External 12v DC power brick

Headcase_Fargone

Limp Gawd
Joined
Mar 25, 2010
Messages
284
I'm putting together a low power home server (emphasis on the low power) and I've reached a bit of a dilemma. I chose the Intel D945GSEJT Atom board specifically because of its mobile chipset.

The trouble is, the only internal power connector on the board is a 4pin 12v connector. That's right, this board has no 20 or 20+4 pin ATX connector on it. That means the power supply won't power up.

That leaves me two options. I can get try to get creative, as this guy did, or I can use a 12v AC-DC adapter to power the board.

My concern with the power adapter is that it's only capable of supplying 60w. I'll have two 3.5" Samsung green drives (5400 rpm I believe) running with this thing as well as a CompactFlash adapter where the OS is stored.

Does anyone think this 60w brick would supply enough power for all of that? Or do I need to break out the soldering iron and try my luck?
 

Elledan

[H]ard|DCer of the Month - April 2010
Joined
Oct 18, 2001
Messages
15,913
Few PSUs are okay with a heavily cross-loaded configuration (12V-only). Quite a few go horribly out of spec and/or drop to abysmal efficiencies.

What is the official TDP for the mainboard, CPU & RAM combined? The HDDs will be about 10-15 Watt each (5,400 rpm, so closer to 10, but check the official ratings). You got about 30 Watt for the mainboard, CPU and RAM, basically.

On a sidenote, I'm positive I have seen 90 Watt PSUs as well used with laptops and such. Not sure about a 12V variety, though. They may have been 19V adapters as noted in that forum thread you linked.

Edit: just saw that shop you linked also has an 8.5A adapter, for 102W output: http://www.mini-box.com/110w-12v-8-5A-AC-DC-Power-Adapter
 

Headcase_Fargone

Limp Gawd
Joined
Mar 25, 2010
Messages
284
This here's the board. It's an Atom with a mobile chipset that takes a single SO-DIMM for memory. TDP is very low. I think it maxes out around 12W, which was the main point of getting this particular board.

@Elledan, the 8.5A adapter concerns me since the one recommended is 60W and 5A. Even if the connector fit, wouldn't I run the risk of frying the board?

As for HDDs being 10-15W each, what about on spin-up during boot? I've read that they consume a much greater amount during that time, which is my main concern.

Someone I know suggested I simply jumper the case's power switch pins straight into the green and black wire pins on the Mini-ATX's 20pin connector. Would that actually work for turning it on and off?
 

Elledan

[H]ard|DCer of the Month - April 2010
Joined
Oct 18, 2001
Messages
15,913
With PSUs it's the same story: get the voltage right and make sure it can provide at least enough amperes. The ampere rating is just what it can provide. The hardware won't suddenly pull more than it needs, basically ;)

HDD spin-up takes a bit more power, but unless you have a lot of HDDs and/or are short on your power budget, I wouldn't worry about it too much.

An ATX PSU needs a constant link between the green wire and ground to be 'on'. Case switches are generally momentary switches and thus won't suffice.
 
Joined
Mar 1, 2005
Messages
3,094
HDD's can pull upto +12V@3A during start of spin-up, that is 36W. This is a short, under 2-sec transient.
 

Headcase_Fargone

Limp Gawd
Joined
Mar 25, 2010
Messages
284
HDD's can pull upto +12V@3A during start of spin-up, that is 36W. This is a short, under 2-sec transient.

70W is what I seem to remember reading for two 3.5" HDDs so I guess the 60W power brick is out. And doesn't sound like wiring the pins directly to the power switch will work either, so not sure what I'm going o do now.

I really don't understand why this board has an internal 12v connector if there aren't any PSUs out there capable of powering it up.

Anyone have any ideas?
 
Joined
Mar 1, 2005
Messages
3,094
70W is what I seem to remember reading for two 3.5" HDDs so I guess the 60W power brick is out. And doesn't sound like wiring the pins directly to the power switch will work either, so not sure what I'm going o do now.

I really don't understand why this board has an internal 12v connector if there aren't any PSUs out there capable of powering it up.

Anyone have any ideas?
Spin-up produces only a short transient, you do not need a PSU rated as high as short transients, the 60W brick "might" be ok, if 60W is enough to meet the max sustained requirements & it is designed to handle these spikes & transients. If the manufacturer recommends it , it "should" be fine.
 

Red Squirrel

[H]F Junkie
Joined
Nov 29, 2009
Messages
9,211
Don't hard drives also need a 5 volt rail? You'll probably want a separate power supply for the hard drives, just need to turn it on ahead of time or jurry rig something.
 

Zero82z

Fully [H]
Joined
Jan 20, 2004
Messages
27,897
That motherboard has a built-in VRM to produce 3.3V and 5V for the SATA power connector. All you need to do is feed it with a +12V source and it will take care of the rest. No need for secondary PSUs or anything like that.
 

BillParrish

Supreme [H]ardness
Joined
Aug 25, 2006
Messages
7,520
In my worthless opinion, in the same situation I would go for the higher powered Brick, Elledan has the right idea. If the 60W was recommended for the board by the manuf (acutally I found it in the Intel spec - BUT before the spec was updated ) and you intended to hang a few extras off of it And Zeor82z observation is important too, I take the onboard conversion into account below.

Lets run the numbers.

DRIVES:
As example (as I cannot be sure these are exact same drives but we will use their numbers as I highly suspect all Samsung Green drives will be about this draw and this is the 2TB drive which is likely the worst case for current draw)

http://www.samsung.com/global/business/hdd/productmodel.do?type=94&subtype=98&model_cd=513

Power Requirements
Power Requirements Voltage +5V±5%
Spin-up Current (Max.) 2.0A

Seek (typical) 7.1W
Read/Write (typical) 6.2W
Idle (typical) 5.4W
Standby (typical) 1W
Sleep (typical) 1W

So spin up for 1 drive is about 5V x 2A = 10Watts - Max and since the board has to make the +5 from the +12 lets assume that conversion is 75% efficient (a guess and low balled for extra margin) so 10W / .75 = 13.3 Watts of +12 for one drive, so 26.6 W for two and just because, make that 30W of spin up power for 2 drives.

BOARD:
http://downloadmirror.intel.com/17597/eng/D945GSEJT_SpecUpdate05.pdf <---- Spec update (power requirements where changed)
http://downloadmirror.intel.com/17597/eng/D945GSEJT_TechProdSpec.pdf <-------- original board spec.

You have to read secion 2.7 carefully, it gives the board power requirment first as a totally loaded system with a bunch of stuff, basically a complete system including NIC, 2 HD's, 2GB memory, Flash drive, CD etc. etc. and that is the total power requirement and then it subtracts the addons to give the board itself needing about 12 watts.

So for a loaded system Intel is calculating 55.44 watts (and we have HD's included)

Likely this is where the 60W supply recommendation came from. (edit: It is, look in the original spec. Interesting that while the spec update increased the loaded power requirement from the 42W in the original spec to 55.4W in the update, the 60W recommendation was not changed. Shaving it a bit close IMO. /shrug )

----------------------------------------------------

What if we subtracted the HD power from the Intel numbers and put in our 30W startup number calculated above (BTW this is as mentioned in a post above a short term draw and likely a power supply rated at what would look insufficient, more than likely could supply the start up current without damage etc. but lets go way overboard on the numbers so that we never have to worry about it. )

Intel gave the 2 HD's 9.84 Watts of power (obvisously not the start up draw) so take that away from the 55.44 Watts leaving 45.6 Watts to which we add our 2 drive start up draw of estimated 30W and we get 75.6W of peak power draw.

-----------
IMO the 60W might do (as the cpu is not fully loaded during system post ) but concerns about having the drives wake from deep sleep where they would have to spin up and the whole board go to some close to full power mode makes it iffy. I also do not like it that at high system/cpu load you are using a substancial percentage of the power supply capacity with not a lot of extra reserve. Working it hard in plain english.

So if me I would go with the 102W adapter. As Elledan stated, the board will only pull what it needs leaving the "overhead" as reserve. This places less stress on the power supply. Like the engine in your car, it will do 102 MPH even tho you cruise at 75 and you burn less gas at 75. And running it at 102+MPH for any great length of time will likely result in engine parts all over the road while it will do 75 for almost unlimited time and a much much less chance of a catastrophic failure.

-----------------------------------------------------------------------

Buy the 102W adapter and forgetaboutit, you can hang just about anything you want off that little feller with plenty of reserve, low stress on the power supply components which usually translates to long life.

OR

I am completely wrong.
 
Last edited:

Headcase_Fargone

Limp Gawd
Joined
Mar 25, 2010
Messages
284
Well it looks like I'll be ordering a 102w brick then if no one can come up with a reason not to.

Thanks much for the well thought-out responses, all. Love this forum for this very reason.
 

Elledan

[H]ard|DCer of the Month - April 2010
Joined
Oct 18, 2001
Messages
15,913
You're most welcome, Headcase_Fargone :) Let us know how it works out for you.
 

Headcase_Fargone

Limp Gawd
Joined
Mar 25, 2010
Messages
284
According to a support guy at Mini-Box.com this board is only capable of supplying up to 60W through its onboard circuitry. So it looks like that 8.2a brick won't do me any good.

I am seeing on this blog here that someone else tried shorting the pins on his Mini ITX connector and it worked "somewhat." He also says he's running two 3.5" HDDs off the 60w brick though, so now I don't know what to think.
 
Top