Re: [OT] ATX-PSU and amperage on connectors...

Hello Douglas,

Am 2008-02-27 20:52:19, schrieb Douglas A. Tutty:
Here are the wire sizes according to my copy of the 2002 Canadian
Electrical cord (still in force), table 12 "Allowable Ampacity of
Flexible Cord and Equipment Wire (Based on Ambient Temperature of 30C"
Note that cables of 4 or more wires (e.g. if you shrink-wrap 4 drive
wires together) would be 80%.

AWG Amp
===========
26 1
24 2
22 3
20 4
18 6
16 8
14 17

This AWG thing is nice, since I don not know I in Europe...
I am counting in mm²

Elecrically, these would be fine with 26 or 24 AWG without overheating
the insulation. However, you don't provide inrush current requirements

Since I do not know them, I know only, what is written on the Drives.

of the device. Too much resistance in the wire could end up
undervoltaging the drive motors.

I know.

Put the two most power-hungry devices on the same power cable: Teac-CDR
and the AsusTek DVD for a total of 3.3A each of 5v and 12v, and you
would need 20 AWG wire. However, as I said in a previous entry, for
moveable wire, the minimum (unless you went with some high-tech
mechanically supported wire) would be 18 AWG (which is what my PSU's
happen to use).

It seems, that the 3 cables (3 HDD connector on each cable)
on my 600W PSU has cables of 0.5mm²

one of my problems is, that most DC-DC-Step-Down-regulators do not
support High-Voltage entry and most are limited to 14-16 Vin.

This mean, I need some High-Power (>=25A) DC-DC Step-Down regulators to
get 12Vout from 18-30Vin and then I can build the +5V and +3.3V from it.


And there will go your efficiency. You could probably get 70-80% with
one DC-DC converter but if you do two in a row, there's two places for
waste. If you have to go that route, its probably no more waste to use
a true-sine-wave inverter to turn your 24VDC to 110VAC and then use a
normal AC PSU.

Not realy right, since according to ATX12V the AC PSU should have an
efficiency of at least 66%. Most standard AC PSUs have around 80%

So if my 24/12V DC Step-Down-Regulator make arround 90% and the 3.3/5V
DC Step-Down-Regulators arround the same, I have effectiv 81%...

If I use a DC/AC sin-wave converter, it will have not more then 80%
which result in a effectiv efficiency between 53% to 64%.

Realy bad...

HOWEVER, I have the need to be OVER 80%...

For what is the 8pin power connector? -- I have never seen it

Don't know. Don't want to open my box while I writing email to look.
What does the ATX speck on Wikipedia say?

This connector is not mentionedin ATX12V since it is currently NO
standard...

IIRC, there's a single-chip solution for the -5 and -12V that comes in a
TO-220 package (looks like a normal 1A regulator), one pin regulated +5
(or +12V) in, centre pin common (connected to heat-sink), third pin is
-5V (or -12V) output. I know its linear but it doesn't really matter
for 0.3A and 0.8A. IIRC, they were made by TI.

Dallas does the same thing but smaller... cost arround 0.80US$/chip

I needed these when I designed and built my own computer back in 1986.
It had 8 Zilog Z-80 8MHz CPUs with an 8-phase clock running at 64 MHz.

8Mhz? the standard version was only 2 and 4 MHz and the INCOMPATIBLE
C-MOS version 4 and 6 MHz.

How do you have gotten running this pig with 8 MHz?

Note: I have bought the Sinclai ZX-81 in 1983 and in 1984 I have bought
my first "real" CPU building my own computer... Before I have
used only 8038/39/49 (Single-Chip-Computers with many I/O and
AD/DA)

Everything was TTL including the static RAM (64K for each processor). I
started on it after reading two books for the first time: 2001 A Space
Odessy, and Mitchner's Space. Got me (a math flunky) into learning
about calculating Hohmann transfer orbits (of all things) and I needed a
128-bit calculator... Output was in hex, input was in hex. Programming
was in Z-80 machine code. No secondary storage (who could afford
that?). PSU was a 30# (that I rewound) transformer putting out 50A
rectified 8VDC then running to linear regulators. PSU weighed about
50#, connected with 4AWG welding cables to the computer. Bascially, the
PSU was a welding unit by the time I had it made. Don't ask me the
efficiency. It sure made a nice BBVVVWWWOOOMMMMMMMMM when I turned it
on. Just incase the electrolytic caps blew (each about the size of a
500 Ml Mason Jar), I built the cases out of the external cladding of a
hot-water-tank: 14 gauge steel. :)

:-)

Its amazing what ones parents let one build in the basement when they
don't know what one can find in an old TV...

... You are like me! Oh, in 2 Month I am 40y.

At what voltage? At 3V that's 30A. My MB doesn't have any 10AWG wire
going to it, but then again, this may be why there's extra power plugs
that go to the MB, 24-pin then the 4-pin. Each wire on the 4-pin is
good for 8A.

Hmmm, my 600W (redunant) PSU has 38A on 3.3V and 44A on 5V,
25A on 12V¹ and 20A on 12V²

Well, considering that Soekris boards run with CF cards off of a single
5W wall-cube...

:-) ...but the CPUs are a little bit smaller.
They are only ARM7 and I use a VIA C5/1000MHz

One thing I do not know is, can the "normal" 80 GByte SATA TravelStar be
used 24/7 if there is only the OS on it and more or less NO access?

Why not? What's special about the TravelStar if its a SATA disk? Are
you spinning the drive up and down?

They are ALL SATA drives since today I would not more buy a PATA
drive.

The Hitachi E5K and E7K series are for Blade Servers and 24/7 use
while "normal" Hitachi K5K or K7K are only for 7/5 use...

So it can be, IF I have only the OS on it, they can run 24/7 since
I do not shutdown the drives before the die...

You may give up some efficiency though; it may be more efficient to turn
the 24VDC once into 24VHF and run that through the torid to the
different power taps for your different voltages, then rectify those to
the individual DC outputs. Its been years since I looked at designing
switching power supplies since they're basically off-the-shelf items
now. Since those days, I became a Stationary Power Engineer, then a
degree nurse, then a CCU nurse, then left OS/2 for Debian, then a nurse
prof, then a disabled nurse....

:-/

Last thursday I was in a Electronic-Shop in Offenburg/Germany and have
bought AMP-Connectors but unfortunatly I have gotten only the 20pin from
the mainboard... Now I am looking for the 2pin, 4pin, 6pin, 8pin and
24pin connectors to put on the modular boards.


I think they are standard Molux (spelling? but its a brand name

You mean "Molex" but they are only the HDD and Floppy connectors.
I have seen only the cable plugs from the manufacturer AMP but not
the counterpart for the PCB. However, I have ask the Electronic-
Shop to ask there Distributor, whether I can order it.

origionally). I think they were invented for the Apollo program. Can
you get them off a junk-yard computer? They shouldn't wear out. Do you

Unfortunatly not...

have a pin-tool for placing and removing the pins from the housing?

Yes, I have all Tools to work with it... (Expensive stuff :-/ )

The other thing to keep in mind (but I don't know how to address it) is
power-factor. Since these aren't all resistance loads, you can't equate
VA with Watts. With the inductance loads of the drive motors, your
current will be higher than the Watts/Volts would suggest. This will
also induce noise. You'll need to have a power-factor corections
circuit.

I know, curently I am learning about...

National Semiconductors have very good stuff apout it. They have High
Efficiency Step-Down regulators (I was looking for one with 24Vin and
12Vout with 30A) which can have over 90% and there I have found a bunch
of Application Notes and other VERY useful documents of suff I have
never learned @university over 10 years back.

Thanks, Greetings and nice Day
Michelle Konzack
Systemadministrator
Tamay Dogan Network
Debian GNU/Linux Consultant


--
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