AP8959NA3 high power usage - almost like 120v equivalent

[cuddylier_apc]

Hi

I just got a AP8959NA3 and updated it to the latest firmware: 6.4.4.

When I check the power usage for a server that uses 0.6 amps on a 120v APC PDU, it shows as 0.7 amp on the 208v PDU. I tried a few servers and the same results showed, the 208v PDU showed about the same power usage in terms of numbers as the 120v equivalent. The servers were booted into an OS on each test to ensure the power usage wasn't monitored at e.g. boot time.

Does anyone have any idea why this might be? The circuit feeding it is definitely 20 amp 208v.

Thanks

[BillP]

Hi Ryan,

Is the 120V PDU tried also an APC PDU? If so, what model? To clarify, is your question why are the values not the same or why are they not more different because of the higher input voltage with 208V?

A few things come to mind regardless.

1.) Low loads (< 1A) are where the APC PDUs are the least accurate.

2.) There can be what we call "parasitic loads" on the PDU which ultimately is a very tiny amount of Amperage the PDU can consume itself from the internal circuitry. 

3.) Relating to item #2 I mentioned, here is the knowledge base we have on accuracy of the current readings Rack PDUs: http://www.apc.com/us/en/faqs/FA156074 It talks a little bit where we "squelch" to try and remove any false readings from the internal circuitry of the Rack PDU. And, accuracy is a bit different between our different generations of PDU if the 120V is an AP7XXX series or even another vendor.

[cuddylier_apc]

On 5/25/2017 6:09 PM, Angela said:

Hi Ryan,

Is the 120V PDU tried also an APC PDU? If so, what model? To clarify, is your question why are the values not the same or why are they not more different because of the higher input voltage with 208V?

Yes, AP7830. Why the values are not more different, they are pretty much the same despite the voltage being 120v vs 208v.

The AP7830 is currently at 14 amp load so maybe it's really accurate due to that? The 208v APC is at 0 - 1 load but it shows 0 load when I turn off the only server I have on.

I just want to make sure that as I start using this PDU, the power usage doesn't continue like this as it would be a hassle having to migrate servers off it.

[B-DoubleE_apc · Accepted solution]

Hi Ryan,

It could be a combination of a few factors - PDU load measuring is more accurate with higher load percentages, and the 208v PDU you have has more accurate current measuring overall. So you have an AP7830 with high load (making it more accurate), and an AP8959 with low load (that is generally more accurate than the AP7830, yet at low load so it's difficult to give an accurate measurement). Would you be able to put more load on the 208v PDU for testing purposes to see how