MR42 running in low power

[CWMARS]

Hi,

I have two MR42 access points connected to the PoE ports of a Meraki MX68.  They both were showing low power so I first thought I would upgrade the firmware of the MX68, this changed one of the APs to full power but the other one is still showing low power.  I know I should check cables (though we installed new ones) since the MX has no way to test cables like the switches but due to the COVID-19 issue we cannot access the bldg or hardware.  Any other thoughts as to what I can maybe do remotely to correct this power issue?

Thanks,

Anne

[ww]

Try disable/enable the Port the low powered AP is on.  Not much else you can do

[CWMARS]

Thanks, I did try that before upgrading the firmware. It's funny that after the firmware upgrade one of the APs went to full power.  All is left is to swap cables at this point.

Thanks,

Anne

[nikiwaibel]

upgrade the firmware on the MX as well (iirc there was an issue with some ports on the MX with more then 4 ports).

then swap the cables ends on the MX and see if the issue moves. then swap the cable ends on the APs (if that's possible) and see if the problem moves (obviously only works in case you have low power on one AP and the other is fine).

that way you should be able to figure out if it's because of the cable(s), the MX port(s) or the AP(s).

if you can't figure it out / fix it, create a case in the dashboard.

[CWMARS]

Thanks for the info!  Unfortunately we can't do any cable troubleshooting because this site is closed due to the COVID-19 issue.  I have tried upgrading the firmware to v.15.27 and opened a ticket with Meraki support but they said I have to check cables before any further troubleshooting can take place.

Thanks,

Anne

[cmr]

Try powering off the one that goes to full power to see if it is somehow a power budget issue

[PhilipDAth]

The last time this exact scenario happen to me it was the cabling.

The formula for power loss is:

P = I²R, where P=lost power, I=current and R=resistance

Or something pretty similar to that.

The power lost increases proportionally with the resistance of the cable.  So the cable can work perfectly good for data, but due to resistance loses sufficient power so that it can not properly power what is plugged into its end.

Using a cable with a large copper core diameter reduces resistance.  Using a shorter cable reduces resistance.  Sometimes the ends are not fitted off poorly causing increased resistance.

But often - you just have to replace the cable with another one.

<rant on>

Let me go completely off-topic for a bit.  This has really big implications that many people don't realise in the non-networking world.

Lets say I have a 30m extension code.  I plug my electric saw into this, and the cord into a powerpoint.  Lets say I live in a country that uses 240V.  If I buy the cheapest extension lead with a core size of 1.0mm^2 instead of an extension lead with a core size of 2.5mm^2 I'll loose about 7% to 8% of the power to my saw - or my saw will be about 8% less powerful.

Lets say I was now driving a motor that has to run at a fixed speed such as a compressor.  The compressor motor will now get hot and will eventually over a long period of time damage itself.

Lets say I am putting in a big machine in a factory.  Using the smallest core size allowed by regulations might make my big machines run properly but the resulting power loss (compared to using a larger wire with a larger core size) may result in that machine using more electricity than it needed to for the rest of its life.

</rant on>