Help! HP R5000 UPS voltage issue

unclerunkle

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Mar 2, 2011
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Really, really hoping someone has a moment to help me here.

I have an HP R5000 UPS set to 240v output that I recently noticed outputs 113v on L1 and 127v on L2 when on battery power using a true RMS multimeter. I'm sure not all my devices connected use both phases, but my understanding is that the UPS should only have a 5% voltage tolerance when on battery power according to the manual. I thought that would mean the transformer would keep each leg in sync based on the reference to neutral but is that 5% spec just referring to the total voltage @ 240v? If that's the case, how do I balance these better so voltage is closer to 120 for each leg?

I must be doing something wrong. :confused:


Specs: Document Display | HPE Support Center
Manual: https://images10.newegg.com/UploadFilesForNewegg/itemintelligence/HP/c029452291404298930063.pdf
 

Blinky 42

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Did you try and set to to one of the other output voltages to see if the 2 legs are more balanced?
Did you test it under load or at idle?
Overall I wouldn't expect it to cause a lot of problems except loss of efficiency as long as you are feeding your equipment with the 240V it is generating and not trying to split it up into 120V somehow. Is a single phase UPS so you don't want to try and split the 2 legs. Use a transformer to convert the 240 back down to 120 if that is needed, or add a 120V UPS
 
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unclerunkle

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Mar 2, 2011
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Wisconsin
Did you try and set to to one of the other output voltages to see if the 2 legs are more balanced?
Did you test it under load or at idle?
Overall I wouldn't expect it to cause a lot of problems except loss of efficiency as long as you are feeding your equipment with the 240V it is generating and not trying to split it up into 120V somehow. Is a single phase UPS so you don't want to try and split the 2 legs. Use a transformer to convert the 240 back down to 120 if that is needed, or add a 120V UPS
Thanks for the reply! My first mistake I guess is that I didn't understand single vs split phase 240v. Dumb mistake on my part, but I'm learning.

Did you try and set it to one of the other output voltages to see if the 2 legs are more balanced?

Great idea! I tried it and any setting between 200v and 240v still results in a 14v differential between the hot legs. I believe this is possibly due to some 120v-only devices pulling only from one leg and therefore creating a higher impedance on the first hot leg. I'll have to check all of my devices and see the voltage ratings to be sure.

Did you test it under load or at idle?

Under a 10% load. Maybe that's not enough?

Overall I wouldn't expect it to cause a lot of problems except loss of efficiency as long as you are feeding your equipment with the 240V it is generating and not trying to split it up into 120V somehow. Is a single phase UPS so you don't want to try and split the 2 legs. Use a transformer to convert the 240 back down to 120 if that is needed, or add a 120V UPS

Makes sense, thank you. I had thought of splitting up the ~120 as a partial home backup solution but, yeah, not so great an idea anymore. I should have realized this by it just being single phase 240v in the first place. I'll look into a transformer for any 120v only pieces of equipment in the rack instead of those <assumedly> just tapping off one of the 240v legs and creating a differential through the impedance difference.


I did have one question - how do I know my dual 120/240v compatible servers are using both 120v hots and not just one for some reason? As long as they say 240v compatible, I'm assuming I shouldn't have to worry about that?
 

Blinky 42

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Yes you really don't want to split the outputs and use one leg as 120V, it isn't designed for that and the different load on each leg is probably a big cause of the difference in voltage you are measuring. It is trying and the actual peak to peak is still 240V but it is making unhappy faces at you internally ;)

Check the power supplies on the stuff you want to power, many devices with switching power supplies will auto-range and work on 120 or 240, which makes it easy for the manufacturers as they only need a different cord or plug head on the device but the bulk of it is the same world-wide. i keep a C14 to NEMA cord in my laptop bag just for that purpose - connect up cell chargers, laptops etc while @ a colo.

If you do have equipment that is 120 only, see what the total VA is for it all. You may be better off just getting a 120V UPS in addition vs a transformer and get more runtime out of the whole setup. The transformers are often as big as the UPS would be anyway.

Remember for 240V single phase, the 2 legs are 180 degrees from each other. If built correctly all power supplies with IEC connectors should pull the load from the 2 lines and the 3rd is the ground/earth and connected to the chassis. For 240 it is 240V @ peak between the 2 lines. For 120V the neutral happens to be tied to the ground @ the breaker box (in the US at least) so you only see one side of it - the 120V peak, but from the perspective of the power supply it is just getting 120V peaks @60Hz instead of 240V from the same 2 lines.

That is also why you need a mechanical (motor + generator deal) or fancy electronic converter to run real 3-phase equipment from single phase power because the 3-phase basically always has power across a pair where single phase is power then nothing @ 60/50Hz.
 
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unclerunkle

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It's all coming together now. One thing I also struggled with was understanding the 240v of the UPS vs the US electrical system. In case others follow this thread in the future, I'll attempt to explain it here. The UPS is 240v single phase peak to peak with 2 legs 180 degrees from each other. US household wiring is two 120v phases also 180 degrees from each other. Notice the difference in my last statement; read it again if you need. In the end, the UPS just needs to maintain 240v irrespective of each of the hot leg voltages (it is assumed the loads connected will be balanced and are 240v capable) whereas the US electrical system maintains constant a 120v on each phase. Stated differently, the UPS is 240v hot to hot, whereas the US grid is 120v hot to neutral (neutral is tied to ground only at the electrical panel). For intended operation, the UPS should have equal voltages on each hot leg, but there is nothing pegging that voltage there. In fact, after checking my connected devices, all are 240v capable and the voltage seems to equalize the higher the load I have on the UPS, but that's probably specific to my UPS and its rating.

To get 120v off my 240v system, I would need a 240v to 120v transformer or, as was suggested by Blinky 42, a 120v UPS capable of 240v input to further increase runtime on battery. The 120v devices would be last to turn off in that instance if connected to the larger 240v UPS. Connecting the 120v UPS to the grid is another option for depletion of both UPS systems' batteries at the same time.

Now, if I want to get two true 120v hot legs off my 240v system that are 180 degrees out of phase, I would get a 120/240v split-phase autotransformer. The autotransformer would keep the secondary voltage steady on each hot leg at 120v and absorb any load unbalance via the neutral wire. The neutral wire on the autotransformer carries the difference of current between the two 120v legs, or zero current when the load on both legs are equally and or perfectly balanced (i.e. consuming equal amounts of power). YouTuber David Poz has a neat video on his off-grid system using an autotransformer.
 
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