[cisco-voip] Maximum number of 7970's on a 3750-48ps-s

[Robert Kulagowski]

Pennington, Craig wrote:
> I noticed we have reached our maximum power output for the 3750 (540 
> watts).  I then noticed it is set to the default settings of auto with 
> 15.4 watts max on a port with the switch reporting each 7970 as using 
> 10.3 watts.  I tried to do the power inline auto max XXXXX (where XXXXX 
> is the number of milli-watts between 4000 and 15400) to lower the max 
> setting in hopes of increasing the number of ports that would give 
> power. 540/15.4 gives you a max of 35 powered ports.  And that is what I 
> have, 35 phones, on each switch and I need to add more.  When I tried to 
> lower the milli-watts below 15400 the port would say deny power and the 
> phone would not boot.  has anyone had any luck trying to lower the power 
> on a 3750 to service more 7970's?

Yes, but notice that the phones aren't using 15.4 watts in the first place:

# sh cdp neigh det
Device ID: SEP0015C65C6D56
Entry address(es):
   IP address: 10.255.5.62
Platform: Cisco IP Phone 7970,  Capabilities: Host Phone
Interface: FastEthernet1/0/15,  Port ID (outgoing port): Port 1
Holdtime : 124 sec

Version :
SCCP70.8-2-1S

advertisement version: 2
Duplex: full
Power drawn: 6.300 Watts
Power request id: 27990, Power management id: 1
Power request levels are:10250 6300 0 0 0
Management address(es):


So when we're configuring a switch, we do:
# interface range fa1/0/1-48
# power inline consumption 6300

To lock all the ports to 6300 mw.

And a 3750 has 370 available watts:
# sh power inline

Module   Available     Used     Remaining
           (Watts)     (Watts)    (Watts)
------   ---------   --------   ---------
1           370.0      227.8       142.2
2           370.0      134.0       236.0

so 370 divided by 10.250 is what gives you the 36 phone limit.