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3850 POE issues

frankTD4
Level 1
Level 1

I know this has been discussed, but my situation may be more unique. We were having issues with a 24 port POE 3850 not being able to power all necessary cameras (13 I believe). It has two 710w power supplies which is more than enough for this application. Ultimately, using POE injectors for a few of the cameras “fixes” the problem. All the cameras come up as device type 0 with a max of 15.4w. I’m curious is longer runs are requiring more wattage and if doing an auto max (wattage) command will expand that ability and power the cameras. It’s just weird to me that the injectors work, installed right before the switch, but the switch can’t handle it.

3 Replies 3

Leo Laohoo
Hall of Fame
Hall of Fame

There are many reasons around this and one of them boils down to whether or not the cameras support either CDP or LLDP for PoE negotiation.  

If the cameras do not support CDP or LLDP, then the switch will provide 15.4wac regardless if the cameras actually use less than 15.4wac or not.  If this is the case, then it is very much possible to manually configure each port to draw the less than 15.4wac that the cameras can operate.  

Next, IOS-XE and PoE.  Classic IOS and IOS-XE are two different beasts.  The cameras may operate nicely with classic IOS but acts differently with IOS-XE (because latter is buggy AF).  In some cases, I would say "upgrade the firmware" but most of the time using a power injector is the only true solution.  

I’ll have to check whether cameras support that, but most of the cameras are working directly connected to the switch. Only a few need the injector. All the same cameras too. Not sure if it’s a thing but if the distance is causing a voltage drop will the camera pull more current and require more wattage

What do you get from a "show power inline" command when the cameras won't come up? The switch has to assume the PoE device will pull the maximum available power per port unless the device informs the switch how much it actually needs via CDP or LLDP. If they aren't Cisco cameras then they would almost certainly use LLDP. Do you have LLDP enabled on this switch?