and IDE drive only (no floppy or CD)...

Cool. That's my base system for my card MP3 player.

>
> - MOTHERBOARD:
>     - 5V around board, which may be regulated to lower for
>       processor, etc, but that should not affect me.
>     - The motherboard has a 12V requirement (standard ATX
>       PS), but does it really need it, or does it pass on
>       the 12V to other devices?

It passes them on to other devices. The MB itself doesn't need 12V.

>     - AFAIK, the parallel port does not require 12V.

Right.

>     - AFAIK, USB does not require 12V.

Right.

>     - Does the built-in serial require a +/-12V supply?  Or
>       does it generate +/-12V (like a MAX232 for example)?

The former. This is one spot where the +/- 12V is critical.

>       If I need to supply it, and decide not to use serial
>       comms, then can I just ignore it?

Yes.

>   Or can I just supply
>       it with +/-5V (as an RS423 device) and make sure the
>       other end handles that level?

Yes. Or even better a +12/-5 system.

>
> - COOLING FAN:
>     - I can always get or modify the fan for 5V use, or I
>       could generate 10-ish volts for that.  So no prob
>       here.

Right.

>
> - AUDIO CARD:
>     - I believe line-out sound levels go to 10V, so +/-12V
>       is probably needed there.  Any way around this?

I haven't had any problem with my sound card running on only +5 and +12.

>
> - VIDEO CARD:
>     - No idea?  Anyone know anything about these?  Or would
>       it vary by manufacturer?  (Which I doubt).

My onboard video worked find with just +5 and +12.

>
> - HARD DRIVE:
>     - Have an IDE laptop drive which says 5V at 500ma, so I
>       should be okay here.

Interesting. Good idea.

>
> Anything else I'm missing?

It's ATX right? So what about 3.3V? isn't it required. That's one reason why
I've remained with Baby AT MB for projects like this.

Also I'm using full sized 3.5" HD so I'm supplying 12V via a LDO regulator
and using a 7AHr 12V Gel cell as a micro UPS so that the system doesn't reboot
when the start is activated.

BAJ

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2002\08\30@190252 by Pic Dude

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Byron A Jeff scribbled:

> On Fri, Aug 30, 2002 at 10:14:18AM -0400, Pic Dude wrote:
> > I need to build a power-supply to run a PC in a car,
>
> Join the club.

On piclist, doesn't "club" have an implication of a "solution"? :-)


> > so I'm
> > trying to figure out why I really need +/- 12V, which may be
> > tough to produce with the ignition off (not enough overhead
> > for the regulator).
>
> You'll need a Low DropOut regulator.

Among other things, since a low dropout still needs overhead
voltage above 12V.  Figure 1V (just a guess since I haven't
yet investigated this).  So I need 13V min at all times in the
car.  If the current requirement for the 12V portion is low
enough (to be determined), I could regulate 12V to 8V, run that
thru a doubler to get 15-16 volts, and regulate that to 12V.
Complicated, but the best I've thought of so far.  I've searched
for 12V-output DC-to-DC converters with inputs of up to 10V
max, but no dice yet.


{Quote hidden}

I'm sure I can do without serial.  I was planning on building
a controller/keypad for it, but I could do this thru the
keyboard port, parallel port, low-voltage serial, etc.


{Quote hidden}

Both audio and video still leave the 12V requirement, and with
on-board audio/video on the Mini-ITX board I'm looking at, it
will be tougher to split the power rail.


> > Anything else I'm missing?
>
> It's ATX right? So what about 3.3V? isn't it required. That's one
> reason why
> I've remained with Baby AT MB for projects like this.

But 3.3V is no problem to generate in an automobile.  Anything up
to 9V should be a simple regulator design.  It's the 12V that's
kicking my butt.  Doable, but not simple.

> Also I'm using full sized 3.5" HD so I'm supplying 12V via a LDO regulator
> and using a 7AHr 12V Gel cell as a micro UPS so that the system
> doesn't reboot
> when the start is activated.

Hmmm... that's a good idea, but still space consuming.  One of
the cars that this is going in has very, very limited space, so
I'm being very picky here.

What did you do for the 5VSB signal?

Cheers,
-Neil.

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2002\08\30@224450 by Mike Singer
picon face
part 1 2967 bytes content-type:text/plain; (decoded 7bit)

Mainstream thing is cheaper then specific.

Mike.


Nate Duehr wrote:
{Quote hidden}


part 2 5963 bytes content-type:application/x-compressed; (decode)

part 3 154 bytes
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2002\08\30@231509 by Roman Black

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face
Pic Dude wrote:

> > > I need to build a power-supply to run a PC in a car,

> > You'll need a Low DropOut regulator.
>
> Among other things, since a low dropout still needs overhead
> voltage above 12V.  Figure 1V (just a guess since I haven't
> yet investigated this).  So I need 13V min at all times in the
> car.  If the current requirement for the 12V portion is low
> enough (to be determined), I could regulate 12V to 8V, run that
> thru a doubler to get 15-16 volts, and regulate that to 12V.


How about this idea; build a simple SMPS that
generates 3v and has an isolated output, and put it
in SERIES with the 12v car supply. Done right, it would
BE the regulator and self-adjust to maintain 12v to
the PC. So input voltage can be 8v to 15v, and the
output is always regulated 12v. The total SMPS power
only needs to be 1/4 the power of the total supply,
unlike all other solutions which require the SMPS
to supply 100% of the power. :o)
-Roman

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2002\08\30@234229 by Mike Singer

picon face
Slightly in an olinized mood:

How 'bout to spend this time working somewhere at
McDonalds to earn some cash in order to buy real
12vDC/AC sine inverter for as little as $30?
(16 min of Olin's billable time).

Have look at TrippLite APS.

Mike.



Roman Black wrote:
{Quote hidden}

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2002\08\31@144405 by Byron A Jeff

face picon face
On Fri, Aug 30, 2002 at 06:59:29PM -0400, Pic Dude wrote:
> Byron A Jeff scribbled:
>
> > On Fri, Aug 30, 2002 at 10:14:18AM -0400, Pic Dude wrote:
> > > I need to build a power-supply to run a PC in a car,
> >
> > Join the club.
>
> On piclist, doesn't "club" have an implication of a "solution"? :-)

I haven't worked it through to completion. But I've already given you the
basic jist:

* Use a 12V gel cell as a temp UPS
* Use an LDO.

{Quote hidden}

Closer to 0.2-0.3V.

> So I need 13V min at all times in the
> car.

This usually isn't a problem for 3 reasons:

1) You normally have 13-14V when the vehicle is running.
2) The gel cell is usually above 12V
3) and the 0.2-0.3V is less than the 5% variation that most computer items
  require for regulation (i.e. it'll run fine at 11.8V. I have emperical
  evidence.)

>  If the current requirement for the 12V portion is low
> enough (to be determined), I could regulate 12V to 8V, run that
> thru a doubler to get 15-16 volts, and regulate that to 12V.

Not necessary. Alternator + car battery + small gel cell means that the input
voltage will never be below 12V. With an LDO you can get 11.7 to 11.8V
consistently with that input.

This part I have tested. I've booted an ordinary PC from a 12V gel cell using
an LDO regulator that produced 11.7V. It worked fine.

> Complicated, but the best I've thought of so far.  I've searched
> for 12V-output DC-to-DC converters with inputs of up to 10V
> max, but no dice yet.

Why not give my idea a run first? If it works, you're done. If not then you
can look at the more complicated solution. The only single advantage that your
original solution has is that it'll work when the vehicle is starting. But
with my proposal you can test without the gel cell and it'll work just as long
as you are not trying to start. That's the whole purpose of the gel cell: to
carry 12V input while the vehicle is starting.

I went this route because a gel cell + 1 steering diode is a lot less
compilicated than a buck boost regulator/doubler.

{Quote hidden}

The it should be a problem.

{Quote hidden}

I'm not sure about that. My 12V requirement was for the hard disk. So I
never tested the audio/video with 5V only. You can quite easily simply by
removing the 12V line from your PS and trying to boot. Since you have a 5V
only HD, it should boot fine. You can then test the audio (because the
video test will be instanteanous at boot. ;-)

{Quote hidden}

I find it to be exactly the opposite. a 12V LDO linear regulator is no problem.
Generating a multiamp 3.3V or 5V regulator from a 13-14V input is the
challenge. I'm using a variation of Russell's inspired switching regulator
from a year or so ago. I simplified it by using an opamp as the control
element. It give 5V output and boots my MB just fine.

I found that ATX added too many compiliations in terms of starting, persistant
5V, and the like. AT is a much simpler beast.


>
> > Also I'm using full sized 3.5" HD so I'm supplying 12V via a LDO regulator
> > and using a 7AHr 12V Gel cell as a micro UPS so that the system
> > doesn't reboot
> > when the start is activated.
>
> Hmmm... that's a good idea, but still space consuming.  One of
> the cars that this is going in has very, very limited space, so
> I'm being very picky here.

Well since it carries for such a limited time, I'm sure that a smaller
battery could do the job. 1.2AHr's are really small and probably could carry
the board for the 15-30 seconds that the main electrical system is in dropout.

It's an untested theory though.

>
> What did you do for the 5VSB signal?

5VSB?

BAJ

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'[EE]: Why does a PC need 12V?'
2002\09\01@163827 by Mircea Chiriciuc
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Usually it's used for HDD, and COM ports. The sound cards which are needing
12V are the ones with power stage on board.

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2002\09\02@043119 by Leonardo De Palo

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Hi,

for your reference, the PC104 board, that are PC compatibler are powered ad
only 5Volt.


Leo
----- Original Message -----
From: "Mircea Chiriciuc" <.....saschaKILLspamspam.....GO.RO>
To: <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
Sent: Sunday, September 01, 2002 10:29 PM
Subject: Re: [EE]: Why does a PC need 12V?


> Usually it's used for HDD, and COM ports. The sound cards which are
needing
> 12V are the ones with power stage on board.
>
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>
>

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2002\09\03@152220 by Pic Dude

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face
Byron A Jeff scribbled:

> Why not give my idea a run first? If it works, you're done. If
> not then you
> can look at the more complicated solution. The only single
> advantage that your
> original solution has is that it'll work when the vehicle is starting. But
> with my proposal you can test without the gel cell and it'll work
> just as long
> as you are not trying to start. That's the whole purpose of the
> gel cell: to
> carry 12V input while the vehicle is starting.
>
> I went this route because a gel cell + 1 steering diode is a lot less
> compilicated than a buck boost regulator/doubler.

I've been scared about the size of the batteries, but after a
bit of head-banging this weekend, I think I really like this
now.  If the car bettery ever gets disconnected, etc, I can
setup APM to gracefully shutdown the system.  However, I'll
need to have this supply 5V as well at that time.  Should not
be a problem though, since Linux can shutdown quite quickly.


> > What did you do for the 5VSB signal?
>
> 5VSB?

The ATX allegedly requires a delayed/pulsed 5V signal during
startup.  I've not traced down the exact tech specs/timing
yet, so I'll leave it at this for now, until I find out more.

Either way, I just realized that you did mention that you
were using an AT MB instead of the ATX, so this should not
be a concern to you.

Cheers,
-Neil.

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