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lapsio
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LtAP - power draw in "off" state?

Sun Dec 01, 2019 3:08 am

Hello

When Routerboards are "powered down" in software using /system shutdown they don't actually go blackout, just kinda... stop processing stuff. What is power draw of LtAP in such state? I connected it to car battery and I'd like to write script which would turn off LtAP after detecting input voltage dropped below 12.4V in order to avoid deep battery discharge. Is that possible?

What are other options to turn on/off MikroTik powered by cigarette lighter socket in car automatically?
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RogerWilco
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Re: LtAP - power draw in "off" state?

Sun Dec 01, 2019 3:50 am

Not really. You can just write your script to disable interfaces? Not ideal, but would make the LtAP power go down.
 
mkx
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Re: LtAP - power draw in "off" state?

Sun Dec 01, 2019 11:20 am

A bit of a history about Linux kernel which seems to be relevant for how ROS shuts itself down...

Before there was ACPI to handle power related stuff, machines had no way of actually powering themselves off. When one requested a shutdown on such machines, OS kernel (including linux) would stop all processes and at the end it would emit message to power off the hardware. After that it would sit indefinitely in an idle loop. Mind that all the hardware was still powered, just doing nothing. Which somehow reduced power consumption, but not much. E.g. CPU power draw perhaps dropped to 50% of max power draw, depending on how CPU handled unused parts of itself ... and capabiliry of kernel to issue specific low-power idle instructiobs on any given CPU.
Only way of restarting machine from this state was to cut the power ...

And I suspect that ROS, (until v7) still using ancient linux kernel, behaves exactly like this. I also don't know if RB hardware is ACPI capable, i.e. does it support software power-off and power-on at all ... absence of power buttons (it must not be a toggle switch) on most devices might indicate that they are not HW ready for such use ...

So even if one does monitor supply voltage and issues /system shutdown, the box won't restart automatically.

My solution would be hardware solution: get an under-voltage protection module, they are available from favourite Chineze online retailer for less than a buck each ... one can set cut-off voltage as well as power-on offset ... and that should deal with the issue just fine.
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Metod
 
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lapsio
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Re: LtAP - power draw in "off" state?

Sun Dec 01, 2019 11:03 pm

My solution would be hardware solution: get an under-voltage protection module, they are available from favourite Chineze online retailer for less than a buck each ... one can set cut-off voltage as well as power-on offset ... and that should deal with the issue just fine.
Could you recommend such module? The only UVP relays I can find are ones with Tt (delay) rather than power-on offset and that is obviously not good for car battery since after load is unplugged voltage on battery jumps up so such UVP module would keep toggling on/off infinitely. Could even damage LtAP.
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mkx
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Re: LtAP - power draw in "off" state?  [SOLVED]

Mon Dec 02, 2019 8:59 pm

One example is XH-M609 undervoltage protection module ... I paid 2,11€ and got free shipping (it took a month ;-) ). It is completely configurable (actually works from some 6 V upwards), offset is configurable as well. My setting is shut-off at 11.8V and power-up again at 1.2V higher (which translates to 13V).
BR,
Metod

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