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Subject: [worldcruising] Re: PC Power Supplies
From: mark melvin (mark_melvin@XXX.XXX)
Date: Fri Dec 01 2000 - 10:57:51 EST
Roger,
PC's have a special power supply that takes in AC current and puts
our very carefully managed +/-12VDC, +/-5 VDC, and +3.3VDC on newer
"ATX" style motherboards (which are almost all of them made in the
past 3-4 years except for homebuilts. Older motherboards are "AT"
style). Fluctuations in the output voltages are fatal to CPUs and
hard drives, so building your own is _NOT_ a good idea, to do all the
proper rectification the parts would cost you more than an assembled
unit.
Most DC laptop adapters (car adapters) that run a laptop from the
cigarette lighter of a car take in 12VDC, turn it into 120VAC to feed
the laptop's built in AC->DC power supply. Horribly inefficient but
most people don't realize that. Some DC laptop adapters do bypass the
DC->AC and feed their DC to the the rectification side of the
laptop's internal supply, but those are rare and not as stable; the
laptops used with them tend to end up with lower battery life if used
long term because the rectification circuit is starting with a lower
DC voltage than the AC->DC supply would have generated.
The regular PC (not laptop) AC->DC power supply modules are easy and
cheap ($20) to replace with new AC->DC power supplies, but what
you're talking about is a DC->DC power supply.
Many companies make these, but you're not going to find them in
CompUSA or Radio Shack, you need an industrial supplier.
Here's a link to one of them
http://www.sinetic.com/Specs%20Brochure/SACE925SER.pdf
I have no connection to this company and don't know how their prices
compare to their competitors, but it will give you a starting point.
I'm planning to do the same thing one day.
Mark
--- In worldcruising@XXX.XXX> wrote:
> Jay...\
> Am I to understand that there is no AC on the output side of a
desktop PC
> supply. What I am trying to do is feed the PC directly from the
boat DC
> supply, without going through an inversion stage to get to AC. Is
that
> possible?
>
> Thanks
> Roger
> -----Original Message-----
> From: Jay Prince [mailto:JayPrince2@XXX.XXX]
> Sent: Saturday, November 18, 2000 9:51 PM
> To: worldcruising@XXX.XXX
> Subject: Re: [worldcruising] PC Power Supplies
>
>
>
> PCs run a switching power supply that provides +12V and +/-5V and
> possibly -12V DC. You can often get commodity (ie: poor quality)
> supplies from PCs retail places. These power supplies draw a lot
of
> air in to keep them cool and probably won't last very long in a
> marine environment. (Course I'm new to the effects of a marine
> environment on electronics.)
>
> Most laptops have a smaller single voltage power supply. Mine,
for
> instance, is 24 volts and inside the laptop is switching
equipment to
> generate the voltages the laptop wants. You can easily coat or
cover
> the self contained (no fan) small power supplies that come with
most
> laptops.
>
> If you want to, you can find smaller switching power supplies from
> Asian suppliers-- not "PC standard", so you'll have to fabricate
an
> adapter to the PC standard power connector on your PCs
motherboard.
> You could do this and possibly have powersupplies that don't need
> active cooling.
>
> Anyway, there is a company that sells high quality power supplies-
> check computer shopper. You should find lots of sources there.
>
> Jay
>
>
>
> >This is great if you want to run a laptop. I want to convert a
> >desktop. This will require replacing the internal power supply
and
> >using an external LCD screen. Does anyone have a source for
> >replacement internal power supplies?
> >
> >Thanks
> >Roger
>
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