Low PoE on MS220

[Deniz]

I am connecting Cisco APs to MS220, and I see that power draw level never exceeds 6W, hence APs shut their radios down and not possible to turn them on. Any idea why this occurs? 

Output from Meraki Switch:

PoE usage

5.6 W AT (Advertised 30 W AT)

[BlakeRichardson]

@Deniz what model MS-220 and what model access point are you using. It would be nice to be able to find out the specs for each device to see if I can help you work out whats going on.

[MerakiDave]

If it's a newer quad-radio AP with 3x3:3 or 4x4:4 like MR42/52/53/84 etc then they can draw a maximum power greater than traditional 802.3af 15 watts, so even though they tend to draw less than that on average, if they do not see PoE+ 802.3at negotiation upon bootup during LLDP negotiation, then they are forced to run in low power mode.  If you've done the basic L1 troubleshooting, and confirmed via packet capture for example that the proper LLDP negotiations are taking place and the AP is still ending up in low power mode, open a support ticket.

[PhilipDAth]

There is something additional at play here.

The switch says it supports 802.3at (aka 30W).  These are my thoughts:

* Cisco enterprise AP's ship with the radios disabled.  Perhaps they have not been enabled?

* You have exceeded the power budget of the MS220.  If you only plug in the AP (and no other PoE devices) does it work?

[Deniz]

Thanks for reply, Philip!

Yes, AP radios were down by default, so once I turned them on it is working now,

but I still see that PoE consumption is not in the right level.

MS220-8P is the model of switch, and although I turned on both radios, here is the result:

PoE usage

6.2 W AT (Advertised 30 W AT)

I am using Cisco AP3700 which requires minimum 15.4W, others AP turns down its radios.

See "Power Draw" section:
https://www.cisco.com/c/en/us/products/collateral/wireless/3700-series-access-point/data_sheet_c78-7...

The total summary of PoE usage of the switch is below: (1x MR33 and 1xAP3702 are in use)

PoE usage

Consumption

16.1 W / 124 W

Budgeted

60 W / 124 W

[PhilipDAth]

The AP and the switch you are using support dynamic power negotiation.  As such, the actual power consumed will depend on the AP requirements - which will vary by load, client type and client connection parameters.  I bet you looked at this when the AP was sitting idle.

I bet once a bunch of machines are using the AP for actual data throughput  on both the 2.4Ghz and 5Ghz radios that this number will jump a lot.

[Deniz]

Yes, you have a point there, but as you also can see in the data sheet,

if AP receives PoE power at 802.3af, then it will function as 3x3:3. This is the moment I dont get the point of so level PoE consumption.
So, at this moment, even though AP is idle, I dont believe that AP is fully functioning with this PoE level.

Based on what you say, I need to connect many users, for AP to consume more power and go beyond 15.4W in order to function fully, i.e. with 4x4:3 ?

[PhilipDAth · Accepted solution]

The AP will never run at 4x4 because there are no 4x4 clients to request this. Most clients are 2x2 with the odd 3x3. The best you'll get is it using four radios when talking to a 2x2 client using diversity.

[Deniz]

Thanks Philip, yes indeed that was the reason. Realized that the documents show the Power draw on "switch side", not meaning that AP will consume that much PoE power.

[Ludo]

Hello,

I use this subject because my problem is maybe similar (or not ?)

A Meraki Access Point MR33 doesn't power up on a MS220. I've tried to let only one port with POe activated, but no change. It seem to me that it worked before. Since the MS220 was plugged on an APC surgearrest. Could that be the reason of the no power up ?

On an other POe switch (HPE OfficeConnect 1420 8G POe+), the access point work.

Thanks

[Deniz]

Hi Ludo,

Can you see if AP is drawing any power at all? You can see that in switch port details. 

Or you can go to Switch and check power tab to see budgeted and consumption PoE usage. 

In my case, it was working but i was curious why AP was drawing so low power from switch and you can find the explanation of why in above responds. 

[Ludo]

Hello,

For the switch, nothing is connected to the port... I've tried severals ports, it's the same.

[Deniz]

I know you have already mentioned, but still might be worth of checking if PoE is enabled on the ports.

Additionally, have you viewed the logs if you can see anything there? 

Or do you have anything similar to shown on this page (brown or red colour on ports)? 
https://documentation.meraki.com/MS/Monitoring_and_Reporting/Switch_Port_View

[redsector]

And, sorry for this question: is the patch-cable in order? Once I had a defective cabel with that kind of problems.

[Ludo]

I've tried with a new cable, don't work.

The port is black on the configuration page (and Poe is activated for this port).

The switch is the MS-220-8P (so with Poe capability).

I plugged the switch into an other electrical outlet (without APC surge protection), nothing change.

I will test a reset at the end of the day, if nothing changes, I will ask for an RMA ticket.

[redsector]

Yes, if the pin needle factory reset doesn´t help you should open a case to get an RMA.

[PhilipDAth]

You will also note in the link you provided that the numbers have a little * with the comment "This is the power required at the PSE, which is a switch or injector.".  Injectors (at least none that I have seen) don't support dynamic power negotiation.  So these are the worst case numbers, not the minimum power consumption.

[redsector]

I agree to that.