Joining the rails on a Dell DA-2 together, this alright?

PSUs: The source of DC power for all components in the PC & often a big noise source.

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jonj678
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Joining the rails on a Dell DA-2 together, this alright?

Post by jonj678 » Mon Mar 08, 2010 8:08 pm

The Dell DA-2 is mentioned in various places on these boards, the main point is that it provides three wires at 12V, three wires at ground, and offers six amps on each of these three rails.

The approach used in a thread on here was to connect two of these lines to a 150W pico-psu and the other to the motherboard's 4 pin socket.

I would like to solder the three 12V lines together, likewise the three 0V lines, and treat this as a single 12V, 18A source from which I take the 4 pin cable and the pico psu.

It's mostly convenience, but also to reassure myself that if the processor tries to draw more than 6A at 12V, there will be more available. I suspect the two approaches are electrically identical as the pico passes the 12V through unchanged, but I'm unsure enough for it to be worth a post.

Cheers

p.s. is there any sense to putting capacitors between the 12V and ground lines in an attempt to smooth out the current before it gets to the components? I'm a little worried that the Dell brick will output 12V with a lot of noise even if it is within the +/-5V required by the atx spec.

Jon

ces
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Post by ces » Mon Mar 08, 2010 8:46 pm

Let me add something.

How about taking two Pico-PSUs and hooking them up in parallel... and using two separate AC to DC sources to power them.

What kind of trouble can that stir up?

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Post by electrodacus » Mon Mar 08, 2010 9:05 pm

ces wrote:How about taking two Pico-PSUs and hooking them up in parallel... and using two separate AC to DC sources to power them.
It will work connected in parallel but you need to connect 20 wires that is a lot of soldering :).
You can use less wires if you know what are you doing. Minimum will be the +12V output from PicoPSU then 5V ,Power on and of course Ground so a minimum of 4 wires. I considered that the 5VSB , 3.3V and -12V don't need more than one PicoPSU can deliver.
I will sell in the future a kit with two of my PSU connected in parallel and a 220W brick (just got the brick today and did a small review Link ).

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Re: Joining the rails on a Dell DA-2 together, this alright?

Post by Vicotnik » Mon Mar 08, 2010 9:29 pm

jonj678 wrote:I would like to solder the three 12V lines together, likewise the three 0V lines, and treat this as a single 12V, 18A source from which I take the 4 pin cable and the pico psu.
That's how I do it. Had a little problem with the +12v rail dropping a bit low at first when I used the stock barrel connector and didn't feed the 4pin directly from the brick. Works very nice now though.
jonj678 wrote:p.s. is there any sense to putting capacitors between the 12V and ground lines in an attempt to smooth out the current before it gets to the components? I'm a little worried that the Dell brick will output 12V with a lot of noise even if it is within the +/-5V required by the atx spec.
The DA-2 seems very sturdy, but more caps cannot hurt I guess. I don't know enough about this to say for sure, but I think it would be a bit overkill.

jonj678
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Post by jonj678 » Tue Mar 09, 2010 2:06 am

Thank you, that's very useful.

Continuing in the same sort of vein, were I to buy two DA-2 supplies, plug them both in, and wire all six ground lines to each other, and likewise all six 12V lines, will it all work out well or will the adapters object?

I can't help feeling using two of them (for 36A @ 12V without noise) in parallel would be more reliable if they were removed from their cases and connected together earlier on in the ac to dc conversion circuitry. I'm looking for a book on switching power converters which I get on well with so I should be better informed soon, at present I'd be blindly guessing where they should be wired together, and that's probably not sensible.

Cheers

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Post by ryboto » Tue Mar 09, 2010 8:33 am

I'm confused...why would you want to rely on the PicoPSU? It sounds like you're going to try to use a lot of power relative to what the Pico really supports. The whole point of splitting the "rails" is to ensure the Pico isn't overloaded with current.

As for the "rails", if you look a the board, all 3 power wires come from the same point/feed. So, there's 1 single rail. Splitting up where the wires go doesn't cut the current by a specific amount, it just means you might have 1 wire to carry current to something vs 3.

I was thinking about using two DA/2's, but the longer I live with a power brick, the more I find it annoying. First I had to shorten the lines, and use a screw terminal to make sure I wasn't losing 0.7v like I was when I used a mutliated 24-pin adapter. Second, I have to keep the thing connected even in transport, because disconnecting the screw terminals is a pain. So in the end, it isn't convenient. I only save 1'' in height and width using the modified NSK1300 vs a slightly larger microatx case that can fit a full size psu AND tower heatsink. Once I have the money, I'll probably sell the Pico/brick.

It was a fun DIY project, but really reduces portability/upgrade options.

jonj678
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Post by jonj678 » Tue Mar 09, 2010 9:11 am

The attraction of the pico is it's size and the lack of fans. A mini-itx case which doesn't have to fit a psu can be significantly smaller than one which does need to. Plus I want to learn some more about computer electronics and this seems a fair starting point.

Happy to hear the wires are joined at the PCB as it means connecting them back together at the other end can't go wrong.

With care it may be possible to fit the brick inside the case, I'm not sure about this yet. Depends on a few things. Not found a connector I like the look of, but it seems likely that I'll cut the end off the Dell and put one of my own choosing on, so avoiding the severe voltage drop you've noticed.

Any ideas on whether using two of them in parallel would be viable?

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Post by ryboto » Tue Mar 09, 2010 10:50 am

jonj678 wrote:The attraction of the pico is it's size and the lack of fans. A mini-itx case which doesn't have to fit a psu can be significantly smaller than one which does need to. Plus I want to learn some more about computer electronics and this seems a fair starting point.

Happy to hear the wires are joined at the PCB as it means connecting them back together at the other end can't go wrong.

With care it may be possible to fit the brick inside the case, I'm not sure about this yet. Depends on a few things. Not found a connector I like the look of, but it seems likely that I'll cut the end off the Dell and put one of my own choosing on, so avoiding the severe voltage drop you've noticed.

Any ideas on whether using two of them in parallel would be viable?


You're going to use two bricks with two Pico's? Should work fine. How would you do it? Splice all of the grounds/12v's together? A

As for a small itx case, silverstones sg07 can fit a full size atx PSU and tower heatsink. Issue I have with a lot of mitx cases is their insistence on putting the PSU above the CPU socket, reducing cooling options for the CPU.

The fanless argument is hard to keep up too...if you're going to use two bricks, you've basically created a PSU the size of an atx, and you can get fanless ATX psu's.

Though, at the same time, I too was drawn to the Pico. In hindsight, it's not a very elegant solution, but it was/is fun to work with.

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Post by jonj678 » Tue Mar 09, 2010 8:01 pm

Hopefully one brick will be sufficient, but if not I'd want to use two bricks with one pico.

One mains cord running to both bricks, then splicing all six grounds together and all six 12V also together. Then run cpu/gpu from this 12V rail and use a pico to convert the 12V into the 3.3, 5V etc which the board needs.

The concern is that since the bricks will be different they'll have different ideas about what 12V is. leading to current flowing back into one of them. I imagine the pcb does the conversion in a couple of steps, mains ac down to 14V or so then produces 12V regulated from this. If so, then it should be possible to run wires between the two boards between the two stages, forcing the voltage before regulation to be exactly equal should help keep the final output close together.

You're quire right that fanless psu's exist, I think this layout will be more flexible. I can't find a case I like so am probably making one.

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Post by ryboto » Wed Mar 10, 2010 5:37 am

jonj678 wrote: You're quire right that fanless psu's exist, I think this layout will be more flexible. I can't find a case I like so am probably making one.
If I worked at a machine shop, I'd do the same. As for splicing the two bricks together, personally, I'd just feed the video card/atx-4 pin 12v with one, and feed the Pico with the other. Don't solder all of them together and then solder another connection, just go straight to the GPU/board. It wouldn't matter then if the bricks have slightly different 12v.

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Post by ces » Wed Mar 10, 2010 6:51 am

ryboto wrote:
jonj678 wrote: As for a small itx case, silverstones sg07 can fit a full size atx PSU and tower heatsink.
Are you sure about that? How tall of a tower heatsink can you fit into that case?

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Post by ryboto » Wed Mar 10, 2010 8:52 am

ces wrote:
ryboto wrote:
jonj678 wrote: As for a small itx case, silverstones sg07 can fit a full size atx PSU and tower heatsink.
Are you sure about that? How tall of a tower heatsink can you fit into that case?
Not sure, but it looks big enough for a tower. Still, I don't think they're going to sell it with the option for a standard atx psu, looks like you'll be forced to use their "custom" 600W unit. Lan Gear has plans to release one that does exactly what you quoted me as saying, check it out..
http://www.lan-gear.com/miniITX_spec_mom.php

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