Smart-UPS C Output Voltage

[BillP]

This question was originally posted by $pecialist on APC forums on 11/14/2016

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Hi,

I have an SMC3000I UPS. The issue is that I can't seem to fix the output voltage at 230V.

Input voltage at the facility is usually on the high side 245VAC 50hz in the day & 251VAC 50hz at night.

Using the default settings, it seemed like UPS is not regulating the output at all:

Sensitivity: Medium ; Green Mode: 1 (Enabled) ; Output Setting: 230V
UPS INPUT: 245VAC ; UPS OUTPUT: 245VAC

Test #1:

Sensitivity: Medium ; Green Mode: 0 (Disabled) ; Output Setting: 230V
INPUT: 245VAC ; OUTPUT: 245VAC ; AVR: none

Test #2:

Sensitivity: High; Green Mode: 0 (Disabled) ; Output Setting: 230V
INPUT: 245VAC ; OUTPUT: 245VAC ; AVR: none

Test #3:

Sensitivity: High; Green Mode: 0 (Disabled) ; Output Setting: 220V
INPUT: 245VAC ; OUTPUT: 217VAC ; AVR compensating for high input
voltage

During Test #3 the UPS output reading was 221V without load, 217V with load. I was hoping I can at least get it to output at 220V, +/- 1V but voltage dropped when equipments are powered up.

I would like to know if there's an issue with the UPS or is there some configurations I missed. The requirement is to have a 230V output at all times.

[Brad_C]

This was originally posted on APC forums on 11/15/2016

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If you want (need) voltage regulation then you've bought the wrong UPS.

That unit will boost and trim as required to keep the voltage nominal, and it'll give you a solid 230V on battery, but what you appear to need is an RT series ups. Full on-line double conversion. Something like a SURTD3000XLI.

[voidstar_apc]

This was originally posted on APC forums on 11/15/2016

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Brad's right -- getting +/- 1V requires a double-conversion UPS. The line-interactive UPS you have runs its inverter only when needed. Boost and trimming the voltage is done with fixed transformer taps which raise or lower the voltage by 10% or 20%. Page 5 of the manual for your UPS (link) describes the voltage range it will provide at each sensitivity level.

Double conversion UPSes always operate their inverters. It's less efficient, more expensive, but tolerates dirtier power and generate a specific voltage.

[BillP]

This reply was originally posted by $pecialist on APC forums on 11/15/2016

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Voidstar & Brad, Thanks for your input. This is a bitter pill to hard to swallow.

So does that mean the other Line Interactive models (SMT & SMX) will function the same way ?

Since I configured the sensitivity to High, does that mean the AVR will only regulate output to 230V when input voltages dropped below 207V & rises above 253V ? But I had always assumed the sensitivity settings is a threshold for UPS run on battery when input is out of range.

[voidstar_apc]

This was originally posted on APC forums on 11/15/2016

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Yes, most line-interactive models behave the same way. There are a few sold as "line interactive" that are really double-conversion, but it's best to get one advertised as double-conversion if you need the feature.

On 11/15/2016 5:09 AM, $pecialist said:

Since I configured the sensitivity to High, does that mean the AVR will only regulate output to 230V when input voltages dropped below 207V & rises above 253V ? But I had always assumed the sensitivity settings is a threshold for UPS run on battery when input is out of range.

The UPS performs course voltage adjustments using the AVR transformer without needing to go on battery. This doesn't create exactly 230V. The output voltage range is based on what equipment today should be able to handle -- I assume you have some specialized devices that cannot.

Based on the tech spec on APC's website I've diagrammed it below for 230V nominal:

               0V         ~170V           207V     230V     253V    300V
Input voltage: |            |--------------|========|========|-------|          >
                \          / \            / \                /\     / \         /
                 On Battery     AVR Boost        On Line      AVR Trim  On Battery (out: 230V)
                (output 230V) (out: 207V-253V)  (out = in) (out: 207V-253V)

The UPS will boost the voltage if it falls below 207V and trim it if it rises above 253V. That puts the output voltage back in the 207V-253V range; it doesn't produce exactly 230V. When the UPS can no longer keep the output voltage within that range by boosting or trimming then it will go to battery.

Sensitivity also affects how a line-interactive UPS responds to distorted voltage. The UPS must react before attached equipment notices a power loss, so any slight disturbance will cause the UPS to temporarily transfer to battery. Not all voltage distortions become a loss of power -- when the UPS transfers in absence of a power failure we call that a "nuisance transfer". High sensitivity causes the UPS to react faster at the expense of more nuisance transfers. Double-conversion UPSes always run their inverters so they don't have to react which is why they can accept dirtier power than line-interactive UPSes.

[BillP · Accepted solution]

This reply was originally posted by $pecialist on APC forums on 11/23/2016

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Thanks to both of you. Very informative.