On-board PC power supply

[TheBeastie]

Not sure where to go here and wonder if anyone can help. I have built an ITX PC using an M3-ATX PSU. Running it off a bench PSU it goes fine but putting it into The Beastie it refuses to fire up the PC. I have checked the power and it is getting 12.75V off the auxilliary battery. I put it back on the bench PSU and it is fine - so the PC working. On a hunch I have just re-set the bench PSU to about 12.5V and lo and behold the PC will not start. As soon as I ramp it up to about 13.2V or so we are back in business. Once it is running I can wind back the voltage a bit without seeming to upset it.

Am I right in thinking this means I will not be able to fire up the PC unless the engine is running (and the split charge supplying a tad extra voltage to the auxilliary), but that once started I should be able to run it with the engine off?

[LandyManLuke]

Googling that PSU, it seems it supports 6-24v supply. Reading further, it appears to have programmable characteristics, maybe it has some built in hysteresis to stop it cylcing on and off on a flat battery?

I have a 12v DC-DC PSU from lin-itx that runs a PC fine on any old 12v battery. never had any problems.

[TheBeastie]

Thanks. Yes I was aware 6v-24v too so surprised. What I had done is not set jumpers for switch on/off automatically with ignition since did not want that but have fed same 12v fused supply to both the +ve and also to the ignition feed. This works fine on the PSU. Will test boot up with engine running but have current on-going issues with engine (serious groan) so reluctant to do unnecessary starts.

My hunch is once engine running and slightly higher voltage (so any sensor such as you mention will be satisfied) it will start but wondered if anyone else had come across this. Once engine sorted (which is the bigger issue) then will let you know.