Cisco IP phone rebooting whenever UPS power kicks in

[SajithThrimavithana]

Hi,

One of our clients has a PoE+ Cisco 24 port switch and 24 Cisco IP phones attached into it.

Switch is getting power via a UPS. When ever there's a power failure, UPS can provide power until generator kicks in. 

The issue is rather strange. When ever main power goes down and UPS kicks in, a Cisco DX650 phone reboots itself, while the rest of the phones attached to switch (3905, 7942) remain to work without any issue. I thought may be power drawn out from the switch is high and it causes this but when i check power inline states ; 

Module   Available     Used     Remaining
          (Watts)     (Watts)    (Watts)
------   ---------   --------   ---------
1           370.0       85.8       284.2

Which indicates switch is quite comfortable supplying the required power. This is the DX650's power stats;

Interface Admin  Oper       Power   Device              Class Max
                            (Watts)
--------- ------ ---------- ------- ------------------- ----- ----
Gi1/0/1   auto   on         13.7    IP Phone DX650      4     30.0

What could be the reason for this ? Thanks in advance. 

[Philip D'Ath]

I'm guessing it is a low end standby UPS.  You'll probably find that it is not kicking in the power fast enough, or is letting "bad" power through.

A line interactive UPS is probably the minimum you want to use.  This is always supplying a filtered power feed out of the UPS.  This is a great compromise for small business.

And if you can afford it, and don't mind a shorter battery life (before batteries have to be thrown away and replaced), use a "Double Conversion On-line" UPS.  In this case the load is always supplied by battery.  The output power is always perfect and there are never power spikes.  The mains supply is only used to keep the battery charged in this case.

I found this article talking about them.

http://www.apc.com/site/support/us/en/faq/?page=content&country=ITB&lang=en&locale=en_IN&id=FA157448&redirect=true

[SajithThrimavithana]

Thank you very much Philip.

I will be checking on the UPS and it's status. 

Will put results here asap. 

[SajithThrimavithana]

Hi,

The UPS is a VFI type, online UPS. So I think UPS is not the problem here. 

Any idea what causes this ? 

Here's a link to UPS specs, one we have is 18000w / 20000VA.

Riello MST20

[Leo Laohoo]

When the UPS kicks in, what is the uptime of the switches?