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Old 11-09-2012, 04:14 AM   #1
Ulysses_
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Powerful AC adaptor/s for a DC-powered system


A DC-powered system for use off-grid will occasionally be used at grid-connected locations too. But fanless AC to DC adapters at the psu's rated 270W peak (or higher) are hard to find. The closest I have found so far is this one:

http://www.mini-box.com.au/12v16A%20...20adapter.html

While the system is very unlikely to ever reach 270W, it would still be nice to have an adapter at least as powerful as the psu for future system extensions.

Does such an adapter exist?

What if I buy two smaller adapters and put them in parallel? Or in series?

Last edited by Ulysses_; 11-09-2012 at 04:21 AM.
 
Old 11-09-2012, 04:35 AM   #2
pixellany
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In general, I would assume that a switching AC-DC convertor would NOT work when wired in parallel. (If you put them in series, you'd have the wrong voltage.)

Can you give a more complete description of the equipment, how it is setup for DC-only, etc.?
 
Old 11-09-2012, 05:35 AM   #3
cascade9
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275watts peak, not 270. You shouldnt be going over 220 watts with that PSU. *edit- and you wont be going over 100-125 watts real usage from everything I know. Getting a 275 watt AC-DC converter 'just in case' would be pretty much pointless.

Yes, they exist.

http://www.alibaba.com/product-gs/60..._360w_12v.html

You wont be getting one from there-

Quote:
Minimum Order Quantity: 100 Piece/Pieces sample order is welcomed
Supply Ability: 10,000 Piece/Pieces per Day Fast Delivery
Not something I would suggest getting, even if you had the option.

Also you would do better to get a 230v AC-> 24v not 12v with that PSU.

Quote:
Originally Posted by pixellany View Post
Can you give a more complete description of the equipment, how it is setup for DC-only, etc.?
Ulysses_ doesnt know what hardware is going to be run. If you want to dig though this thread, its where I've given a few suggestions-

http://www.linuxquestions.org/questi...sd-4175433532/

Last edited by cascade9; 11-09-2012 at 05:36 AM.
 
Old 11-09-2012, 05:39 AM   #4
Ulysses_
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It's meant for a 24V battery when off-grid, that is the only absolute constraint.

The recommended psu accepts anything from 6V to 34V DC input though, so two 12V adapters in series are just as acceptable as one powerful 12V adapter. Or one powerful 24V adapter.

Do I put two adapters in series then? What happens when they get old?

Maybe buy one adapter now, and a second one whenever the need arises?

Last edited by Ulysses_; 11-09-2012 at 06:05 AM.
 
Old 11-09-2012, 02:50 PM   #5
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I have a good basic i7-3770 that I use on a kill-a-watt meter. I have never seen it go over 145W and that is the total of switch,router, Ooma, computer, audio system and monitor.

There was a site that was dedicated to DC home products. Everything from toasters to toothbrushs. Might try to see if they have products for your system. Even the best power inverters use a lot of power. I have a number of them and the best one I have is a tripp lite 3Kw model that shuts down on low use.

Last edited by jefro; 11-09-2012 at 02:52 PM.
 
Old 11-09-2012, 03:05 PM   #6
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People locally to you sell automation stuff - plcs, & industrial pcs.

A phone call or two in that direction might save you a lot of hassle.
 
Old 11-09-2012, 03:09 PM   #7
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My inverter is a 3kW one too. It draws 10W for itself when in economy mode with a distorted sinewave. Or 15W in perfect sinewave mode. Plus the losses due to the 93% efficiency, probably another 8W with a 100W load. Definitely very wasteful, a DC psu is essential.
 
Old 11-09-2012, 07:25 PM   #8
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See if you can find those DC home or some such named web sites.

There is some youtube posts on how to convert a common psu. I can't access them now but you might look at it.

At the price of this stuff you can buy an electric line. http://www.powerstream.com/DC_PC.htm

For home, I have never had a pure sine wave like at work. The tripp lite shuts down to almost nothing but isn't that good for electronic systems. It is the stepped sine output.

Last edited by jefro; 11-09-2012 at 07:27 PM.
 
Old 11-10-2012, 05:29 AM   #9
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It says 70% typical efficiency at that site, at 24V DC full load with the 300W psu. A bit of a surprise this efficiency.

Whereas the 220-275W pico psu's spec says >93% at 50% load. What is going on here?

Last edited by Ulysses_; 11-10-2012 at 05:41 AM.
 
Old 11-10-2012, 09:24 AM   #10
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It's all in the internal design.
Given that the drive current is comparatively steady, you would expect the efficiency to rise as power output rises, but this isn't always the case.

Remember there are numerous supplies being fed from the one switching Tx. So to prevent overvoltage, the windings can't provide too much extra voltage (Otherwise you could get 18V on your 12V Line, or 7V on your 5V line). So there can come a stage when you are creating extra power (For, e.g. the 5V line) but not using it; so the efficiency goes down.

Inductors like anything tuned component have a 'sweet spot' efficiency wise, and this also affects efficiency.
 
Old 11-10-2012, 03:11 PM   #11
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Industrial stuff is way behind. They'd rather the thing work over it using less power. I guess there could also be some calculation issue between source and output that messes up the equation.

There are some web pages also on how to modify a standard psu that might work.

The other solution is to get a few power supplies that are 24V to the voltages and current you need.
 
Old 11-11-2012, 03:38 AM   #12
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Quote:
Originally Posted by jefro View Post
Industrial stuff is way behind. They'd rather the thing work over it using less power. I guess there could also be some calculation issue between source and output that messes up the equation.

There are some web pages also on how to modify a standard psu that might work.

The other solution is to get a few power supplies that are 24V to the voltages and current you need.
There is a calculation between source and output on Linear supplies, which are grossly inefficient.
In Switch mode, not really - it's the inductor that makes sure of that. I would not be optimistic about modifying a standard psu to run off 24V, or finding reasonably priced equivalents. 5V 50A would be rare and never cheap. Ditto 12V 35-40A.
 
  


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