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totti4ever
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Optimize power consumption of CRS328 (-24P-4S+) - currently at 25W

Tue Jun 28, 2022 10:24 pm

Hey there,

I did an analysis on the consumptions of my racket population (router, switch etc) and have two questions on my switch:
  • On the Health tab it states PSU1 = 0mA @ 26.47V and PSU2 =112mA @ 52.67V, which results to 5.9W according to some online calculator. But when I measure the consumption with a shelly plug it says 25W. Interestingly connecting my Unifi AC adds 8W to that measurement, which is the same as statet on the PoE tab of the Switch. So where does the difference come from??
  • Are there any ways to optimize the power consumption of the Switch? Would it make it better or worse to switch from SwOS to ROS?
    8 devices are connected, one with PoE

Thanks a lot for any insights :-)
 
marekm
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Re: Optimize power consumption of CRS328 (-24P-4S+) - currently at 25W

Wed Jun 29, 2022 3:55 pm

Health tab shows measurements on the DC output of the power supply.
The "shelly plug" is on the AC input of the CRS328 built-in power supply.
No power supply is 100% efficient, there are always some losses.
Cheap watt-meters are not very accurate either - especially with low power and non-linear loads like switching power supplies.
No need for an online calculator for a simple DC power calculation, just multiply voltage by current.
With AC it is more complicated, as there may be phase shifts and harmonics. Sometimes different electricity meters (old mechanical one vs new electronic one) measure quite different results.
If you need just one PoE device, it may be better to use separate PoE injector and a switch without PoE (like CRS326) which has a smaller power supply, wasting less power at light load.
 
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mkx
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Re: Optimize power consumption of CRS328 (-24P-4S+) - currently at 25W

Wed Jun 29, 2022 10:50 pm

No power supply is 100% efficient, there are always some losses.
It's even worse: the rated efficiency (e.g. 92%) is only achieved when power supply works close to or at rated capacity. When under light load, efficiency goes down and at (near) idle state it still consumes quite considerable input power.
 
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chechito
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Re: Optimize power consumption of CRS328 (-24P-4S+) - currently at 25W

Thu Jun 30, 2022 12:42 am

as mkx says

this switch has a 500watt of power supply so using it almost empty lead to worst case efficiency

if you load it up to al least 20-25% rated capacity you will see much better efficiency
 
llag
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Re: Optimize power consumption of CRS328 (-24P-4S+) - currently at 25W

Tue Jul 05, 2022 12:59 pm

Hey there,

I did an analysis on the consumptions of my racket population (router, switch etc) and have two questions on my switch:
  • On the Health tab it states PSU1 = 0mA @ 26.47V and PSU2 =112mA @ 52.67V, which results to 5.9W according to some online calculator. But when I measure the consumption with a shelly plug it says 25W. Interestingly connecting my Unifi AC adds 8W to that measurement, which is the same as statet on the PoE tab of the Switch. So where does the difference come from??
  • Are there any ways to optimize the power consumption of the Switch? Would it make it better or worse to switch from SwOS to ROS?
    8 devices are connected, one with PoE
I always interpreted the figures on the health tab to be only the power consumption of the POE devices fed by the switch.
Total consumption from the wall is then the POE load + the consumption of the switch itself + power supply loss.

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