You're totally barking up the wrong tree.

PCs are sensitive to power supply problems. It would be risky as hell to build your own off of a car's noisy 12V off homemade regs at these current levels.

Additionally linear regs are gonna be not only inefficient but hot and require huge heatsinks. And LM317 in a TO220 pkg won't even have the current OR heat dissipation rating your need, and no you can't put several in parallel to improve the ratings. You could use a bipolar power transistor as a follower but there are are more issues that come with that and it does nothing to improve the efficiency anyways.

You need a 110V inverter- end of story.

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I thought what I'd do was I'd pretend I was one of those deaf-mutes.

 

Actually not, what you want is a PC power supply that's switchmode, accepts 12V DC from a car battery, and generates the require motherboard voltages directly. Generating 110V from 12V first is inefficient, and 12V PC power supplies are available - but probably MORE expensive than a mains inverter.

__________________
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PC power supplies can actually run off DC if the voltage is equal to the peak voltage of the AC they are supposed to run on. This is because most PC power supplies rectify the mains voltage into DC before they do their SMPS magic on it.

So all you really need is a high current DC-DC boost converter circuit that will boost your 12v up to say 180v. Regulation doesn't need to be perfect as long as you make sure there are no damaging spikes.

You're still messing with SMPS circuits but technically you are "inverting" nothing.

And since its DC and its only one voltage the complexity is greatly reduced. the PC PSU does most of the work for you.

 

As Darfk has mentioned in his first post, there is no car involved- only a 12V battery.
I feel, converting 12V to 120V or 230V depending on the country concerned, the efficiency works out around 80%. then the PC psu( again SMPS) has its own efficicency. thus overall losses are more.

If a single DC -DC converter is designed with charging facility for the battery( which itself can float across with charge controll element, it will work ot almost at the same price or a 10% extra.
Now the overall efficiency will be better. It is imperative that +12 and +5 also need to be produced from the same Converter as the battery voltage may varry between 10 to 13.8V.

Finally Darfk will have to use a converter- call it inverter or any other name..

Telecom installations follow this method of course at 50V DC.
The computer terminals of electronic exchanges used to be supplied with 50V DC workability.

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Regards,
Sarma.

 

This is very interesting Glyph, I will have to look into it!

By the way, thanks everyone.
I have considered almost every reply.

 

Have you considered google?, in-car MP3 players based on computers were really common a few years ago, here's one, complete with homemade direct from 12V PSU.
http://www.bobblick.com/techref/proj...p3/yammp3.html

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

Every PC SMPS that I have disassembled used a small transformer from the 60 Hz AC line to provide the startup bias voltages. This will burn with a DC input.

 

Must admit I don't recall EVER seeing a conventional mains transformer in a PC power supply?. The startup is usually done by a high value resistor, which commonly goes O/C, I've replaced quite a few over the years.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

I think I have seen one PC power supply with a small low frequency transformer but it was very old. I don't think any modern PC power supplies use this kind of transformer anymore.

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Just a thought, is -5V (RAM & very old PROMs) and -12V (RS232) even used on modern motherboards anymore?
PS most standard ATX motherboards might be pretty unreliable in a mobile (bumpy) environment, PCI cards will probably come loose.
Mini ITX car enclosures are available

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Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com

 

A lot of early PC power supplies had a small mains transformer to power the start-up circuitry, used to be a problem to get replacements.