Grex Hardware Conference

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Grex Hardware Item 184: Connecting a SMPS to a mobo
Entered by vivekm1234 on Mon May 15 15:42:22 UTC 2006:

I have a old PC, a Cyrix 233MHz. You have to press a switch(functions like
a light-switch) to power on and off. The Motherboard supports ATX and has 2
pins for a "Power Switch" and 2 more pins for "Reset".

My SMPS (power supply) is 233Watts and has 4 wires going to the above
mentioned switch. I wanted to know if there was a way to auto-poweroff this
PC? Right now i have to toggle the light-type-switch on and off.

I was thinking of hooking up those 4 wires bypassing the switch. The SMPS
would then be always "ON" and feed power permanently to the mobo.

To switch the mobo on and off i was thinking off hooking the reset switch to
the 2 power-switch pins on the mobo. Would this enable the
"Auto-power-down-feature" so that when i shutdown the mobo will switch off.

9 responses total.

#1 of 9 by ball on Mon May 15 23:41:47 2006:

Cyrix MII 233 MHz?  If the power switch is latching, you
probably have an AT PSU rather than ATX.  If your mainboard
supports APM (possible) or ACPI (unlikely) you may be able
to configure it to enter a light sleep if it's left alone
for a while, and perhaps even suspend (to disk, or perhaps
to RAM) until it's woken by an event such as a phone call, a
"magic packet" or perhaps hitting a power key on the key-
board.

#2 of 9 by vivekm1234 on Tue May 16 02:11:54 2006:

Yep Cyrix MII 233 MHz. Yes the power switch is latching. Yes it has APM and
can enter light sleep, doze disks etc.

I wanted to switch it off. The UPS is common with another comp and i don't
want this Cyrix drawing power.
,

#3 of 9 by ball on Tue May 16 05:51:31 2006:

How much power does it draw when suspended?

#4 of 9 by vivekm1234 on Tue May 16 12:32:08 2006:

Re #3 No idea, i don't have a wattmeter. The fan makes a lot of noise as well!
I suppose the only way would be to buy a new SMPS?

#5 of 9 by ball on Tue May 16 15:15:36 2006:

The new PSU would cost more than the machine's worth and
would only work if your mainboard had an ATX power
connector and if you fitted a momentary power switch to the
case.  My machines draw little when suspended.  Can you
borrow a Wattmeter (or at the very least an Ammeter)?

#6 of 9 by vivekm1234 on Wed May 17 04:47:14 2006:

Hey my UPS can specify current output power! I just need to plug a PC directly
into the mains and then measure UPS-output when the othe PC is shutdown.

#7 of 9 by ball on Wed May 17 23:27:11 2006:

Let us know what you find out.

#8 of 9 by vivekm1234 on Sun May 21 16:37:24 2006:

Both PC's running full blast: 17inch monitor, mobo, drives, hard disks, fans,
SMPS, Speakers, Modems consume around 210Watts.
If i switch of the 17inch PC, power consumption drops to 100Watts, the Cyrix
PC consumes around 40Watts minus the 15inch monitor.
There isn't a big difference in power consumption between the 17inch Celeron
400 and the 15inch Cyrix 233! Both consume around 100+-10-15watts each.

I haven't tried the PC in hibernate mode. Having some problems..I'll try it
later.

#9 of 9 by gull on Thu May 25 17:55:29 2006:

Yeah, you would think the 400 MHz system would draw more power, but 
even as processors have gotten more power-hungry, hard disks and other 
peripherals have gotten more efficient. 
 
I find, lately, that processor power consumption/heat generation has 
gotten to the point where one of the biggest challenges in building a 
system is effectively getting the heat out of the case. This is 
especially true of rack systems, where you only have the end panels to 
work with. The desktop system trick of ducting an opening on the side 
panel straight in to the processor fan doesn't work because that area 
is likely to be blocked by whatever's racked in the next slot up.

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