[c-nsp] 7606 power supply issue

[Richard A Steenbergen]

On Thu, Dec 21, 2006 at 11:11:37PM +0100, Asbjorn Hojmark - Lists wrote:
> The only PSUs supported with the 7606 running SX are the 2700W
> PSUs (AC or DC). The 1900W PSUs are *not* supported in SX. See
> the release notes at http://tinyurl.com/yk2oyk
> 
> They *are* supported in SR (see http://tinyurl.com/ylfaz3) but
> why bother when the 2700W PSUs cost the same?

cisco CISCO7606 (R7000) processor (revision 1.0) with 983008K/65536K bytes 
of memory.

                        Power-Capacity PS-Fan Output Oper
PS   Type               Watts   A @42V Status Status State
---- ------------------ ------- ------ ------ ------ -----
1    PWR-1900-AC/6      1869.42 44.51  OK     OK     on 
2    PWR-2700-AC        2669.10 63.55  OK     OK     on 

IOS (tm) s72033_rp Software (s72033_rp-ADVIPSERVICESK9_WAN-M), Version 
12.2(18)SXF6, RELEASE SOFTWARE (fc1)

Seems to be working just fine for me, with mixed 1900W and 2700W too. Even 
Cisco doesn't seem crazy enough to not support a particular type of power 
supply in one train but not another, sounds like a documentation issue to 
me.

As for the why, a 1900W PS will do all 1900W on a 110V feed, while the 
2700W requires 220V or else it functions like a 1350W PS:

                        Power-Capacity PS-Fan Output Oper
PS   Type               Watts   A @42V Status Status State
---- ------------------ ------- ------ ------ ------ -----
1    PWR-2700-AC        1319.22 31.41  OK     OK     on


For example, some of us happen to be customers of a certain well-known US 
carrier neutral colo company who is currently experiencing rampant power 
shortages and demanding multifold pricing increases on new power services, 
if you can even get power upgrades at all (think 4-6 month waiting list 
and having to argue your case for why you need the power). If the only 
reason you need a 208V circuit is to run your cats at full capacity, you 
could very easily save enough money in power by not having to upgrade to 
cover the cost of the entire power supply every 3-4 months.

Also, the smallest breaker size typically sold by most colos would be 20A 
of 208V, or 4160W (8320W if you have A+B power feeds). Unless you are 
doing a lot of PoE, even a very well loaded 7606 (think dual SUP720-3BXL 
and 4 slots of 6704-10GE or 6748-SFPs without DFCs) runs under 1900W of 
total load. For folks operating smaller loads, you may be buying 2-4x more 
power than you actually need just to fully energize that 2700W power 
supply.

-- 
Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)