240v to 208v conversion in Symmetra UPS

[Anonymous user]

Can someone explain how the Symmetra LX 16kVA converts 240v power to 208v power? I install SmartHomes and would like to use this UPS as it is a great size for the typical home installation. Does the UPS use transformers to stepdown the power? Home installations usually have 240v but the equipment I use operates more efficiently at 208, another reason this UPS would be perfect for this application.

Please help.

[Anonymous user]

It's a double conversion UPS.
Input voltage is turned into DC, then the output power is completely regenerated with an inverter.
See page 6
http://www.apcmedia.com/salestools/SADE-5TNM3Y_R5_EN.pdf

In bypass mode, it is likely using transformers.

[BillP · Accepted solution]

I believe what you are looking for is the reason that you can output 208v even with an input of 240v. In order to explain this, you need to understand the difference between 208 and 240. Both are derived by referencing (2) 120v hot legs to eachother, only difference being the "phase angle" between the 2 legs.

The Symmetra LX UPS system actually has the ability to alter the phase angle on the output side of the UPS. KVAR is correct - the UPS recreates the waveform to produce output power, however, with the ability to change the phase angle between the 2 phases (or hot legs) we can output 208v, even with 240v input (or vice versa).

In bypass, the UPS passes the voltage through, without the ability to change the phase angle, therefore outputting what is input to the UPS. This would be the only concern for your installation. If the UPS is in bypass, you will output 240v in bypass rather than 208v.

Generally, APC recommends matching the output with the input for this very reason, however, it is always an option to output one voltage or the other regardless of the input voltage.

Shoot me a personal message if you need me to clarify any of this for you, I tried to keep it simple for you.

[Anonymous user]

The inverter generates two phases separated by 120° yielding 120v and 208v(120 * sqrt 3) in 208/120 mode and separated by 180° in 120/240 mode.

The former duplicates two of the three phases found in 208Y/120v service found in commercial buildings but your house current is usually out of phase by 180° yielding 120 & 240.


N+1, what's the no load power consumption and what's the efficiency in ~1-2kW output range likely to be seen in home use?

[Anonymous user]

Thanks KVAR,

Im trying to remember back to College power classes, it has been awhile. The load on this UPS would likely be approx 6000-8000 watts, and will be powered from a separate 100amp feed to the house. We install several large servers that store most of the home's configuration tools, networking gear, one small 120v circuit (20amps max) that is powered even when the power is out (for alarm clocks and such around the house). This customer specifically also requires a home office and small business tools (a few servers and other networking gear). Its quite a complicated setup, but very fun to configure, especially when there is no maximum budget.

Thanks for your detailed explanation again.