Using Cisco 2921/51 with an RPS 2300: stupid combination?

[hpoel]

Dear experts,

Researching the subject of using a Cisco 2921 router with an RPS 2300, I came across a  table in the 2900 Hardware Installation Guide that I can hardly believe:  table 5-3 seems to tell me that in order to back up ONE 2921 with RPS  power, I will need an RPS with TWO 750 Watt or TWO 1150 Watt power  supplies. When I read this, I couldn't believe what I was reading.

Is it really true that I need to throw at least 1500  Watts of backup power at a router that has a main power supply of approx  300 W?

Hans

[paolo bevilacqua]

The product is made to backup more than a 300W device only.

It is designed to work with two PSs because the objective it exactly to provide redundacy.

However it not use full power all the time, only the power your device requires and only during backup.

When not active, it will use very little.

So it actually make good sense.

[hpoel]

Paolo, Thanx for your answer, but I think you missed my point.

My only objective here is to provide power backup to ONE Cisco 2921, nothing more.

It has its own AC power, so it just needs a backup through the RPS2300.

I could decide that a 3925 is a better solution, because it allows 2 built-in PSs, but it is still considerably more expensive than a 2921.

The table I mentioned says that I need an RPS2300 with ONE 750W or 1150W PS for a 2911, but TWO for 2921 or 2951.

That's where my astonishment is: can anybody explain why the 2921/51 require a SECOND PS in the RPS2300 in order to function?

Grtz,

Hans

[paolo bevilacqua]

Because some 2921 and bigger router configurations can exceed the load supported by using one single PS.

[hpoel]

Then let me rephrase my question.

After quite a bit of CCO digging, it turns out that the 750W PS can deliver 25A @ 12V, i.e. 300W.

The 1150W PS is also limited to 25A @ 12V, it just has more 52V steam.

From 2900 info, I find that the 2921 (with AC non-PoE PS) system can consume up to 320W, the 2951 up to 340W, although basic consumption is only 60W resp. 70W.

I can now see that a worst case scenario exists in which the 2921 can draw more (data) power than the 750W PS (which is basically built for Catalyst fixed config switches) can provide, so that a second PS is needed.

Now my rephrased question: if my 2921 is just loaded with an odd VWIC and a PVDM3 module (consumption unknown, but let's say around 100W, would the 2921 accept the RPS2300 with only a single PS, or would it insist on having 2?

Hans

[paolo bevilacqua]

I don't know if it would work of if the software enforces the requirement.

Maybe start with one PS then add another if needed.

[Raghavendra Rai · Accepted solution]

Hello all,

Few months back(6 months) I had ordered a 2921 router with a Switch module

( Service module).Also one  RPS2300 with ONE 750W PSU to back-up power for this 2921.

It was workig absolutely fine with one 750W PSU and it make sense as the total power required is not even 200W.

SYSTEM POWER

===============

Motherboard Components Power consumption = 79.1 W

NM/SM slot 1 Power consumption = 27.6 W

Total System Power consumption is: 106.7 W

Last month I placed an order for another same unit (2921+RPS-2300 with one 750W PSU) for a different location.

This noon when i recieved the box and installed, I was shocked to see that RPS-2300 is not backing power for 2921 router..

Router says RPS connected cannont back-up power  for 2921 router.. I think Cisco has added some code in such a way that it will not back-up power incase only one 750W PSU is choosen

Is it not a marketting trick used by Cisco ?? 750W power supply is more than enough for my router wit the module..

Can any one please suggest me some work-arround for this??

Appreciate your suggestions!!

Thanks,

Raghavendra

[Raghavendra Rai]

Friends,

Is there any work around for this?

I want to make a RPS-2300= with one 750W PSU to back up power for 2921 router.

Now the router is not taking power from an RPS with one 750W PSU.

Please help..

Thanks,

Raghavendra

[ramonito.b.escarro]

I don't think this is the answer for this post...

I am having the same problem.

router#show environment 
SYSTEM POWER SUPPLY STATUS
==========================
 Internal Power Supply Type: AC
 Internal Power Supply 12V Output Status: Normal
 External Redundant Power Supply is present, but not available due to supplying power to another system or insufficient power.
SYSTEM FAN STATUS
=================
 Fan 1 OK, Low speed setting
 Fan 2 OK, Low speed setting
 Fan 3 OK, Low speed setting
 Fan 4 OK, Low speed setting
SYSTEM TEMPERATURE STATUS
=========================
 Intake Left temperature: 23 Celsius, Normal
 Intake Right temperature: 25 Celsius, Normal
 Exhaust Left temperature: 28 Celsius, Normal
 Exhaust Right temperature: 27 Celsius, Normal
 CPU temperature: 55 Celsius, Normal
 Power Supply Unit temperature: 42 Celsius, Normal
REAL TIME CLOCK BATTERY STATUS
==============================
 Battery OK (checked at power up)
SYSTEM POWER
===============
 Motherboard Components Power consumption = 72.9 W
 NM/SM slot 1 Power consumption = 10.7 W
 Total System Power consumption is: 83.6 W
 Environmental information last updated 00:00:11 ago

The router is only consuming 83.6W and still it seems the external RPS is not providing enough power?

Thanks,

[paolo bevilacqua]

How many PS you have in the 2300? I think you need two.

[ramonito.b.escarro]

Hi,

I plugged in two PSU with 750W

router#sh envi
SYSTEM POWER SUPPLY STATUS
==========================
 Internal Power Supply Type: AC
 Internal Power Supply 12V Output Status: Normal
 External Redundant Power Supply is present and available to backup the system.
SYSTEM FAN STATUS
=================
 Fan 1 OK, Low speed setting
 Fan 2 OK, Low speed setting
 Fan 3 OK, Low speed setting
 Fan 4 OK, Low speed setting
SYSTEM TEMPERATURE STATUS
=========================
 Intake Left temperature: 23 Celsius, Normal
 Intake Right temperature: 23 Celsius, Normal
 Exhaust Left temperature: 29 Celsius, Normal
 Exhaust Right temperature: 26 Celsius, Normal
 CPU temperature: 56 Celsius, Normal
 Power Supply Unit temperature: 40 Celsius, Normal
REAL TIME CLOCK BATTERY STATUS
==============================
 Battery OK (checked at power up)
SYSTEM POWER
===============
 Motherboard Components Power consumption = 71.5 W
 NM/SM slot 1 Power consumption = 10.1 W
 Total System Power consumption is: 81.6 W
 Environmental information last updated 00:00:02 ago

My question is why does an 81.6W router need two 750W PSU external RPS? If at 12V max is 300W and -52V would be 400+W?

Thanks,

[paolo bevilacqua]

As discussed before,probably because Cisco wants to have redundancy in a system that is designed to provide redundancy.

[sankarccie]

Dear Frds,

We have a 2300 RPS with single 1150WAC power supply (C3K-PWR-1150WAC) which is connected to one 2921 Router. But it is not backing the rotuer.

When i issue sh env rps or sh env all in Router 2921

its giving *unknow rps connected or unsupported device connected*

Is this also require redundancy in a system ???

Regds,

Sankar V

[Raghavendra Rai]

Dear all,

I am sorry to say this, RPS-2300 is not a great product from Cisco. I have faced lot of issues after ordering this product..

There is no clear ordering guide or nor the SE's of Cisco aware about this product..

Avoid RPS-2300 as much as possible..

Thanks,

Raghavendra