Possible to customize Power Supply for external use ? 5

[mikeguava]

Hi,

I am trying to build a mini PC which has a very high power consumption ( ~400 - 450 Watts)
I cannot find any standard PSU that meet my size requirments and I am considering custumizing a Power Supply to have it sit externally - by lengthening all the cables ( 20 Pin etc. ). This would help the size of the unit as well as in terms of heat.

Question: Would the extending the cable length cause any problems - I am talking about 3m / 9feet in total length.

Thanks in advance for any input.

Mike

 

[edfair]

Provided that you supplied a GOOD frame ground connection between the supply and the cabinet and extended the cables with a wire size sufficient to eliminate a voltage drop over the distance I would suspect that you could do it with minimal expectation of problems.
There is always jitter in the power lines and that will be amplified by the longer length. It will also be somewhat dependent on the speed of the processor and the quality of the M/B.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[mikeguava]

Thanks a lot for your reply Ed. Gives me hope.
I am actually going to use an Intel P4 3.8GHZ on a Mini ITX Mobo ( 6.9"X6.9") - the motherboard obviously is tiny - not sure what this has done in terms of the quality of the motherboard...

Making an extra connection - grounding the PSU and the computer I would have not thought of. Going to buy some cables at the harware store now.

Cheers

Mike

 

[ceh4702]

Well they do make some fairly lightweight Power Supply boards for Mini-ITX but they usually top out at 200 Watt. They are fed by a Standard 110V AC to 12V DC converter. They sell them on many Mini-ITX type of sites:

http://www.idotpc.com/TheStore/Peripheral/case/Default_ps_itx.asp?Cate.id=14

This is just an example.

They make a 200w P4 SFF power supply that works off of 12VDC power, but I guess if you were smart enough you could wire 2 together like they do for servers.

Look for some car kits if this is an automobile computer. You need special parts to guard against variances in the electrical system:

http://www.idotpc.com/TheStore/Peripheral/_Spec.asp?Product.id=909&Cate.id=14&Product.status=green

This is a kind of dropout regulator.

400 watts is a lot of power for a small computer.

Just explain what you are trying to do maybe some people have some ideas. I think Via or someone may have a discussion group for Mini-ITX and smaller SFF type of computers.

If you do not like my post feel free to point out your opinion or my errors.

 

[mikeguava]

Thanks for your reply ceh4702!
I actually considered using 2 of the Dc2DC boards, but I am kind of hesitant about doing so - not sure how solid the current would be. 200Watts would be below of my draw.
the Mini-itx board is actually a fully blown 915G chipset motherboard - added with drives and a P4 3.8GHZ CPU and an ATI Radeon X850 PE I probably will need at least around 350 watts. The Videocard alone draws around 90 watts. I believe the CPU drwas around 150watts - not sure about the motherboard. Drives will be another 30watts.

I know that this sounds lots for a little computer but I am trying to enter a new miniture - high power territory here.

i tried going to the miniture discussion forums - but user there actually focusing on small power - small heat - kind of the opposite of what I am doing by going P4 and high end 3d.

Thanks a lot for your input

Mike

 

[garebo]

I wish they had pm's here as i would like to talk to Edfair more about the grounding thing. I do understand the length of the wiring being an issue, no prob with that.
But i dont quite understand the grounding issue. When one sits a mobo on a desktop and sets it up with power supply, hard drive, cdrom, etc, and tests all before putting in a case, its not grounded is it? And if it is grounded then isnt that all the grounding needed? Or is it just that when we do this on a test basis we only do it for a short period of time?

And are you telling mikeguava that he needs to ground the power supply to the case if he is going with an external power supply? How would he do that?
I hope these things would apply to mikeguava's situation as well, dont want to intrude here.

thanks



Good advice + great people = tek-tips

 

[edfair]

National electrical code requires that the case of equipment connected to the power grid be connected to an earth ground for protection from ground faults. That is why you will see a green/yellow striped wire conimg out of some power supplies and attaching to the case. Some don't have it because the wire is attached inside the power supply and the power supply mounting screws give the grounding. And some don't have it becaues the computer case is fully insulated. And some don't get grounded because the AC power line is the 2 wire type supplied before the 1950s.

Motherboards have a frame ground through the 0 volt line that theoretically attaches to the frame through the standoffs. But the ground pads are connected by traces and throughhole connectors that can fail.

Assuming that the PS fails with 120 applied to any of the voltage pins on the power supply connector. It zaps 0v connectors on the PS connector but leaves 120v on the M/B and standoffs. You now have 120v AC potential between the computer case and the power supply case. That is what the external ground wire protects from.

Hope you understand the concern.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[paparazi]

Interesting and do-able (if that's a word lol)
I think it would be a shame to deface a lovely new Antec or Enermax by cutting and joining the wiring so consider buying a 20pin extension harness (usually about 10inches long) and cutting and extending this instead.
At least this way your expensive PSU will be left untouched.
Martin

We like members to GIVE and not just TAKE.
Participate and help others.

 

[edfair]

Agreed. That way it can be put back into a case without a 9 foot loop of wire to get in the way. Would have mentioned that but just made an assumption that it was obvious.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[gus669]

Well what I did for my Mid-Tower ATX case is took an extra 300 watter I had laying around shorted the green and black wires on the ATX connector with a piece of 10 gauge wire. Electrical tape around the connector plugged it in and I can run all my lights and fans with that PSU.(heck I got 7 lighted fans, and 2 neon tubes, and a partridge in a pair tree in my case)

Then I use my 430watt Enermax to run the mobo and everything else. Now I did have to hack the connectors on the fans and lights and elongate them a bit. But it fits snuggly out of site behind my desk, and I use the switch on the back to turn it on or off.

Now I'm building a Micro-ATX. Tonight as a matter of fact. I know I am going to run out of power with only 230 watts. So what would be wrong with doing the same thing only I'll run the drives on the external and the mobo, CPU Fan, and cards off the 230watter. Alls I would have to do is put the 2 PSU's on the same surge protector, and then maybe use a remote control switch to turn them on or off. I proably wouldn't need to extend the PSU wiring more than the length of a server tower so it should be okay.

 

[edfair]

Would make one suggestion to the mix: Add one exhaust fan to run off the drive power supply. Were the M/B power supply to shut down the drives wouldn't overheat the cabinet. Probably overkill, but I like having all the bases covered.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[paparazi]

I would say in the absense of a power supply in the case that this will allow possible adaptation for a large extraction fan
All those large heat sources are going to need some major cooling.
Martin

We like members to GIVE and not just TAKE.
Participate and help others.

 

[mikeguava]

Get extension instead of cutting into a harness" thanks for the great advise - I had originlly planned on doing it - but in getting lost in details ( finding a power supply that has adjustable pots - so that I can raise the voltage to counteract current loss due to the longer cables )
I already ordered an extension cord...but was about o run off to the hardware store to get wires and very likely I could have cut into the harness in my enthusiasm to get this PSU done...but it certainly was on my mind to avoid it at one point

Do you guys thing I should get heavier gage wire or can I stay with the AWG 18 ?

Cheers

Mike

 

[mikeguava]

I would say in the absense of a power supply in the case that this will allow possible adaptation for a large extraction fan
All those large heat sources are going to need some major cooling."

Actually I am custom building and designing the case. It is going to be 8 inches by 8 inches by 8 inches. Nice and tiny. There will be a large an opening on the the top of the cube to let the hot air just rise out - with a nice silent fan helping the rising heat to move on.

BTW you guys rock. I am glad I found this forum - set to home from now on

Cheers


Mike

 

[paparazi]

Three meters isn't really that long, voltage drop will be minimal, but obviously going up one gauge will help keep this extremely low.
Earth/Ground wire needs to be heavier

Solder wires where you can

Martin


We like members to GIVE and not just TAKE.
Participate and help others.

 

[Frank4d]

You likely won't have any problem with the 12 volt output using 18 AWG wire over 10 feet. Most 12 volt devices run perfectly fine with only 10 or 10.5 volts.

And you won't have a problem with the 3.3 volt output to the MOBO. One of the wires (usually brown) is a sense wire that witll adjust the 3.3 volt output at the MOBO to be 3.3 volts no matter how long the wire is.

You may have a problem with the 5 volt output using long wire (but there is a workaround). Consider a device like a optical drive which uses 5 volts at 7 amps at the end of a 10 foot cable.

If the wire is 18 AWG, it will have a resistance of 0.0639 ohms (from a wire resistance calculator).

Using the formula R=E/I, the resistance for the device you are powering is 5 volts / 7 amps (for this example)... or 0.71428 ohms.

And the voltage delivered to the device you are powering is 5 volts X 0.71428 ohms / (0.0639 ohms + 0.71428 ohms) = 4.59 volts.

4.59 volts is considered marginal for many 5.0 volt devices. I would expect random resets, data errors, etc.

What I do for a work-around in projects at work is splice a larger wire (maybe 12 or 14 AWG) close to the PSU output... run the large wire for 10 feet or so... and then splice the wire to a smaller wire close to the connector at the end.

Your numbers may vary depending on the load you are powering, wire length, and wire size. You want to keep the 5 volt output at the load above 4.75 volts for reliable operation.

 

[edfair]

18 ga will be fine. And when you are cutting the extension stagger the cuts. If you cut them square you end up with a lump of splices. Might also wnat to do a line splice and use heat shrink tubing for insulation.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[mikeguava]

Again
this forum are awesome! Thanks so much guys for all this advise. I have been wasting a few days trying to find the "perfect" PSU that doesn't exist - now with all your help I finally feel comfortable enough to do what I really wanted to do.

So I am going to get some 14 AWG ( trying to keep the cable size somewhat under control) for the 5 volt outputs as well as for the ground.

Definetly going to solder and shrink tube the cord. Staggering the cuts - something I had not considered at all - very helpful.

Is there actually heat shring tubing large enought o get all the wires in? I'll go search online for it.

Has anyone messed around with the "pots" of the PSUs yet? I read that some Power supplies have adjustable wheels to raise the voltages of the rails. This is how I was thinking of adjusting the correct voltages at the end of the line.

Thanks a lot

Mike

 

[mainegeek]

Is there actually heat shring tubing large enought o get all the wires in? I'll go search online for it."

Can probably find this at Radio Shack. They also sell several sizes of plastic coil for wrapping and/or creating
wire harnesses with.

Any ROM drives going in this case? Just curious as to how
the bay(s) are configured for air flow and component clearance. I'm assuming vertically side mounted.

 

[edfair]

14 ga is overkill. You would be using something capable of 20 amps in open ait to a connector that is rated at 5a. The ground wire , however, needs to be large enough to carry everything the branch circuit can put out, which is usually 15 amp and would call for 16 minimum or 14 nominal.

Haven't done a survey of power supplies but think you may have a problem finding one with pots. They generally don't want anything that would encourage a user to open the box.



Ed Fair
Give the wrong symptoms, get the wrong solutions.