Matching UPS to Backup Generator

[Anonymous user]

I have installed a 20KVA generator to power my home office during power failures. I understand that the transition from utility power to backup power will be easier if I use UPS units that employ double-conversion technology and that have total harmonic distortion of less than 30%. Do any APC units suitable for small offices satisfy this criteria?


Thank you.

[Anonymous user]

On a more basic level, I have installed a Generac 20kW house generator to back up for power outages. I seems certain UPS units "accept" the power from the generator and recharge the UPS thereby allowing it to provide uninterrupted power for an indefinite time.
Other UPS units do not recharge when powered by the generator, and hence are exhausted after 15 minutes or so.

Could you recommend which APC units will accept generator power?
Can you provide a primer (?link) to help explain why this happens?

Thanks.

David

[BillP]

Welcome to the APC Forum David.

I have listed the APC knowledgebases below to help you:

- [UPS won't turn on when powered by the generator|http://nam-en.apc.com/cgi-bin/nam_en.cfg/php/enduser/std_adp.php?p_faqid=7354&p_created=1135178608&p...]
- [Using generators with Back-UPS products|http://nam-en.apc.com/cgi-bin/nam_en.cfg/php/enduser/std_adp.php?p_faqid=1066&p_created=1010390400&p...]
- [Generator Sizing for Single Phase Symmetra UPS Systems|http://nam-en.apc.com/cgi-bin/nam_en.cfg/php/enduser/std_adp.php?p_faqid=7300&p_created=1126035179&p...]

Basically whenever a customer calls in and request for UPS sizing on a generator, the size of the generator should be 3 to 5 times higher that the total VA(load) that it would be supporting. Let's say the generator would be supporting 1kVA of load the size of it should be around 5kVA to avoid harmonic distortion and voltage fluctuations. Our Smart-UPS product line works well with generators.

Regards,
JonPro

[TheNotoriousKMP_apc · Accepted solution]

Steve,

While your thought process is correct, you may be over-budgeting for a UPS. The Double-Online Coversion UPS's do have a 0 millisecond transfer time, however, due to their design are also more expensive. Does any of your equipment require absolutely no disruption in power (which would force a reboot/drop of the load)? If not, you should be able to get by with the 2-4 millisecond transfer time that a normal Smart-UPS offers. Those are models that start with "SUA." This may also be more cost-effective if you have multiple workstations, etc. within the small office, instead of trying to run cabling and conduit to one centralized UPS.