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July 6th, 2022 09:00
PowerEdge Rack Server Current Draw Mismatch
The table below is taken from an actual cab. I have gone onto each DRAC and recorded the information below. My issue is that some of my PDUs are exceeding their ratings but only on one side. Why do some of the servers pull 0.2A more on one PSU than the other and why is it normally PS1?
The servers are a mixture of 13G and 14G but both are affected equally
| U | PS1 (A) | PS2 (A) | Hot Spare | Redundancy Policy |
| 32 | 0.6 | 0.6 | Disabled | Not Redundant |
| 30 | 0.6 | 0.4 | Disabled | Not Redundant |
| 28 | 0.4 | Enabled | Not Redundant | |
| 26 | 0.6 | 0.6 | Enabled | Not Redundant |
| 24 | 1.0 | 0.8 | Enabled | AB Grid Redundant |
| 22 | 0.6 | 0.6 | Disabled | Input Power Redundant |
| 20 | 0.6 | 0.6 | Enabled | Not Redundant |
| 18 | 0.6 | 0.6 | Disabled | A/B Grid Redundant |
| 16 | 0.6 | 0.4 | Disabled | Not Redundant |
| 14 | 0.6 | Disabled | Not Redundant | |
| 12 | 0.6 | 0.4 | Disabled | Input Power Redundant |
| 10 | 0.4 | 0.4 | Disabled | Not Redundant |
| 8 | 0.8 | 0.6 | Disabled | Not Redundant |
| 6 | 0.6 | 0.8 | Disabled | Not Redundant |
| 4 | 0.6 | 0.6 | Disabled | Input Redundant |
| 2 | 0.8 | 0.6 | Enabled | Not Redundant |
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DELL-Charles R
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July 6th, 2022 13:00
Hello Jaimie,
This should help. iDRAC user guide: Page 169
https://dell.to/3uuApo0
After Hot Spare is enabled, PSUs can become active or go to sleep based on load. If Hot Spare is enabled, asymmetric electrical current sharing between the two PSUs is enabled. One PSU is awake and provides the majority of the current; the other PSU is in sleep mode and provides a small amount of the current. This is often called 1 + 0 with two PSUs and hot spare enabled.
jaimie.harris
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July 7th, 2022 02:00
Charles
I understand the hot spare rule but as you can see most of my servers do not have hot spare enabled and there is still a small mismatch between PS1 and PS2. 0.2A is not a great deal per server but balancing the load between PS1 and PS2 might allow me to fit in another server in the rack without exceeding my power budget
DELL-Erman O
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July 7th, 2022 03:00
Hello, as far as I know amperage does not need to match however PSUs have to supply enough amperages as required. Unfortunately, I don't have much detailed information to add other than what Charles said. I found a doc for PSU missmatch behavior for 12G. It's useful for generic information. https://dell.to/3yfV28k
jaimie.harris
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41 Posts
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July 7th, 2022 10:00
The supplied document is about mismatched physical PDUs not current draw. Does anyone have an answer?
Why does the current draw sometimes differ on PS1 and PS2?
When it does differ, why is it almost always PS1 that takes the most current?
DELL-Charles R
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July 8th, 2022 05:00
Hello Jaimie,
Either PSU1 or PSU2 can be configured as the primary PSU. You may work with trying different ones having different primary PSU selected.
Configuring power supply options using web interface Page 169 : https://dell.to/3uuApo0
To configure the power supply options:
1. In iDRAC Web interface, go to Configuration > Power Management > Power Configuration.
2. Under Power Redundancy Policy, select the required options. For more information, see iDRAC Online Help.
3. Click Apply. The power supply options are configured.