Hi,

I have a vehicle PC (powered by a battery) and I am trying to come up with a circuit to safely shutdown the computer without corrupting the SSD disk. I have a rocker switch that turn on/off the power from the whole system and also a PC power button connected to the motherboard button+/- pins to turn on/off just the PC. In the BIOS i have the button configured to 1 click to safe shutdown and long press to hard off PC.
I'd like to:

- when rocker is ON and i turn it OFF there would be some capacitor holding the 12V for the motherboard for 3 or 4 seconds while some timer sends the short pulse to the motherboard to shutdown. This way the computer would shutdown safely and after that the system would be off (without some standby current draining the battery).

i found this circuit: https://forum.allaboutcircuits.com/threads/making-a-delay-off-timer.75748/
But the 12V the guy stated will drop and the relay will loose the power so basically that capacitor is only holding the control signal but not the power itself. I guess that a big capacitor on my 12V BUS won't be enough right? it depends how much current i would be consuming at the time the system is brought down right?

Can someone help me or suggest something that might help me?

Best regards
qwerty88

 

You can use a capacitor to keep the relay powered ,then when it's discharged the relay would disconnect the power from your motherboard.

Or use a P-fet to do the power on/off control.

https://www.edn.com/design/power-ma...automatic-shutoff-circuit-uses-few-components

 

1)The PC takes how long to do an orderly shutdown ?

2) How much current does the motherboard draw when running ? Thats a loaded
question because it depends on applications/software running

3) Latency you can tolerate as to how fast the PC has to react to shutdown request
and start the shutdown ?

4) Battery PC is running off ? Its V.

5) Some newer BIOS's in motherboards can enable a fast shutdown via
V sensing. Whats the model of your motherboard ?

Regards, Dana.

 

Typically the power supplies intended for carputers already have this solved.. They stay on battery all the time but hibernate/sleep/shutdown based on ignition status..
http://www.mini-box.com/M3-ATX-DC-DC-ATX-Automotive-Computer-car-PC-Power-Supply?sc=8&category=981

 

You can use a capacitor to keep the relay powered ,then when it's discharged the relay would disconnect the power from your motherboard.

Or use a P-fet to do the power on/off control.

https://www.edn.com/design/power-ma...automatic-shutoff-circuit-uses-few-components

Thanks for the p-fet tip! But that transistor only handles 1A as it says in the document. But in its datasheet it says 9A. Can I use this MOSFET for a 5A load?

 

Typically the power supplies intended for carputers already have this solved.. They stay on battery all the time but hibernate/sleep/shutdown based on ignition status..
http://www.mini-box.com/M3-ATX-DC-DC-ATX-Automotive-Computer-car-PC-Power-Supply?sc=8&category=981

Hi I know. I'm actually using a picopsu like that with ignition. But the thing is that when I disconnect the rocker switch the 12V Will drop and so those picopsu features don't work .

 

1)The PC takes how long to do an orderly shutdown ?

2) How much current does the motherboard draw when running ? Thats a loaded
question because it depends on applications/software running

3) Latency you can tolerate as to how fast the PC has to react to shutdown request
and start the shutdown ?

4) Battery PC is running off ? Its V.

5) Some newer BIOS's in motherboards can enable a fast shutdown via
V sensing. Whats the model of your motherboard ?

Regards, Dana.

Hi!

1- normally it takes 2 or 3 seconds when I click the pushbutton on the motherboard but sometimes takes longer (I'm using Ubuntu and sometimes does not shutdown fast).

2- I measure and the whole vehicle consumes top 4A but almost all of it is the PC consumption.

3 and 4- didn't understand

5- I'm using this motherboard GA-H270N-WIFI

 

Hi I know. I'm actually using a picopsu like that with ignition. But the thing is that when I disconnect the rocker switch the 12V Will drop and so those picopsu features don't work .

huh? then you don't have it hooked up properly to use them and now seem to want to find another method to avoid just fixing what you don't have correct now?
Good luck..

 

Thanks for the p-fet tip! But that transistor only handles 1A as it says in the document. But in its datasheet it says 9A. Can I use this MOSFET for a 5A load?

Use this fet instead with that circuit.

https://www.mouser.co.uk/ProductDet...=sGAEpiMZZMshyDBzk1/Wi/S6olPLoOa4anCkxM24/ZE=

 

Use this fet instead with that circuit.

https://www.mouser.co.uk/ProductDetail/STMicroelectronics/STF10P6F6?qs=sGAEpiMZZMshyDBzk1/Wi/S6olPLoOa4anCkxM24/ZE=

Thank you Dodgydave
I have drawn a circuit that i think might work along with that PMOS. Can you check if you think it will work?

 

I have had to do a power-disconnect a few times when some malware attacks and the computer won't shut off. That is, unplug the AC adapter and then remove the battery. It never damaged anything except the malware. Of course, when I start it back up it asks what to do because the shutdown was not orderly. If files were open that would be different, but I never leave files open unless I am working on them.