Problem with M2 and PC reboots

LaroCroft · 05-19-2008, 05:07 PM

I have a question about my M2 ATX power supply:

I have a IEI Nano board that just needs 12V from the power supply and 5V for Standby only. I have connected 3 displays over a relay switch directly to the battery. Two of these displays sometimes didn’t came up again because battery voltage was too low. I think this has to be a problem of the displays because battery voltage was still over 12V if that happens. But I thought why not connecting the tft displays directly to the 12V rail of the M2 ATX.

With that configuration I ran into the following problem:
PC starts… All 3 displays are powered up. Then because the third display is not used for booting the display powers off by itself. After booting is complete and windows enables the third display the pc reboots again.

So how can that be. The specification of the M2 ATX gives me 8A on the 12V rail. If I summarize:

PC board running: 2,3A
displays 1+2 each 8W: 1,4A
Some other stuff like touchscreen: ~1A
display 3 15W: 1,25A

Makes 5,95A!

So why causes switching on the third display with 15W the A2 to crash the 12V rail? I think this is happening and the reason why the board reboots. Is there any limitation on adding load on a running M2 ATX?

JimmyFitz · 05-19-2008, 05:18 PM

Quote: Originally Posted by LaroCroft

I have a question about my M2 ATX power supply:

I have a IEI Nano board that just needs 12V from the power supply and 5V for Standby only. I have connected 3 displays over a relay switch directly to the battery. Two of these displays sometimes didn’t came up again because battery voltage was too low. I think this has to be a problem of the displays because battery voltage was still over 12V if that happens. But I thought why not connecting the tft displays directly to the 12V rail of the M2 ATX.

With that configuration I ran into the following problem:
PC starts… All 3 displays are powered up. Then because the third display is not used for booting the display powers off by itself. After booting is complete and windows enables the third display the pc reboots again.

So how can that be. The specification of the M2 ATX gives me 8A on the 12V rail. If I summarize:

PC board running: 2,3A
displays 1+2 each 8W: 1,4A
Some other stuff like touchscreen: ~1A
display 3 15W: 1,25A

Makes 5,95A!

So why causes switching on the third display with 15W the A2 to crash the 12V rail? I think this is happening and the reason why the board reboots. Is there any limitation on adding load on a running M2 ATX?

Sounds like there may be something of a surge that is drawn when the display first turns on. Typically, these are ignored at initial startup but once the supply stabilizes, a new surge might push over the limit long enough to cause a shutdown.