mjohnson

How come it's so expensive to build a DC-DC power supply that can only provide power to a small range of CPUs and to a limited peripherial configuration, while an inverter can power just about any PC configuration for a lot less money?
I could understand a DC-DC PS costing little more ($10-$50) than an inverter, but it seems that these PS's cost about $100+ more than inverters. Why such a discrepency?

(ps: just making an observation -- I know nothing of electronics so I'm oblivious to the finer details of building these devices...)

(pps: I'd be interested in getting the MP3 OnDemand PS product but it's too expensive, I'd rather go with an inverter and deal with the noise...)

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LowLife

They really aren't that expensive... The one I use you can get from Arise for $79. It has all the outputs you need for an AT motherboard (+/-5v & +/-12v). Surely if you bought an inverter AND a normal computer power supply, aren't you pretty close to $79? Plus, this thing is so much smaller and compact... Only 5"x2"x3"... Why would *anyone* use an inverter?

LowLife

PS I have a link to Arise on my page, if you don't know which one I'm talking about...
<a href="http://www.sunflower.com/~jahelka/MobileMP3/">My Mobile MP3</a>

tenfoot

The PSU i'm building won't cost me much more than £20 (about $30 to those of you over the pond)

mjohnson

Will either of you two's PS power a system that includes:

K6 2-266
VGA LCD
SoundCard
2 hardrives (or 1 hardrive and a zipdrive)
(plus a CDROM - *brownie points*)

LowLife

mjohnson: I don't know if it would or not. I'm pretty confident that it would work great! You need to add up the current that will be drawn at each voltage and see if it is below the supplied current of the power supply. For example, look on the top of your CD-Rom and see what current it draws at +5v and +12v. Do that for the rest of your components and see what you get. From what you listed, I think it will work fine! I don't however, know what power requirements that VGA LCD screen has...
The ACE-865V supplies 6A at +5v, 2A at +12v, 0.3A at -5v, and 0.5A at -12v. You probably needn't be concerned about the negative voltages, they are primarily only used on some screwey vid cards, and for some devices that you plug into your serial port.

tenfoot: I realize that it is way cheap to build your own power supply. The reason I didn't, is because I figure I'm going to be plugging a whole bunch of expensive parts into it (ie. motherboard, hard drive, and whatever else you use.). I would rather have a supply that has all of the safety and protection circuts built in to it. To me its worth the extra money to protect my expensive parts! Also, does the supply you are building have -12v and -5v? This one does...

Just my 2 cent,
LowLife

sj

There is on simple answer: demand.
If there would be more demand, series and competition of building PS would higher and prices lower.
Just pure economics.

mda

Tenfoot, I'm in the UK too.
Will your PSU support -5 & -12 volts?
I guess not by the cost, but would you be able to add these features?

twins22

mjohnson, the other part of the cost is the components. While you can get some manufactures to send you "samples" of their product, others do not. Some parts you have to buy via the internet and pay shipping, handling, minimum orders, etc. Total truth is sj said "supply and demand." If more competition enters the scene then the price will go down. By the way, I am working on a home based DC-DC solution. I'll post details when it's finished and verified working!

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tenfoot

I don't know about what the PSU will power cos I haven't build it yet. The components are on order...

It's based on the ones at www.jarcom.com/inmotion and
www.mp3uk.freeserve.co.uk

twins22

My design is based on inmotion's PSU also. I have included the ability to produce +5, +12, -12, -5, and 3.3VDC, just in case I scrap the AT motherboard and go with an ATX. The MAX chips are free from www.maxim-ic.com, and I got the inductors/coils/chokes from Coiltronics as sample items as well. Some more inductors are coming from Gowanda. The rest of the components have totaled a little more than $35 for 2 units ($17.50 each. Some parts I've had lying around or friends have scrounged. All in all, I'd say that $25-$30 would be a close estimate for a home built PSU based on the inmotion design.

inmytree

In reply to lowlife's comment of "why would *anyone* use an inverter"

Why the hell would anyone use DC-DC.. inverters are cheap as ****.. and as for power supplies.. they cost like $5.. with an inverter you don't have to **** with anything.. you just plug it in and go.. if you wanna remove it and use it in the house.. no problems.. why get DC-DC and run into problems about accessories not working.. at least with an inverter everything will work..

airedale

I totally agree with you "inmytree" I think that they are much easier to use, plus if you have a place to hide them, why not, it saves a lot of time money and trouble!

snakebite

in response to inmytree, Not all countries use 110v, in Australia we have 240v. That means you are stepping 12VDC up to 240VAC then from 240VAC back to 12VDC etc.An inverter over here for this sort of application costs **** loads of money and they are very lossy, so I say **** inverters build (or buy) DC-DC.
Also, I use a car battery charger to to run my player on the rare occasion that it is out of the car

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tseland

Most power supplies (at least mine) has a swich that lets you choose between 230 or 115V, so you can use an american inverter.

I live in Norway (230V)

mjohnson

This is kind off tangent to what we have been talking about but what's the feasiblity of using a solar-powered power supply?

Presumably, you'd have a back-up battery to provide power when there was no sun.

You could let your car bake all day in the sun while you're at work and (re)charge up the battery.

But I'm sure going the solar-power route would be some major bucks....

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